Variations in the course, distribution and termination of the sciatic nerve in a selected adult Kenyan population

Abstract

Background: Anatomical variations for the sciatic nerve have been described on the relationship of the nerve to the piriformis muscle and its termination point. Few studies have been conducted on the relationship of the nerve to bony landmarks in the gluteal region. Global, regional and local published data on the latter is limited. The sciatic nerve is the largest terminal branch of the sacral plexus. It gives branches to the hip joint and the hamstring muscles before it terminates into the tibial and common peroneal trunks. The nerve is usually in the operative field during posterior approaches to the hip joint and hence should be looked for. Objective: To describe variations in the course, distribution and termination of the sciatic nerve in a selected adult Kenyan population. Methods: This was a descriptive anatomical cross sectional study that was conducted at the Department of Human Anatomy of Moi University. Ethical approval was sought from Institutional Research and Ethics Committee. Sixty three left lower limbs, that met the inclusion criteria, were dissected as detailed in the Cunningham’s Manual of Practical Anatomy, 15th edition. This was illustrated using photographs. Descriptive statistics such as frequencies and percentages were used for categorical variables while measures of central tendency and measures of spread were used for continuous variables. Results: In most cases the sciatic nerve passed through the midpoint between the greater trochanter of the femur and the ischial tuberosity (50.8%) or medial to it (46.03%). For any given nerve branch to the hamstring muscles, the branching occurred distal to the ischial tuberosity (>90%) and in the upper half of the thigh (>83%). However, branching to the short head of biceps femoris occurred in the lower half of the thigh in 23.8% of cases. The long head of biceps femoris had one , two or three branches in 47.62%, 42.86% and 9.52% of specimens respectively. Semitendinosus and semimembranosus muscles had one or two branches (90.48% versus 9.52%). Short head of the biceps femoris muscle was supplied by a single branch in all specimens.The hamstring part of the adductor magnus muscle had one or two branches (98.41% versus 1.59%).The sciatic nerve terminated in the thigh in sixty-two (62) cases and in the pelvis in one (1) specimen only.In instances where the sciatic nerve terminated in the thigh, this happened mostly in the lower third (80.65%) compared to the middle third (19.35%). Conclusion: The course and termination of the sciatic nerve was found to be similar to the findings in the previous studies conducted locally, regionally and globally. However, more branches to some of the hamstring muscles were found in this study compared to the few studies conducted globally. Recommendation: Caution should be taken when placing retractors at, or medial to the midpoint between the greater trochanter of the femur and the lowest point of the ischial tuberosity. Surgeons should minimise dissections through inter- muscular planes in the upper part of the thigh.