Piriformis Syndrome

Abstract

The function of the piriformis muscle is to externally rotate the hip when the hip is in extension and to abduct the hip when it is in flexion. In approximately 20 % of the population, the piriformis muscle belly is split and one or more parts of the sciatic nerve passes through the piriformis muscle [1]. Typically, when it passes through, it is the peroneal portion of the sciatic nerve that pierces the piriformis muscle. The sciatic nerve itself, as a single nerve, is the largest in the human body. Historically, piriformis syndrome has been an overused diagnosis as it has been conflated with a lumbosacral radiculopathy which epidemiologically is much more common. Because the L5, S1, and S2 nerve roots innervate the piriformis muscle, the piriformis muscle is often tight and in spasm in the presence of a lumbosacral radiculopathy. Further, because the L5 and S1 nerve roots are so commonly inflamed, and because these spinal nerves are the primary feeders of the sciatic nerve, the diagnosis of piriformis syndrome or “sciatica” is often given when in fact the L5 and/or S1 nerve roots are the actual cause. In fact, true piriformis syndrome involves irritation or inflammation of the piriformis muscle that may result in compression or inflammation of the sciatic nerve.