Gluteal+Region+and+Posterior+Thigh

toc =**Lecture Notes**=

[|Lecture 1]

=**Objectives**=


 * 1. Demonstrate the surface anatomy of the sciatic nerve.**

The sciatic nerve arises from the sacral plexus (L4-S3), passes through the greater sciatic foramen into the inferior gluteal region, and then descends into the posterior thigh. Medial to it are the inferior gluteal nerve and vessels, and the internal pudendal nerve and vessels. The sciatic nerve runs inferolaterally under the cover of gluteus maximus, midway between the greater trochanter and the ischial tuberosity. This is clinical important for gluteal injections, which should be performed in the region high near the crest of the ileum where the gluteus maximus does not cover, avoiding the sciatic nerve.

The nerve rests on the ischium and then passes posterior to the obturator internus, quadratus femoris, and adductor magnus muscles. At the apex of the popliteal fossia, the sciatic nerve divides into the common fibular (peroneal) and tibial nerves.

The sciatic nerve supplies no structures in the gluteal region. It innervates the hamstring muscles (long head of biceps femoris, semimembranosis, and semitendonosis) by its tibial division. The short head of the biceps femoris is innervated by the common fibular division.

The sciatic nerve is so large that it receives its own blood supply from the inferior gluteal artery.


 * 2. Demonstrate the large gluteal muscles and understand their role in gait.**

The three gluteal muscles are the gluteus maximus, medius, and minimus. Gluteus maximus attaches from the ileum, sacrum, sacral tuberous ligament. Upper 3/4 insert into the iliotibial tract. The fibers pass laterally and the lower 1/4 of gluteus maximus attaches to the posterior femur at the gluteal tuberocity at the proximal part of the femur. Gluteus maximus does not take origin from all of the iliac surface; there is a portion of the ileum that is not covered by gluteus maximus that is covered by fascia lata, exposing the gluteus medius muscle and its fascia.

Most of gluteus medius is usually covered by gluteus maximus. The gluteus medius originates at the ileum, descending and attaching to the greater trocanter of the femur.

Gluteus minimus is the third and deepest muscles and completely buried by gluteus medius. Gluteus minimus originates at the ileum and attaches at the greater trocanter just like gluteus medius.

Gluteus maximus only used for powerful hip extension (rising from seated positon, climbing stairs, running but //non// walking on a flat surface). Gluteus medius and minimus are important for abduction of the hip joints when the limb is not bearing weight. These muscles are essential for normal walking and abduction is not part of a normal gait. When the weight is shifted to one side of the lower limb and begins to bear weight, on the weight bearing side, gluteus medius and minimus contract, fixing the hip and tip the hip slightly; this shifts the hip on the non-weight bearing side upwards, freeing the non-weight bearing limb to swing freely. If gluteus medius and minimus are paralyzed, the pelvis cannot shift so the leg would drag on the floor. A person with this condition will compensate by swinging the leg to the side in order to avoid dragging the leg. Trendalenburg sign is the inability to shift/stabilize the pelvis on one side due to paralysis of gluteus medius and minimus (if you ask the patient to stand on one leg, they cannot stabilize and will fall).

Gluteus maximus is innervated by only the inferior gluteal nerve. The superior gluteal nerve innerves gluteus medius and minimus, and tensor fascia lata. Most of the gluteal maximus muscle blood supplies is from the inferior gluteal artery (and some form superior gluteal artery).


 * 3. Describe the course the pelvic structures take to enter the gluteal region.**

The piriformus muscle attaches to the pelvic side of the sacrum and the greater trochanter. The superior gluteal artery goes the gluteal region superior to the piriformus. The inferior gluteal nerve and vessels comes out inferior to the piriformus. The sciatic nerve and pudendal nerve are also inferior to piriformis, exiting the greater sciatic foramen. The posterior cutaneous nerve runs parallel with the sciatic nerve and also comes out of the greater sciatic foramen.

Most of the muscle body of the obturator internus is facing the pelvis, lining the inside of the obturator membrane. The obturator internus tendon comes through the lesser sciatic foramen, attaching to the greater trochanter.

The obturator externus is on the external surface of the obturator membrane, out in the lower limb, and attaches to the greater trochanter of the femur. The obturator foramen is covered by the obturator membrane and by obturator externis and internis muscles.


 * 4. Demonstrate the six, small hip lateral rotator muscles.**

Group of six small muscles that laterally rotate the hip joint: piriformus, superior gemellus, inferior gemellus, obturator internus tendon, obturator externus, and quadratus femoris. The piriformus muscle is the keystone muscle that attaches to the pelvic side of the sacrum and the greater trochanter by passing through the greater sciatic foramen.

Inferior to piriformus is the superior gemellus muscle originating from the ischial spine to the greater trochanter. There is an inferior gemellus muscle also originating on the ischial tuberocity and inserting to the greater trochanter. The superior and inferior gemellus muscles are superior and inferior to the tendon of obturator internus. Most of the muscle body of the obturator internus is facing the pelvis, lining the inside of the obturator membrane. The obturator internus tendon comes through the lesser sciatic foramen, attaching to the greater trochanter. Very commonly, the superior and inferior gemellus will attach to the obturator internus and then all attach to the greater trochanter.

Quadratus femoris is attached to the ischial tuberocity and inserts to the intertrochanteric crest. Behind the quadratus femoris, the obturator externus is on the external surface of the obturator membrane, out in the lower limb, and attaches to the greater trochanter of the femur. The obturator foramen, is covered by the obturator membrane and by obturator externis and internis muscles.

Nerve supply are small nerves from the sacral plexus except for obturator externis (name of nerves are all “nerve to…”). Obturator externis is innervated by the obturator nerve (L2-4) as it goes down towards the medial thigh. Blood supply are from the inferior gluteal arteries.


 * 5. Understand the course structures take from the gluteal region to the perineum.**

Gluteus maximus attaches from the ileum, sacrum, sacral tuberous ligament. Upper 3/4 insert into the iliotibial tract. The fibers pass laterally and the lower 1/4 of gluteus maximus attaches to the posterior femur at the gluteal tuberocity at the proximal part of the femur.

The piriformus attaches from the pelvic side of the sacrum to the greater trochanter by passing through the greater sciatic foramen.

Inferior to piriformus is the superior gemellus muscle originating from the ischial spine to the greater trochanter. There is an inferior gemellus muscle also originating on the ischial tuberocity and inserting to the greater trochanter.

The superior and inferior gemellus muscles are superior and inferior to the tendon of obturator internus. The obturator internus tendon comes through the lesser sciatic foramen, attaching to the greater trochanter.

Quadratus femoris is attached to the ischial tuberocity and inserts to the intertrochanteric crest. Behind the quadratus femoris, the obturator externus is on the external surface of the obturator membrane, goes out into the lower limb, and attaches to the greater trochanter of the femur.