The posteroanterior 45° flexion weight-bearing radiograph of the knee

Biomechanical studies suggest that radiographs of the osteoarthritic knee taken in 30 degrees to 60 degrees of flexion more accurately demonstrate the true degree of articular cartilage loss than radiographs taken with the knee in full extension. Conventional anteroposterior weight-bearing full-extension radiographs were compared with posteroanterior 45 degrees flexion weight-bearing radiographs of 35 patients with 45 symptomatic knees (90 compartments) presenting with suspected osteoarthritis. In 35 compartments, there was a 2-mm or greater loss of joint space in the 45 degrees flexion views compared with those taken in full extension. Also, in 11 compartments (10 knees), there was a normal joint space on the full extension radiographs, but marked narrowing on the flexion view. Both results are statistically significant. It is concluded that the posteroanterior 45 degrees flexion weight-bearing radiograph is a useful additional tool in the assessment of knees with early degenerative change.