PROCEDURE - GLUTEAL

1. PRE-WORK (before lab) review the organization of the human pelvis and femur from your atlas or on an articulated skeleton in the lab.
    (Figure418) (Netter334) (Netter337) (Netter479)

Identify the ilium, ischium, and pubis that make up the bony pelvis and review their relationship posteriorly with the sacrum.

Multiple ligaments stabilize the pelvis attachment to the sacrum. Superiorly there are iliolumbar ligaments and sacroiliac ligaments along the iliac crest and posterior superior iliac spine. Inferiorly, the important sacrotuberous and sacrospinous ligaments span from the pelvis to the sacrum.

Sacrotuberous ligament - This ligament spans the inferior margins of the posterior sacrum over to the ischial tuberosity converting the greater sciatic notch into the greater sciatic foramen.

Sacrospinous ligament - This ligament spans from the anterior surface of the sacrum over to the ischial spine converting the lesser sciatic notch into the lesser sciatic foramen.

Femur - 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 are attachment points for several muscles acting on the femur.

2. Turn the donor to the prone position and palpate for the posterior aspect of the sacrum and iliac crest.

Identification by palpation can be somewhat difficult in the gluteal region due to adipose deposits and embalmed tissue density. Bony elements will become easier to palpate as superficial structures are dissected away in later steps.

3. Starting at the region of skin previously removed from the lumbar region of the back make a midline incision inferiorly towards the anus.
    (Figure501)

Skin over the sacrum is thin and is attached tightly to the sacrum itself so you may need a very shallow incision.

4. Make a second incision approximately 5mm deep inferolateral towards the hip.
    (Figure501)

5. Using a hemostat, clamp the skin at the corner where the incision lines intersect and pull the corner of skin so that you can reflect the skin laterally. 
    (Figure501b)

The skin region directly over the sacrum at the midline may not separate as a single sheet, requiring removal of small pieces until you reach thicker subcutaneous tissue lateral to the sacrum.

6. As you proceed laterally widen and deepen the cut until you reach the plane between the superficial (hypodermis) and the gluteus maximus muscle.
    (Figure501b) (Figure103)

The most superficial muscle of the gluteal region is the gluteus maximus muscle. Inferior to the iliac crest, the thoracolumbar fascia becomes the gluteal aponeurosis covering some of the gluteal muscles.

7. Reflect the gluteal skin flaps laterally to the level of the hip leaving them connected along their lateral edge.
    (Figure501b) (Netter180) (Netter471) (Photo5001)

8. Make an additional incision inferiorly along the posterior side of the thigh to a level just distal to the popliteal fossa (the depressed/concave area posterior to the knee).
    (Figure501a) (Netter471)

9. At the distal end of this posterior incision make a shallow T incision several inches laterally and medially.
    (Figure501a) (Netter471)

10. Reflect the skin and superficial fascia laterally from the posterior thigh staying superficial to the fascia lata.
    (Netter474)

The fascia lata is a strong fibrous layer that is typically pale to white in color. The lateral region of the fascia lata along the thigh thickens into a tendon-like band called the iliotibial tract.

When in the correct plane pushing fingers between the skin and fascia lata will separate the layers relatively easily.

As you separate the superficial fascia you will observe numerous cutaneous nerve branches and superficial veins which can be separated as needed. (Photo5006)

Do not cut through the deep fascia of the thigh at this time. If you are dissecting into muscle fibers, then you are too deep and have pierced the fascia lata to enter the posterior compartment of the thigh. 

CLINICAL EXERCISE - Caudal Epidural

11. Caudal epidural is the name given to injections into the epidural space using the sacral hiatus as an entry point for the needle.

In this clinical exercise, you will insert a needle into the epidural space in your donor in an intervention. 

For the steps to take:
                                 ------ click here ------

12. Examine the quadrilateral shaped gluteus maximus muscle in the gluteal region.
    (Netter485) (Photo5001)

Use your fingers to palpate for the rudimentary spinous protuberances at the midline of the sacrum and note the insertion of the gluteus maximus muscle along the lateral margins of the sacrum and iliac crest.

Follow the direction of the muscle fibers inferolaterally and observe how the muscle inserts into the iliotibial tract.

The muscle is formed by muscle fascicles separated by fibrous connective tissue septa, thus, it may not be as distinct in boundaries as other muscles you have studied.

13. Identify the superior edge of the gluteus maximus muscle and force your fingers deep to (underneath) the muscle to open a space.
    (Figure502) (Netter485) (Photo5046)

The superior edge of the gluteus maximus muscle fuses with the gluteal aponeurosis, so it is likely you will need to use a scalpel to start and extend an opening for your fingers.

14. Push your fingers inferolaterally toward the greater trochanter of the femur, opening the space between the gluteus maximus and underlying muscles.
    (Figure502) (Netter485) (Photo5046)

If you have the correct plane between the gluteus maximus and gluteus medius muscles, your fingers will slide smoothly over the posterolateral surface of the greater trochanter of the femur.

The gluteus maximus muscle attaches to the iliotibial band, so there are no significant connections of the gluteus maximus to the greater trochanter. In contrast, the gluteus medius and minimus both attach to the greater trochanter of the femur.

In the living, a bursa protects the gluteus maximus muscle as it rubs across the bone of the greater trochanter. Inflammation of this bursa (trochanteric bursitis) is a common cause of hip pain.

15. Blunt dissect medially until your fingers are stopped by the gluteus maximus muscle attachment to the sacrum and edge of the iliac crest.
    (Figure502) (Netter485) (Photo5046)

16. While lifting the gluteus maximus muscle slightly, cut through the medial attachments to the sacrum as close to the bone as possible.
    (Figure502a) (Netter485)

This should allow you to lift and begin separating the muscle from the deeper gluteus medius muscle.

17 At the inferior edge of the gluteus maximus muscle lift the muscle, separating it from the fatty fascia located along the inferior edge of the muscle.
    (Figure502b) (Netter485)

The inferior edge is approximately the level of the coccyx extending inferolaterally towards the hip.

18. Reflect the gluteus maximus muscle laterally and as you are lifting observe the inferior gluteal nerves/vessels penetrating the deep surface of the muscle.
    (Photo5047)

The gluteus maximus muscle is innervated by the inferior gluteal nerve and supplied by the inferior gluteal vessels.

The gluteus maximus muscle receives most of its blood supply from the inferior gluteal vessels. However, it also receives anastomosing supply from branches of the superior gluteal vessels.

19. Transect the inferior gluteal neurovascular bundle such that you can fully reflect the gluteus maximus muscle laterally to expose the gluteus medius muscle.
    (Figure503) (Netter485) (Photo5047) (Photo5002)

Leave the gluteus maximus muscle attached at its distal lateral attachments to the iliotibial band.

Reflection of the gluteus maximus muscle exposes the underlying gluteus medius and piriformis muscles.

20. Clean any gluteal aponeurosis fascia from above the gluteus medius muscle.
     (Figure503) (Netter485) (Photo5002)

The gluteal aponeurosis can be tightly attached to the gluteus medius muscle.

If the aponeurosis is particularly thick in your donor you may need a scalpel to sever the gluteal aponeurosis attachment to the iliac crest and use slicing motions to work inferiorly removing the fascia from the gluteus medius muscle.

21. Observe the gluteus medius muscle spanning from the ilium laterally to insert onto the greater trochanter of the femur.
     (Figure503) (Netter485) (Photo5002)

The gluteus medius muscle is a broad muscle with the fibers oriented more sharply inferiorly than those of the gluteus maximus muscle.

Any fibers that do not insert into the greater trochanter of the femur are likely residual fibers of the gluteus maximus muscle, as that muscle inserts into the iliotibial tract and not the femur itself.

Deep to the gluteus medius muscle is the gluteus minimus muscle. The fiber orientation and function are nearly identical to the gluteus medius muscle (just smaller and deeper). We will not be exposing gluteus minimus in the lab.

The gluteus medius and gluteus minimus muscles are the principle stabilizer of pelvic position during gait. They pull superiorly on the greater trochanter of the femur in order to stabilize the pelvis when one foot is lifted off the floor. Additionally, the msucles act as abductors and internal (medial) rotators of the femur.

22. At the inferior border of the gluteus medius muscle, in the gap between gluteus medius and piriformis muscles, observe the superior gluteal artery and nerve emerging through the pelvic wall.
    (Figure503) (Netter485) (Netter492) (Photo5002)

The superior gluteal vessels and nerve emerge between the gluteus medius muscle and the piriformis muscle (i.e. superior to the piriformis muscle, giving rise to the name superior gluteal).

The inferior gluteal vessels and nerve emerge inferior to the piriformis muscle.

23. Observe the piriformis muscle inferior to the gluteus minimus muscle, which runs in almost the same plane.
    (Figure503) (Netter485) (Netter492) (Photo5002)

Piriformis is a key topographical landmark for this region. Along its superior border is the superior gluteal neurovascular bundle. Along its inferior border is the inferior gluteal neurovascular bundle. The sciatic nerve and pudendal neurovascular bundle also emerge inferior to the piriformis muscle.

The piriformis muscle is one of the muscles forming the lateral rotator group. This group of muscles are all attached to the greater trochanter of the femur and function as lateral (external) rotators of the hip muscle group.

The other lateral rotator group muscles are the superior gemellus muscle, obturator internus, obturator externus, inferior gemellus muscle, and quadratus femoris muscle. The lateral rotator muscles all act on the greater trochanter of the femur to pull it posteromedially, thereby rotating the thigh/lower extremity laterally.

24. Palpate the greater trochanter of the femur and then palpate medially to find the bony protuberance of the ischial tuberosity.
    (Figure504) (Netter492) (Photo5048)

25. Dissect into the region between the greater trochanter of the femur and the ischial tuberosity to find the sciatic nerve.
    (Figure504) (Netter492) (Photo5048)

The sciatic nerve is the largest nerve in the body, ranging up to 1-2cm diameter. The sciatic nerve provides branches innervating the posterior thigh, all of the leg and all of the foot.

26. Clean fascia from the nerve to follow it 6-7cm inferiorly where it courses into the posterior thigh.
    (Figure504) (Netter492) (Photo5048)

This may involve separating part of the posterior fascia lata to follow the nerve that distance.

27. Follow the sciatic nerve superiorly and observe that it emerges from the inferior edge of the piriformis muscle.
    (Figure504) (Netter492) (Photo5048)

Adjacent to the sciatic nerve is commonly the posterior cutaneous nerve of the thigh (sometimes called the posterior femoral cutaneous nerve).  Branches from this nerve innervate skin of the gluteal region and thigh, but we will not be dissecting this nerve specifically.

28. Observe medial to the emergence of the sciatic nerve for the transected ends of the inferior gluteal neurovascular bundle where they emerge at the inferior border of the piriformis muscle.
    (Figure504) (Netter492)

PROCEDURE - POSTERIOR THIGH

29. 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)

30. 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'.

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

32. 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)

33. Follow the long head of the biceps femoris muscle distally, where the short head of the biceps femoris joins to the long head approximately half to two-third distance to 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 biceps femoris tendon inserts distally into the head of the fibula on the lateral side of the leg (currently covered by skin).

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 and acts only on the knee (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.

34. 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)

35. 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)

36. Push 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 arises from 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).

37. Retract the mid-thigh region of 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 distal to the popliteal fossa.

As you follow the sciatic nerve, you may observe small branches splitting from the sciatic nerve to innervate each of the posterior compartment muscles.

These posterior thigh branches all arise from the part of the sciatic nerve which will later become the tibial nerve. In some books you will see posterior thigh muscle innervation listed as 'tibial nerve', but that is technically incorrect since the tibial nerve has not yet formed so it should be listed as 'sciatic nerve'. Most specifically, one could say the posterior thigh innervation arises from 'the tibial division of the sciatic nerve'.

PROCEDURE - POPLITEAL FOSSA

38. 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 of the leg (inferomedial and inferolateral).

39. 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 tibial nerves.
    (Figure509) (Netter507) (Netter532) (Photo5011)

This division typically occurs at the level of the knee, but can occur higher in the thigh in some individuals. These nerve branches are 'pre-sorted' and travel in loose fascia (i.e. the epineurium) forming the sciatic nerve. Thus, the sciatic nerve can easily be split into the two divisions proximally if inadvertently dissecting.

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

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 gastrocnemius muscle.

Either nerve can give rise to cutaneous branches (e.g. the sural nerve). If you see the origin of the sural cutaneous nerve, try to preserve that division intact as we will examine the sural nerve with the posterior leg lab.

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.

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

40. 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) (NetterBP108) (Photo5011)

There can be fat packing around the nerve and vessels within the popliteal fossa in many individuals. This may need to be removed to see the popliteal sheath containing the popliteal artery and vein.

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.

The popliteal vessels end by bifurcating into the anterior and posterior tibial vessels. This bifurcation will not be visible yet.

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. 

CHECKLIST

Skeletal Structures

Pelvic bone
    Ilium
    Ischium
    Pubis
    Ischial tuberosity
    Ischial spine

Sacrum 

Femur
    Greater trochanter of the femur
    Lesser trochanter of the femur

Soft Structures

Gluteal muscles
    Gluteus maximus muscle
    Gluteus medius muscle

Lateral rotator muscle group
    Piriformis muscle

Superior gluteal artery and nerve

Inferior gluteal artery and nerve

Sciatic nerve

Fascia lata

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