What is the anatomy relevant to administration of a piriformis injection?

Updated: Nov 03, 2020
  • Author: Mary Louise Caire, MD; Chief Editor: Erik D Schraga, MD  more...
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The piriformis exits the pelvis through the greater sciatic foramen and inserts on the greater trochanter of the femur. The obturator internus exits the pelvis by passing through the lesser sciatic foramen; it also inserts on the greater trochanter of the femur. Both muscles assist in the external rotation and abduction of the thigh. [6]

The primary symptom of piriformis syndrome is buttock pain, with or without posterior thigh pain, that is aggravated by sitting or activity. Associated low back pain is common and can be a result of piriformis pain, but it can also suggest the involvement of other structures, such as facet joints or iliopsoas muscles. In an isolated piriformis syndrome, the major findings include buttock tenderness from the sacrum to the greater trochanter and reproduction of buttock pain on prolonged hip flexion, adduction, and internal rotation. [7]

Pain is often referred down the posterior portion of the leg, following the distribution of the tibial and peroneal branches of the sciatic nerve. These branches become inflamed as they pass over, under, or through the tight piriformis. Pain is thought to be caused by myotendinous breakdown of the piriformis, as well as by focal demyelination of the affected branches of the sciatic nerve.

The piriformis is usually tight and contracted, with focal trigger-point tenderness on palpation. Piriformis syndrome is frequently associated with sacroiliac dysfunction and leg length discrepancies.

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