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 forming several foramina relevant for the gluteal region anatomy.

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 - Observe on the proximal femur the head, neck and greater trochanter of 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, but bony elements will become easier to palpate as superficial structures are dissected away.

3. Starting at the region of skin previously removed from the lumbar region of the back make a midline incision inferiorly towards the anus following your pre-operative pen mark.
    (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 following the inferolateral pre-operative pen mark laterally out to 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 skin just lateral to the midline.

6. As you proceed laterally widen and deepen the cut until you reach the plane between the superficial (hypodermis) and deep fascia covering the muscles.
    (Figure501b) (Figure103)

The most superficial muscle of the gluteal region is the gluteus maximus muscle.

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

Inferior to the iliac crest, the thoracolumbar fascia becomes the gluteal aponeurosis.

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

9. At the level just superior to the popliteal fossa extend the incision a couple of inches laterally and medially.
    (Figure501a)

These lateral/medial incisions will make it easier to reflect skin and superficial fascia in the next step.

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. 

11. Remove any deep fascia sufficiently to identify the quadrilaterally shaped gluteus maximus muscle.
    (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.

CLINICAL EXERCISE - Caudal Epidural

12. 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 have the chance to insert a needle into the epidural space in your donor in a mock surgical intervention.  For the steps to take:
                                 ------ click here ------

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 will be 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.

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

19. Transect the inferior gluteal nerve and vessels 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 to its distal lateral attachments at the iliotibial band.

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

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

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

You should be able to feel the bony point of the greater trochanter of the femur at the lateral end where the gluteus medius muscle inserts.

The gluteus medius muscle is a broad muscle arising from the surface of the ilium and inserting into the lateral surface of the greater trochanter of the femur. The fibers of the gluteus medius muscle run more sharply inferiorly than those of the gluteus maximus muscle. 

21. At the inferior border of the gluteus medius muscle observe the superior gluteal artery and nerve emerging through the pelvic wall.
    (Figure503) (Netter485) (Netter492)

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

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

22. Push a blunt probe or finger deep to the gluteus medius muscle following the plane of the superior gluteal vessels as they pass deep to the gluteus medius muscle.
    (Figure546) (Netter485) (Netter492) (Photo5003)

Since the fibers of gluteus medius and gluteus minimus are very similar in orientation, it can be difficult to find the plane between these muscles. In some individuals the plane will be indistinct.

Branches of the superior gluteal vessels travel in the plane between the more superficial gluteus medius muscle and the deeper gluteus minimus muscle. Forcing a finger along those branches between the muscle groups should help separate the plane between the gluteus medius and gluteus minimus muscles.

The gluteus medius and gluteus minimus muscles primarily function as abductors of the hip joint . They pull superiorly on the greater trochanter of the femur in order to stabilize the pelvis when one foot is lifted off the floor. This action is critical for stabilizing the pelvic position during walking/running.

23. Blunt dissect to extend the space between the gluteus medius and gluteus minimus muscles as far medially and inferolaterally as possible.
    (Figure546) (Netter485) (Netter492) (Photo5003)

Medially your fingers will be stopped by the gluteus medius attachments to the ilium.

Laterally your fingers will be stopped by the gluteus medius attachments to the greater trochanter of the femur.

24. While lifting the gluteus medius muscle slightly, cut through the medial attachments to the ilium as close to the bone as possible paralleling the curve of the iliac crest.
    (Figure546) (Netter485) (Netter492) (Photo5003)

25. Reflect the gluteus medius muscle laterally and observe the deeper gluteus minimus muscle.
    (Figure504) (Netter492) (Photo5004)

The gluteus minimus muscle arises from the surface of the ilium and inserts into the anterior side of the greater trochanter of the femur.

The gluteus medius and minimus muscle are innervated by the superior gluteal nerve and supplied with blood primarily from branches of the superior gluteal vessels.

As with the other gluteal muscles, the gluteus minimus muscle is formed by a number of fascicles separated by fibrous connective tissue septa. These can give the appearance of separate muscles, but are all part of the gluteus minimus muscle.

26. Observe the junction between the inferior edge of the gluteus minimus muscle and the superior edge of the piriformis muscle.
    (Figure504) (Netter492) (Photo5004)

The superior gluteal artery and nerve emerge from the gap between these two muscles.

27. Observe the piriformis muscle inferior to the gluteus minimus muscle, which runs in almost the same plane.
    (Figure504) (Netter492) (Photo5004)

The piriformis muscle arises from the anterior sacral surface and enters the gluteal region through the greater sciatic foramen and attaches to the greater trochanter.

Piriformis is a key topographical landmark for this region. Along its superior border are the superior gluteal nerve, artery, and vein. Along its inferior border are the inferior gluteal nerves and vessels. The sciatic nerve, the pudendal nerve and the internal pudendal artery and vein also emerge inferior to the piriformis muscle. These are examined below.

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

29. 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.

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

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

31. 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.

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

33. Clean fascia lateral to the ischial tuberosity deep to the sciatic nerve to observe muscle fibers of the lateral rotator group muscles spanning to the greater trochanter of the femur.
    (Figure504) (Netter492) (Netter493) (Photo5048)

The sciatic nerve runs directly posterior (i.e. superficial) to the lateral rotator muscle group.

This group of muscles are all attached to the greater trochanter of the femur and form part of the lateral (external) rotators of the hip muscle group. Observe the presence of these muscles, but we will not dissect the individual muscles of the group.

The muscles are the superior gemellus muscle, obturator internus, obturator externus, inferior gemellus muscle, and quadratus femoris muscle. In addition to these muscles, the piriformis muscle is also considered one of the group of lateral rotators.

The lateral rotator muscles all act on the greater trochanter of the femur to pull it posteromedially, thereby rotating the thigh/lower extremity laterally.

PROCEDURE - ANAL

34. Partially spread the donor's lower extremities as this will make access into the anal triangle easier.
    (Figure549)

Placing the wood block between the legs may assist in keeping the donor's lower extremities spread while working in this region.

The anal triangle is an region formed by imaginary lines from the left and right ischial tuberosity and the midline coccyx. The anus, ischiorectal fat, and inferior rectal branches of the pudendal neurovascular bundle are the important structures in the region.

35. Identify the sacrotuberous ligament between the hard point of the ischial tuberosity and the edge of the sacrum.
    (Figure504) (Netter493) (Photo5048)

Pressing your fingers onto the ligament you will feel a slight 'bounce' to the tight ligament which can give a guide to where the ligament is positioned.

The triangularly shaped sacrotuberous ligament is attached to the ischial tuberosity and spans to the sacrum. Only limited movement is possible between these bony points. The ligament primarily serves to stabilize the sacroiliac joint and as a shock absorber during locomotion.

36. Clean any remaining fascia from the posterior surface of the sacrotuberous ligament to define the borders of the ligament.
    (Figure504) (Netter493) (Photo5048)

The pudendal nerve courses deep to the sacrotuberous ligament, which must be severed in order to view the nerve.

37. Insert a blunt probe just deep to the sacrotuberous ligament passing from superior to inferior.
    (Photo4020)

38. Using the blunt probe as a guide, transect the sacrotuberous ligament in the middle.
    (Photo4031)

Transecting the sacrotuberous ligament exposes the area of the lesser sciatic foramen where we will observe the pudendal branches.

39. Reflect the cut ends of the ligament laterally and medially exposing the fascia below.

40. Blunt dissect into the fascia below the sacrotuberous ligament to find the pudendal neurovascular bundle.
    (Figure503) (Netter493) (Photo4021)

The pudendal neurovascular bundle (nerve, artery and vein) exits the pelvis through the greater sciatic foramen, inferior to the piriformis muscle and medial to the sciatic nerve. 

The pudendal neurovascular bundle travels deep to the sacrotuberous ligament and superficial to the sacrospinous ligament (i.e. through the lesser sciatic foramen you opened by cutting the sacrotuberous ligament).

The pudendal neurovascular bundle bifurcates into rectal (to the anus) and perineal (to the perineum) branches as it passes out from under the sacrotuberous ligament. 

We will not dissect the nerve further than the nerve's passage deep to the sacrotuberous ligament.

The bifurcation of the nerve can occur prior to emerging from the greater sciatic foramen, in which case you will see two neurovascular bundles passing deep to the sacrotuberous ligament (one turns to the anus and a second towards the perineum).

The perineal branch continues anteriorly to the medial side of the ischial tuberosity and then to the perineum. The location just distal to the ischial tuberosity is the approximate target for injecting anesthesia in a pudendal nerve block. Most commonly, the needle approach is from the inferior aspect using the ischial spine as a palpable landmark. The needle is inserted parallel to the plane of the urogenital triangle in order to anesthetize the main branch of the pudendal nerve innervating the urogenital region. (Figure444)

CHECKLIST

Skeletal Structures

Pelvic bone
    Ilium
    Ischium
    Pubis
    Ischial tuberosity
    Ischial spine

Sacrum 

Femur
    Greater trochanter of the femur

Soft Structures

Fascia lata
    Iliotibial tract (band)

Gluteal muscles
    Gluteus maximus muscle
    Gluteus medius muscle
    Gluteus minimus muscle

Lateral rotator muscle group
    Piriformis muscle

Sciatic nerve

Superior gluteal artery and nerve

Inferior gluteal artery and nerve

Sacrotuberous ligament

Pudendal nerve (neurovascular bundle)