Stress radiographical measurements of post-traumatic knee instability. A clinical study.

In a prospective, consecutive, clinical and stress radiographical study, comprising 153 traumatic knee injuries, the value of stress radiographical measurements, gonylaxometry, was studied. Clinical evaluation, gonylaxometry and preoperative evaluation under general anaesthesia were carried out in that order. Then the operative findings were recorded as drawings on standard diagrams. These were used as a basis for evaluation of the preoperative tests. Of all the methods evaluated, gonylaxometry was found to provide the most accurate information regarding the knee injury. Very close to this result were the findings under general anaesthesia. Anterior drawer sign was measured gonylaxometrically when damage to the anterior cruciate ligament was present; posterior drawer meant damage to the posterior cruciate ligament. Partial ruptures of cruciate ligaments did not allow antero-posterior displacements exceeding the critical levels of the test. Small positive medial instability was found with ruptures of profound medial structures, higher values with total rupture of the long superficial collateral band, and still higher values when cruciate ligament ruptures were also present. The predictive values of a positive radiographical test were 100 per cent as regards medial instability and 98 per cent for drawer looseness. The predictive values of a negative test were 96 per cent for drawer and 92 per cent for medial instability. These figures are based on the total material. 95 per cent confidence limits are given.