Radiologic technique for measuring instability in the knee joint.

The measurement of anteroposterior instability as well as lateral and medical instability in the knee joint based upon radiologic films exposed while forces are being exerted on the patient in a specially constructed stress apparatus is described. Measurements on the films require detailed knowledge of the landmarks of the joint, alignment of baselines to special points, especially on the lateral projection, where anterior and posterior displacement should be measured for each tibial condyle to calculate the mean.