[Relationships between piriformis muscle and sciatic nerve: radioanatomical study with 104 buttocks]

The relationships between the piriformis muscle and the sciatic nerve are close and may be changing. In some cases, these relationships are the cause of a piriformis syndrome, an under-diagnosed etiology of non discal sciatica. The aim of the study was to explore, by the MRI, the sciatic nerve and the piriformis muscle. MATERIELS AND METHODS: One hundred and four buttocks were explored by MRI for 52 randomly selected patients.

In 59.6% of cases, no variation of the piriformis muscle and sciatic nerve were found. In 26% of cases, the sciatic nerve was divided into the pelvis. In 9.6% of cases, it was divided into the pelvis, the piriformis muscle was bifid and the common peroneal nerve ran between both heads. The piriformis muscle was bifid in 10.6% of cases, hypertrophic in 13.5% of cases and atrophic in 2.9% of cases.