Gluteus maximus

Musculus gluteus maximus

Also known as: glutes, buttock muscle, GMax

The largest and most superficial gluteal muscle, and by mass the largest muscle in the body. It is a powerful extensor and lateral rotator of the hip, used for rising, climbing and running.

Overview

Gluteus maximus is a thick, coarse-fibred quadrilateral muscle forming the shape of the buttock. It arises from the outer surface of the ilium behind the posterior gluteal line, the posterior surface of the sacrum and coccyx, the sacrotuberous ligament and the thoracolumbar fascia (erector spinae aponeurosis). Its fibres run inferolaterally. About three-quarters of the muscle (the superficial fibres and the upper deep fibres) insert into the iliotibial tract. The deep lower fibres insert into the gluteal tuberosity of the femur.

It is the main extensor of the flexed hip. It is relatively inactive in quiet standing and level walking, but it works strongly when rising from a chair or squat, climbing stairs, running and jumping. It also laterally rotates the thigh. Through the iliotibial tract it helps stabilise the extended knee and the hip, and it braces the sacroiliac joint. It is supplied by the inferior gluteal nerve (L5–S2), which, with the inferior gluteal vessels, leaves the pelvis below piriformis. The sciatic nerve lies deep to the muscle, which is why intramuscular injections are given only in the superolateral quadrant.

Location

Buttock, superficial to the other gluteal muscles and the sciatic nerve.

Anatomy

Origin

Outer surface of the ilium posterior to the posterior gluteal line, dorsal surface of the sacrum and coccyx, sacrotuberous ligament and thoracolumbar fascia.

Insertion

Most fibres: iliotibial tract (to the lateral condyle of the tibia). Deep inferior fibres: gluteal tuberosity of the femur.

Action

Extension (from the flexed position) and lateral rotation of the hip; steadies the femur and pelvis; assists knee stability through the iliotibial tract.

Innervation

Inferior gluteal nerve (sacral plexus).

Nerve roots

L5–S2

Arterial supply

Inferior and superior gluteal arteries (internal iliac); first perforating artery (profunda femoris).

Relations

Covers piriformis, the gemelli, obturator internus, quadratus femoris, the sciatic nerve, the ischial tuberosity and the greater trochanter. The trochanteric and ischial bursae lie deep to it.

Clinical significance

Safe intramuscular injection

Divide the buttock into quadrants (or use the ventrogluteal site). Injections are placed in the superolateral quadrant, which avoids the sciatic nerve (inferomedial) and the superior gluteal neurovascular bundle.

Inferior gluteal nerve palsy

Weak hip extension: difficulty rising from a chair or climbing stairs, and a backward lurch of the trunk on heel strike ("gluteus maximus gait").

Ischial (weaver’s) bursitis

Inflammation of the bursa between gluteus maximus and the ischial tuberosity, from prolonged sitting on hard surfaces.

Test yourself

Which muscle is the prime mover for rising from a seated position and climbing stairs, and is supplied by the inferior gluteal nerve?

Gluteus medius
Gluteus maximus
Iliopsoas
Biceps femoris

Answer: Gluteus maximus

Gluteus maximus (inferior gluteal nerve, L5–S2) is the powerful hip extensor used when extending from a flexed position. It is relatively inactive during level walking.