Establishment of an Ankle Posttraumatic Osteoarthritis Model in Rats and Evaluation of Associated Pain

Research Type: Level 1 - Randomized controlled trial (RCT), Meta-analysis of randomized trials with homogeneous results Introduction/Purpose: Ankle osteoarthritis (OA) is the most common joint disorder causing chronic pain and reduced quality of life. Despite its impact, no drugs have been developed to prevent OA. Understanding the pathophysiology of ankle OA and the mechanisms underlying OA-related pain is crucial for advancing treatment strategies. While posttraumatic injuries are a major cause of ankle OA, no reliable rat model currently replicates posttraumatic OA with pain-related behavior assessments. To address this limitations, we developed a model by resecting the calcaneofibular ligament (CFL) and anterior talofibular ligament (ATFL) to induce OA and assess pain-related behaviors. The model will provide insights into the relationship between ankle structure changes and joint pain in ankle OA, which can also be used to test potential treatments. Methods: With IACUC approval, 12 adult male Wistar rats were divided into two groups: the Resection group (CFL and ATFL resection) and the Control group (skin and capsule incision only). Pain-related behaviors were assessed using three methods: (1) ankle mechanical hyperalgesia (AMH) via a Pressure Application Measurement device (Ugo Basile), (2) Von Frey (VF) test using BIOSEB filaments to measure the 50% withdrawal threshold, and (3) static weight-bearing and string-pulling (SWBSP) test using BIOSEB Static Weight Bearing Touch device. At 20 weeks after surgery, all rats were sacrificed. Ankle joints were fixed in 10% neutral buffered formalin and decalcified in decalcifier (StatLab Immunocal Decalcifier). Histological analysis involved Safranin-O and Fast Green staining, with cartilage degeneration scored using the OARSI system. Data were analyzed using a two-tailed Student’s t-test with significance set at 5%. Results: Pain-related behavior assessment (Fig.1): The Resection group displayed a significantly lower threshold in AMH at 11, 13, 16, 17, 18 and 20 weeks after surgery. In the SWBSP test, significantly higher scores were observed in the Resection group than in the Control group at 20 weeks after surgery, indicating less load on the left paw compared to the right. In VF, the Resection group had a lower threshold compared to the Control group at 20 weeks after surgery. Histological analysis: Safranin-O and Fast Green staining showed that the Resection group had more cartilage degradation and exhibited higher OARSI scores, indicating the generation of OA phenotype. Conclusion: It has been reported that the properties of cartilage differ between the knee and ankle joints, but most cases of OA in animal experiments involve the knee joint. Furthermore, there is few reports of robust studies evaluating pain in ankle OA. In this study, there was a higher OARSI score in the Resection group. Moreover, this model reproduced the pain of ankle OA. This model will not only allow the mechanistic study to define therapeutic targets but also serve as a robust model to test treatments to restore the structural integrity of ankle joints and reduce pain.