Quadratus femoris muscle

Origin and insertion

Quadratus femoris originates from the upper part of the lateral border of ischial tuberosity, inferior to the lower rim of acetabulum. This attachment is superior to the origins of adductor magnus muscle and lateral to the obturator externus muscle.

From there this flat muscle runs laterally to insert onto the quadrate tubercle located on the intertrochanteric crest of femur, superior to the insertions of adductor magnus and lateral to triceps coxae muscles.

Relations 

Like all the small deep gluteal muscles, the posterior surface of quadratus femoris is covered by the gluteus maximus muscle. Anteriorly, the quadratus femoris muscle is in close relation to the tendon of obturator externus muscle, which separates it from the capsule of the hip joint. 

Quadratus femoris is the most inferiorly placed of all external rotators of the hip, sitting immediately below the gemellus inferior muscle. Moving inferior still, the adductor magnus muscle can be found. Here, the inferior part of quadratus femoris lies parallel with the superior border of adductor magnus. A gap exists between these two muscles; through which the medial circumflex artery passes. On occasion, these two muscles are fused together, in which case the gap disappears. A bursa may be found between quadratus femoris muscle and lesser trochanter.
 
Near to the insertion of quadratus femoris the cruciate anastomosis (the anastomosis between medial and lateral circumflex arteries, the gluteal artery and the first perforating artery) is found.

Test your knowledge on the quadratus femoris muscle in cross section with this quiz.

Innervation

Quadratus femoris muscle is innervated by the nerve to quadratus femoris. This arises from the spinal nerves L4 - S1, derived from the sacral plexus. In addition to quadratus femoris, this nerve innervates also supplies the gemellus inferior muscle and the hip joint. 

Blood supply

Quadratus femoris receives its blood supply predominantly from the inferior gluteal artery, a large branch of the internal iliac artery. The smaller part of the muscle can be supplied by the descending branch of the medial circumflex femoral artery. The venous blood is drained by the inferior gluteal vein which is a tributary of the internal iliac vein.

Function

The main action of the quadratus femoris muscle is external (lateral) rotation of the thigh. Although this is a small muscle it is a pretty powerful rotator of the hip, acting synergically with the other external rotators; gluteus maximus, piriformis, superior gemellus and inferior gemellus and obturator internus muscles. Acting together, these muscles produce a strong external rotation of the thigh which is limited by antagonistic muscles and the iliofemoral ligament. 

Quadratus femoris muscle is unusual in that it can assist in the production of both abduction and adduction movements of the leg. When the leg is in the anatomical position, quadratus femoris, pectineus and the inferior fibers of gluteus maximus assist the thigh adductor muscles (adductor longus, magnus and brevis) to adduct the thigh at the hip joint. In contrast, when the hip is flexed, quadratus femoris, along with piriformis, superior and inferior gemelli, obturator internus and obturator externus all act to abduct the thigh.  

Due to its specific location inside the hip joint, the quadratus femoris muscle is one of the most important stabilizers of this joint. It keeps the head of the femur in place and thus prevents injuries in numerous activities. 

To expand your knowledge check out our resources about the muscles of the hip joint.