[Plain radiography of the knee: the articular surfaces].

Lateral knee radiographs allow recognition of both medial and lateral femoral and tibial surfaces, groove and anterior borders of the trochlea and lateral facet and ridge of the patella. Analysis of these lines allows detection of focal contour abnormalities, femoral trochlear dysplasia and patellar tilt. Qualitative radiological analysis of the osseous surfaces detects the particular aspect of abraded subchondral bone ("drawn with chalk"), preventing the trap of false joint spaces on non weight-bearing views. Occasionally, very subtle bone abnormalities can be recognized in cases of cartilaginous, subchondral or even meniscal lesions. However, these focal abnormalities are not constant, and their visualization is somewhat anecdotal.