A simple rig for stress radiography of the knee

A simple rig for obtaining stress radiographic measurements of the knee is presented. Lateral instability (varus), medial (valgus), anterior and posterior (drawer), as well as rotatory instability can be measured. The rig works by means of weights over pulleys, and the same forces are applied as when using a hydraulically-operated machine. The rig is small and inexpensive. A group of subjects showed values of stability within the same 'normal' area as those obtained with the hydraulically-operated stress machine. Data were processed on a microcomputer.