Stress radiography in acute ligamentous injuries of the knee.

Stress radiography was performed on 60 acute ligamentous injuries of the knee under general anaesthesia using a simple standard technique. Laxity on angular stress in extension was evident when the posterior cruciate ligament was torn in association with a collateral capsular tear. The same test repeated in 20-30 degrees of flexion was abnormal when the collateral capsule alone was abnormal when the collateral capsule alone was torn and laxity always exceeded 5 degrees. Where both cruciate ligaments were torn the laxity exceeded 10 degrees. Lateral stress radiographs in the presence of an isolated capsular tear demonstrated rotatory laxity with a glide rarely exceeding 10 mm. The addition of a torn anterior cruciate ligament resulted in sagittal laxity greater than 7 mm and a tear of the posterior cruciate ligament, irrespective of the associated pathology, resulted in a laxity exceeding 12 mm.