"ANATOMICAL VARIATIONS OF THE SCIATIC NERVE AND THEIR RELEVANCE IN HIP ARTHROPLASTY"

Abstract

Background: The sciatic nerve is the largest peripheral nerve of the lower limb, and its anatomical course in relation to the piriformis muscle and posterior hip structures is clinically significant in hip arthroplasty. Although the classical description places the sciatic nerve emerging inferior to the piriformis muscle, multiple anatomical variations have been documented, including high division, accessory bundles, and atypical relationships with surrounding musculature. These variations may increase the risk of iatrogenic nerve injury, postoperative neuropathy, altered surgical exposure, and variable response to regional anesthesia. Understanding these variations is essential for orthopedic surgeons performing hip arthroplasty through posterior, anterolateral, or minimally invasive approaches.

Objective: To determine the anatomical variations of the sciatic nerve in patients undergoing hip arthroplasty and to assess their clinical relevance regarding surgical exposure, intraoperative nerve protection, and postoperative neurological outcomes

Methodology: An observational descriptive study was conducted in the Orthopedic Surgery Department Sughra Shafi Medical Complex Narowal over a period of one year from 1^st January to 31^st December 2024. A total of 50 patients undergoing primary hip arthroplasty for osteoarthritis, femoral neck fractures, or avascular necrosis were selected through consecutive sampling. Intraoperative exploration was performed using standard posterior or anterolateral approaches to document the sciatic nerve course, bifurcation pattern, and relationship with the piriformis muscle. Variants were classified according to Beaton and Anson’s anatomical classification. Postoperative neurological assessment was conducted on day 1, day 7, and at 6-week follow-up. Data were analyzed descriptively, and associations between anatomical variation and postoperative nerve deficits were assessed using chi-square testing.

Results: Sciatic nerve anatomical variations were found in 18% (n = 9) of patients. The most common variant was high division of the tibial and common peroneal components above the piriformis (10%), followed by the peroneal component passing through the piriformis muscle (6%). A rare pattern with both divisions emerging above the piriformis was observed in 2% of cases. Patients with nerve variations showed higher rates of transient postoperative neuropraxia (11.1%) compared to those with classical anatomy (4.8%). The posterior surgical approach demonstrated greater intraoperative difficulty in nerve identification among variation cases. No permanent nerve deficits were observed. High bifurcation and intrapiriformis course were significantly associated with increased risk of temporary nerve irritation (p < 0.05).