PROCEDURE - POSTERIOR THIGH

1. PRE-WORK (before lab) review the organization of the bony lower extremity from your atlas or on an articulated skeleton in the lab. 
    (Netter479) (Netter504)

a) The proximal femur articulates with the pelvis in a ball and socket joint.  The head and neck of the femur project medially at a sharp angle into the socket on the pelvis. A superolaterally directed bony knob, the greater trochanter, extends from the proximal end of the femur. A smaller, inferomedial ridge of bone, the lesser trochanter, is present just inferior to the neck/head. These trochanters form attachment points for several muscles acting on the femur.

b) On the distal end of the femur, the bone diverges into two articulating surfaces of the knee joint, the lateral and medial condyles of the femur.

c) The femoral condyles rest on plateaus of bone present on the tibia, the lateral and medial condyles of the tibia. This flat surface is commonly called the tibial plateau.

d) Lateral to the tibia is the smaller fibula, which has a head that articulates with the lateral side of the tibia. 

e) The tibia and fibula terminate at the ankle in a medial malleolus (tibia) and lateral malleolus (fibula) that articulate with the talus to form the ankle joint.

CLINICAL EXERCISE - Malleolar Fixation

2. The leg and ankle are common locations for fractures, which can cause instability of the bony architecture of the ankle and need stabilization (fixation) with hardware.

In this clinical exercise with your donor, you have the chance to drill into the bones of the leg at the ankle to stabilize the fibula and tibia with a bone screw in a mock surgical intervention.  For the steps to take:
                                ------ click here ------

3. With the donor in the prone position reflect the previously dissected skin away from the posterior thigh.

4. Extend the skin incision along the posterior side of the lower extremity from the thigh down to the heel of the foot.
     (Figure505)

5. Working from superior to inferior, remove any subcutaneous tissue until the fascia lata is exposed.
    (Figure505) (Netter474)

The fascia lata is a continuous sheath of strong connective tissue encasing the thigh. The lateral aspect of this sheath thickens forming the iliotibial band. Inferiorly, the fascia lata is continuous with the crural fascia of the leg (i.e. the fascial sheath changes name when you are in the leg).

6. Continue reflecting skin from across the popliteal fossa (depressed/concave area posterior to the knee) and inferiorly along the posterior leg.
    (Figure505) (Figure506) (Netter474) (Photo5007)

As you reflect the skin and superficial fascia of the popliteal fossa and leg, look for the small saphenous vein entering the popliteal fossa from the subcutaneous tissue. Trace about 10cm on the vein if you find it.

We will not fully trace the vein fully, but it originates in the foot and courses in the superficial fascia of the posterior leg before entering the popliteal fossa.

The sural nerve carries cutaneous sensory information and courses parallel to the small saphenous vein in the inferior half of the leg (i.e. the sural nerve emerges from the crural fascia into the subcutaneous tissue about halfway down the posterior side of the leg).

The sural nerve is the 'nerve of choice' for nerve grafts. The nerve is long, easily accessible in the superficial fascia, and the absence of the nerve has limited side effects (loss of sensation from the posterolateral lower leg and lateral side of the foot).

7. Reflect any remaining skin and superficial fascia from the posterior thigh and leg as far as the foot, preserving a small segment (~5cm) of the small saphenous vein and sural nerve if possible.

You may observe numerous additional small veins within the superficial fascia which are not individually named. These form the superficial venous system of the lower extremity. (Photo5006)

Varicose veins is the condition where a vein becomes twisted and enlarged, usually benign. Risk increases with age and these are most common in the superficial venous system in the leg. While the term 'varicose veins' applies to any vein in the body undergoing this process, the term is almost synonymous in common use with occurrence in the leg due to the high probability of the condition occurring there.

8. Using scissors, make a longitudinal incision in the posterior surface of the fascia lata from the level of the gluteal muscles to the popliteal fossa following the line of the previous skin incision.
    (Netter474)

9. Spread the fascia lata widely opening the posterior compartment of the thigh.
    (Netter474) (Netter485)

The semitendinosus, semimembranosus and biceps femoris muscles occupy the posterior compartment of the thigh and are referred to collectively as the 'hamstrings'.

As you spread the fascia lata you may observe branches of the posterior cutaneous nerve of the thigh. This nerve lies deep to the fascia lata, but its branches pierce through to innervate the skin of the posterior thigh.

10. Return to the gluteal region and using blunt dissection follow the sciatic nerve inferiorly from the gluteal region to where it passes deep to a muscle, which will be the long head of the biceps femoris muscle.
    (Figure507) (Netter485) (Netter492) (Photo5008)

11. Blunt dissect superiorly to define the boundaries of the long head of the biceps femoris muscle, following the muscle to its proximal attachment to the ischial tuberosity.
    (Figure508) (Netter485) (Netter492) (Photo5008)

12. Retract the long head of the biceps femoris laterally and observe the sciatic nerve continuing deep to the muscle.
    (Netter485) (Netter492) (Netter531) (Photo5008)

Follow the sciatic nerve only as far as the popliteal fossa at this time.

As you follow the sciatic nerve, you may observe small branches splitting from the nerve and innervating each of the posterior compartment muscles. The sciatic nerve innervates all three muscles of the posterior compartment of the thigh.

13. Follow the long head of the biceps femoris muscle distally, identifying the short head of the biceps femoris which joins to the long head near the knee.
    (Figure508) (Netter485) (Netter492) (Photo5009)
    (iPhoto5004)

The short head arises from the femur and shares a common tendon with the long head of the biceps femoris. The tendon inserts distally into the head of the fibula on the lateral side of the leg.

The long head spans both the hip and knee joint, so the long head has action on both joints (hip extension and knee flexion), while the short head spans only the knee joint (knee flexion).

The blood supply to the biceps femoris muscle is from perforating branches of the profunda femoris artery in the anterior compartment of the thigh. We will examine this artery later.

14. Return to the ischial tuberosity and identify the attachment of the semitendinosus muscle just medial to the origin of the long head of the biceps femoris muscle.
    (Figure507) (Figure508) (Netter485) (Photo5008)
    (iPhoto5004)

15. Blunt dissect following the semitendinosus muscle distally as it runs parallel and medial to the biceps muscle before diverging to form a long cord-like tendon that attaches to the medial side of the proximal tibia.
    (Figure508) (Netter485)
    (iPhoto5004)

16. Force your fingers deep to the semitendinosus muscle, retracting the muscle to expose the semimembranosus muscle deep to the semitendinosus muscle.
    (Figure508) (Netter485) (Photo5008)

The semimembranosus muscle also attaches to the ischial tuberosity, passes medially, and forms a broad membrane-like distal tendon which inserts into the medial condyle of the tibia.

Since both the semitendinosus and semimembranosus span the hip and knee joints they act on both joints  (hip extension and knee flexion).

PROCEDURE - POPLITEAL FOSSA

17. Examine the popliteal fossa (pit of the knee) and observe that it is a diamond shaped transitional region between the thigh and leg forming a shallow depression.
    (Figure509) (Netter507) (Photo5010)

The popliteal fossa is the triangular region posterior to the knee demarcated by the semimembranosus & semitendinosus (superomedial edge), biceps femoris (superolateral edge), and the two heads of the gastrocnemius muscle (inferomedial and inferolateral).

18. Spread the fascia lata so you can observe the apex (superior part of the fossa) and follow the sciatic nerve into the popliteal fossa where it divides into the common fibular and the tibial nerve.
    (Figure509) (Netter507) (Netter532) (Photo5011)

This division typically occurs at the level of the knee, but can occur higher in the thigh in some individuals. The nerve branches are 'pre-sorted' and travel in loose fascia (i.e. the epineurium), so the two divisions separate easily if inadvertently stretching that fascia.

The common fibular nerve was previously known as the common peroneal nerve. This older terminology also applied also to the superficial and deep fibular nerves (i.e. previously called the superficial and deep peroneal nerves). Thus, depending on the source you may see the modern or older terminology.

19. Remove any fat within the fossa while taking care not to damage vessels or nerves as you find them, and observe the presence of the two muscle bellies of the gastrocnemius muscle at the inferior edge of the popliteal fossa.
    (Figure509) (Netter507) (Photo5011)

20. Spread the medial and lateral muscle bellies of the gastrocnemius apart to approximately ~10cm distal along the leg to better expose the contents of the popliteal fossa.
    (Figure509) (Netter507) (Photo5011)

If the muscle bellies are tightly connected to each other, you may need to use a scalpel to start the separation so you can spread the bellies.

21. At the bifurcation of the sciatic nerve, follow the common fibular nerve laterally as far as the neck of the fibula.
    (Figure509) (Netter507) (Photo5011)
    (iPhoto5002)

The common fibular nerve in the popliteal fossa runs distally along the medial edge of the biceps femoris tendon to the fibular head.

The lateral position of the fibular nerve as it courses around the bones of the knee leaves this nerve vulnerable to compression against the bone in injury (analogous to the ulnar nerve 'funny bone' vulnerability at the elbow).

Several cutaneous branches arise from the common fibular nerve, including articular branches around the knee and potentially sural nerve contributions, all innervating skin of the knee and leg. We will not dissect these specifically.

22. Return to the bifurcation of the sciatic nerve and follow the tibial nerve until it passes deep to the gastrocnemius muscle.
    (Figure509) (Netter507) (Photo5011)

The tibial nerve occupies a central position in the popliteal fossa running superior to inferior through the fossa. At the inferior edge of the popliteal fossa the tibial nerve passes deep to the plantaris and gastrocnemius muscles.

The tibial nerve can also give rise to contributions to the sural nerve, providing cutaneous sensation to the leg. It is common to see sural nerve contributions from the fibular only, tibial only, or from both nerves. 

23. Retract the tibial nerve gently laterally and observe connective tissue of the popliteal sheath deep to the nerve, which houses the popliteal artery and vein.
    (Figure509) (Netter507)

24. Using scissors slice open the sheath and observe the popliteal vein.
    (Figure509) (Netter507) (Photo5011)
    (iPhoto5002)

The popliteal vein is typically lateral and more superficial than the artery.

25. Gently retract the popliteal vein and observe the deeper popliteal artery.
    (Figure509) (Netter507) (NetterBP108) (Photo5011)

The popliteal vessels bifurcate into the anterior and posterior tibial arteries as they pass the level of the popliteal fossa. This bifurcation may not be visible yet.

The popliteal artery is a continuation of the superficial femoral artery, which passes from the anterior compartment of the thigh into the popliteal fossa by way of the adductor hiatus. The superficial femoral artery changes name to the popliteal artery when it passes through the hiatus.

Genicular branches arising from the popliteal artery form an elaborate collateral network called the genicular anastomosis around the knee joint. The main branches forming the anastomosis are paired superior genicular arteries (arising around the femoral epicondyles), paired inferior genicular arteries (arising around the epicondyles of the tibia/fibula), and a middle genicular branch (supplying the cruciate ligaments). We will not dissect these specifically. (Photo5054)

The deepest structure of the popliteal fossa is the popliteus muscle which courses from the tibia to the lateral epicondyle of the femur. This muscle essentially forms the 'floor' of the popliteal fossa with the popliteal artery, vein and tibial nerve all coursing across the superficial side the popliteus muscle. In the elderly, this muscle is indistinct so we will not dissect for this structure. 

PROCEDURE - POSTERIOR LEG

26. Using scissors make a longitudinal incision in the posterior surface of the crural fascia from the level of the popliteal fossa to the calcaneus at the foot following the line of the previous skin incision.
    (Netter474) (Netter507) (Netter514)

The crural fascia is a dense fascia that fuses around the knee and is continuous with the fascia lata proximally. This fascia forms a sleeve surrounding the leg.

An extension of this fascia, the transverse intermuscular septum, divides the posterior leg into a superficial posterior and deep posterior compartment. This will be examined in following steps.

Additional septa form an anterior and lateral compartment, which will be examined in another lab session. 

27. Starting at the popliteal fossa, identify the two heads of the gastrocnemius muscle and follow each head proximally to their attachments to the epicondyles of the femur.
    (Figure510) (Netter507) (Photo5011) (Photo5012)

The gastrocnemius muscle is the most superficial calf muscle with medial and lateral heads attached to the epicondyles of the femur. The muscle spans both the knee and ankle joints and acts on both joints (knee flexion and ankle plantar flexion).

28. Follow the gastrocnemius muscle distally and observe that the two heads of the muscle come together and form a tendon which merges into the calcaneal tendon.
    (Figure510) (Netter507) (Photo5012)

The calcaneal tendon is commonly called the Achilles' tendon and inserts onto the calcaneal tuberosity (most posterior bone of the foot).

The calcaneal tendon is formed by the merging of the tendons from all the posterior superficial compartment muscles (i.e. the gastrocnemius, soleus, and plantaris tendons).

29. Transect the gastrocnemius muscle approximately in the middle of the muscle bellies.
    (Figure510a)

This is ~10cm distal to the popliteal fossa or about a third the length of the leg.

30. Reflect the two halves of the gastrocnemius muscle to expose the deeper soleus muscle.
    (Figure510) (Netter508)

The soleus muscle arises from both tibia and fibula and forms a tendinous arch between the bones at the lower border of popliteus. The popliteal artery and tibial nerve pass deep to this tendinous arch as they course inferiorly.

Since the soleus muscle crosses only the ankle joint the muscle action is plantar flexion at the ankle.

31. Follow the soleus muscle distally and observe that the soleus tendon fuses into the calcaneal tendon.
    (Netter508)

32 Examine along the medial surface of the soleus muscle for the long thin tendon of the plantaris muscle coursing just deep to the gastrocnemius muscle.
    (Figure510) (Netter508) (Photo5014)

33. Follow the plantaris muscle tendon proximally to the small plantaris muscle located within the popliteal fossa.
    (Figure510) (Netter508) (Photo5014)

The plantaris muscle lies in the popliteal fossa attached to the lateral femoral epicondyle and has a long, thin distal tendon running between gastrocnemius and soleus fusing into the calcaneal tendon.

The functional significance of this muscle is debated. One hypothesis is that the muscle provides balance  proprioceptive feedback due to the unusually high density of proprioceptive receptor organs in the muscle and tendon.

However, function is sufficiently minimal that the long tendon can be readily harvested for reconstruction elsewhere with little to no discernable deficit to the patient.

34. Transect the calcaneal tendon ~3 cm superior to its calcaneal attachment and reflect the gastrocnemius and soleus muscles superiorly.
    (Figure510b)

35. Detach the soleus muscle from its tibial origin and reflect the muscle laterally to expose the layer of fascia separating the superficial and deep posterior compartments of the leg.
    (Netter514)

This separating layer of fascia is the transverse intermuscular septum.

Separating the soleus muscle from the edge of the tibia is the surgical approach used in a fasciotomy procedure to access the deep posterior compartment as a treatment for compartment syndrome in this location, although with less exposure than we are performing here.

36. Slit the thin transverse intermuscular septum along the midline of the leg and remove the fascia.
    (Netter514)

Several nerves/vessels are close to the deep side of the transverse intermuscular septum so work carefully on the fascia removal so as to avoid damage to those structures.

37. Return to the tibial nerve in the popliteal fossa and follow the nerve distally as far as the ankle.
    (Figure511) (Netter509) (Netter532)

The tibial nerve passes out of the popliteal fossa through (deep to) the tendinous arch of the soleus muscle and penetrates the transverse intermuscular septum to run distally.

As the tibial nerve courses through the leg, the nerve gives off branches to each of the muscles of the posterior compartment of the leg.

Logically, branches to the superficial posterior compartment muscles occur near the popliteal fossa, prior to the nerve penetrating through the transverse intermuscular septum, and branches to the posterior deep compartment muscles occur distal to the penetration where the nerve is in the posterior deep compartment.

38. Follow the popliteal artery distally to where you will find a lateral branch, the fibular artery, and continuation of the posterior tibial artery distally on the leg.
    (Figure511) (Netter509) (NetterBP108)

The fibular artery supplies the lateral compartment of the leg via perforating branches going through the fascia into that compartment. The fibular artery has considerable variation and in cases can be completely absent.

The anterior tibial artery arises before the split to the fibular artery, but as the anterior tibial artery goes directly anteriorly through the interosseous membrane it is not readily observable.

Thus, the segment of artery just before the fibular artery branch is technically the posterior tibial artery (as it is distal to the anterior tibial artery split), but we can't see that split directly.

The posterior tibial artery continues in the posterior deep compartment of the leg, accompanied by one or two posterior tibial veins.

The fibular artery (previously known as the peroneal artery) courses in the groove between the flexor hallucis longus muscle and the tibialis posterior muscle. These muscles are examined in the next steps.

39. Continue to follow the posterior tibial artery distally and observe that the artery continues in the leg alongside the tibial nerve.
    (Figure511) (Netter509) (NetterBP108)

The posterior tibial artery and tibial nerve run in the groove between the tibialis posterior and flexor digitorum longus muscles. These muscles are examined in the next steps.

40. Blunt dissect to isolate the three deep muscles of the posterior compartment of the leg.
    (Figure513) (Netter509)

Flexor hallucis longus - This muscle is the most lateral. It arises from the fibula and inserts into the distal phalanx of the great toe (follow it only as far as the ankle). 

The fibular artery runs in the groove medial to the flexor hallucis longus muscle.

Tibialis posterior - This muscle is centrally located. It arises from the posterior side of the interosseous membrane and attaches to the plantar surface of the foot (follow it only as far as the ankle).

The posterior tibial artery and tibial nerve run in the groove medial and slightly superficial to the tibialis posterior muscle. 

Flexor digitorum longus - This muscle is the most medial. It arises from the tibia and inserts into the distal phalanges of the toes (follow it only as far as the ankle).

41. Observe that all three muscles, the tibial nerve and posterior tibial vessels all pass to the foot by coursing posterior to the medial malleolus.
    (Figure513) (Netter509)

The passage of these tendons around the medial malleolus will be examined in the next session.

The flexor digitorum longus is the most medial muscle in the deep posterior compartment, but the tendon inserts on more lateral structures in the foot.

Thus, the flexor digitorum longus tendon crosses superficially over the tibialis posterior tendon just prior to passing the medial malleolus. More distally, the flexor digitorum longus tendon then also crosses superficially over the flexor hallucis longus tendon before splitting into tendons going to each of the four lateral (small) toes.

CHECKLIST

Skeletal Structures

Femur
    Head
    Neck
    Greater trochanter
    Lesser trochanter
    Medial and lateral condyles

Tibia
    Medial and lateral pleteaus
    Medial malleolus

Fibula
    Head
    Lateral malleolus

Soft Structures

Fascia lata

Sural nerve

Small saphenous vein

Sciatic nerve

Muscles of the posterior compartment of the thigh
    Biceps femoris muscle & tendon
        Short and long heads
    Semitendinosus muscle & tendon
    Semimembranosus muscle & tendon

Popliteal fossa

Common fibular nerve

Tibial nerve

Popliteal artery & vein

Crural fascia

Posterior tibial artery

Fibular artery

Muscles of the posterior compartment of the leg
    Superficial posterior compartment of the leg
        Gastrocnemius muscle & tendon
            Lateral and medial heads
        Soleus muscle & tendon
        Plantaris muscle & tendon
        Calcaneal tendon
    Deep posterior compartment of the leg
        Flexor digitorum longus muscle & tendon
        Flexor hallucis longus muscle & tendon
        Tibialis posterior muscle & tendon