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Anteromedial Rotatory Instability After Combined Anterior Cruciate Ligament and Medial Collateral Ligament Injury in a Murine Model

Year: 2026

Type: article

Abstract: Background: Combined anterior cruciate ligament (ACL) and medial collateral ligament (MCL) injuries lead to anteromedial rotatory instability (AMRI), yet their in vivo biomechanics and effects on osteoarthritis (OA) severity relative to isolated injuries remain unclear. Purpose: To establish a murine AMRI model via combined ACL and MCL transection (ACLT+MCLT) and compare OA progression with isolated ACL transection (ACLT) and destabilization of the medial meniscus (DMM). Study Design: Controlled laboratory study. Methods: A total of 36 eight-week-old male C57BL/6 mice were used. Twelve underwent ex vivo biomechanical testing of anterior tibial translation (ATT) at neutral position, 15° internal rotation (IR), and 15° external rotation (ER) in ACLT+MCLT versus ACLT. The remaining 24 were randomized to the sham, ACLT, DMM, and ACLT+MCLT groups and underwent 6 weeks of treadmill running. ATT was assessed via photographic and radiographic evaluations. Gait, micro-computed tomography (CT) (osteophytes, subchondral bone plate), histology (OARSI score, cartilage thickness), and immunohistochemistry (type II collagen, Aggrecan, matrix metalloproteinase 13 [MMP13]) were analyzed. Data were compared using analysis of variance (ANOVA) with post hoc tests and repeated-measures ANOVA where appropriate. Results: ACLT+MCLT showed significantly increased ATT at 15° ER versus ACLT (photographic: 1.32 ± 0.28 vs 1.01 ± 0.33 mm; P < .05; loaded radiographic: 3.46 ± 0.78 vs 2.53 ± 0.50 mm; P < .001), confirming AMRI-like instability. After 6 weeks, ACLT+MCLT caused the most severe gait impairment, including increased stride width versus ACLT and DMM (3.46 ± 0.31 vs 2.80 ± 0.23 and 3.03 ± 0.17 cm; both P < .05) and reduced stride length versus sham and ACLT (5.05 ± 0.52 vs 6.87 ± 0.36 and 5.99 ± 0.57 cm; both P < .05). Micro-CT showed the greatest osteophyte number and subchondral bone plate thickness in ACLT+MCLT mice (15 ± 2.83 and 221 ± 36 μm, respectively; all P < .05 vs ACLT and DMM). Histologically, ACLT+MCLT had the highest OARSI score (5.75 ± 0.50) and lowest cartilage thickness (117.5 ± 15 μm). Immunohistochemistry showed reduced type II collagen and Aggrecan expression (13.80% ± 2.29% and 18.60% ± 0.92%) and increased MMP13-positive cells (77.10% ± 5.51%). Conclusion: Combined ACL and MCL injury created a valid murine AMRI model and induced more severe OA and dysfunction than isolated injury, confirming the detrimental effect of coupled rotational anterior instability. This model offers a preclinical tool for AMRI research; clinical translation requires human studies. Clinical Relevance: The established AMRI animal model simulates the complex rotatory instability of the knee after combined ACL and MCL injuries, as observed clinically. It provides a crucial preclinical tool for evaluating the efficacy of different ligament management strategies (eg, single-stage combined reconstruction vs staged treatment) in restoring joint stability and delaying OA progression. The findings suggest that in cases of significant rotatory instability, aggressive surgical intervention to restore rotational stability may be critical to protecting cartilage and improving long-term outcomes.

Source: Orthopaedic Journal of Sports Medicine

DOI: 10.1177/23259671261480904