The role of the ischiofemoral ligament in hip dislocation resistance: A cadaveric study

Background: The ischiofemoral ligament (ISFL) contributes to posterior hip stability, but the extent to which the ISFL prevents dislocation after total hip arthroplasty (THA) remains unclear. This study aimed to investigate whether the ISFL independently contributes to dislocation resistance during hip flexion and internal rotation. Methods: A total of nine fresh-frozen cadaveric hips were tested using a custom jig under three conditions: (1) ISFL preserved, posterior capsule incised; (2) ISFL preserved, capsule repaired; and (3) both ISFL and posterior capsule disrupted. Dislocation occurrence and internal rotation angle under 2 N·m torque were measured at flexion angles from 0 to 105°, in 15° increments. Results: In condition (1), dislocation occurred in four hips at 60°, eight at 75°, and all nine by 90°. In condition (2), no dislocations occurred at any flexion angle. In condition (3), dislocation began at 30° and was universal by 60°. Following capsular repair in condition (2), the internal rotation angle increased by 10.8% overall compared to the angle before capsulotomy. At flexion angles ≥60°, the increase was 15.2%, which was statistically significant. Conclusion: The ISFL contributes to posterior hip stability in shallow flexion but is insufficient to prevent dislocation in mid-to-deep flexion. Posterior capsular reconstruction, particularly of the inferior portion, markedly enhances dislocation resistance, underscoring its importance for achieving stable THA.