Introduction: Recently there has been a trend for recommending weight bearing 30û ßexion views as the standard view in place of full extension view for the routine radiography of the Knee. It has been shown that this view can pick up more abnormalities and can show a joint space diminution, which cannot be seen on full extension views. It has not been shown by any study that this is not due to the differential thickness of cartilage in different places on femoral condyle thus implying a natural cause rather than pathological process (abnormal wearing of cartilage) of the observed decrease in joint space. So this prospective randomised double blind study was designed. Methods: 22 patients with arthroscopically proven non osteoarthritic knees were included in the study. Knee radiographs were taken in weight bearing full extension and 30û ßexion PA views. The radiographs were randomised and read by a consultant, registrar & senior house ofþcer. Results: Appropriate statistical tests were applied and results analysed. There was up to 2mm difference in the joint space on the two views. Conclusion: The decrease in the joint space if seen on 30û ßexion views as compared to full extension views may be due to the differential thickness of inherent normal cartilage and so is not always due to a pathological process. Based on this a classiþcation was devised to signify the importance of measured differential thickness in the cartilage of femoral condyle.

There have been many reports which suggest that in patients with tibiofemoral osteoarthritis, a reduction in joint space is demonstrated better on weight-bearing radiographs taken with the knee in semiflexion than in full extension. The reduction has been attributed to the loss of articular cartilage in the contact area in a semiflexed arthritic knee. None of these studies have, however, included normal knees. We have therefore undertaken a prospective, double-blind, randomised study in order to evaluate the difference in the joint-space of arthroscopically-proven normal tibiofemoral joints as seen on weight-bearing full-extension and 30° flexion posteroanterior radiographs. Twenty-two knees were evaluated and the results showed that there may be a difference of up to 2 mm in the two views. This difference could be attributed to the inherent differential thickness of the articular cartilage in different areas of the femoral and tibial condyles and a change in the areas of contact between them.