Buttock Augmentation - Surgical Anatomy of The Buttocks

Surgical Anatomy of The Buttocks

Muscular origins and insertions

Anatomically, the mass of each buttock principally comprises two (2) muscles — the gluteus maximus muscle and the gluteus medius muscle — which are covered by a layer of adipose body fat. The upper aspects of the buttocks end at the iliac crest (the upper edges of the wings of the ilium, and the upper lateral margins of the greater pelvis), and the lower aspects of the buttocks end at the horizontal gluteal crease, where the buttocks anatomy joins the rear, upper portion of the thighs. The gluteus maximus muscle has two (2) points of insertion: (i) the one-third (1/3) superior portion of the (coarse line) linea aspera of the thigh bone (femur), and (ii) the superior portion of the iliotibial tract (a long, fibrous reinforcement of the deep fascia lata of the thigh). The left and the right gluteus maximus muscles (the butt cheeks) are vertically divided by the intergluteal cleft (the butt-crack) which contains the anus.

The gluteus maximus muscle is a large and very thick muscle (6–7 cm) located on the sacrum, which is the large, triangular bone located at the base of the vertebral column, and at the upper- and back-part of the pelvic cavity, where it is inserted (like a wedge) between the two hip bones. The upper part of the sacrum is connected to the final lumbar vertebra (L5), and to the bottom of the coccyx (tailbone). At its origin, the gluteus maximus muscle extends to include parts of the iliac bone, the sacrum, the coccyx, the sacrosciatic ligament, and the tuberosity of the ischium. Like every pelvic-area muscle, the gluteus maximus muscle originates from the pelvis; nonetheless, it is the sole pelvic muscle not inserted to the trochanter (head of the femur), and is approximately aligned to the femur and the fascia lata (the deep fascia of the thigh); its tissues cover only the rear lateral face of the trochanter, and there form a bursa (purse) that faces the interior of the thigh.

Innervation

The motor innervation of the gluteus maximus muscle is performed by the inferior gluteal nerve (a branch nerve of the sacral plexus) and extends from the pelvis to the gluteal region, then traverses the greater sciatic foramen (opening) from behind and to the middle to then join the sciatic nerve. The inferior gluteal nerve divides into three (3) collateral branches: (i) the gluteus branch, (ii) the perineal branch, and (iii) the femoral branch. The first ramification — the gluteus branch — is a branch nerve that is very close to the emergence of the inferior gluteal nerve to the area, next to the inferior border of the pyramidalis muscle. As it arises, the inferior gluteal nerve then divides into four (4) or more fillets (bands of nerve fibres) that travel (in a crow’s-foot configuration) between the gluteus maximus muscle and its (front) anterior fascia; the thickest nerve-bands are the superior-most and the inferior-most fillets. The superior-most fillet runs almost vertically, near the sacrum, and innervates the superior portion of the gluteus muscle; the inferior-most fillet, which has the greatest calibre, travels very close and parallel to the sacrotuberous ligament; the inferior-most fillet provides fine-gauge branch-nerve ramifications that innervate the gluteus muscle through its anterior (front) face.

• In surgical and body contouring praxis, the plastic surgeon creates the implant-pocket — either for the gluteal prosthesis or for the injections of autologous fat — by undermining the gluteus maximus muscle with a dissection technique that avoids the sacrum, the sacrotuberous ligament, and the tuberosity of the ischium; which, if accidentally cut, might isolate the posterior (back) portion of the muscle and lead to denervation, the loss of nerve function and of innervation.

Vascularization

The superior gluteal artery, the inferior gluteal artery, the superior gluteal veins, and the inferior gluteal veins irrigate the gluteus maximus muscle with arterial and venous blood. The vascularization, the entrance of the blood vessels to the muscle tissues, occurs at the anterior (front) face of the muscle, very close to the sacrum. As the arteries and the veins enter the mass of the gluteal muscle, they divide into narrower blood-vessel ramifications (configured like the horizontal branches of a tree), most of which travel parallel to the muscle fibres.

• In surgical and body contouring praxis, the plastic surgeon effects the implant-pocket undermining of the gluteus maximus muscle by carefully separating the muscle fibres to avoid severing the pertinent blood vessels, which would interfere with the blood irrigation of the muscle tissue. Therefore, to create an implant-pocket, either for a gluteal prosthesis or for lipoinjection, a low-angle muscle-dissection is performed in order to avoid the risk of severing any major branch — superior or inferior — of the gluteal artery, which travels very close to the sacrum and to the sacrotuberous ligament.