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The piriformis muscle is a posterior hip muscle. It is part of a group of muscles known as the pelvitrochanteric muscles. The pelvitrochanteric muscles are given this name because they extend from the pelvic bone and course dorsally, crossing the hip, to insert either on or near the greater trochanter of the femur.
The piriformis muscle has its origin on the ventral side of the sacrum and courses posteriorly, exiting through the greater sciatic foramen into the gluteal region, after which it goes on to insert onto the greater trochanter of the femur. In some cases the tendon of the piriformis muscle has been known to join with the tendons of the superior gemellus, inferior gemellus and obturator internus muscles, forming a common tendon, prior to insertion.
Innervation of the piriformis muscle comes from direct branches from the sacral plexus (L5, S1).
As a posterior hip muscle, the main function of the piriformis is the stabilization of the pelvis together with the other posterior hip muscles. In addition, the piriformis supports further hip movements such as abduction, retroversion and extension of the hip joint.
Fractures of the greater trochanter of the femur, femoral neck fractures and ruptures that may occur during the implantation of a total hip endoprosthesis can all cause the insufficiency of the posterior hip muscles.
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