Clinical, arthroscopic and kinematic correlates of osteoarthritis progression in sheep

Purpose: To describe structural and functional progression of osteoarthritis in a sheep model. Methods: Twenty-two adult female sheep were allocated to two n = 11 groups that underwent arthroscopic medial meniscal release in one knee joint followed by I.A. saline or hyaluronate 3 months later. Clinical assessments, lameness scoring, CT imaging, kinematic assessment using a Tekscan Walkway 7 system and arthroscopy (in a subgroup of n = 3) were performed preoperatively then at 3 and 6 months. Results: Second look arthroscopy 3 months after meniscal release confirmed that the sheep had loss of meniscal load sharing in the medial compartment as well as fissures and partial thickness cartilage erosions in the medial tibial plateau (Outerbridge grade 2). Synovial membrane hypertrophy and debris in the synovial fluid were also present. After six months of meniscal insufficiency there were larger partial and full thickness chondral erosions (Outerbridge grade 3) as well as involvement of the opposing femoral condyle. All sheep could be trained to walk at 1 ± 0.1 m/sec using leader sheep and a behavior modification (food reward). Three months after meniscal release clinical assessment of lameness and pain was unrevealing but gait analysis showed that sheep in the saline treated group had reduced impulse (kg*sec) (P < .05) and maximum force (kg)(P < .05) in the operated leg. Interestingly, clinical lameness did not develop until 6 months postoperatively (Fig 1) at which time arthroscopy revealed more extensive erosions in the tibial plateau and involvement of the opposing femoral condyle (Outerbridge grade 2–3). CT imaging showed that all sheep were developing medial tibial plateau osteophytes and significant medial enlargement in the coronal plane (P < .01) in both groups (Fig 2). Conclusions: Unlike some previous reports we were able to collect kinematic data on all sheep though this required training for 4 weeks before the study started. Assessment of pain and lameness in sheep is controversial since they are a “prey” species, which implies that they are unlikely to demonstrate behavior that would make them appear more susceptible to predation. Our data show that Outerbridge grade 2 lesions 3 months postoperatively were sufficient to create measurable gait abnormalities when clinical lameness was not detectable. More severe erosive lesions to the level of the subchondral bone were associated with clinically detectable lameness six months after meniscal release. This suggests that the arthroscopic meniscal release model in the sheep provides adequate opportunity for measuring changes in OA progression with therapeutic interventions.View Large Image Figure ViewerDownload Hi-res image Download (PPT)View Large Image Figure ViewerDownload Hi-res image Download (PPT)