Morphology of Piriformis- its clinical implications in Piriformis syndrome

Abstract

Background and Aim: Anatomical variations of neuromuscular structures of gluteal region are common. Each and every anatomical variation reflects a different and case specific clinical presentation. Piriformis is the key muscle to this region. This work was done to re-investigate the morphology of this muscle and structures related to it, in sufficient number of specimens to correlate with clinical syndrome. Materials and Methods: 60-lower extremities with gluteal region belonging to 30 embalmed adult human cadavers named as specimens comprised the material for this study. Gluteal region was dissected to see the variations in the origin, insertion and accessory slips of piriformis muscle. Results and Conclusion: Out of 60 specimens, piriformis consisted of one belly in 55 specimens (91.67%) and two bellies were observed in 5 specimens (8.33%). In two specimens belonging to one male cadaver, the piriformis was found being pierced by common trunk for inferior gluteal and common peroneal nerves whereas in three specimens piriformis was also being pierced by one root of posterior cutaneous nerve of thigh An accessory muscle was observed bilaterally in one cadaver. This accessory muscle was present below the piriformis on right side& it was related with the emergence of tibial nerve in between the piriformis and accessory muscle which is a rare pattern. On left side this accessory muscle was present above the piriformis & was associated with presence of superficial branch of superior gluteal artery between the upper border of piriformis and this accessory muscle. All these variations should be kept in mind during physical examination or evaluating radiological images of patients with low back pain. KEY WORDS: Anatomical variation, Piriformis, Pirifomis syndrome, extraspinal sciatic.