MUSCULOSKELETAL-INTEGUMENTARY
OVERVIEW OF THE LOWER LIMBS
The functional requirements of the lower limb (lower extremity) are weight bearing, locomotion, and maintenance of equilibrium. As such, it is constructed for strength at the cost of mobility. The lower limb is divided into four parts: hip, thigh, leg, and foot. The term thigh refers to the portion of the lower limb between the hip and the knee/popliteal fossa. The term leg refers only to the portion of the lower limb between the knee and ankle, not to the entire lower limb.


SURFACE ANATOMY REVIEW
Surface anatomy was studied as part of your assigned exercises during the ORSA course. These structures are key landmarks for extrapolating the position of internal structures and determining where to make your initial skin incisions.

Palpate the following subcutaneous structures on a volunteer or on your cadaver (refer to The Anatomical Basis of the Physical Exam: OSTEOLOGY AND SURFACE ANATOMY LABORATORY EXERCISES): This is a good time to also review the following important clinical landmarks:


SKELETON OF THE LOWER EXTREMIITES
Review the osteological structures that you learned during the ORSA course. As part of the Musculoskeletal Block, you will need to learn some additioanl bones and bony features. Refer to a skeleton, individual bones, and figures.

Review the following on the Pelvis: New pelvic osteology: Review the following on the Femur:
New osteological features on the Femur: New osteological features on the Patella:
Review the following on the Tibia: New osteological features on the Tibia: Review the following on the Fibula: New osteological features on the Fibula:
At this point, you will need to learn the bones and bony features of the ankle and foot in greater detail than you did in ORSA. Note: You will not be asked to identify bones of the ankle or foot, or their features, in isolated bones. You are, however, responsible for identifying these bones and features either on the skeleton or in an articulated foot (a foot in which all of the bones are wired to each other). Refer to Figure 6.21 and identify the following:

PROSECTION ASSIGNMENT: SUPERFICIAL VEINS AND CUTANEOUS NERVES OF THE LOWER LIMBS
Upon completion of this session, the student will be able to:
  1. Identify and demonstrate the major cutaneous nerves of the lower limb, their source and the areas they innervate.
  2. Identify and demonstrate the major superficial veins of the lower limb.
  3. Describe the subcutaneous venous drainage of the lower limb, its relation to the deep veins and the significance of perforating veins.
  4. Describe the lymphatic drainage of the lower limb and areas draining into the superficial and deep inguinal lymph nodes.

Prosection Overview: Superficial Fascia of the Posterior Lower Limb
Most of the subcutaneous connective tissue and fat were removed from the prosection specimen, leaving selected superficial veins and cutaneous nerves intact.

Prosection Instructions
With the cadaver in the prone position, examine the structures contained in the superficial fascia of the posterior aspect of the lower limb (Figure 6.3B).
  1. Find the small (short) saphenous vein where it passes posterior to the lateral malleolus (Figure 6.20) at the ankle (Figure 6.3B). The small saphenous vein arises from the lateral end of the dorsal venous arch. Clean the small saphenous vein and follow it superiorly until it pierces the deep fascia in the popliteal fossa where it drains into the popliteal vein.
  2. Identify the sural nerve (L. sura, calf of the leg). The sural nerve pierces the deep fascia halfway down the posterior aspect of the leg and courses parallel to the small saphenous vein. The sural nerve innervates the skin of the lateral aspect of the ankle and foot.
  3. Use an illustration to study the cutaneous innervation of the posterior surface of the lower limb and note that the cluneal nerves innervate the skin of the gluteal region (L. clunis, buttock) (Figure 6.3B). The cluneal nerves are branches of the dorsal rami of L1 to S3. You do not need to identify the cluneal nerves in the cadaver.
  4. Posterior cutaneous nerve of the thigh lies deep to the deep fascia (Figure 6.3B, ghosted). Note that the posterior cutaneous nerve of the thigh may have been cut during skinning. Branches of the posterior cutaneous nerve of the thigh pierce the deep fascia to supply the skin from the posterior surface of the thigh down to the popliteal fossa.

Prosection Instructions: Superficial Fascia of the Anterior Lower Limb
  1. Turn the cadaver to the supine position and refer to Figure 6.3A.
  2. Find the great (long) saphenous vein (Gr. saphenous, manifest; obvious) where it arises from the medial end of the dorsal venous arch of the foot (Figure 6.3A). Follow it proximally. Note the following:
    1. At the ankle, the great saphenous vein passes anterior to the medial malleolus (Figure 6.20).
    2. At the knee, it passes one hand's breadth posterior to the medial margin of the kneecap, over the posterior border of the medial epicondyle of the femur (Figure 6.6).
    3. Beginning at the level of the knee, the great saphenous vein courses anterolaterally to eventually lie on the anterior surface of the proximal thigh.
    4. Perforating veins connect the great saphenous vein to the deep venous system.
    5. Many superficial veins join the great saphenous vein, and some of these are quite large. Most of these are not named.

      6. YOU SHOULD BE AWARE OF THE FOLLOWING VEINS, BUT DO NOT ATTEMPT TO IDENTIFY THEM:

    6. The accessory saphenous vein drains the superficial fascia and skin of the medial side of the thigh (Figure 6.3A).
    7. Three small superficial veins (superficial external pudendal, superficial epigastric, and superficial circumflex iliac) join the great saphenous vein near its proximal end.
  3. About 4 cm inferior to the inguinal ligament, the great saphenous vein passes deeply through the saphenous opening and drains into the femoral vein. The saphenous opening is an opening in the deep fascia of the thigh, called the fascia lata.
  4. Identify the following: (Figure 6.3A):
    1. Lateral femoral cutaneous nerve (lateral cutaneous nerve of the thigh) - this nerve is a branch of the lumbar plexus and you will study its origin from the lumbar plexus in the posterior abdominal wall prosection. This nerve passes deep to the lateral end of the inguinal ligament and innervates the skin of the lateral thigh.
    2. Anterior cutaneous branches of the femoral nerve - innervate the skin of the anterior thigh. These branches enter the superficial fascia lateral to the great saphenous vein.
    3. Use an illustration to study cutaneous branches of the obturator nerve - innervate the skin of the medial thigh.
    4. Saphenous nerve - a branch of the femoral nerve that pierces the deep fascia on the medial aspect of the knee and accompanies the great saphenous vein into the leg. The saphenous nerve innervates the skin on the anterior and medial aspects of the leg and the medial side of the ankle and foot.
  5. In the distal third of the leg, identify the superficial fibular nerve. The superficial fibular nerve pierces the deep fascia proximal to the lateral malleolus. Follow the superficial fibular nerve distally and identify the dorsal digital nerves. The superficial fibular nerve innervates the skin of the dorsum of the foot. The dorsal digital nerves innervate the dorsal skin of toes.
  6. The skin between the first toe and the second toe is innervated by the dorsal digital branches of the deep fibular nerve. Clincally, this innervation pattern is used for the assessment of deep fibular nerve function.
  7. Identify the superficial inguinal lymph nodes. Two subgroups can be identified (Figure 6.4):
    1. Horizontal group - about 2 cm below the inguinal ligament
    2. Vertical group - around the proximal end of the great saphenous vein
  8. Note that the superficial inguinal lymph nodes collect lymph from the lower limb, inferior part of the anterior abdominal wall, gluteal region, perineum, and external genitalia. The superficial inguinal lymph nodes drain into the deep inguinal lymph nodes.
  9. Examine the deep fascia of the lower limb. It is named regionally: fascia lata (L. latus, broad) in the thigh, crural fascia in the leg, and pedal fascia in the foot. The lateral portion of the fascia lata is particularly strong and is called the iliotibial tract.
IN THE CLINIC: Great Saphenous Vein
Superficial veins and perforating veins have valves that prevent the backflow of blood. If these valves become incompetent, then the veins become distended, a condition known as varicose veins. Portions of the great saphenous vein may be removed and used as graft vessels in coronary bypass surgery. The distal end of the vein is attached to the aorta so that the valves do not impede the flow of blood.
Dissection Review
  1. Review the superficial fascia of the lower limb.
  2. Trace the course of the superficial veins from distal to proximal.
  3. Review the location and pattern of distribution of each cutaneous nerve that you have dissected in the lower limb.
  4. Review the extent and bony attachments of the deep fascia and name its parts.



PROSECTION ASSIGNMENT: THE HIP JOINT
The hip joint is a ball and socket joint and consists of the head of the femur (ball) which fits snugly in a deepened cavity, the acetabular fossa (socket). The joint allows free movement in all directions. The fibrous capsule is a very thick sleeve (compare to the capsule of the shoulder joint) further thickened as a series of extremely strong ligaments which hold the bones in position.
  1. Review the bony features that are relevant to the hip joint:
    • Acetabulum - formed by the three bones, the ilium, ischium, pubis
    • Acetabular notch
    • Head of the femur
    • Fovea for ligament of the head of the femur
    • Neck of the femur
    • Intertrochanteric line of the femur
    • Intertrochanteric crest of the femur
  2. On the anterior view of the hip: (Figure 499, Figure 563)
    • Identify the iliopsoas muscle, a powerful flexor of the thigh to its attachment on the lesser trochanter of the femur. The tendon of the Iliopsoas muscle guards the anterior part of the capsule of the hip joint
    • Reflect the muscle medially and laterally and identify the fibrous capsule. Proximally it is attached to the acetabular brim, labrum and transverse acetabular ligament and distally along the whole length of the intertrochanteric line of the femur.
    • Identify the iliofemoral ligament, a broad, strong band attached proximally to the anterior inferior iliac spine and distally to the intertrochanteric line of the femur (Figure 563). The iliofemoral ligament becomes lax in flexion and taut in extension. It prevents overextension of the hip joint.
  3. On the posterior view of the hip, from superior to inferior, identify the following muscles and then reflect them medially and laterally: (Figure 506, Figure 564)
    • Gluteus medius and gluteus minimus muscles. These attach to the greater trochanter. They abduct and medially rotate the thigh.
    • Piriformis muscle attaches to the greater trochanter. It laterally rotates the extended thigh.
    • Superior gemellus muscle, obturator internus muscle and inferior gemellus muscle attach to the greater trochanter. All 3 muscles are reflected as a group. All are lateral rotators of the extended thigh.
    • Quadratus femoris muscle attaches to the intertrochanteric crest. It laterally rotates the thigh.
    • Obturator externus tendon lies just deep to the quadrates femoris muscle. It is also a lateral rotator of the thigh.
  4. Identify the sciatic nerve as it enters the gluteal region below the piriformis muscle. It then passes inferiorly superficial to the obturator internus muscle, superior and inferior gemellus muscles and the Quadratus femoris muscle.
  5. With the above muscles reflected, identify the capsule of the hip joint. Note that posteriorly the capsule does not extend all the way to the intertrochanteric crest and part of the neck of the femur is "bare" or extracapsular (Figure 564). The capsule is thinnest and weakest posteriorly.
  6. Identify the ischiofemoral and pubofemoral ligaments which extend horizontally across the capsule of the joint from the acetabular margin to the neck of the femur. The ischiofemoral ligament also becomes taut and limits extension of the hip joint.
  7. On the dissected cadaveric specimen of the pelvis:
    • On the left hip joint, identify the iliofemoral, ischiofemoral and pubofemoral ligaments.
    • Flex and extend the thigh at the hip joint and observe that the iliofemoral ligaments become taut
    • On the right hip joint, a circumferential cut has been made on the joint capsule. Observe that the head of the femur is held firmly within the deepened acetabulum. Remove the head of the femur from the acetabulum.
    • Identify the articular cartilage of the head of the femur (Figure 567)
    • Identify the cut end of the ligament of the head of the femur and the fovea for the ligament of the head of the femur (Figure 567)
    • On the acetabulum, identify the lunate surface in the acetabulum. Identify the acetabular labrum, a fibrocartilagenous rim which deepens the joint cavity so that the femoral head is not easily dislocated from the joint cavity (Figure 568)
    • Inferiorly the bony acetabulum is incomplete and is known as the acetabular notch. It is partially covered by the transverse acetabular ligament
    • Identify the ligament of the head of the femur and observe that it is attached to either side of the acetabular notch (Figure 568)

    Note: Return the femoral head into the joint cavity when you have finished studying the internal aspect of the hip joint.


    PROSECTION ASSIGNMENT: THE KNEE JOINT
    The knee joint is of the hinge variety. The chief movements occurring at the knee joint are flexion and extension. However a slight degree of medial rotation of the femur is necessary to the completion of the act of extension ("locking" of the joint).

    Review the bony features that are relevant to the knee joint. The 3 bones are the femur, tibia and patella. The fibula is only indirectly associated with the knee joint.
    • Medial condyle of the femur
    • Lateral condyle of the femur
    • Intercondylar fossa of the femur
    • Medial condyle of the tibia
    • Lateral condyle of the tibia
    • Superior articular surface of the tibia
    • Intercondylar eminence of the tibia
    • Articular surface of the patella
    • Anterior surface of the patella

    Study the following on the knee prosection where the joint cavity is not completely opened
    1. On the anterior view of the knee (Figure 497), identify:
      • Quadriceps femoris muscle and tendon
      • Patella
      • Patellar ligament
    2. Reflect the quadriceps femoris muscle, tendon, patella and patellar ligament inferiorly and identify (Plate 380, Figure 572):
      • Suprapatellar bursa
      • Articular surface of the patella
      • Alar and interpatellar synovial folds
      • Medial femoral condyle
      • Lateral femoral condyle
      • Patellar surface of the femur


    3. On the medial view of the knee (Figure 5.25) identify:
      • Sartorius and gracilis muscles, which have been cut and reflected together
      • Semitendinosus tendon
      • Semimembranosus tendon
      • Tibial collateral ligament (Figure 5.65)


    4. On the lateral view of the knee (Figure 527) identify:
      • Biceps femoris tendon attaching on the head of the fibula
      • Iliotibial tract (Figure 5.63)
      • Fibular collateral ligament (Figure 5.63)


    5. On the posterior view of the knee:
      1. Reflect the popliteal vessels (Plate 340) inferiorly
      2. Reflect the lateral head of the gastrocnemius muscle inferiorly and identify the popliteus muscle (Plate 362). Observe that the popliteus tendon passes between the fibular collateral ligament and the joint capsule.
      3. The arcuate popliteal ligament (Plate 382) spans the superficial surface of the popliteus tendon
      4. Reflect the medial head of the gastrocnemius muscle inferiorly and identify the semimembranosus tendon which expands upward and laterally as the oblique popliteal ligament. It reinforces the posterior surface of the joint capsule.
      5. On the posterior surface of the joint capsule observe the genicular arteries piercing the joint capsule.



    Study the following on the knee prosection where the joint cavity is opened anteriorly and posteriorly
    1. On the anterior view of the knee (Figure 574)
      • The anterior cruciate ligament extends from the lateral femoral condyle deep in the intercondylar notch superiorly to the anterior part of the tibial plateau inferiorly. The anterior cruciate ligament prevents the posterior or backward displacement of the femur on the tibia. It limits the extension of the lateral femoral condyle to which it is attached. When it becomes taut, it causes medial rotation of the femur. This allows the medial condyle which has a longer and more curved articular surface than the lateral condyle to reach its full extension, placing the knee joint in a "locked" position
      • The posterior cruciate ligament is fixed to the medial condyle of the femur superiorly. Its tibial attachment will be observed on the posterior view of the knee joint
      • The medial meniscus and the lateral meniscus (Figure 573, Figures 585-587). Both menisci are C-shaped fibrous tissue (not cartilage), are triangular in cross section and are attached to the tibial surface. The medial meniscus is also securely attached to the tibial collateral ligament and both are frequently torn together in sports injuries
    2. On the posterior view of the knee (Figure 577)
      • The articular capsule of the knee has been removed. Identify the posterior cruciate ligament and its attachment onto the posterior intercondylar surface of the tibia.
      • Identify the anterior cruciate ligament, the medial meniscus and the lateral meniscus.



    PROSECTION ASSIGNMENT: THE ANKLE JOINT
    The ankle joint is the most frequently injured major joint in the body. Motion at the ankle consists purely of dorsiflexion and plantarflexion. It is a hinge joint. Functional inversion and eversion of the foot occurs at the transverse tarsal joint between the talus and navicular bones medially, and the calcaneus and cuboid bones laterally.
    1. Review the bony features relevant to the ankle joint
      • Lateral malleolus on the distal end of the fibula
      • Medial malleolus on the distal end of the tibia
      • Posterior malleolus (not a true anatomical term but used by orthopedic surgeons) on the posterior, distal end of the tibia)
      • Articular surface of the body of the talus
    2. On the medial view of the ankle (Figure 534)
      • Reflect the flexor retinaculum and identify the tendons of Tibialis posterior, Flexor digitorum longus and Flexor hallucis longus muscles
      • The joint capsule is thickened as the deltoid ligament (Figure 606). It is attached above to the medial malleolus and spreads out inferiorly to attach to the navicular, the talus and the sustentaculum tali of the calcaneus. Note: The different parts of the deltoid ligament are named for the bones they connect.
    3. On the posterior view of the ankle (Figure 602)
      • Reflect the calcaneal tendon inferiorly and observe that the joint capsule is very thin.
      • Identify the posterior tibiofibular ligament which somewhat strengthens the posterior aspect of the joint capsule.
      • For your interest: Note that a small accessory bone, the os trigonum, is present. The os trigonum is the most commonly occurring accessory bone in the foot, occurring in an estimated eight to ten percent of the population. This interesting bone sits at the most posterior aspect of the talus, at the border of the talus and the calcaneus.


    4. On the lateral view of the ankle (Figure 533)
      • Identify the tendons of the fibularis longus and fibularis brevis muscles
      • The joint capsule is thickened as the lateral collateral ligament (Figure 604), which is attached above to the lateral malleolus and below as 3 slips to the talus and calcaneus.


    5. On the anterior view of the ankle (Figure 5.82)(Figure 5.82)
      • Reflect inferiorly the extensor retinaculum and identify the tendons of the Tibialis anterior, Extensor hallucis longus and Extensor digitorum longus muscles.
      • Identify the medial and lateral malleoli
      • Identify the anterior tibiofibular ligament (Figure 5.117)
      • The joint capsule is thin anteriorly and has been incised to expose the joint cavity. Identify the articular surface of the body of the talus (Figure 5.117)



    PROSECTION ASSIGNMENT: THE POSTERIOR ABDOMINAL WALL AND LUMBAR PLEXUS

    Learning Objectives:
    1. Identify and demonstrate the abdominal attachments of the two major posterior abdominal wall muscles and know the action of these muscles on the vertebral column.
    2. Describe the nerves of the lumbar plexus in terms of their: spatial relationship to the posterior abdominal wall muscles; distribution to the abdominal wall, the genital region, and the lower limb; and categorization into purely cutaneous nerves and those which also innervate muscles.
    3. Locate the lumbar sympathetic trunk and white and gray rami communicantes; explain why there are no white rami below the L2 level.

    Prosection Overview
    The posterior abdominal wall is composed of the vertebral column, muscles that move the vertebral column, muscles that move the lower limb, and the diaphragm. The nerves that supply the abdominal wall and the lumbar plexus of nerves that supply the lower limb will be dissected with the posterior abdominal wall.

    Prosection Instructions: Muscles of the Posterior Abdominal Wall
    1. Identify the psoas major muscle (Figure 4.47). The proximal attachments of the psoas major muscle are the lumbar vertebrae (bodies, intervertebral discs, and transverse processes). Its distal attachment is the lesser trochanter of the femur. The psoas major muscle is a strong flexor of the thigh and vertebral column.
    2. Look for the psoas minor muscle. The psoas minor muscle is absent in approximately 40% of cases and may be present on only one side of the cadaver. The psoas minor muscle has a long flat tendon that passes down the anterior surface of the psoas major muscle to its distal attachment on the iliopubic eminence of the ilium. The psoas minor muscle, when present, is a weak flexor of the vertebral column.
    3. Identify the iliacus muscle (Figure 4.47). The proximal attachment of the iliacus muscle is the iliac fossa. Its distal attachment is on the lesser trochanter of the femur. Like the psoas major muscle, the iliacus muscle flexes the thigh. The iliacus and psoas major muscles form a functional unit and together they are called the iliopsoas muscle.
    4. Identify the quadratus lumborum muscle (Figure 4.47). The proximal attachments of the quadratus lumborum muscle are the 12th rib and lumbar transverse processes. Its distal attachments is the iliac crest. The quadratus lumborum muscle flexes the vertebral column laterally and anchors the inferior end of the rib cage during respiration.
    5. Identify the transversus abdominis muscle. The transversus abdominis muscle forms the lateral part of the posterior abdominal wall. The transversus abdominis muscle lies posterior to the quadratus lumborum muscle.

    Prosection Instructions: Lumbar Plexus
    The nerves of the posterior abdominal wall arise from the ventral rami of spinal nerves T12 to L4. The lumbar plexus (L1 to L4) is formed within the psoas major muscle and its branches can be seen as they emerge from the lateral border of this muscle. The lumbar plexus can be seen only after removal of the psoas major muscle. The nerves of the lumbar plexus are variable in their branching. Use the peripheral relationships of the nerves (their region of distribution or a point of exit from the abdominal cavity) for positive identification.
    1. Identify the genitofemoral nerve. It is found on the anterior surface of the psoas major muscle (Figure 4.47). It is the motor nerve to the cremaster muscle, which you will learn about in the next block, and supplies a small area of skin inferior and medial to the inguinal ligament. The two parts of the genitofemoral nerve divide on the anterior surface of the psoas major muscle superior to the inguinal ligament.
    2. Palpate rib 12 and identify the subcostal nerve about 1 cm inferior to it (Figure 4.47).
    3. Find the iliohypogastric and ilioinguinal nerves (Figure 4.47). They descend steeply across the anterior surface of the quadratus lumborum muscle. Frequently, these two nerves arise from a common trunk and do not separate until they reach the transversus abdominis muscle.
    4. Identify the lateral cutaneous nerve of the thigh (Figure 4.47). The lateral cutaneous nerve of the thigh (lateral femoral cutaneous nerve) passes deep to the inguinal ligament near the anterior superior iliac spine. The lateral cutaneous nerve of the thigh supplies the skin on the lateral aspect of the thigh.
    5. Identify the femoral nerve (Figure 4.47). The femoral nerve is the largest nerve of the lumbar plexus (indeed, it is so large that it may be mistaken for a muscle tendon). It lies on the lateral side of the psoas major muscle in the groove between the psoas major and iliacus muscles. The femoral nerve innervates these two muscles. The femoral nerve passes deep to the inguinal ligament and provides motor and sensory branches to the anterior thigh.
    6. Identify the obturator nerve (Figure 4.47) on the medial side of the psoas major muscle. The obturator nerve supplies motor and sensory innervation to the medial thigh.
    7. Identify the lumbosacral trunk (Figure 4.47). The lumbosacral trunk is a large nerve that is formed by a contribution from the ventral ramus of L4 and all of the ventral ramus of L5. Recall that the lumbosacral trunk passes into the pelvis to join the sacral plexus.

    IN THE CLINIC: Meralgia Paraesthetica
    Entrapment of the lateral cutaneous nerve of the thigh where it passes deep to the inguinal ligament can result in pain in the lateral thigh.

    Prosection Instructions: Abdominal Part of the Sympathetic Trunk
    Study the location of the sympathetic trunk on a transverse section of the abdomen (Figure 4.43).
    1. Identify the sympathetic trunk on the vertebral bodies between the crus of the diaphragm and the psoas major muscle.
    2. Identify white and gray rami communicantes that pass posteriorly from the sympathetic ganglia to lumbar ventral rami. Note that each ramus communicans passes deeply between the psoas major muscle and the vertebral body. The gray rami communicantes of the lower lumbar region are the longest in the body because the sympathetic trunk crosses the anterolateral surface of the lumbar vertebral bodies.

    Prosection Instructions: Abdominal Aorta and Inferior Vena Cava
    Use an illustration to study the abdominal aorta. Observe that the abdominal aorta has three types of branches (Figure 4.45):
    1. Identify at least one lumbar artery (Figure 4.46). Four pairs of lumbar arteries supply the posterior abdominal wall. Trace one lumbar artery to its origin from the posterior aspect of the abdominal aorta. Note that the lumbar arteries pass deep to the psoas major muscle.
    2. Observe the bifurcation of the abdominal aorta at vertebral level L4 (Figure 4.46). In a thin person, the umbilicus projects superior to the bifurcation of the aorta.
    3. Identify the common iliac arteries, which arise at the bifurcation of the aorta.
    4. At the bifurcation of the common iliac arteries, identify the external iliac artery. At the point where the external iliac artery passes under the inguinal ligament, it is renamed the femoral artery, which supplies blood to the lower extremity. The other branch of the common iliac artery is the internal iliac artery. The internal iliac artery supplies the pelvic organs and perineum, which will be studied in the next block. The internal iliac artery also gives rise to the superior and inferior gluteal arteries, which we will identify in the gluteal region dissection.

    Review:
    1. Use the dissected specimen to review the proximal and distal attachments, as well as the action of each of the muscles of the posterior abdominal wall.
    2. Review the three muscles that form the anterolateral abdominal wall (external abdominal oblique, internal abdominal oblique, and transversus abdominis).
    3. Follow each branch of the lumbar plexus peripherally. Review the region of innervation of each of these nerves.
    4. Use an atlas drawing to review the sympathetic trunk.



    DISSECTION LABORATORY #1: ANTERIOR AND MEDIAL COMPARTMENTS OF THE THIGH
    Learning Objectives: Upon completion of this laboratory, the student will be able to:
    1. Define the femoral triangle and adductor canal, their contents and the spatial relationships of the structures passing through them.
    2. Identify the femoral and obturator arteries and veins and their branches. Give their areas of distribution.
    3. Identify the muscles of the anterior and medial thigh, including their nerve and vascular supply. Describe their role in locomotion.
    4. Predict what nerve or nerves are involved and the probable level of the injury, given a loss of function and/or cutaneous sensation involving the anterior and medial thigh regions.

    Dissection Instructions: Skin Removal
    1. Refer to Figure 6.2A. Make a vertical cut from the midpoint of the inguinal ligament (F) passing over the patella to the dorsum of the foot (G).
    2. Make a cut through only the skin (not the superficial fascia) across the dorsum of the foot at the webs of the toes (H to H). The skin is very thin on the dorsum of the foot. Do not cut too deep.
    3. Make one cut along the dorsal midline of each toe to the proximal end of the nail (H to P).
    4. Remove the skin from the thigh, leg, and dorsum of the foot as far laterally and medially as possible. Make as many transverse skin incisions as are needed to speed up the skinning process but attempt to take the skin off in as few flaps as possible. These flaps can then be used to place over the cadaver after your dissection to keep it moist (alternatively, at the conclusion of each dissection, place linen towels over the structures to prevent drying out of the tissues).
    5. Turn the cadaver into the prone position and refer to Figure 6.2B.
    6. Remove the skin from the gluteal region. Make a midline incision and work from medial to lateral. Detach the skin along line J to K and the lateral side of the hip.
    7. Make a cut along the midline of the thigh and leg from the gluteal fold to the heel (E to I).
    8. Extend the previous transverse skin incisions around the limb to join incision E-I. Begin at line E-I and work both medially and laterally.

    Dissection Overview: Anterior Compartment of the Thigh
    The fascia lata is connected to the femur by intermuscular septa (Figure 6.5) to form the three fascial compartments of the thigh: anterior (extensor), medial (adductor), and posterior (flexor). The anterior compartment of the thigh contains five muscles: sartorius, rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis. The rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis collectively are called the quadriceps femoris muscle. The shared action of the quadriceps femoris is extension of the leg at the knee joint. The major blood supply to the lower limb (femoral artery and deep femoral artery) passes through the anterior compartment of the thigh.

    The order of dissection will be as follows: The fascia lata of the thigh will be reviewed and its saphenous opening will be studied. The anterior surface of the superior part of the fascia lata will be opened to expose the femoral triangle. The femoral triangle will be dissected and its contents traced distally. The adductor canal will be dissected and the sartorius muscle identified. The anterior surface of the inferior part of the fascia lata will be incised and the remaining anterior thigh muscles will be studied.

    Dissection Instructions: Saphenous Opening
    1. Remove any remnants of superficial fascia that remain on the anterior surface of the fascia lata from the level of the inguinal ligament to the knee. The superficial inguinal lymph nodes must be removed during this step of the dissection. Preserve the great saphenous vein.
    2. Locate the great saphenous vein superiorly and observe that it turns posteriorly to disappear approximately 4 cm inferior to the inguinal ligament. Use a probe to dissect the connective tissue around the great saphenous vein where it passes deeply. Insert your finger beside the great saphenous vein and move your finger around the vein to define the margins of the saphenous opening (Figure 6.7). The saphenous opening is a natural opening in the fascia lata that is filled with a rather weak layer of fascia. Observe that the great saphenous vein passes through the saphenous opening to enter the deeper part of the anterior thigh. Trace the great saphenous vein through the saphenous opening and observe that it drains into the anterior surface of the femoral vein.
    3. Again insert your finger into the saphenous opening inferior to the great saphenous vein. Push your finger inferiorly deep to the fascia lata until your fingertip reaches the level of the sartorius muscle. Use scissors to make an incision through the fascia lata from the saphenous opening to the sartorius muscle (Figure 6.7, incision 1).
    4. Use scissors to make a second incision through the fascia lata that extends laterally from the superior margin of the saphenous opening, parallel to the inguinal ligament (Figure 6.7, incision 2). This incision should extend laterally to a point that is directly inferior to the anterior superior iliac spine.
    5. Use scissors to make a third incision through the fascia lata that extends medially from the superior margin of the saphenous opening, parallel to the inguinal ligament (Figure 6.7, incision 3). This incision should extend medially to a point that is directly inferior to the pubic tubercle.
    6. Use blunt dissection to separate the fascia lata from deeper structures. Reflect the flaps of fascia lata medially and laterally. You have opened the superficial boundary (roof) of the femoral triangle.

    Dissection Instructions: Femoral Triangle
    1. Identify the femoral triangle (Figure 6.8). The femoral triangle is bounded superiorly by the inguinal ligament, laterally by the medial border of the sartorius muscle, and medially by the medial border of the adductor longus muscle. The base of the femoral triangle is the inguinal ligament and the apex is located inferiorly.
    2. The contents of the femoral triangle are:
      • femoral nerve and its branches
      • femoral sheath (Figures 5.32 and 5.34 below; Figure 6.8), which contains the femoral artery, the femoral vein and some of its tributaries (notably, the great saphenous vein), and lymphatic vessels and nodes
    3. The femoral sheath is an extension of transversalis fascia into the thigh that envelops the proximal end of the femoral artery and femoral vein, and some deep inguinal lymph nodes. The femoral sheath is subdivided into three compartments (Femoral Sheath Illustrations):
      • Lateral - containing the femoral artery
      • Intermediate - containing the femoral vein
      • Medial - containing lymphatics (you will not see these)
    4. Note that the lateral to medial arrangement of structures within the femoral triangle that pass under the inguinal ligament (including the femoral nerve and the contents of the femoral sheath) can be arranged by use of the mnemonic device NAVL (pronounced navel): femoral Nerve, femoral Artery, femoral Vein, Lymphatics.
    5. The medial compartment of the femoral sheath is also called the femoral canal and its proximal opening into the abdominal cavity is called the femoral ring. Observe the femoral canal and femoral ring from the abdominal side of the inguinal ligament.
    6. Use blunt dissection to clean the femoral artery and femoral vein within the femoral triangle. Three small arteries arise from the femoral artery just distal to the inguinal ligament (Figure 6.9B): superficial external pudendal artery, superficial epigastric artery, and superficial circumflex iliac artery. Respectively, these arteries pass medially, superiorly, and laterally from their origin and they supply the superficial fascia of the abdominal wall, proximal thigh, and part of the perineum. Do not attempt to dissect these small arteries that arise from the femoral artery.
    7. Three large arteries arise within the femoral triangle (Figure 6.9B): deep artery of the thigh (also called the deep femoral artery, or profunda femoris artery), lateral circumflex femoral artery, and medial circumflex femoral artery. The medial and lateral circumflex femoral arteries usually arise from the deep artery of the thigh, but each may arise from the femoral artery very close to the origin of the deep artery of the thigh.
    8. Preserve the major veins (femoral vein, deep vein of the thigh, great saphenous vein), but remove their tributaries to clear the dissection field.
    9. Inferior to the apex of the femoral triangle, note that the femoral artery courses distally between the sartorius muscle and the adductor longus muscle (Figure 6.9A).
    10. Retract the femoral artery medially and identify the deep artery of the thigh. The deep artery of the thigh courses parallel to the femoral artery but posterior to the adductor longus muscle (Figure 6.9C). The deep artery of the thigh supplies the medial and posterior compartments of the thigh.
    11. Identify the lateral circumflex femoral artery. The lateral circumflex femoral artery usually arises from the deep artery of the thigh very close to the femoral artery. The lateral circumflex femoral artery passes laterally, deep to the proximal end of the rectus femoris muscle, and supplies the muscles and soft tissues of the lateral part of the thigh. It has three branches, each of which participates in an anastomosis:
      • Ascending branch - anastomoses with the superior gluteal artery
      • Transverse branch - anastomoses with the medial circumflex femoral artery
      • Descending branch - courses inferiorly on the anterior surface of the vastus intermedius muscle and anastomoses with the genicular arteries at the knee
    12. Identify the medial circumflex femoral artery. The medial circumflex femoral artery typically arises from the deep artery of the thigh close to the femoral artery. The medial circumflex femoral artery passes posteriorly, between the pectineus and iliopsoas muscles. In addition to supplying the soft tissues of the region, the medial circumflex femoral artery is an important blood supply to the head and neck of the femur.
    13. The floor of the femoral triangle is formed by the iliopsoas muscle, pectineus muscle, and the adductor longus muscle (see figure to right).
    14. The iliacus and psoas major muscles collectively are named the iliopsoas muscle. The proximal attachment of the iliacus muscle is the iliac fossa and the proximal attachments of the psoas major muscle are the transverse processes and bodies of lumbar vertebrae (vertebrae T12 to L5). The distal attachment of the iliopsoas tendon is the lesser trochanter of the femur. The iliopsoas muscle is a strong flexor of the thigh.
    15. The proximal attachment of the pectineus muscle is the superior ramus of the pubis, and its distal attachment is the pectineal line of the femur. The pectineus muscle adducts and flexes the thigh.
    16. Use blunt dissection to clean the floor of the femoral triangle.
    17. Expose the femoral nerve, which lies on the floor of the femoral triangle on the lateral side of the femoral artery (Figure 6.8). Follow the femoral nerve inferiorly and observe that it divides into numerous branches. The femoral nerve innervates the anterior thigh muscles and the skin of the anterior thigh. Its motor branches will be identified later.
    18. Verify that the anterior cutaneous branches of the femoral nerve enter the superficial fascia by penetrating the fascia lata along the anterior surface of the sartorius muscle (Figure 6.3).


    IN THE CLINIC: Femoral Triangle
    The pulse of the femoral artery can be palpated about 3 cm inferior to the midpoint of the inguinal ligament. Within the femoral triangle, the femoral vessels are accessed for diagnostic purposes. A catheter introduced into the femoral artery can be advanced proximally into the aorta and its branches. A catheter introduced into the femoral vein can be advanced through the inferior vena cava into the right atrium of the heart.
    IN THE CLINIC: Femoral Hernia
    The femoral ring is a site of potential herniation. A femoral hernia is a protrusion of abdominal viscera through the femoral ring into the femoral canal. A femoral hernia may become strangulated due to the inflexibility of the inguinal ligament.

    Dissection Instructions: Adductor Canal and Sartorius Muscle
    1. The adductor canal is a fascial compartment located deep to the sartorius muscle that conducts the femoral artery and vein through the inferior part of the thigh. The adductor canal begins at the apex of the femoral triangle and ends at the adductor hiatus, which is located just above the knee (Figure 6.9C). The femoral vessels pass through the adductor hiatus (defined in step 5) to reach the popliteal fossa.
    2. Use scissors to cut the fascia lata along the superficial surface of the sartorius muscle. The cut should extend from the anterior superior iliac spine to the medial epicondyle of the femur.
    3. Use a probe and your fingers to separate the sartorius muscle from the deep fascia that is both anterior and posterior to it. Retract the sartorius muscle laterally so that its superior and inferior attachments can be defined and its blood and nerve supplies can be identified. The proximal attachment of the sartorius muscle is the anterior superior iliac spine and its distal attachment is the medial surface of the proximal tibia. Observe that the sartorius muscle crosses both the hip joint and the knee joint. It flexes and laterally rotates the thigh and flexes the leg.
    4. Transect the sartorius muscle near the apex of the femoral triangle. Reflect the distal part of the sartorius muscle inferiorly. Posterior to the sartorius muscle observe a sheath of connective tissue that encloses the femoral vessels. This connective tissue sheath is the adductor canal.
    5. Use scissors to open the adductor canal and examine the femoral vessels. Observe that the femoral vein lies posterior to the femoral artery. Inferiorly, the femoral artery and vein pass through the adductor magnus muscle to reach the popliteal fossa in the back of the knee; this opening in the adductor magnus muscle is the adductor hiatus. Use blunt dissection to follow the femoral artery distally through the adductor hiatus, where its name changes to popliteal artery (Figure 6.9C).
    6. The nerve to vastus medialis and the saphenous nerve accompany the femoral vessels in the adductor canal. The nerve to vastus medialis is the motor nerve to the vastus medialis muscle, and the saphenous nerve is a cutaneous nerve that innervates the skin of the medial side of the leg, ankle, and foot. Note that the saphenous nerve does not pass through the adductor hiatus.

    Dissection Instructions: Quadriceps Femoris Muscle and Tensor Fasciae Latae
    1. Insert your finger deep to the fascial lata near the apex of the femoral triangle and direct it inferiorly toward the knee. Use scissors to make a vertical cut through the fascia lata from the apex of the femoral triangle to the patella. Make a transverse incision in the fascia lata above the patella. This incision should extend from the medial femoral epicondyle to the lateral femoral epicondyle.
    2. Use blunt dissection to release the fascia lata from the anterior surface of the deeper structures and open the fascia lata widely. Follow the inner surface of the fascia lata laterally with your fingers. Here, the fascia lata is continuous with the lateral intermuscular septum (see transverse section of the thigh above). The lateral intermuscular septum is attached to the linea aspera on the posterior aspect of the femur.
    3. The quadriceps femoris muscle occupies most of the anterior compartment of the thigh (see transverse section of the thigh above). The four parts of the quadriceps femoris muscle are the rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis. The tendons of all four muscles unite to form the quadriceps femoris tendon. The quadriceps femoris tendon is attached to the patella. The patellar ligament (patellar tendon) attaches the patella to the tibial tuberosity, so the ultimate attachment of the quadriceps femoris muscle is the tibial tuberosity (Figure 6.11).
    4. Identify the rectus femoris muscle in the midline of the anterior thigh. The proximal attachment of the rectus femoris muscle is the anterior inferior iliac spine. The rectus femoris muscle crosses both the hip joint and the knee joint. It flexes the thigh and extends the leg.
    5. The rectus femoris muscle may be transected near its midlength and its halves reflected superiorly and inferiorly as shown in Figure 6.11 to assist in dissecting the lateral circumflex femoral artery and the motor branches of the femoral nerve (see below), if necessary. However, the rectus femoris muscle is usually sufficiently mobile that transection is not necessary.
    6. Identify the vastus lateralis muscle on the lateral side of the anterior thigh (Figure 6.11). The proximal attachment of the vastus lateralis muscle is the linea aspera of the femur.
    7. Identify the vastus medialis muscle on the medial side of the anterior thigh. The proximal attachment of the vastus medialis muscle is the linea aspera of the femur.
    8. Identify the vastus intermedius muscle, which is between the vastus lateralis and vastus medialis muscles. The proximal attachments of the vastus intermedius muscle are the anterior and lateral surfaces of the femur (see transverse section of the thigh above).
    9. The distal attachment of the rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis muscles is the tibial tuberosity and these muscles extend the leg.
    10. Observe the descending branch of the lateral circumflex femoral artery, which can be seen on the anterior surface of the vastus intermedius muscle, deep to the rectus femoris muscle.
    11. Identify the motor branches of the femoral nerve to the anterior thigh muscles (Figure 6.11). The motor branches of the femoral nerve are located between the rectus femoris muscle and the three vastus muscles. Note that the femoral nerve innervates the sartorius muscle and the pectineus muscle in addition to innervating the quadriceps femoris muscle.
    12. Identify the tensor of the fascia lata (tensor fasciae latae muscle). To locate it, you will palpate a muscle mass located within the proximal fascia lata inferior to the anterior superior iliac spine (Figure). The proximal attachment of the tensor of the fascia lata is the anterior superior iliac spine and its distal attachment is the iliotibial tract. The tensor of the fascia lata is an abductor and medial rotator of the thigh.

    IN THE CLINIC: Patellar Tendon (Quadriceps) Reflex
    Tapping the patellar ligament stimulates the patellar reflex (quadriceps reflex; knee jerk). Tapping activates muscle spindles in the quadriceps femoris muscle, and afferent impulses travel in the femoral nerve to spinal cord segments L2, L3, and L4. Efferent impulses are then carried by the femoral nerve to the quadriceps femoris muscle, resulting in a brief contraction. The patellar tendon reflex tests the function of the femoral nerve and spinal cord segments L2 to L4.
    Dissection Review
    1. Replace the anterior thigh muscles in their correct anatomical positions.
    2. Use the dissected specimen to review the boundaries and contents of the femoral triangle.
    3. Review the origin and course of the femoral artery and its branches in the thigh.
    4. Use the dissected specimen to review the attachments and actions of the muscles of the anterior compartment of the thigh.
    5. Recall the rule of innervation of the anterior compartment of the thigh:
        6. All muscles in the anterior compartment of the thigh are innervated by the femoral nerve.

    Dissection Overview: Medial Compartment of the Thigh
    The medial compartment of the thigh contains six muscles: gracilis, adductor longus, adductor brevis, pectineus, adductor magnus, and obturator externus. The shared function of this group of muscles is to adduct the thigh. Therefore, they are also known as the adductor group of thigh muscles.

    The order of dissection will be as follows: The fascia lata will be removed from the medial thigh. The gracilis muscle will be studied. The adductor muscles will be dissected by following the medial circumflex femoral artery, the deep artery of the thigh, and the branches of the obturator nerve. Note: The anterior and posterior branches of the obturator nerve pass anterior and posterior, respectively, to the adductor brevis muscle. The branches of the deep artery of the thigh and the obturator nerve are excellent aids to help you define the plane of separation between the muscles of the medial compartment of the thigh.

    Dissection Instructions: Medial Compartment of the Thigh
    1. On the medial aspect of the thigh, use your hands to separate the fascia lata from the muscles of the medial compartment. Begin at the medial border of the femoral triangle and work medially. Be careful not to remove the gracilis muscle. Use scissors to cut the fascia lata and remove it and any remnants of superficial fascia that may adhere to it.
    2. Identify the gracilis muscle. The proximal attachment of the gracilis muscle is the pubic bone and its distal attachment is the medial condyle of the tibia. With your fingers, define the gracilis muscle from its proximal attachment to its distal attachment. Using scissors, trim away any remaining superficial fascia or fascia lata so that the gracilis muscle is clearly visible and separated from deeper structures. The gracilis muscle crosses both the hip and knee joints. It adducts the thigh and assists in flexion of the leg.
    3. Use an (Figure) to observe the proximal attachments of the gracilis muscle, pectineus muscle, and adductor longus muscle along a curved line on the pubic bone.
    4. Observe the anterior surface of the pectineus and adductor longus muscles. They fan out to their distal attachments on the pectineal line or the linea aspera of the femur. Both muscles are adductors of the thigh.
    5. Note that the deep artery of the thigh passes between the pectineus and adductor longus muscles, then courses inferiorly between the adductor longus muscle and the adductor brevis muscle. Follow the deep artery of the thigh distally between the pectineus and adductor longus muscles and use blunt dissection to define the muscle borders.
    6. Continue to follow the deep artery of the thigh posterior to the adductor longus muscle to separate the adductor longus muscle from the adductor brevis muscle. Transect the adductor longus muscle 5 cm inferior to its proximal attachment and reflect it as shown in Figure 6.12.
    7. The adductor brevis muscle can now be seen at a deeper plane. The proximal attachment of the adductor brevis muscle is on the pubic bone and its distal attachments are the pectineal line and linea aspera of the femur. The adductor brevis muscle adducts the thigh.
    8. Perforating arteries (branches from the deep artery of the thigh) penetrate the adductor brevis and adductor magnus muscles. They encircle the femur and supply the muscles of the posterior compartment of the thigh. There are multiple perforating arteries. Just dissect one example.
    9. Refer to Figure 6.12 and note that the anterior branch of the obturator nerve crosses the anterior surface of the adductor brevis muscle and that the posterior branch of the obturator nerve crosses its posterior surface.
    10. Superiorly, the anterior branch of the obturator nerve passes deep to the pectineus muscle but is superficial to the adductor brevis muscle (Figure 6.12). Follow the anterior branch of the obturator nerve superiorly to separate the pectineus muscle from the adductor brevis muscle. Note that the superior border of the adductor brevis muscle is deep to the pectineus muscle. Use blunt dissection to clean the adductor brevis. Do not damage the anterior branches of the obturator nerve.
    11. The posterior branch of the obturator nerve lies between the adductor brevis muscle and the adductor magnus muscle. Find this nerve as it emerges from the inferior border of the adductor brevis muscle. Use blunt dissection to follow the posterior branch of the obturator nerve superiorly to separate the adductor brevis muscle from the adductor magnus muscle. Alternatively, follow the anterior branch of the obturator nerve superiorly to the bifurcation of the obturator nerve. Identify the posterior branch of the obturator nerve and trace its path inferiorly, separating the adductor brevis and adductor magnus muscles.
    12. Raise the adductor brevis muscle and observe the adductor magnus muscle. The proximal attachments of the adductor magnus muscle are the ischiopubic ramus and the ischial tuberosity, and its distal attachment are the linea aspera (adductor part) and adductor tubercle (ischiocondylar or hamstring part) of the femur. The most medial part of the adductor magnus muscle (the part that attaches to the adductor tubercle) is the ischiocondylar portion and it is innervated by the tibial division of the sciatic nerve rather than by the obturator nerve. The adductor magnus muscle adducts and extends the thigh.
    13. Trace the tendon of the ischiocondylar portion of the adductor magnus muscle inferiorly to its attachment on the adductor tubercle. On the lateral side of this tendon, observe the adductor hiatus, which is an opening in the adductor magnus tendon (Figure 6.12). Note that the femoral artery and vein pass from the anterior compartment of the thigh into the posterior compartment of the thigh by passing through the adductor hiatus.
    14. Study an illustration of the obturator externus muscle. Do not attempt to dissect this muscle, as it lies deep to the pectineus muscle and iliopsoas tendon. The proximal attachment of the obturator externus muscle is the margin of the obturator foramen and the external surface of the obturator membrane. Its distal attachment is on the posterior side of the femur, on and around the greater trochanter of the femur. The obturator externus muscle is a lateral rotator of the thigh.

    Dissection Review
    1. Replace the medial thigh muscles in their correct anatomical positions.
    2. Use the dissected specimen to review the attachments and action of each muscle dissected.
    3. Trace the deep artery of the thigh from its origin to one of its perforating arteries (it terminates as the fourth perforating artery).
    4. Trace the medial circumflex femoral artery from its origin to where it passes between the iliopsoas and pectineus muscles.
    5. Trace the course of the anterior and posterior branches of the obturator nerve superiorly as far as the superior border of the adductor brevis muscle.
    6. Recall the rule for innervation of the medial thigh muscles:
      • The obturator nerve innervates the muscles of the medial compartment of the thigh with the following exceptions:
      • The pectineus muscle receives motor innervation from both the femoral nerve and the obturator nerve.
      • The ischiocondylar portion of the adductor magnus muscle is innervated by the tibial division of the sciatic nerve.



    DISSECTION LABORATORY #2: THE GLUTEAL REGION
    Learning Objectives: Upon completion of this laboratory, the student will be able to:
    1. Describe the anatomy of the gluteal region, including the gluteal muscles, their nerve supply, and their actions in locomotion.
    2. Identify the sacral plexus, its general plan, and its major branches in the hip and posterior thigh regions.

    Dissection Overview: The Gluteal Region
    The gluteal region (Gr. gloutos, buttock) lies on the posterior aspect of the pelvis. It is the most superior part of the lower limb. It contains muscles that extend, abduct and laterally rotate the thigh.

    The order of dissection will be as follows: The fat and superficial fascia will be removed from the gluteal region. The borders of the gluteus maximus muscle will be defined and it will be reflected laterally to expose the muscles that lie deep to it. Muscles that lie deep to the gluteus maximus muscle will be studied. Arteries and nerves in the region will be studied. Note that the piriformis muscle will be a key landmark in understanding the relationships of this region.

    Review of Relevant Osteology
    Refer to a skeleton and an illustration of an articulated pelvis with intact ligaments. On the pelvis, identify (Figure 6.13):
    • Greater sciatic notch
    • Lesser sciatic notch
    • Ischial spine
    • Ischial tuberosity
    • Sacrospinous ligament
    • Sacrotuberous ligament
    • Greater sciatic foramen
    • Lesser sciatic foramen

    On the femur, identify:
    • Greater trochanter
    • Intertrochanteric crest
    • Trochanteric fossa
    • Gluteal tuberosity

    Dissection Instructions: The Gluteal Region
    1. Place the cadaver in the prone position.
    2. Remove the superficial fascia from the surface of the fascia lata in the gluteal region. You should be able to see the gluteal aponeurosis (Figure 6.14) before you proceed to step 3.
    3. Identify the gluteus maximus muscle (Figure 6.14). The proximal attachment of the gluteus maximus muscle is the sacrum and the sacrotuberous ligament. The distal attachment of the gluteus maximus muscle is the iliotibial tract, and through it, the lateral condyle of the tibia. The deeper part of the inferior half of the gluteus maximus muscle attaches to the gluteal tuberosity of the femur. The gluteus maximus muscle is a powerful extensor of the thigh.
    4. Clean the superficial fascia from the inferior border of the gluteus maximus muscle. The inferior border should be visible from its proximal attachment on the sacrum and coccyx to its distal attachment on the iliotibial tract (Figure 6.14).
    5. Remove the fascia lata from the surface of the gluteus maximus muscle and use your fingers or a probe to define the superior border of the muscle. The superior border of the muscle should be visible from its proximal attachment on the iliac crest to its distal attachment on the iliotibial tract (Figure 6.14).
    6. The fascia lata is relatively thin over the superficial surface of the gluteus maximus muscle, but superior to the muscle it becomes thicker and forms the gluteal aponeurosis. The gluteal aponeurosis spans from the superior border of the gluteus maximus muscle to the iliac crest.
    7. Insert your fingers between the gluteus maximus muscle and the gluteal aponeurosis (Figure 6.14, arrow) and separate the gluteus maximus muscle from the aponeurosis.
    8. Use scissors to detach the gluteus maximus muscle from its proximal attachment. Start at the superior border of the muscle and cut the gluteus maximus muscle close to the ilium, sacrum, and sacrotuberous ligament (Figure 6.14, dashed line).
    9. Push your fingers deep to the gluteus maximus muscle and palpate the inferior gluteal artery, vein, and nerve, which are located near the center of the muscle. The inferior gluteal nerve is the only nerve supply to the gluteus maximus muscle, but the muscle receives blood from both the superior gluteal artery and the inferior gluteal artery.
    10. Use scissors to cut a small "button" out of the gluteus maximus muscle attached to the inferior gluteal artery and vein and inferior gluteal nerve. Use your fingers to loosen the gluteus maximus muscle from deeper structures and reflect it laterally. The gluteus maximus muscle should remain attached only along its distal attachment, widely exposing the deeper structures of the gluteal region (Figure 6.15).
    11. Use a scalpel to incise the gluteal aponeurosis along the iliac crest. Use skinning motions to remove the gluteal aponeurosis from the superficial surface of the gluteus medius muscle. Note that the aponeurosis is firmly attached to the underlying gluteus medius muscle and that it serves as an origin for that muscle.
    12. Identify the gluteus medius muscle. To define its inferior border, insert your finger or a probe lateral to the superior gluteal artery and vein (Figure 6.15) and open the interval between the gluteus medius muscle and the piriformis muscle.
    13. The proximal attachment of the gluteus medius muscle is the deep surface of the gluteal aponeurosis and the lateral surface of the ilium. The distal attachment of the gluteus medius muscle is the greater trochanter of the femur; it is an abductor of the thigh.
    14. The piriformis muscle is located inferior to the gluteus medius muscle. Note that its superior border lies adjacent to the inferior border of the gluteus medius muscle. To define its inferior border, insert your finger or a probe lateral to the inferior gluteal vessels (Figure 6.15) and open the interval between the piriformis muscle and the superior gemellus muscle.
    15. The proximal attachment of the piriformis muscle is the sacrum and its distal attachment is the greater trochanter of the femur. The piriformis muscle is a lateral rotator of the thigh. Verify that the piriformis muscle passes through the greater sciatic foramen and nearly fills it.
    16. Note that the superior gluteal artery, vein, and nerve exit the pelvic cavity and enter the gluteal region by passing over the superior border of the piriformis muscle (i.e., they pass between the piriformis muscle and the gluteus medius muscle).
    17. Use blunt dissection to clean the inferior border of the piriformis muscle. Note that the sciatic nerve, posterior cutaneous nerve of the thigh, inferior gluteal artery and vein, inferior gluteal nerve, nerve to obturator internus, internal pudendal artery and vein, and pudendal nerve exit the pelvic cavity and enter the gluteal region by passing under the inferior border of the piriformis muscle. The pudendal nerve and internal pudendal vessels will be studied during the next block.
    18. Identify the sciatic nerve (Figure 6.15). The sciatic nerve is the largest nerve in the body and it has a tibial division and a common fibular division. These two divisions will separate to form the tibial and common fibular nerves, respectively. In about 12% of specimens the divisions may emerge separately with the common fibular nerve (common peroneal nerve) passing over the superior border of the piriformis muscle or through the center of the piriformis muscle.
    19. Attempt to identify the posterior cutaneous nerve of the thigh deep to the fascia lata. The posterior cutaneous nerve of the thigh can usually be seen passing vertically down the posterior midline of the thigh. Dissect the posterior cutaneous nerve of the thigh from the fascia lata.
    20. Preserving the posterior cutaneous nerve of the thigh, use your fingers to tear the fascia lata posterior to the sciatic nerve and follow the sciatic nerve for 6 or 7 cm into the thigh.
    21. Trace the posterior cutaneous nerve of the thigh proximally to where it lies medial to the sciatic nerve (Figure 6.15). Note that the posterior cutaneous nerve of the thigh was cut from its distal target when the posterior thigh was skinned. It will likely appear as a free hanging nerve.
    22. At the inferior border of the piriformis muscle, identify the cut ends of the inferior gluteal artery and vein, and the inferior gluteal nerve, which lie on the medial side of the posterior cutaneous nerve of the thigh (Figure 6.15).
    23. Identify the tendon of the obturator internus muscle (Figure 6.15). The obturator internus tendon is inferior to the superior gemellus muscle. The proximal attachment of the obturator internus muscle is the margin of the obturator foramen and the inner surface of the obturator membrane. The distal attachment of the obturator internus muscle is on the posterior aspect of the greater trochanter of the femur. The obturator internus muscle is a lateral rotator of the thigh. The obturator internus muscle exits the lesser pelvis by passing through the lesser sciatic foramen.
    24. Identify the two gemellus muscles (L. gemellus, twin) (Figure 6.15). The proximal attachment of the superior gemellus muscle is the ischial spine superior to the obturator internus muscle. The proximal attachment of the inferior gemellus muscle is the ischial tuberosity inferior to the obturator internus muscle. Both gemellus muscles attach with the obturator internus tendon on the greater trochanter of the femur and both are lateral rotators of the thigh. Note: The two gemellus muscles may be large enough to hide the obturator internus tendon.
    25. Identify the quadratus femoris muscle (Figure 6.15), which is inferior to the inferior gemellus muscle. The proximal attachment of the quadratus femoris muscle is the ischial tuberosity and its distal attachment is on the intertrochanteric crest of the femur. The quadratus femoris muscle is a lateral rotator of the thigh.
    26. To expose the gluteus minimus muscle, first locate the branches of the superior gluteal artery and vein superior to the piriformis muscle (Figure 6.15). Insert your finger superior to the superior gluteal artery and vein and deep to the gluteus medius muscle. Push your finger superiorly along the course of these vessels to open the plane of separation between the gluteus medius muscle and the gluteus minimus muscle.
    27. Use scissors to transect the gluteus medius muscle, following the course of the superior gluteal vessels. Gently reflect the proximal portion of the muscle superiorly and observe the superior gluteal nerve.
    28. Reflect the distal part of the gluteus medius muscle and identify the gluteus minimus muscle (Figure 6.15). The proximal attachment of the gluteus minimus muscle is the lateral surface of the ilium. The distal attachment of the gluteus minimus muscle is on the greater trochanter of the femur and it abducts the thigh.
    29. Trace the superior gluteal nerve and vessels laterally to where they supply the tensor fasciae latae muscle.
    IN THE CLINIC: Intragluteal Injections
    The gluteal region is commonly used for intramuscular injections. These injections are made in the superior lateral quadrant of the gluteal region. Injections into the two inferior quadrants of the gluteal region would endanger the sciatic nerve, or the nerves and vessels that pass inferior to the piriformis muscle. Injections into the superior medial quadrant may injure the superior gluteal nerve and vessels. Intragluteal injections into the superior lateral quadrant are relatively safe since the superior gluteal nerve and vessels are well branched in this region.
    Dissection Review:
    1. Replace the muscles of the gluteal region in their correct anatomical positions.
    2. Review the attachments, action, and innervation of each muscle.
    3. Study the functions of muscles in the gluteal region:
      • Extend your thigh. This movement is accomplished by the gluteus maximus muscle.
      • Abduct your thigh. This movement is accomplished by the gluteus medius muscle, gluteus minimus muscle, and tensor of the fascia lata.
      • Laterally rotate your thigh. This motion is accomplished by the piriformis muscle, obturator internus muscle, superior gemellus muscle, inferior gemellus muscle, and quadratus femoris muscle.
    4. Review the anatomy of the safe intragluteal injection site.
    5. If you have completed the dissection of the pelvis and perineum prior to dissection of the lower limb, study the continuity of muscles, vessels, and nerves observed in the gluteal and pelvic regions:
      • Within the pelvis identify the obturator internus muscle and follow the muscle posteriorly into the gluteal region.
      • Within the pelvis identify the piriformis muscle and then follow this muscle laterally to its attachment on the greater trochanter of the femur.
      • Within the pelvis study the gluteal vessels and their relationship to the piriformis muscle and the sacral plexus.
    6. Review the sacral plexus and its contribution to the sciatic nerve. Note that the muscles of the gluteal region are innervated by branches of the sacral plexus



    DISSECTION LABORATORY #3: POSTERIOR COMPARTMENT OF THE THIGH, POPLITEAL FOSSA, AND POSTERIOR COMPARTMENT OF THE LEG
    Learning Objectives: Upon completion of this laboratory, the student will be able to:
    1. Describe the muscular anatomy of the posterior thigh, its muscles, their nerve supply, and their actions in locomotion.
    2. Predict the functional loss and cutaneous areas affected by a given nerve injury to the hip and posterior thigh region; or conversely, given a functional and/or cutaneous loss, be able to predict which nerve or nerves are involved and the probable level of the injury.
    3. Define the popliteal fossa and give the spatial relationships of its contents. 4.Recall the general plan of the collateral circulation at the hip and knee.
    4. Identify the muscles of the posterior compartment of the leg and give their functional significance in locomotion.
    5. Identify the vascular supply of the posterior compartment of the leg.
    6. Identify the nerves of the posterior compartment of the leg, the muscles and cutaneous regions supplied by them, so that given a functional and/or cutaneous loss one can predict the nerve and the probable level of injury.


    Review of Relevant Osteology
    Refer to a skeleton. On the pelvis, identify (Figure 6.6B):
    • Ischial tuberosity

    On the femur, identify:
    • Lateral lip of linea aspera
    • Lateral supracondylar line
    • Medial condyle
    • Lateral condyle
    • Popliteal surface

    On the fibula, identify:
    • Apex
    • Head
    • Neck

    On the tibia, identify:
    • Medial condyle
    • Soleal line


    Dissection Overview: The Posterior Compartment of the Thigh
    The posterior compartment of the thigh contains the posterior thigh muscles: biceps femoris, semimembranosus, and semitendinosus. The muscles of the posterior group extend the thigh and flex the leg. The posterior thigh muscles are commonly known as the "hamstring" muscles.

    The order of dissection will be as follows: The muscles of the posterior compartment of the thigh will be studied. The course and branches of the sciatic nerve will be studied. The dissection will be extended inferiorly to include the popliteal fossa. The muscular boundaries of the popliteal fossa will be identified and the contents of the popliteal fossa will be studied.

    Dissection Instructions: The Posterior Compartment of the Thigh
    1. Place the cadaver in the prone position. Use scissors to incise the fascia lata from the level of the gluteus maximus muscle to the knee and open it widely.
    2. Use blunt dissection to clean the sciatic nerve and follow it inferiorly. Note that the sciatic nerve passes deep to the long head of the biceps femoris muscle (Figure 6.16).
    3. Identify the long head of the biceps femoris muscle. The proximal attachment of the long head of the biceps femoris muscle is the ischial tuberosity and its distal attachment is the head of the fibula. The long head of the biceps femoris muscle is innervated by the tibial division of the sciatic nerve.
    4. Retract the long head of the biceps femoris muscle laterally to observe the short head of the biceps femoris muscle (Figure 6.16). The proximal attachment of the short head of the biceps femoris muscle is the linea aspera of the femur. The tendon of the short head of the biceps femoris muscle joins the tendon of the long head. The biceps femoris muscle extends the thigh and flexes the leg. The short head of the biceps femoris muscle is innervated by the common fibular division of the sciatic nerve.
    5. On the medial side of the thigh, identify the semitendinosus muscle (Figure 6.16). The semitendinosus ("half tendon") muscle is named for the long, cord-like tendon at its distal end. The proximal attachment of the semitendinosus muscle is the ischial tuberosity and its distal attachment is the medial surface of the superior part of the tibia. The semitendinosus muscle extends the thigh and flexes the leg. The semitendinosus muscle is innervated by the tibial division of the sciatic nerve.
    6. Use your fingers to separate the semitendinosus muscle from the semimembranosus muscle. The semimembranosus ("half membrane") muscle is named for the broad, membrane-like tendon at its proximal end. The proximal attachment of the semimembranosus muscle is the ischial tuberosity and its distal attachment is the posterior part of the medial condyle of the tibia. The semimembranosus muscle extends the thigh and flexes the leg. The semimembranosus muscle is innervated by the tibial division of the sciatic nerve.
    7. Verify that the hamstring part of the adductor magnus muscle arises from the ischial tuberosity deep to the proximal attachment of the posterior thigh muscles. Confirm that the adductor magnus muscle forms the deep boundary of the posterior compartment of the thigh (Figure 6.16). The hamstring part of the adductor magnus muscle is innervated by the tibial division of the sciatic nerve.
    8. Follow the sciatic nerve through the posterior compartment of the thigh to the area behind the knee (Figure 6.16). Note that the sciatic nerve gives off unnamed muscular branches to the posterior thigh muscles. The sciatic nerve typically divides at the level of the knee but this division may occur more superiorly, in the thigh or in the gluteal region.


    IN THE CLINIC: Sciatic Nerve
    The sciatic nerve and its branches innervate the posterior muscles of the thigh and the muscles of the leg (which act on the foot). The cutaneous branches of the sciatic nerve innervate a large area of the lower limb. Thus, when the sciatic nerve is injured, significant peripheral neurologic deficits may occur: paralysis of the flexors of the knee and all muscles below the knee, and widespread numbness of the skin on the posterior aspect of the lower limb.


    Dissection Overview: Popliteal Fossa
    1. Define the borders of the popliteal fossa (L. poples, ham):
      • Superolateral - biceps femoris muscle
      • Superomedial - semitendinosus and semimembranosus muscles
      • Inferolateral and inferomedial - the two heads of the gastrocnemius muscle
      • Posterior - skin and deep (popliteal) fascia
      • Anterior - popliteal surface of the femur, the posterior surface of the capsule of the knee joint, and the popliteus muscle
    2. At the superior border of the popliteal fossa, the sciatic nerve usually divides into the tibial and common fibular nerves (Figure 6.16).
    3. Identify the adductor hiatus, which is an opening in the adductor magnus muscle, between its hamstring and adductor parts, and is the terminal end of the adductor canal.
    4. Use blunt dissection to follow the common fibular nerve laterally along the superolateral border of the popliteal fossa. Note that the common fibular nerve parallels the biceps femoris tendon and passes superficial to the lateral head of the gastrocnemius muscle.
    5. Remove the remnants of the deep fascia (popliteal fascia) to expose the medial and lateral heads of the gastrocnemius muscle. Use your fingers to separate the tibial nerve from the loose connective tissue that surrounds it and follow the nerve inferiorly. The tibial nerve passes deep to the plantaris muscle and gastrocnemius muscle at the inferior border of the popliteal fossa (Figure 6.16).
    6. At the inferior border of the popliteal fossa, insert your index fingers between the two bellies of the gastrocnemius muscle. Pull the muscle bellies apart for a distance of 5 to 10 cm. This will expose the structures that pass from the popliteal fossa into the leg. Identify the muscle belly of the plantaris muscle.
    7. The popliteal artery and vein are located deep to the tibial nerve. Note that the popliteal artery and vein are enclosed by a connective tissue sheath. Use scissors to open the sheath. Extend the incision superiorly and inferiorly.
    8. Use a probe to separate the popliteal artery from the popliteal vein. Preserve the popliteal vein but remove its tributaries to clear the dissection field. Verify that the popliteal artery and popliteal vein begin by passing through the adductor hiatus and are continuous with the femoral artery and femoral vein, respectively. The femoral artery and vein change names to popliteal artery and vein when they pass through the adductor hiatus. Recall that the femoral nerve descends in the adductor canal but does not pass through the adductor hiatus.
    9. Use an atlas illustration to study the superior lateral genicular artery and the superior medial genicular artery, which are branches of the popliteal artery that participate in the formation of the arterial anastomoses around the knee joint (genicular anastomosis) (Figure 6.17). These arteries are located deep in the popliteal fossa, proximal to the attachments of the gastrocnemius muscle. You do not need to dissect these arteries.
    10. Distally, the popliteal artery passes deep to the plantaris and gastrocnemius muscles (Figure 6.16).
    11. Using an atlas illustration, observe that the genicular anastomosis receives contributions from the femoral artery, lateral circumflex femoral artery, and anterior tibial artery.
    12. Part of the floor of the popliteal fossa is formed by the popliteus muscle (Figure 6.17). Retract the inferior end of the popliteal artery and vein and identify the popliteus muscle. It will be seen better when the posterior muscles of the leg are dissected.
    13. At the medial side of the knee, observe that the sartorius, gracilis, and semitendinosus tendons converge on the proximal end of the tibia in an arrangement that is named the pes anserinus (L. goose's foot).


    Dissection Review:
    1. Replace the muscles of the posterior compartment of the thigh into their correct anatomical positions.
    2. Using the dissected specimen, review the attachments and actions of the posterior thigh muscles.
    3. Trace the course of the sciatic nerve from the pelvis to the knee. Review its terminal branches.
    4. Trace the femoral artery and vein from the level of the inguinal ligament to the popliteal fossa, naming its branches.
    5. Review the course of the deep artery of the thigh through the medial compartment of the thigh, and then review the course of its perforating vessels through the adductor magnus and brevis muscles into the posterior compartment of the thigh.
    6. Review the genicular anastomosis around the knee, naming the branches of the popliteal artery and lateral circumflex femoral artery that participate.
    7. Review the principal muscle groups of the thigh, the group functions, and the innervation of each muscle group (Figure 6.18):
      • The anterior thigh muscles are innervated by the femoral nerve.
      • The medial thigh muscles are innervated by the obturator nerve.
      • The posterior thigh muscles are innervated by the tibial and common fibular divisions of the sciatic nerve.
    8. Recall the exceptions to the rules of innervation stated above:
      • The pectineus muscle receives motor innervation from both the femoral nerve and the obturator nerve.
      • The ischiocondylar portion of the adductor magnus muscle is innervated by the tibial division of the sciatic nerve.



    Dissection Overview: The Posterior Compartment of the Leg
    The posterior compartment of the leg lies posterior to the interosseous membrane, tibia, and fibula (Figure 6.19). A transverse intermuscular septum divides the muscles of the posterior compartment into superficial and deep groups. The superficial posterior group contains three muscles: gastrocnemius, soleus, and plantaris. The group action of the superficial posterior muscle group is plantar flexion of the foot. The deep posterior group contains four muscles: popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus. The shared actions of the deep posterior muscle group are inversion of the foot, plantar flexion of the foot, and flexion of the toes. The tibial nerve innervates both the superficial and deep posterior muscle groups.

    The order of dissection will be as follows: The superficial veins and cutaneous nerves of the posterior aspect of the leg will be reviewed. The crural fascia of the posterior aspect of the leg will be incised and the superficial posterior group of leg muscles will be examined. The muscles in the superficial posterior group will be reflected to expose the muscles of the deep posterior group. The vessels and nerves of the posterior compartment will be dissected. The muscles of the deep posterior group will be identified. The tendons of the deep posterior group of muscles will be organized where they pass posterior to the medial malleolus by use of a mnemonic device.

    Dissection Instructions: The Posterior Compartment of the Leg
    1. Incise the crural fascia from the popliteal fossa to the calcaneus and open the posterior compartment.
    2. Identify the gastrocnemius muscle (Figure 6.22). The gastrocnemius muscle is the most superficial muscle in the posterior compartment of the leg. The proximal attachments of the two heads of the gastrocnemius muscle are the femoral condyles. The distal attachment of the gastrocnemius muscle is on the calcaneal tuberosity by way of the calcaneal tendon (Achilles' tendon). The gastrocnemius muscle plantar flexes the foot.
    3. Use scissors to transect the medial and lateral heads of the gastrocnemius muscle proximal to the point where they join (Figure 6.22). Reflect the proximal and distal portions of the muscle.
    4. Identify the soleus muscle, which is located deep to the gastrocnemius muscle. The proximal attachments of the soleus muscle are the soleal line of the tibia and the head of the fibula. The distal attachment of the soleus muscle is the calcaneal tendon. The soleus muscle plantar flexes the foot.
    5. Identify the tendon of the plantaris muscle (Figure 6.22). The belly of the plantaris muscle lies in the popliteal fossa and its proximal attachment is the lateral supracondylar line of the femur. In the proximal part of the leg the plantaris tendon courses between the gastrocnemius and soleus muscles. In the distal part of the leg the plantaris tendon may be seen on the medial side of the tendon of the gastrocnemius muscle. The plantaris tendon joins the calcaneal tendon and ultimately attaches to the calcaneus. The plantaris muscle is a plantar flexor of the foot and a weak flexor of the knee. The plantaris muscle and tendon may be absent.
    6. The tibial nerve and posterior tibial artery and vein exit the popliteal fossa by passing deep to the tendinous arch of the soleus muscle (Figure 6.19). They course distally in the transverse intermuscular septum that separates the superficial posterior muscle group from the deep posterior muscle group (Figure 6.19).
    7. Use scissors to transect the calcaneal tendon about 5 cm superior to the tuberosity of the calcaneus (Figure 6.22, dashed line). Use your fingers to separate the calcaneal tendon from the muscles that lie deep to it.
    8. While protecting the tibial nerve and posterior tibial artery and vein as they pass anterior to the soleus muscle, bluntly detach the soleus muscle from its proximal attachment to the soleal line of the tibia but leave the muscle attached to the fibula (note that you will not make the cut along the dashed line just distal to the tendinous arch of the soleus muscle depicted in Figure 6.22. Retract the soleus muscle laterally and the distal part of the gastrocnemius muscle inferiorly to expose the transverse intermuscular septum.
    9. Identify the posterior tibial artery and vein, and the tibial nerve in the transverse intermuscular septum (Figure 6.23). The posterior tibial artery is usually accompanied by two veins. Remove the veins to clear the dissection field.
    10. Use a probe to follow the posterior tibial artery and the tibial nerve proximally. Observe that the popliteal artery bifurcates at the inferior border of the popliteus muscle to form the posterior tibial artery and the anterior tibial artery. Dissect the initial portion of the anterior tibial artery as it passes between the tibia and fibula through an opening in the interosseous membrane.
    11. Retract the contents of the popliteal fossa laterally and identify the popliteus muscle (Figure 6.23). The proximal attachment of the popliteus muscle is the lateral condyle of the femur and its distal attachment is the posterior surface of the proximal tibia. The popliteus muscle rotates the femur on the tibia to unlock the extended knee. It is also a weak flexor of the leg.
    12. Identify the tibialis posterior muscle. The proximal attachments of the tibialis posterior muscle are the tibia and fibula. The distal attachments of the tibialis posterior muscle are the plantar surfaces of several tarsal bones. The tibialis posterior muscle is an inverter and plantar flexor of the foot.
    13. The proximal attachment of the flexor digitorum longus muscle is the tibia. Distally, its tendons attach to the bases of the distal phalanges of the lateral four toes. The flexor digitorum longus muscle flexes toes 2 to 5 and plantar flexes the foot.
    14. The proximal attachment of the flexor hallucis longus muscle (L. hallux, great toe; genitive case, hallucis) is the fibula, and its distal attachment is the distal phalanx of the great toe. The flexor hallucis longus muscle flexes the great toe and plantar flexes the foot.
    15. At the ankle, observe the flexor retinaculum. Note that the tendons of the posterior compartment muscles of leg pass posterior to the medial malleolus, deep to the flexor retinaculum. Trace these tendons, the tibial nerve and the posterior tibial vessels past the flexor retinaculum. You may need to cut the flexor retinaculum and reflect it to properly see these structures at the ankle.
    16. Posterior to the medial malleolus, observe that the posterior tibial artery and the tibial nerve lie between the tendons of the flexor digitorum longus and flexor hallucis longus muscles, deep to the flexor retinaculum (Figure 6.23). Posterior to the medial malleolus, the following mnemonic device may be used to identify the tendons and vessels in anterior to posterior order: Tom, Dick And a Very Nervous Harry (Tibialis posterior, flexor Digitorum longus, posterior tibial Artery, posterior tibial Vein, tibial Nerve, flexor Hallucis longus). Note: On practical exams, we will occasionally cover up everything except the medial malleolus, the calcaneus tendon, and the structures described above passing in between. You must use the mnemonic to distinguish between the tibialis posterior tendon, flexor Digitorum longus tendon, posterior tibial artery, tibial nerve, and flexor hallucis longus tendon.
    17. Once again, observe the vascular distribution in the posterior compartment of the leg (Figure 6.23). Identify the fibular artery. The fibular artery arises from the posterior tibial artery about 2 or 3 cm distal to the inferior border of the popliteus muscle. The fibular artery courses distally between the tibialis posterior muscle and the flexor hallucis longus muscle. It supplies blood to the muscles of the lateral compartment of the leg and lateral side of the posterior compartment of the leg.
    18. The perforating branch of the fibular artery usually arises just above the ankle joint (Figure 6.23). It perforates the interosseous membrane and anastomoses with a branch of the anterior tibial artery (it may be hard to find). Occasionally, the perforating branch of the fibular artery will give rise to the dorsalis pedis artery.
    Dissection Review
    1. Replace the muscles of the posterior compartment of the leg into their correct anatomical positions.
    2. Use the dissected specimen to review the attachments and action of each muscle dissected.
    3. Follow the popliteal artery into the posterior compartment of the leg and identify its branches. Follow the posterior tibial artery distally and identify the origin of the fibular artery. Review the distribution of the arteries of the posterior compartment of the leg.
    4. Follow the tibial nerve through the popliteal fossa and posterior compartment of the leg, observing that it gives off numerous muscular branches.
    5. Review the relationships of the nerve, tendons, and vessels posterior to the medial malleolus and use this pattern to organize the contents of the deep posterior compartment of the leg.
    6. Recall the rule of innervation of the posterior compartment of the leg:
      • All muscles in the posterior compartment of the leg are innervated by the tibial nerve.



    DISSECTION LABORATORY #4: ANTERIOR AND LATERAL COMPARTMENTS OF THE LEG
    Learning Objectives: Upon completion of this laboratory, the student will be able to:
    1. Describe the arrangement, specializations and compartments of the fascia of the leg.
    2. Identify the muscles of the anterior and lateral compartments of the leg and give their functional significance in locomotion.
    3. Identify the vascular supply of the anterior and lateral compartments of the leg.
    4. Identify the nerves of the anterior and lateral compartments of the leg, the muscles and cutaneous regions supplied by them, so that given a functional and/or cutaneous loss one can predict the nerve and the probable level of injury.


      Review of Relevant Osteology

      The two bones of the leg are unequal in size. The larger tibia is the weight-bearing bone of the leg. The fibula is surrounded by muscles except at its proximal and distal ends. The tibia and fibula are joined by an interosseous membrane (      Figure 6.19). The crural fascia is attached to the fibula by two intermuscular septa: anterior and posterior. The tibia, fibula, interosseous membrane, and intermuscular septa divide the leg into three compartments: posterior, lateral (fibular), and anterior.

      Refer to a skeleton. On the tibia, identify (Figure 6.20):

      On the fibula, identify (Figure 6.20):
      In the articulated foot, identify the seven tarsal bones (Figure 6.21):
      On the calcaneus, identify (Figure 6.21):
      Identify the five metatarsal bones and the tuberosity of the fifth metatarsal bone.

      Identify 14 phalanges (singular, phalanx). Note that the first toe has only two phalanges, whereas the other toes each have three phalanges.


      Dissection Overview: Anterior Compartment of the Leg

      The anterior compartment of the leg contains four muscles: tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius. The deep fibular nerve innervates the muscles of the anterior compartment. The group actions of the muscles in the anterior compartment are dorsiflexion of the foot, inversion of the foot, and extension of the toes.

      The order of dissection will be as follows: The distribution of cutaneous nerves over the lower anterior surface of the leg and dorsal surface of the foot will be reviewed. The anterior aspect of the deep fascia of the leg and foot will be examined and the extensor retinacula will be identified. The anterior compartment of the leg will be opened and the relationships of tendons, vessels, and nerves will be examined on the anterior surface of the ankle. The tendon of each muscle of the anterior compartment will be followed into the foot. The intrinsic muscles of the dorsum of the foot will be identified. The deep vessels and deep nerve of the leg and dorsum of the foot will be dissected.

      Dissection Instructions: Anterior Compartment of the Leg

      1. Place the cadaver in the supine position.
      2. Recall that the superficial fibular nerve provides most of the cutaneous innervation to the anterior surface of the ankle and dorsum of the foot (Figure 6.3A).
      3. Remove the remnants of superficial fascia on the anterior surface of the leg and dorsum of the foot. Preserve the branches of the superficial fibular nerve.
      4. Observe the crural fascia and note that it is firmly attached to the anterior border of the tibia.
      5. Identify the superior and inferior extensor retinacula on the anterior surface of the ankle (Figure 5-56). The retinacula are transverse thickenings of the crural fascia that hold tendons in place. The superior extensor retinaculum extends across the tendons superior to the ankle joint. The inferior extensor retinaculum is at the level of the ankle joint and it is Y-shaped (although the Y is not always pretty). The stem of the "Y" is attached to the calcaneus. You do not need to be able to distinguish between the superior and inferior extensor retinacula but you may be asked to identify the extensor retinaculum as a whole.
      6. Use a scalpel to make a vertical cut through the crural fascia just below the lateral condyle of the tibia. Use forceps to lift the edges of the crural fascia and observe that the muscles of the anterior compartment are attached to its deep surface. Extend the cut through the crural fascia in the distal direction as far as the inferior extensor retinaculum.
      7. The proximal attachments of the anterior muscles of the leg are on the proximal tibia, fibula, and interosseous membrane. Do not attempt to dissect the proximal attachments.
      8. Note that at this point there are two major muscles visible: The tibialis anterior muscle is medial, and the extensor digitorum longus muscle is lateral. Use your fingers or blunt dissection to spread the two muscles apart. In the interval between these muscles, find the extensor hallucis longus muscle, the anterior tibial artery and vein, and the deep fibular nerve (deep peroneal nerve).
      9. Observe the vessels and nerves and the tendons of the anterior muscles of the leg where they cross the anterior surface of the ankle joint. From medial to lateral, identify (Figure 6.24):
        • Tibialis anterior tendon
        • Extensor hallucis longus tendon
        • Anterior tibial artery and vein
        • Deep fibular nerve
        • Extensor digitorum longus tendon
        • Fibularis tertius tendon
      10. Follow the tendon of the tibialis anterior muscle into the foot. Observe that the distal attachment of the tibialis anterior tendon is the superior aspect of the medial tarsal bones. The tibialis anterior muscle dorsiflexes and inverts the foot.
      11. Follow the tendon of the extensor hallucis longus muscle into the foot. Observe that the distal attachment of the extensor hallucis longus tendon is the distal phalanx of the great toe. The extensor hallucis longus muscle extends the great toe and dorsiflexes the foot.
      12. Observe that the tendons of the extensor digitorum longus muscle attach to the middle and distal phalanges of the lateral four toes. The extensor digitorum longus muscle extends the toes and dorsiflexes the foot. Note that each of these tendons forms an extensor expansion.
      13. On the lateral side of the foot, observe that one of the tendons coming from the extensor digitorum longus muscle does not attach to the phalanges. This is the tendon of the fibularis tertius muscle (the belly of the fibularis tertius muscle is fused with the extensor digitorum longus muscle). Follow the tendon of the fibularis tertius muscle to its distal attachment on the dorsal surface of the fifth metatarsal bone (Figure 6.24). The fibularis tertius muscle dorsiflexes the foot and assists in eversion of the foot. The fibularis tertius muscle is absent in about 5% of specimens.
      14. At the level of the superior extensor retinaculum, identify the anterior tibial artery (Figure 6.24). Trace the anterior tibial artery proximally. If you haven't already, use your fingers to forcibly separate the extensor digitorum longus muscle and the tibialis anterior muscle. Follow the anterior tibial artery proximally between these two muscle bellies.
      15. Use a probe to clean the anterior tibial artery. Note that it passes over the superior border of the interosseous membrane (Figure 6.24). Note that the anterior tibial artery lies directly on the anterior surface of the interosseous membrane and that it gives rise to unnamed muscular branches.
      16. Observe that the deep fibular nerve joins the anterior tibial artery just below the knee (Figure 6.24). The deep fibular nerve is the motor nerve of the anterior compartment of the leg and the muscles in the dorsum of the foot. The deep fibular nerve is a branch of the common fibular nerve.
      17. Return to the ankle region and trace the distal end of the anterior tibial artery deep to the inferior extensor retinaculum. As the anterior tibial artery crosses the ankle joint, its name changes to dorsalis pedis artery (L. pes, pedis, foot).
      18. Use scissors to cut the inferior extensor retinaculum over the extensor digitorum longus tendons. Retract the tendons of the extensor digitorum longus muscle in the lateral direction.
      19. On the dorsum of the foot deep to the tendons of the extensor digitorum longus muscle, identify the extensor digitorum brevis muscle and the extensor hallucis brevis muscle (Figure 6.24). The extensor digitorum brevis and extensor hallucis brevis muscles share a common muscle belly that attaches to the calcaneus. Four tendons arise from this muscle belly and attach to the extensor expansions of toes 1 to 4. The portion of this muscle that attaches on the great toe is called the extensor hallucis brevis muscle. These muscles extend the toes and they are innervated by the deep fibular nerve.
      20. Follow the dorsalis pedis artery onto the dorsum of the foot. In the distal part of the leg, the dorsalis pedis artery passes deep to the extensor hallucis longus tendon to lie on the lateral side of the tendon at the ankle. In the living person, the pulse of the dorsalis pedis artery can be palpated between the tendons of the extensor hallucis longus muscle and the extensor digitorum longus muscle.
      21. The arcuate artery is a branch of the dorsalis pedis artery that crosses the proximal ends of the metatarsal bones. The lateral three dorsal metatarsal arteries are branches of the arcuate artery. Do not look for the arcuate or dorsal metatarsal arteries.
      22. The lateral tarsal artery arises from the dorsalis pedis artery near the ankle joint and passes deep to the extensor digitorum brevis and extensor hallucis brevis muscles. The lateral tarsal artery joins the lateral end of the arcuate artery to complete an arterial arch. Do not look for the lateral tarsal artery.
      23. The deep plantar artery arises from the dorsalis pedis artery near the origin of the arcuate artery. The deep plantar artery passes between the first and second metatarsal bones to enter the sole of the foot. In the sole of the foot, the deep plantar artery anastomoses with the plantar arch.
      24. At the level of the ankle, identify the deep fibular nerve (Figure 6.24). Use blunt dissection to follow the deep fibular nerve into the dorsum of the foot. Note that the deep fibular nerve innervates the extensor digitorum brevis muscle and the extensor hallucis brevis muscle. The deep fibular nerve then continues toward the great toe to give rise to two dorsal digital branches.
      25. Use an illustration and your cadaver specimen to trace the cutaneous branch of the deep fibular nerve to the region of skin between the great toe and the second toe (Figure 6.24). Understand that the skin between the great toe and the second toe is the only skin on the dorsum of the foot that is innervated by the deep fibular nerve.
      Dissection Review:
      1. Use the dissected specimen to review the attachments and actions of the muscles in the anterior compartment of the leg.
      2. Trace the anterior tibial artery through the anterior compartment to the foot, where its name changes to dorsalis pedis artery. Review the branches of this arterial system.
      3. Recall the rule of innervation for the anterior compartment of the leg and the dorsum of the foot:
        • All muscles in the anterior compartment of the leg and the dorsum of the foot are innervated by the deep fibular nerve.


      Dissection Overview: Lateral Compartment of the Leg

      The lateral compartment of the leg contains two muscles: fibularis brevis and fibularis longus. The nerve of the lateral compartment is the superficial fibular nerve. The group action of the muscles in the lateral compartment of the leg is to evert and plantar flex the foot.

      Dissection Instructions: Lateral Compartment of the Leg

      1. Examine the crural fascia on the lateral side of the leg. Identify the superior fibular retinaculum, a thickening of the crural fascia (Figure 5-56). It is found on the lateral side of the ankle posterior to the lateral malleolus.
      2. At the midlevel of the leg, identify the superficial fibular nerve (superficial peroneal nerve) where it penetrates the crural fascia (Figure 6.3A and Figure 6.24). Follow the superficial fibular nerve distally. It is the primary cutaneous nerve to the dorsum of the foot and gives rise to several dorsal digital branches (Figure 6.24). The superficial fibular nerve is a branch of the common fibular nerve.
      3. Use scissors to incise the crural fascia overlying the lateral compartment of the leg. Carry the incision as far inferiorly as the superior fibular retinaculum. Open the crural fascia and observe that the fibularis longus muscle is attached to its inner surface.
      4. Follow the tendons of the fibularis brevis and fibularis longus muscles distally and observe that their tendons pass deep to the superior and inferior fibular retinacula. Note that the tendon of the fibularis brevis muscle is anterior to the tendon of the fibularis longus muscle where they pass posterior to the lateral malleolus.
      5. Follow the tendon of the fibularis brevis muscle inferiorly to its distal attachment on the tuberosity of the fifth metatarsal bone (Figure 6.24).
      6. Follow the tendon of the fibularis longus muscle inferiorly and observe that it turns around the lateral side of the tarsal bones and enters the plantar compartment of the foot en route to its distal attachment on the plantar surface of the medial tarsal bones.
      7. Confirm that the deep fibular nerve and superficial fibular nerve are branches of the common fibular nerve. To do this, push a probe deep to the fibularis longus muscle along the course of the common fibular nerve. Be sure that the probe is superficial to the nerve and cut down through the fibularis longus muscle to the probe. Reflect the cut sides of the muscle and identify the bifurcation of the common fibular nerve.


      IN THE CLINIC: Common Fibular Nerve
      The common fibular nerve is the most frequently injured nerve in the body because of its superficial position and relationship to the head and neck of the fibula. When the common fibular nerve is injured, there is impairment of eversion, dorsiflexion of the foot, and extension of the toes. The result is a condition called "foot drop," resulting in steppage gait (the advancing foot hangs with the toes pointed toward the ground, the knee being lifted high so that the toes may clear the ground). There will also be sensory loss on the dorsum of the foot and toes.
      Dissection Review
      1. Use the dissected specimen to review the attachments and actions of the muscles in the lateral compartment of the leg.
      2. Understand that the fibular artery supplies the muscles of the lateral compartment of the leg by several small perforating branches that penetrate the posterior intermuscular septum.
      3. Recall the rule of innervation for the lateral compartment of the leg:
        • Both of the muscles in the lateral compartment of the leg are innervated by the superficial fibular nerve.
      4. Review the principal muscle groups of the leg, the group functions, and the innervation of each muscle group
        • The posterior leg muscles are innervated by the tibial nerve.
        • The lateral leg muscles are innervated by the superficial fibular nerve.
        • The anterior leg muscles are innervated by the deep fibular nerve.


      PROSECTION ASSIGNMENT: PLANTAR COMPARTMENT OF THE FOOT
      Learning Objectives: Upon completion of this laboratory, the student will be able to:
      1. Describe the bony structure of the foot, including its arches, subtalar and transverse tarsal joints, and the bones and ligaments contributing to its strength and flexibility.
      2. Describe the arrangement, specializations, and compartments of the foot.
      3. Identify the muscles of the foot and give their functional significance in locomotion.
      4. Identify the vascular supply of the foot and give the regions supplied by each.
      5. Identify the nerves of the foot, and the muscles and cutaneous regions supplied by them, so that given a functional and/or cutaneous loss one can predict the nerve and the probable level of injury.


        Overview:

        You will not dissect the plantar compartment of the foot. Prosections are available in the lab and you should study the anatomy as described in the lecture using the prosected specimens.

        Instructions: First Layer

        1. Observe and reflect the plantar aponeurosis.
        2. Identify the flexor digitorum brevis muscle (Figure 6.27). The proximal attachment of the flexor digitorum brevis muscle is the calcaneal tuberosity The distal attachments of the flexor digitorum brevis muscle are the middle phalanges of the lateral four toes. The flexor digitorum brevis muscle flexes the lateral four toes. Trace the flexor digitorum brevis tendons to their distal attachments. Remove remnants of the plantar aponeurosis as necessary.
        3. Identify the abductor hallucis muscle (Figure 6.27). The abductor hallucis muscle is located on the medial side of the flexor digitorum brevis muscle. The proximal attachments of the abductor hallucis muscle is the medial side of the calcaneal tuberosity. The distal attachment of the abductor hallucis muscle is the medial side of the proximal phalanx of the great toe and it abducts the great toe. Use blunt dissection to follow the tendon to its distal attachment.
        4. Identify the abductor digiti minimi muscle (Figure 6.27). The proximal attachment of the abductor digiti minimi muscle is the calcaneal tuberosity and its distal attachment is the lateral side of the proximal phalanx of the fifth (small) toe. The abductor digiti minimi muscle abducts the fifth toe. Follow the tendon to its distal attachment.
        5. In the distal one-third of the sole of the foot, look for common and proper plantar digital nerves, which are branches of the medial and lateral plantar nerves (Figure 6.27). The common and proper plantar digital nerves lie between the tendons just identified.


        Instructions: Second Layer

        1. Identify the medial and lateral plantar nerves and arteries (Figure 6.28).
        2. Identify the quadratus plantae muscle, which is deep to the flexor digitorum brevis muscle (Figure 6.28). The proximal attachment of the quadratus plantae muscle is the calcaneus and its distal attachment is the tendon of the flexor digitorum longus muscle. The quadratus plantae muscle assists the flexor digitorum longus muscle in flexing the lateral four toes.
        3. Identify the flexor digitorum longus tendons. Observe that its four tendons pass through the tendons of the flexor digitorum brevis muscle to insert into the distal phalanges of digits 2-4 (Figure 6.28).
        4. Observe that four lumbrical muscles arise from the tendons of the flexor digitorum longus muscle. The distal attachments of the lumbrical muscles are the extensor expansions of the lateral four toes.


        Instructions: Third Layer

        1. Reflect the quadratus plantae and flexor digitorum longus muscles.
        2. Identify the flexor hallucis brevis muscle (Figure 6.29). The flexor hallucis brevis muscle has a medial head and a lateral head, and each head has its own tendon. A sesamoid bone is found in each of the tendons. The proximal attachment of the flexor hallucis brevis muscle is on the lateral tarsal bones. The distal attachment of the flexor hallucis brevis muscle is the proximal phalanx of the great toe and it flexes the great toe.
        3. Observe that the tendon of the flexor hallucis longus muscle lies between the two sesamoid bones of the flexor hallucis brevis muscle. Verify that the tendon of the flexor hallucis longus is attached to the distal phalanx of the great toe (Figure 6.29).
        4. Identify the adductor hallucis muscle. The adductor hallucis muscle has a transverse head and an oblique head (Figure 6.29). Both heads attach to the lateral side of the proximal phalanx of the great toe. The adductor hallucis muscle adducts the great toe (i.e., moves it toward the second toe).
        5. Identify the flexor digiti minimi muscle. The proximal attachment of the flexor digiti minimi muscle is the fifth metatarsal bone and its distal attachment is the proximal phalanx of the fifth toe. The flexor digiti minimi muscle flexes the fifth toe.


        Instructions: Fourth Layer

        1. Trace the lateral plantar artery distally. At the level of the base of the metatarsal bones, the lateral plantar artery turns deeply to form the plantar arch (Figure 6.29). Follow the plantar arch medially until it passes deep to the oblique head of the adductor hallucis muscle.
        2. The medial end of the plantar arch is formed by the deep plantar branch of the dorsalis pedis artery (Figure 6.24). Use an illustration to study the pattern of distribution of the plantar metatarsal arteries that arise from the plantar arch.
        3. The interosseous muscles are located superior (deep) to the plantar arch. Use an illustration to study the interosseous muscles. The four Dorsal interosseous muscles are ABductors (DAB) and the three Plantar interosseous muscles are ADductors (PAD) of the toes. Recall that the reference axis for abduction and adduction passes through the second toe.
        4. Locate the fibularis longus tendon posterior to the lateral malleolus (Figure 6.29). Follow the fibularis longus tendon into the sole of the foot and note that it turns deeply around the lateral side of the tarsal bones.
        5. The fibularis longus tendon crosses the sole of the foot at its deepest plane. The distal attachment of the fibularis longus tendon is onto the medial tarsal bones.
        6. Attempt to follow the tibialis posterior tendon distally and verify that it has a broad distal attachment on the tarsal bones.
        7. Once again, identify the flexor hallucis longus muscle in the posterior compartment of the leg. Follow its tendon distally until it disappears into an osseofibrous tunnel at the medial side of the ankle. Lift the tendon of the flexor hallucis longus muscle with a probe and verify that it crosses the inferior surface of the sustentaculum tali. The sustentaculum tali acts as a pulley to change the direction of force of the flexor hallucis longus muscle.


        Dissection Review:
        1. Replace the structures of the four layers of the sole of the foot into their correct anatomical positions.
        2. Using the dissected specimen, review the attachments and action of each muscle. Organize the muscles from superficial (inferior) to deep (superior).
        3. Follow the posterior tibial artery from its origin in the leg to its bifurcation in the sole of the foot. Use an illustration and the dissected specimen to review the distribution of the medial and lateral plantar arteries. Review the connection between the deep plantar arch and the deep plantar branch of the dorsalis pedis artery.
        4. Trace the course of the tibial nerve from the popliteal fossa to the medial side of the ankle. Follow its two branches in the sole of the foot (medial and lateral plantar nerves). Use a textbook description to help you relate the motor and sensory function of the lateral and medial plantar nerves to your dissected specimen:
          • The medial plantar nerve innervates the abductor hallucis muscle, flexor digitorum brevis muscle, flexor hallucis brevis muscle, and medial lumbrical muscle. The medial plantar nerve will provide cutaneous innervation to the plantar surfaces of the medial 3½ toes. The motor and cutaneous distribution of the medial plantar nerve is comparable to the distribution of the median nerve in the hand.
          • The lateral plantar nerve innervates all other muscles in the sole of the foot and provides cutaneous innervation to the plantar surfaces of the lateral 1½ toes. The motor and cutaneous distribution of the lateral plantar nerve is comparable to the distribution of the ulnar nerve in the hand.
          • The proper plantar digital nerves innervate the dorsal surface of the toes as far proximally as the distal interphalangeal joint. The nail bed is included in the area innervated by the proper plantar digital nerves. This pattern of innervation has significance for proper application of local anesthesia prior to removal of damaged toe nails.