Deep Gluteal Muscles

Introduction

Introduction to the Deep Gluteal Muscles

The deep gluteal muscles are a group of short, powerful muscles located deep to the gluteus maximus in the buttock. They consist of the piriformis, obturator internus, superior and inferior gemelli, and quadratus femoris. The obturator externus, though located more anteriorly, is functionally related. Together, these muscles are the principal lateral (external) rotators of the hip joint, and they play a crucial role in stabilising the femoral head within the acetabulum during weight‑bearing. The piriformis is the key anatomical landmark of the region, dividing the greater sciatic foramen into suprapiriform and infrapiriform compartments through which critical neurovascular structures pass.

Study

1. General Features and Common Actions

All deep gluteal muscles take origin from the pelvic girdle (sacrum, ilium, ischium, or obturator membrane) and insert on or near the greater trochanter of the femur. Their primary action is lateral rotation of the extended hip. When the hip is flexed, some of these muscles (especially piriformis and obturator internus) become abductors. They also function as stabilisers of the hip joint, drawing the femoral head into the acetabulum.

2. Piriformis

The piriformis is the most superior of the deep gluteal muscles. It originates from the anterior surface of the sacrum between the second and fourth sacral foramina, from the sacrotuberous ligament, and from the margin of the greater sciatic foramen. It passes laterally through the greater sciatic foramen, dividing it into the suprapiriform (above) and infrapiriform (below) compartments. It inserts by a rounded tendon onto the superior border of the greater trochanter of the femur. The piriformis is innervated by the nerve to piriformis (S1, S2) and receives its blood supply from the superior and inferior gluteal arteries. It laterally rotates the extended thigh and abducts the flexed thigh.

The piriformis is the key anatomical landmark for the gluteal region. The superior gluteal nerve and vessels exit the pelvis through the suprapiriform compartment, while the sciatic nerve, inferior gluteal nerve and vessels, posterior femoral cutaneous nerve, and the nerves to the other deep gluteal muscles exit through the infrapiriform compartment. In approximately 15% of individuals, the sciatic nerve (or its peroneal division) pierces the piriformis, a variation that may predispose to piriformis syndrome.

3. Obturator Internus and Gemelli

The obturator internus originates from the internal surface of the obturator membrane and the surrounding bones (pubis and ischium). Its tendon makes a sharp 90‑degree turn around the lesser sciatic notch (which is lined by a bursa) and passes through the lesser sciatic foramen to insert on the medial surface of the greater trochanter (trochanteric fossa).

The superior gemellus arises from the ischial spine, and the inferior gemellus from the upper part of the ischial tuberosity. Both insert into the obturator internus tendon as it reaches the greater trochanter. The superior gemellus is innervated by the nerve to obturator internus (L5, S1, S2), and the inferior gemellus by the nerve to quadratus femoris (L4, L5, S1). Together, this triceps‑like complex laterally rotates the extended hip.

4. Quadratus Femoris

The quadratus femoris is the most inferior of the deep gluteal muscles. It is a flat, quadrilateral muscle extending horizontally from the lateral border of the ischial tuberosity to the quadrate tubercle on the intertrochanteric crest of the femur. It is innervated by the nerve to quadratus femoris (L4, L5, S1) and supplied by the medial circumflex femoral artery. It is a pure lateral rotator of the hip.

5. Obturator Externus

The obturator externus is a flat, fan‑shaped muscle that lies on the anterior aspect of the hip joint, deep to the pectineus and adductor muscles. It arises from the external surface of the obturator membrane and the adjacent pubis and ischium. Its tendon passes posterior to the femoral neck and inserts into the trochanteric fossa of the greater trochanter. It is innervated by the posterior branch of the obturator nerve (L3, L4) and functions as a lateral rotator and adductor of the hip.

6. Clinical Relevance

Piriformis syndrome is a controversial entrapment neuropathy in which the sciatic nerve is compressed by an abnormally tight or hypertrophied piriformis, causing buttock pain and sciatica. Deep gluteal syndrome is a broader term for compression of the sciatic nerve by any of the deep gluteal muscles. Injuries to the quadratus femoris (e.g., hamstring avulsion‑related) can cause groin or buttock pain. The short external rotators are frequently released during posterior surgical approaches to the hip to expose the joint capsule; the sciatic nerve must be carefully protected. Tendinopathy or bursitis of the obturator internus or piriformis can cause chronic deep gluteal pain.

Summary

Summary of the Deep Gluteal Muscles

The deep gluteal muscles—piriformis, obturator internus with gemelli, quadratus femoris, and obturator externus—are the primary lateral rotators of the hip joint. They originate from the pelvic bones and obturator membrane and insert onto the greater trochanter. Innervated by branches of the sacral plexus and the obturator nerve, they also stabilise the hip joint. The piriformis is the key landmark for the greater sciatic foramen and is clinically significant in piriformis syndrome. These muscles are encountered during posterior approaches to the hip.