Evaluation of Pain-Associated Behavioral Changes in Monoiodoacetate-Induced Osteoarthritic Rats Using Dynamic Weight Bearing Analysis.

Pain is the primary clinical indication of osteoarthritis (OA), and behavioral assessments in rodent pain models are widely used to understand pain patterns. These preclinical pain assessments can also help us to understand the effectiveness of emerging therapeutics for prolonged OA pain management. Along with evoked methods like mechanical allodynia and thermal hyperalgesia, non-evoked methods such as dynamic weight bearing (DWB) analysis are valuable tools for behavioral assessments of pain. Both these methods were utilized to study pain-induced behavioral changes in a monoiodoacetate (MIA)-induced osteoarthritic pain model, which is a well-established preclinical OA pain model. However, the utility of DWB analysis as an indicator of long-term pain sensitivity (more than 4 weeks) remains largely unexplored. Understanding the long-term sensitivity of DWB is valuable to study the effectiveness of novel prolonged pain-relieving therapeutics. Here, we studied the dynamic behavioral changes in MIA-induced OA rats over a period of 16 weeks using DWB measurements. Female Sprague Dawley rats were injected in the right knee joint with MIA (3 mg) using X-ray guidance. Multiple dynamic postural evaluations such as ipsilateral weight percentage, paw area, contralateral/ipsilateral weight ratio and area ratio were assessed to understand the behavioral changes. The data showed that the ipsilateral weight bearing percentage alone is not sufficient to assess pain-related behavior beyond 6 weeks. This study shows the advantages and limitations of dynamic weight bearing as an assessment tool for the long-term progression of pain behavior in MIA-induced OA rats.