The acute treatment of articular step-off injuries is based largely on reduction criteria, because the presence of residual incongruity has been correlated with the development of posttraumatic arthrosis (PTA). However, this association has not been demonstrated on a prospective basis. Using the rabbit femoral condyle, we developed a surgical model of articular condylar defect without sacrificing the axial alignment or inherent stability of the knee joint. Twenty weeks after the creation of 5-mm femoral condylar defects, progressive osteoarthritic changes were confirmed by radiographic, histological, and biochemical parameters. Osteophytes were observed on the medial aspect of operated knee joints in 67% of cases. Femoral and tibial articular cartilage at the site of the condylar defect exhibited fibrillation, hypocellularity, and severe loss of safranin-O staining. Focal areas of cartilage were denuded or replaced by pannus. In no case was femoral congruity restored by cartilage repair. Statistically significant decreases in proteoglycan content were demonstrated for cartilage sampled from the weight-bearing region of the condylar defect and from the tibial surface directly beneath it. These changes resemble those arising from previously reported models of osteoarthrosis. We present the model as a valid tool for the study of articular condylar defect and its role in the development of PTA.