Radiographic grading of the severity of knee osteoarthritis: relation of the Kellgren and Lawrence grade to a grade based on joint space narrowing, and correlation with arthroscopic evidence of articular cartilage degeneration.

We examined standing knee radiographs of 92 patients who had chronic knee pain and radiographic evidence of mild or moderate osteoarthritis (OA) according to the Kellgren and Lawrence (K/L) criteria. Because the K/L criteria overemphasize osteophytosis relative to joint space narrowing (JSN), we graded OA severity also with a scoring system that placed greater emphasis on JSN than on osteophytes. In each case, the articular cartilage was visualized directly at arthroscopy. Of 17 patients whose radiographic findings were normal by both the K/L criteria and our JSN-weighted criteria, 7 had advanced tibiofemoral and/or patellofemoral compartment changes of OA seen at arthroscopy, emphasizing the insensitivity of the radiograph for detecting early articular cartilage loss. In addition, tibiofemoral JSN was common in the presence of normal articular cartilage. The JSN-weighted scale provided no advantage over the K/L criteria for assessing the severity of articular cartilage changes of OA.