On roentgenograms made with the patient supine, the knees flexed 20 to
30 degrees, the x-ray tube between the ankles, and the cassette held
proximal to the knees and perpendicular to the x-ray beam, it was found
that a line between the femoral condyles and a line between the margins of
the lateral facet of the patella formed the lateral patellofemoral angle,
an angle that was of diagnostic value in patients with subluxation of the
patella. In 100 clinically normal patients, these lines were parallel in
three and formed an angle open laterally in ninety-seven. In thirty
patients with subluxation of the patella, the lines were parallel in
twenty-four and formed an angle open medially in six. In 100 patients with
chondromalacia of the patella, however, the roentgenographic study was of
no diagnostic value since the lines were parallel in ten and formed an
angle open laterally in ninety.