Articular changes associated with internal derangement of the knee.

A prospective study was made of 100 knees which had been operated on for various kinds of internal derangement. An observer, who did not know the clinical condition of the knee, recorded whether or not there were articular lesions of the femoral condyles. Lesions were found to be localised to a triangular area on the medial condyle and to a strip on the lateral condyle. Similar lesions have been described in association with flexion deformities in rheumatoid and osteoarthritic knees. Lesions were found in 49 out of 50 knees which had been locked for more than three days. They were also found in 29 knees in which there appeared to be full extension before operation, but where there was either a torn meniscus with a history of intermittent locking or serious anterolateral instability. In these cases it was considered that the final "screw-home" mechanism of full extension had been lost. Lesions were not present in 10 knees which appeared locked, but in nine of these the interval between injury and operation was less than three days. Lesions were not found in eight knees where there was full extension and no history of locking or instability. In four knees with a plica syndrome similar lesions were present.