Characteristics of degeneration in an unstable knee with a coronal surfacestep-off

To investigate the effect of instability on the I remodelling of a minor ar ticular surface offset, we created a 0.5 mm coronal step-off of the medial femoral condyle in 12 New Zealand white rabbits and transected the anterior cruciate ligament (ACL), A control group of 12 rabbits had only ACL resect ion and the opposite knee was used as the non-operated control. The osteoar thritic changes at 6, 12 and 24 weeks after surgery were evaluated histolog ically, In addition, changes in the immunological detection of 3-B-3(-) and 7-D-4 chondroitin-6-sulphate epitopes were determined because of the previ ous association of such changes with repair of cartilage and early osteoart hritis. In the instability/step-off group there was rapidly progressing focal degen eration of cartilage on the high side of the defect, not seen in previous s tep-off studies in stable knees. The rest of the femoral condyles and the t ibial plateaux of the instability/step-off group had moderate osteoarthriti s similar to that of the instability group. 3-B-3(-) was detectable in the early and the intermediate stages of osteoarthritis but no staining was see n in the severely damaged cartilage zones. Immunoreactivity with 7-D-4 incr eased as degeneration progressed.