Case Report: Origin of the Piriformis Muscle Through Two Heads in the Form of Biceps, Favorable Division of the Sciatic Nerve in the Common Fibular Nerve and Tibial Nerve

摘要

The piriform muscle is a pelvitrochanteric muscle that gets its name due to its pear shape, whose origin are several fascicles located between the anterior foramina of the sacrum, corresponding to the second, third and fourth vertebrae. These fascicles are fused forming a flattened muscle, which is inserted into the greater trochanter of the femur. It has a well-known relationship with the sciatic nerve, which commonly emerges towards the gluteal region through the lower margin of this muscle, however over time, authors have described variations in the course of this nerve that could be associated with some compression pathology of the sciatic nerve. In a routine dissection of two formalized individuals, one female and one male, we found that the piriformis muscle originated through two heads, each with its own fascia that joined in a bicep-shaped common belly. Through a cylindrical tendon it is inserted into the medial part of the greater trochanter of the femur. The sciatic nerve was divided, the common fibular nerve emerged to the gluteal region through the heads, while in the tibial nerve divided through the inferior margin of the piriformis muscle. It is important to report on the anatomical variations to complement knowledge of these variations, which may explain certain physical and painful disorders such as the so-called piriformis muscle syndrome.