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

Unilateral arch hypertrophy with spinous process tilt: a sign of arch deficiency.

Unilateral arch hypertrophy (UAH) may be generated by a contralateral deficiency which is most commonly a pars defect (43 out of 50 patients studied). Such a defect can also cause rotational instability. When present, both can be easily detected on simple anteroposterior views through the resulting pedicular and pars asymmetry and spinous process tilt. From simple anteroposterior views, one can predict that at least one arch defect does exist, that it is unstable, and not of recent origin

Radiologie de l'instabilité rotulienne: intérêt du cliché de profil et de la vue axiale à 30 degrees rotation externe.

Patellar instability is often missed by conventional axial views because transient subluxation of the patella essentially occurs during the first degrees of knee flexion (0 to 30 degrees), a position in which bilateral routine axial views are impossible to obtain. However, simple radiographic methods enable detection of both patellar instability and the often associated trochlear depth insufficiency. Every lateral radiograph of the knee depicts the depth of the proximal trochlear groove which is superior to 5 mm in a normal population. Upper trochlear depth insufficiency is frequently observed in the case of major patellar instability. Lateral views of the knee recorded during the first degrees of flexion (0 degrees-15 degrees) enable detection of patellar maltracking through the patellar tilt always associated with significant subluxation of the patella. Patellar maltracking may be studied dynamically by lateral fluoroscopy during progressive flexion of the knee. Unilateral 30 degrees axial radiographs with forced lateral rotation of the leg are definitely superior to conventional axial views in detecting transient patellar subluxation. These simple radiographic modalities should replace computed tomography in the search for patellar instability