Bipartite piriformis muscle: an unusual cause of sciatic nerve entrapment.

The sciatic nerve usually emerges below the piriformis muscle; however, variations of the relationship between the sciatic nerve and piriformis muscle are occasionally encountered. In a 28-year-old woman with sciatica, entrapment of the sciatic nerve by a bipartite piriformis muscle was found. She was treated by dissection of the lower head of the piriformis muscle and restitution of the normal anatomical relationship between the nerve and piriformis muscle. Sciatica resolved postoperatively.