Degenerative changes in dog articular cartilage induced by a unilateral tibial valgus osteotomy.

We present preliminary details of the changes that occur in a new model for the study of degenerative arthritis which does not involve intraarticular surgery. A unilateral valgus tibial osteotomy was performed in a group of 8 skeletally mature dogs of mixed breed and sex. Proximal tibial cartilages, femoral condyles and patellas were examined in operated and unoperated knees of experimental and unoperated dogs. Lesions were examined histologically and analyses were made of 35SO4 uptake and uronic acid content as measures of proteoglycan synthesis and content, respectively. Water contents were also determined. Dogs were examined from 22 to 62 weeks after osteotomy. Angulation induced by the osteoarthritis was varied from animal to animal in this preliminary study. Histologically, degeneration of the patella was observed in 3 of 5 experimental dogs and in both operated and unoperated limbs in two of the dogs. Lesions were seen in both limbs and were most common in the tibial plateau where they were present both in the lateral (covered by meniscus) and medical (uncovered) compartments of the operated and unoperated limb. In the tibial plateau initial increases in proteoglycan content and synthesis were recorded in both limbs: later after 30/36 weeks these declined to normal. In the femoral condyles, increases in water content with angulation were seen in the lateral and medial condyles of operated limbs and in the medial condyles of unoperated limbs. Other changes in proteoglycan content were observed in both condyles with a loss of proteoglycan with increased angulation being recorded in the lateral condyle of the operated limb and an increase in proteoglycan with angulation in the medial condyle of the unoperated limb. These early changes are presumably in response to alterations in load bearing in both limbs. CLINICAL RELEVANCE. This study permits an analysis of degenerative changes that can occur when articulation is changed by an osteotomy. Since the changes occur in both limbs, are potentially reversible and are induced by extraarticular surgery, we have an attractive new model for studying degenerative arthritis.