Plain radiography in the degenerate knee - A case for change

We took posteroanterior weight-bearing radiographs, both with the joint ful ly extended and in 30 degrees of flexion, in a consecutive series of 50 kne es in 37 patients referred for the primary assessment of pain and/or stiffn ess. These radiographs were reported 'blind' both by an orthopaedic surgeon and a radiologist. Direct measurement of the joint space, together with gr ading of the severity of erosion according to the Ahlback criteria, was und ertaken, Any other abnormality present was also documented. The radiographs of the knees in 30 degrees of flexion consistently showed m ore advanced erosion in both the medial (p = 0.001) and the lateral (p = 0. 0001) tibiofemoral compartments, when compared with those of knees in full extension. The Ahlback classification of 25 joints was altered, in some cas es by several grades, by the flexed position of the joint. In every case in which another abnormality,vas identified on the radiograph in full extensi on, it was also noted on that of the knee in 30 degrees of flexion, In a fu rther four cases, additional pathology could only be seen in the flexed kne e. Every patient was able to complete the radiological examination without difficultly. Our study supports the adoption of a weight-bearing view in 30 degrees of flexion as the standard posteroanterior radiograph for the asse ssment of tibiofemoral osteoarthritis in patients over 50 years of age.