AB0105 Effects of carrageenan induced synovitis on joint damage and pain in a rat model of knee osteoarthritis

Background Knee osteoarthritis (OA) is associated with ongoing pain and joint damage that can be punctuated by acute flares of pain and inflammation. Acute synovitis in normal knees might resolve without long-term detriment to joint function. Objectives We hypothesised that osteoarthritis is associated with impaired resilience to acute inflammation. Methods We induced synovitis by intra-articular injection of carrageenan into rat knees with or without meniscal transection-induced OA, and measured synovitis, weightbearing asymmetry (an index of pain behaviour), and joint damage up to 35 days after OA induction (23 days after carrageenan-injection). Results Intra-articular injection of carrageenan was followed by weightbearing asymmetry for 1 week, synovitis, indicated by a transient increase in knee diameter for 2 days after injection, and a more sustained (through day 23) increase in synovial macrophages, endothelial cell proliferation and vascular density compared with naive controls. Meniscal transection was followed by weightbearing asymmetry and histological evidence of OA through day 35. Carrageenan-injection in OA knees was followed for 2 days by increased weightbearing asymmetry compared either to OA knees, or to carrageenan-injected, SHAM-operated knees. OA structural damage and synovitis at day 35 were greater after carrageenan injection on day 12 compared to saline-injected, MNX-operated knees, and compared to carrageenan-injected, SHAM-operated knees. Carrageenan injection alone did not induce OA in SHAM-operated knees. Conclusions OA knees were more sensitive to pain behaviour, inflammation and structural damage following an episode of acute inflammatory pain flare than were non-arthritic knees. Preventing inflammatory flares may be particularly important in preventing symptoms and long term joint damage in OA. Disclosure of Interest None declared