Anatomic Variation of the Sciatic Nerve: A Study on the Prevalence, and Bifurcation Loci in Relation to the Piriformis and Popliteal Fossa

OBJECTIVE. To examine and identify sciatic nerve variations in relation to the piriformis muscle, its prevalence, pattern and the course of its bifurcation loci. MATERIALS AND METHODS. Twenty-eight formalin fixed male cadavers comprising 56 lower limbs were used for this study. Dissection of the gluteal region and posterior compartment of the thigh was conducted to expose the sciatic nerve. Variations in the sciatic nerve anatomy, their relationship to the piriformis muscle and points of bifurcation, and other observable features were noted and recorded. RESULTS. Fifty-two lower limbs (93%) showed normal anatomy of the sciatic nerve. Four regions (7.1%) showed variations in the morphology of the sciatic nerve. Of these, one (1.8%) showed a variation of the sciatic nerve with the piriformis muscle. This single case showed a common peroneal nerve emerging on the left between the heads of a double piriformis muscle - a variant not described in the original Beaton and Anson classification, with the tibial nerve deep to the muscle. In two other limbs, the sciatic nerves showed a normal relationship with the piriformis, but had variations in the bifurcation loci (bilateral). The divisions were in upper third and middle third of the right and left thighs respectively. CONCLUSION. Knowledge of the level of bifurcation and distribution of the sciatic nerve and its location is important. This nerve is commonly encountered by neurologists, orthopaedics, and anaesthesiologists. The uncommon anatomical findings described are relevant to surgeons to enable them to perform efficient surgical procedures and avoid errors.