1. With the body in the prone position make the following incisions:

(a)a curved incision from the anterior superior iliac spine along the iliac crest to the posterior superior iliac spine (if not already made);

(b) from the posterior superior iliac spine to the midline and then vertically down to the tip of the coccyx;

(c) from the tip of the coccyx curving downwards and laterally to the middle of the lateral border of the thigh;

(d) a horizontal incision across the back of the leg 10 cm below the knee; and

(e) a vertical incision along the midline of the back of the thigh extending between incisions

(c) and

(d) .Reflect the skin flaps.

2. Note that the superficial fascia in the gluteal region is much more heavily laden with fat, particularly in the female; this being a secondary sex characteristic. Observe the pad of fibrofatty tissue over the ischial tuberosity, the lowest part of the hip bone, which acts as a cushion in the sitting posture.

3. As you dissect, you will come across numerous cutaneous nerves. Do not spend time on them. However, note the posterior femoral cutaneous nerve lying along the midline of the thigh; trace this nerve from the lower posterior part of the knee upwards towards the gluteal fold.

4. Remove the fatty superficial fascia over the gluteal region and observe the large gluteus maximus muscle covered by deep fascia. Clean this muscle and study its attachments. This muscle arises from the posterolateral surface of the sacrum and the adjoining posterior surface of the ilium and sacrotuberous ligament. Its major part is inserted into the posterior part of the iliotibial tract and its smaller deep part into the gluteal tuberosity of the femur. Note that the lower border of gluteus maximus descends obliquely across the horizontally disposed gluteal fold.

5. Divide the muscle at about the middle between its origin and insertion taking great care not to damage the nerves and vessels and sacrotuberous ligament lying deep to it. While reflecting the muscle, observe the ligament and the inferior gluteal nerve and vessels as well as branches of the superior gluteal artery entering the deep surface of the muscle. Now identify the piriformis, which is the key muscle in the dissection of this region. Review its origin from the front of the middle three pieces of the sacrum, using a skeleton. Note its insertion into the upper border of the greater trochanter of the femur.

6. Carefully clean the structures in relation to the piriformis muscle. Identify the large sciatic nerve as it emerges from the middle of its lower border to course down the middle of the back of the thigh. Lying on it is the posterior femoral cutaneous nerve. Clean the inferior gluteal nerve and vessels lying medial to the sciatic nerve. Other structures which are medial to the sciatic nerve are the nerve to obturator internus, the internal pudendal vessels and the pudendal nerve. These vessels and nerves pass across the ischial spine and sacrospinous ligament to enter the lesser sciatic foramen. Observe the extent of the sacrotuberous ligament.

7. Clean the structures that lie caudal to the piriformis. These are from above downwards:

(a)tendon of obturator internus with the gemellus superior and inferior muscles lying above and below it; follow the obturator internus tendon to its insertion into the medial surface of the greater trochanter of the femur;

(b) the quadratus femoris; note its attachments to the lateral border of the ischial tuberosity and the quadrate tubercle of the femur and that the nerve to quadratus femoris supplies the muscle on its deep surface; and

(c) the upper border of the adductor magnus.

8. Now proceed to examine the structures above the piriformis. The muscle seen immediately above the piriformis is the gluteus medius, and the muscle lying partly under cover and partly in front of it is the gluteus minimus. Passing between these two muscles are the superior gluteal nerve and a branch of the superior gluteal artery. Study the attachments of the gluteus medius. It arises from the posterior surface of the ilium and is inserted into the lateral surface of the greater trochanter. Detach the gluteus medius from its insertion, reflect it and trace the superior gluteal nerve which after supplying the medius and the minimus accompanies the deep branch of the superior gluteal artery towards the anterior superior iliac spine where the nerve ends by innervating the tensor fasciae latae muscle.

9. Study the attachments of the gluteus minimus and tensor fasciae latae. The gluteus minimus arises from the posterior surface of the ilium below and anterior to the gluteus medius and is inserted into the front of the greater trochanter. The tensor fasciae latae takes origin from the anterior part of the iliac crest and is inserted into the upper anterior part of the iliotibial tract. Cut the gluteus minimus at its insertion and the tensor fasciae latae from its origin.

10. Now cut the tendon of the obturator internus and the gemelli muscles. Next cut the piriformis and then the quadratus femoris vertically and reflect the cut ends so as to expose the obturator externus deep to the latter muscle.

1. Remove the deep fascia (fascia lata) over the back of the thigh and clean the hamstring muscles consisting of semimembranosus, semitendinosus, long head of biceps femoris and ischial portion of the adductor magnus. Observe that these muscles arise from the ischial tuberosity. Their insertion will be seen later. Trace the nerve supply to these muscles from the tibial part of the sciatic nerve. Clean the short head of the biceps femoris arising from the middle region of the linea aspera and secure its nerve supply from the common fibular part of the sciatic nerve.

2. Identify the profunda femoris artery where it was seen previously behind the adductor longus and in front of adductor brevis and adductor magnus and trace its perforating branches. Note that the upper arteries pierce the adductor brevis and magnus while the lower pierce only the magnus muscle. Trace these vessels towards the vastus lateralis where they form an anastomosis with one another and supply the posterior (flexor) group of muscles. 1

3. Now detach the semimembranosus, semitendinosus, biceps femoris and ischial portion of the adductor magnus from the ischial tuberosity and cut the remainder of the adductor magnus from the ischiopubic ramus. Also cut the sciatic nerve at this level.

Summary

The most prominent feature of the gluteal region is the massive size of the gluteus maximus, which is one of the largest muscles in the human body. Both the large size of the muscle and its insertion into the iliotibial tract are to be associated with the erect posture in humans and their bipedal mode of progression. This large muscle is supplied by the inferior gluteal nerve. Note that the gluteus maximus, medius and minimus are found in three different planes from superficial to deep. At their origins, the maximus is most posterior, minimus is most anterior with the medius in between. A similar relationship is maintained at their insertions. The small muscles at the back of the hip joint are the piriformis, the two obturators, the two gemelli and the quadratus femoris. All except the quadratus femoris are inserted into the greater trochanter. As the capsule of the hip joint is weak posteriorly, these muscles at the back of the hip provide some support for the joint. These muscles form a rotator cuff similar to that around the shoulder joint. Note that they are all lateral rotators of the thigh. The hamstring muscles arising from the ischial tuberosity receive their innervation from the tibial portion of the sciatic nerve. The short head of biceps femoris that arises from the linea aspera is supplied by the common fibular component of the sciatic nerve. The semitendinosus is inserted into the medial surface of the upper part of the shaft of the tibia while the semimembranosus gains insertion into the medial condyle of the tibia. The ischial part of the adductor magnus is attached to the adductor tubercle of the femur, while the biceps femoris has its insertion onto the head of the fibula. These insertions will be seen later. The sciatic nerve innervates not only the hamstring muscles of the thigh, but also the entire leg and foot musculature. It is covered only by the gluteus maximus in the gluteal region and by the long head of biceps femoris in the thigh. The superior and inferior gluteal arteries are distributed chiefly to the gluteal region. The gluteal arteries take part in various anastomoses, which can provide a collateral circulation when the femoral artery is obstructed.