CARTILAGE CHANGES CAUSED BY A CORONAL SURFACE STEPOFF IN A RABBIT MODEL

Coronal stepoffs of 0.5 mm (equal to the cartilage height) were create d on the medial femoral condyles of adult, skeletally mature rabbits a s a model for articular surface incongruity, After 3, 6, 12, and 24 we eks, tissue was analyzed histologically using hematoxylin and eosin an d Safranin O staining, autoradiographs were made of the femoral condyl es, and immunohistologic analysis was done for 3-B-3(-) and 7-D-4 chon droitin sulfate epitopes, An overlapping flap from the high toward the low side and an increase of the cartilage height on the low side of t he defect were observed as permanent features of adaptation throughout the entire followup, Significant degeneration was not seen around the lesion or in the tibial cartilage opposing a stepoff defect. Autoradi ography showed a three-phase response to the lesion: an early increase in radiolabeled sulfate ((SO4)-S-35) uptake, a sharp decline of (SO4) -S-35 uptake, and finally a late recovery of the autoradiographic sign al indicating partial recovery of proteoglycan synthetic activity. Aft er an early increase, immunohistologic analysis for 3-B-3(-) showed a subsiding tendency by 24 weeks, and the staining with 7-D-4 remained e levated uniformly in the vicinity of the lesion, A rabbit femoral step off defect with an offset of 0.5 mm may remodel and not lead to degene ration within the first 6 months after injury in a stable joint.