Sciatic nerve variations around the piriformis muscle and bifurcation level: An anatomical study

Background: The ventral rami from the fourth lumbar to the third sacral spinal nerves form the Sciatic Nerve (SN). SN exits the pelvis through the greater sciatic foramen at the inferior border of the Piriformis Muscle (PM), and then it bifurcates into the common fibular and tibial nerves in the popliteal fossa, however it may present different patterns. Objectives: To identify the SN relation to the PM and the level of bifurcation. Method: Twenty-two lower limbs were dissected to expose the SNs, then the SN position to the PM were studied, and then the levels of the SN bifurcation from the inferior border of the PM were measured and compared to the thigh lengths. Results: SN patterns to PM were as follows: 4% were type B in which one component of the SN passed under the PM, while the other component passed through the piriformis muscle. Twenty three percent were type G in which the divided SN components pass under the PM, and 73% were type A in which the undivided SN passed under the PM. SN bifurcated at the following levels: 18% in pelvic region, 14% in the upper 1/3 of the thigh, and 4% in the middle 1/3 of the thigh. Two SN (9%) showed different patterns where one bifurcated in the pelvis, reunited in mid-thigh, and bifurcated again in the inferior 1/3 of the thigh. Another one bifurcated in the gluteal region at the inferior edge of the piriformis muscle, reunited in upper one third of the thigh, and then bifurcated again in popliteal fossae. The remaining 12 (55%) SN bifurcated in the popliteal fossae. Conclusion: Knowledge of the variants of the SN is needed for the accuracy and the safety of the procedures in this area.