Osteoarthritis (OA) is an age-related
joint disease characterized by degeneration of articular cartilage and is associated with
chronic pain. Although several experimental models of OA have been employed to investigate the underlying etiologies of the disease, there has been relatively little investigation into development of animal models of OA to study the
pain associated with the condition. In the present study, we investigated OA induced by injection of either iodoacetate or
papain into the knee joint of rats, and assessed the joint degeneration with radiographic analyses and measured
pain behavior using hind limb weight bearing. We found that injection of iodoacetate, but not
papain, resulted in a chronic joint degeneration as measured by decreased bone mineral content and bone mineral density,
necrosis of articular cartilage and
osteophyte formation. These pathological changes were associated with
pain that manifested as time- and concentration-dependent alterations in hind limb weight bearing. These alterations in hind limb weight bearing were reversed with
morphine, but were not significantly affected by acute administration of either
indomethacin or
celecoxib. However, administration of 30 mg/kg
celecoxib twice daily for 10 days resulted in a significant restoration of hind limb weight bearing. We conclude that the iodoacetate model of OA is a relevant animal model to study
pain associated with OA, and can be used to test potential therapeutic agents.