The posterior hip musculature
Anatomy and supply
The posterior hip musculature comprises a group of muscles extending from the pelvic bone to the femur. During their course they cross the hip joint dorsally. At the femur they all insert either at or near the greater trochanter which is why they are also referred to as the pelvitrochanteric muscles. The posterior hip muscles are innervated by direct branches of the sacral plexus – with the exception of the external obturator muscle. In detail they consist of:
- Piriformis muscle: runs from the ventral side of the sacral bone (facies pelvica) to the greater trochanter.
- Internal and external obturator muscles: both extend from the obturator membrane and its bony margin to the trochanteric fossa. The external obturator muscle is supplied by the obturator nerve, a branch of the lumbar plexus.
- Superior and inferior gemelli muscles: The superior gemellus muscle originates from the ischiadic spine whereas the inferior gemellus muscle has its origin at the ischial tuberosity. Both insert at the trochanteric fossa.
- Quadratus femoris muscle: runs from the ischial tuberosity to the intertrochanteric crest.
The main tasks of the posterior hip muscles are the stabilization of the pelvis and the outward rotation of the hip joint. In addition particular muscles may support further hip movements: abduction (piriformis muscle), adduction (quadratus femoris muscle, external obturator muscle, gemelli muscles) and retroversion (piriformis muscle, internal obturator muscle, gemelli muscles).
Common causes for the insufficiency of the posterior hip muscles are fractures of the greater trochanter (e.g. by falling on the side), femoral neck fractures (often associated with osteoporosis in elderly) and ruptures during the implantation of a total hip endoprosthesis. Every type of elevated trochanter (e.g. in coxa vara or hip dysplasia) and leg length discrepancies may lead to a weakening in the long term. Symptoms include local pain, limping up to the inability to walk.