Current radiographic evaluation of knee osteoarthritis (OA) depends primarily on the presence and severity of joint space narrowing (JSN) and osteophytes. Radiographic JSN is a function of the actual JSN caused by articular cartilage loss and the observable JSN artifactually caused when the tibial and femoral surfaces diverge due to variations in patient's knee position. Views yielding the greatest JSN are the most accurate. Osteophytes are also dependent on positioning. This study investigated the consequences of positioning on JSN and osteophytes in clinical studies in which the outcome of OA knee is scored.
In total, 1105 patients underwent 1175 paired radiographic examinations using weight-bearing (WB) standard anterior-posterior (AP) extended knee views (AP-WB), semiflexed WB posterior-anterior views with the knee in contact with the film and the 1st metatarsophalangeal (MTP) joint under the film plane (MTP) (method of Buckland-Wright), and WB PA views with the tip of the great toe at the film plane, 20 degrees of knee flexion and 5 degrees downward angulation of the x-ray tube (schuss-tunnel view). Careful attention was given to proper positioning. JSN and osteophytes were scored on a 0-3 scale.
JSN was significantly greater by the MTP and schuss-tunnel methods than by the AP-WB method, but no difference was found between the MTP and schuss-tunnel methods. In addition, disagreement was identified in 34% of MTP and AP-WB scores. In 69.3% of disagreements the scores were more abnormal in the MTP view. When the disagreements were studied, the mean MTP score was 1.68 compared to 1.12 for the AP-WB score. Fifty-seven knees were scored as 3 by the MTP view and as 2 by the AP-WB, and 8 knees were scored as 3 by the AP-WB view and 2 by the MTP view. Little difference in osteophytes was noted among the 3 methods, although fewer osteophytes were identified by the schuss-tunnel method than the AP-WB method.
Using the clinical reading methods of this study, the MTP and schuss-tunnel views were equivalent when compared to each other. When compared with the AP-WB view, the schuss-tunnel view resulted in a lower osteophyte score. These results, based on clinical readings, are similar to previous computerized analyses that indicated that the MTP and schuss-tunnel views were superior to the AP-WB, but that the MTP view was superior to the schuss-tunnel view.