The piriformis muscle syndrome: an exploration of anatomical context, pathophysiological hypotheses and diagnostic criteria.

Introduction: The piriformis muscle syndrome (PMS) has remained an ill-defined entity. It is a form of entrapment neuropathy involving compression of the sciatic nerve by the piriformis muscle. Bearing this in mind, a medical examination is likely to be suggestive, as a classical range of symptoms corresponds to truncal sciatica with frequently fluctuating pain, initially in the muscles of the buttocks.

Pathophysiological Hypotheses: The piriformis muscle is biarticular, constituting a bridge in front of and below the sacroiliac joint and behind and above the coxo-femoral joint. It is essentially a lateral rotator but also a hip extensor, and assumes a secondary role as an abductor. Its action is nonetheless conditioned by the position of the homolateral coxo-femoral joint, and it can also function as a hip medial rotator, with the hip being flexed at more than 90°. The main clinical manoeuvres are derived from these types of biomechanical considerations. For instance, as it is close to the hip extensors, the piriformis muscle is tested in medial rotation stretching, in resisted contraction in lateral rotation. On the other hand, when hip flexion surpasses 90°, the piriformis muscle is stretched in lateral rotation, and we have consequently laid emphasis on the manoeuvre we have termed Heel Contra-Lateral Knee (HCLK), which must be prolonged several tens of seconds in order to successfully reproduce the buttocks-centred and frequently associated sciatic symptoms.

Conclusion: A PMS diagnosis is exclusively clinical, and the only objective of paraclinical evaluation is to eliminate differential diagnoses. The entity under discussion is real, and we favour the FAIR, HCLK and Freiberg stretching manoeuvres and Beatty's resisted contraction manoeuvre.