Gluteus Maximus

Introduction

Introduction to Gluteus Maximus

The gluteus maximus is the largest and most superficial of the three gluteal muscles, forming the prominent contour of the buttock. It is a powerful extensor and lateral rotator of the hip, playing a critical role in rising from a sitting position, climbing stairs, and maintaining the upright posture. Its size and superficial location make it clinically important for intramuscular injections, flap reconstruction, and as a site for pressure sores. Despite its bulk, it is relatively inactive during quiet standing and level walking, but becomes highly active during forceful hip extension.

Study

1. Origin and Insertion

The gluteus maximus has a broad origin from the external surface of the ilium posterior to the posterior gluteal line, the posterior surface of the sacrum and coccyx, the aponeurosis of the erector spinae, and the sacrotuberous ligament. Its fibres pass obliquely downwards and laterally. Approximately three‑quarters of the muscle inserts into the iliotibial tract of the fascia lata, with the remaining deep quarter inserting into the gluteal tuberosity of the femur.

2. Relations

Superficially, the gluteus maximus is covered by deep fascia and skin. Deep to the muscle lie the other gluteal muscles (gluteus medius and minimus), the short lateral rotators (piriformis, superior and inferior gemelli, obturator internus, quadratus femoris), and the sciatic nerve. The muscle is separated from the greater trochanter by a large bursa—the trochanteric bursa of gluteus maximus—which allows smooth gliding. The inferior gluteal artery and nerve enter the deep surface of the muscle. The posterior femoral cutaneous nerve and the perforating cutaneous nerve also have close relations.

3. Nerve Supply

The gluteus maximus is innervated by the inferior gluteal nerve (L5, S1, S2), which arises from the sacral plexus and enters the muscle from its deep surface. This is unique among the gluteal muscles, as the others are supplied by the superior gluteal nerve.

4. Blood Supply

The muscle receives its arterial supply from the superior and inferior gluteal arteries, branches of the internal iliac artery. The inferior gluteal artery is the predominant vessel, accompanied by the inferior gluteal nerve. Venous drainage corresponds to the arteries and drains into the internal iliac vein.

5. Actions

The gluteus maximus is the principal extensor of the hip joint, acting powerfully when rising from a squatting or sitting position. It also laterally rotates the hip. The upper fibres assist in abduction of the thigh, while the lower fibres assist in adduction. Through its attachment to the iliotibial tract, it helps stabilise the knee in extension, particularly during the stance phase of gait. The muscle is largely inactive during slow walking on level ground; it becomes active during rapid walking, running, climbing, and against resistance.

6. Functional Considerations

The gluteus maximus is a phasic muscle, meaning it lengthens and contracts powerfully. It works in concert with the hamstrings to extend the hip. Weakness of the gluteus maximus leads to difficulty climbing stairs, rising from a chair, and a characteristic gait pattern: the trunk lurches backwards at heel strike on the affected side to compensate for loss of hip extension power (gluteus maximus lurch). Prolonged sitting can lead to reciprocal inhibition and atrophy of the muscle (gluteal amnesia).

7. Clinical Relevance

The gluteus maximus is the site of deep intramuscular injections, which must be given in the upper outer quadrant of the buttock to avoid the sciatic nerve and inferior gluteal neurovascular bundle. Pressure sores over the sacral area can extend into the muscle. The muscle is used in myocutaneous flaps for reconstructive surgery, such as coverage of ischial pressure sores and sacral defects. Trochanteric bursitis (greater trochanteric pain syndrome) often involves the bursa between the gluteus maximus tendon and the greater trochanter. Inferior gluteal nerve injury leads to weakness of hip extension and a gluteus maximus lurch. Contracture of the iliotibial tract or gluteus maximus fascia can contribute to snapping hip syndrome.

Summary

Summary of Gluteus Maximus

The gluteus maximus is the largest gluteal muscle, originating from the ilium, sacrum, coccyx, and sacrotuberous ligament, and inserting into the iliotibial tract and gluteal tuberosity of the femur. Supplied by the inferior gluteal nerve and arteries, it acts as the chief hip extensor and lateral rotator, and stabilises the knee. Clinically, it is important for intramuscular injections, pressure sores, flaps, and nerve injuries causing characteristic gait abnormalities.