Gluteus maximus

The gluteus maximus is the largest muscle by volume and mass in the human body, forming the bulk of the buttock. It originates from a broad area including the ilium, sacrum, and coccyx and inserts on the iliotibial band and the gluteal tuberosity of the femur. Its large cross-sectional area reflects its role in generating powerful hip extension forces needed for climbing, sprinting, and rising from seated positions.

The gluteus maximus is the primary extensor and lateral rotator of the hip joint. It is particularly important for powerful activities requiring hip extension against gravity, such as climbing stairs, rising from a seated position, running, and jumping. The upper fibers also contribute to hip abduction, while the lower fibers assist in adduction.

Trendelenburg gait is actually caused by gluteus medius weakness, not gluteus maximus weakness. Gluteus maximus weakness produces a 'gluteus maximus lurch'—a backward trunk lean over the affected hip during stance phase to keep the center of gravity over the weight-bearing limb. This compensates for the inability of the weakened gluteus maximus to extend the hip. Gluteus maximus weakness follows injury to the inferior gluteal nerve.

The inferior gluteal nerve (L5, S1, S2) is the sole motor nerve to the gluteus maximus. Injury to this nerve—from hip surgery, posterior hip dislocation, or pelvic tumors—causes gluteus maximus paralysis. Affected patients have difficulty climbing stairs, rising from a chair, and running, while walking on flat ground may be relatively preserved.

The gluteus maximus myocutaneous flap is a well-vascularized tissue flap used in reconstructive surgery to cover pressure ulcers over the sacrum and ischium, which are common in bedridden patients. The muscle's robust blood supply from the superior and inferior gluteal arteries makes it an excellent choice for covering large, deep wounds that require substantial tissue bulk.