In Vitro Ovine Cam Impingement Model and Its Effect on Acetabular Cartilage

Abstract

Background: Femoroacetabular impingement syndrome is a condition where abnormal contact occurs between the femoral head and the acetabulum, leading to chondral damage and hip osteoarthritis. To better understand and treat femoroacetabular impingement syndrome, it is crucial to establish in vitro models that mimic the condition and assess potential interventions. Purpose: To establish an in vitro ovine cam impingement model and assess the effectiveness of cam excision in reducing the incidence of type 3 acetabular labrum articular disruption (ALAD) (chondral flap) lesions. Study Design: Controlled laboratory study. Methods: Utilizing an ovine in vitro cam impingement model, 40 hips were subjected to testing across 5 groups (n = 8 per group): group 1 (control group), 750 N for 200 cycles; group 2 (cycle decrease), 750 N for 100 cycles; group 3 (load decrease), 500 N for 200 cycles; group 4 (cam excision), cam excision followed by 750 N for 200 cycles; and group 5 (halfway cam excision), 750 N for 100 cycles followed by cam excision under an additional 750 N for 100 cycles loading. Each specimen was subsequently assessed for chondral damage according to the ALAD classification, both macroscopically and microscopically. Results: The control group (group 1) demonstrated the highest ALAD scores (2.7 +/- 0.4, 2.8 +/- 0.3) compared with other groups, whereas the cam excision group (group 4) exhibited lower scores (0.5 +/- 0.5, 0.7 +/- 0.4) than both the cycle decrease group (group 2) (1.6 +/- 0.5, 1.6 +/- 0.5) and the halfway cam excision group (group 5) (1.8 +/- 0.6, 2 +/- 0.5) (P < .05) in both macroscopic and microscopic gradings (P < .05). The load decrease group (group 3) (1 +/- 0.5) also displayed lower scores compared with group 5 (2 +/- 0.5) at histological grading (P < .05). Conclusion: An in vitro sheep model was established that reliably induces mechanical chondrolabral damage in the hip joint. The findings show that reducing the load results in less chondrolabral damage compared with reducing the number of cycles. Furthermore, this model emphasizes the protective effect of cam excision in the management of chondral flap lesions (ALAD type 3).