Buttocks
Buttock
Gluteus Maximus
The gluteus maximus muscle is the most superficial muscle in the gluteal region. It is located in a more superficial plane than the gluteus medius muscle, which in turn overlies the gluteus minimus muscle.
The gluteus maximus arises from the:
- Posterior gluteal line of the ilium
- Posterior surface of the lower part of the sacrum and the side of the coccyx
- Aponeurosis of the sacrospinalis muscle
- Sacrotuberous ligament fascia covering the middle gluteal muscle
The fibres of gluteus maximus are directed obliquely downwards and laterally. The muscle ends in a thick tendinous lamina, which passes across the greater trochanter and is inserted into the iliotibial band of the fascia lata.
The gluteus maximus muscle is divided into two parts:
- Cranial: which contributes to hip abduction
- Caudal: which assists in hip extension and external rotation
Loss of hip extension can make it difficult for patients to rise from a sitting position to standing, which could, theoretically, occur following harvest of an inferior musculocutaneous gluteal flap.
Innervation
Gluteus maximus is innervated entirely by the inferior gluteal nerve (L5, S1, S2), which accompanies the inferior gluteal artery. The nerve arises from the dorsal branches of the ventral rami of the L5-S1 nerve roots. It exits the pelvis beneath the inferior border of piriformis and sinks into the deep surface of gluteus maximus.
Gluteus medius and minimus are innervated by the superior gluteal nerve (L4, L5, S1). This nerve exits the pelvis through the greater sciatic notch, above the superior border of piriformis and immediately disappears beneath the posterior border of gluteus medius, running forwards between gluteus medius and minimus. It also supplies tensor fasciae latae
Arterial Supply
The superior gluteal artery (SGA) and the inferior gluteal artery (IGA) are both branches of the internal iliac artery.
The SGA emerges from the pelvis through the greater sciatic notch, just above the superior border of the piriformis muscle, along with the superior gluteal nerve. It is a short artery, which soon divides into:
- Superficial branch:this provides contributions to the superior portion of gluteus maximus and the overlying fat and skin
- Deep branch:this branch travels laterally between gluteus medius and minimus and divides again into an upper and a lower branch, the lower one being the blood supply to gluteus medius and minimus
The IGA emerges from the pelvis into the buttock between piriformis and the superior gemellus. It supplies muscular branches to piriformis, obturator internus and the inferior portion of gluteus maximus.
The IGA runs in close proximity to important structures such as the sciatic nerve and the posterior femoral cutaneous nerve (FCN) of the thigh. The IGA passes inferiorly with the FCN beneath the fascia of the biceps femoris and semitendinosus muscles.
The sciatic nerve and the IGA run lateral to the ischial tuberosity. At the level of the ischial tuberosity the FCN and IGA are both superficial to the sciatic nerve.