Poster AA6 - Progression of Post-Traumatic Osteoarthritis Following a Non-Invasive ACL Rupture Procedure in Rats

Introduction: Anterior cruciate ligament (ACL) injuries significantly impact knee biomechanics, increasing the long-term risk of osteoarthritis (OA). This study investigates the pathology of OA up to 10-weeks after a non-invasive ACL rupture procedure in an in vivo rat model and examines the efficacy of a standard intra-articular (IA) treatment in slowing OA progression.

Materials and

Methods: In accordance with Canadian animal care guidelines, sixty-one 14-week-old female Lewis rats were allocated into three cohorts and observed over 4-, 7- or 10-weeks periods in this study. In the first and second cohorts, five rats served as Controls and four rats underwent a unilateral non-invasive ACL rupture left untreated and were euthanized after a 4-week observation period. Eight additional rats were observed for a period of 7-weeks after undergoing unilateral non-invasive ACL rupture and were equally distributed among ACL Rupture IA-Treated, and ACL Rupture Non-Treated groups. The IA-Treated group received weekly Hyaluronan injections from Week 4 to 6. In the last cohort, forty-four rats are distributed within the Control, ACL Rupture Non-Treated, and ACL Rupture IA-Treated groups and currently being observed for 4-weeks, 7-weeks and 10-weeks periods.

Unilateral ACL rupture was induced through a rapid tibial compression method using a uniaxial mechanical tester (Figure 1). At necropsy, all articular surfaces were harvested for mechanical characterization through automated indentation and thickness mappings using a triaxial mechanical tester (Biomomentum, Canada) to assess cartilage thickness and instantaneous modulus (IM). Statistical significance was evaluated with a linear model in software R.

Results, Conclusions, and Discussions: For the 1st and 2nd cohorts (N=17 total), a notable increase in cartilage thickness was observed in the medial anterior region of Rupture Non-Treated femoral condyles at the four-week following a non-invasive ACL rupture, compared to Control joints (Figure 2A, p = 0.0035). By the seven-week mark, the cartilage thickness of ACL Rupture samples significantly decreased compared to the Rupture group at four weeks (p = 0.0077), along with a substantial increase in instantaneous modulus (IM) compared to the Control group (Figure 2B, p < 0.0001). Furthermore, a significant increase in cartilage thickness was also observed in tibial plateaus at seven weeks post-ACL Rupture compared to the Control (p < 0.0001) coupled with a significantly lower IM (p = 0.0301).
Treating the injured joints (N=4) with weekly IA-injections at 4 weeks post-ACL rupture resulted in no significant differences between the Rupture IA-Treated group and the Control group in cartilage mechanical properties. The effect of treatment is also well illustrated by the similar distribution of the frequency histogram of instantaneous modulus in the Rupture IA-Treated group and Control group, whereas a prominent contrast is visible in the gradient between the Rupture Non-Treated and the IA-Treated groups (Figure 2C).
With this non-invasive ACL rupture method, crucial stages of OA progression were observed in the 1st and 2nd cohorts of this study. Articular cartilage surfaces transitioned from early-onset osteoarthritis at four weeks with substantial cartilage swelling, to a moderate-advanced OA state at seven weeks characterized by noticeable cartilage thinning and increased stiffness. Additional animals are being observed in the 3rd cohort to determine the further progression of OA to ten weeks post-ACL rupture. Moreover, the model also shows the protective influence of the Hyaluronan IA-injections on the cartilage’s mechanical properties at 7-weeks, which will be reevaluated in the 3rd cohort at 10-weeks.

In conclusion, this clinically relevant ACL injury rat model provides a reproductible and non-surgical way to replicate the progression of post-traumatic osteoarthritis over 10 weeks. As such, it emerges as an effective tool for screening potential therapeutic for cartilage preservation.

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