Sacroiliac Joint Stress Is Affected by Postural Change or Cam Resection in Femoroacetabular Impingement Syndromes: A Finite Element Analysis Study

Background: Patients with femoroacetabular impingement (FAI) frequently experience sacroiliac joint (SIJ) pain. Patients with concomitant lower back symptoms may be at risk for poor patient-reported outcomes after cam resection. Purpose: To investigate whether SIJ stress in patients with FAI changes depending on posture or cam resection. Study Design: Descriptive laboratory study. Methods: Preoperative and postoperative computed tomography (CT) scans were analyzed in 31 patients with FAI who underwent cam resection. We created CT models of the lumbar spine, pelvis, and hip joints, including the SIJ cartilage and surrounding ligaments. For both pre- and postoperative conditions, we constructed models of standing, sitting, and sitting with 10° posterior pelvic tilt positions and measured the equivalent stress in the anterior, superior-posterior, and inferior-posterior regions of the SIJ under a 600-N load. Results: Preoperatively, the equivalent stress in the posterior-inferior SIJ region was generally higher in the sitting than in the standing position (up to 2.87-fold, P < .0001), whereas there was no significant difference between standing and sitting with a 10° posterior pelvic tilt position. After cam resection, the equivalent stress in the lower portion of the SIJ during sitting generally decreased ( P < .0001). A positive correlation was observed between the preoperative posterior-inferior SIJ equivalent stress in the sitting position and preoperative α angle ( r = 0.40; 95% CI, 0.04-0.66). Conclusion: In patients with FAI, the equivalent stress in the lower portion of the SIJ generally increased in the sitting posture. Cam resection decreased the equivalent stress in the posterior-inferior SIJ region in the sitting posture to a level similar to that observed with a 10° posterior pelvic tilt before surgery. Clinical Relevance: These findings suggest that optimizing pelvic posture and appropriate cam resection may help mitigate SIJ-related pain in patients with FAI, providing valuable insights for surgical planning and rehabilitation strategies.