The relation of femoral notch stenosis to ACL tears in persons with knee osteoarthritis

Objective: A significant risk factor for anterior cruciate ligament (ACL) tears in young athletes is a reduced femoral Notch Width Index (NWI). The purpose of this study was to test if persons with knee osteoarthritis (OA) and ACL tears have smaller NWI independent of prior joint injury and osteophyte volume. Methods: We included 160 participants from the progression sub-cohort of the Osteoarthritis Initiative (OAI) Study, an ongoing 4-year, multi-center study, focusing on knee OA. The femoral notch width, the condylar notch width at 2/3 of the notch depth, and the intercondylar notch angle (β) were measured on sagittal and coronal MR-images. NWI = notch width/condylar width at 2/3 of the notch depth, was calculated and outcome of ACL tear frequency was compared between two groups; NWI ≤ 0.20 and NWI > 0.20. The NWI and β were analyzed as continuous variables. Results: Of the 160 subjects [51% female, age 62.1 (±9.9), BMI 30.3 (±4.7) kg/m²] 14.4% showed an ACL tear. Osteophyte bone volume was available for 150 participants, of which 13% had an ACL tear. The continuous measure of NWI on the coronal images was significantly (P = 0.01) smaller in participants with ACL tear [0.246, 95% confidence interval (CI) 0.234-0.258] compared to those without (0.263, 95% CI 0.258-0.268). Adjustment for demographic variables still showed significant results (P = 0.03, mean difference 0.015 95% CI -0.001-0.030) and adjustment for demographic variables and osteophyte bone volume were borderline significant (P = 0.06, mean difference 0.015 95% CI 0.001-0.029). Conclusions: We identified a smaller NWI in participants with knee OA and ACL tears. Further longitudinal investigation is necessary to determine this as an independent risk factor.