Instrumented testing for evaluation of sagittal knee laxity.

Seventy-one patients with untreated ruptures of the anterior cruciate ligament of at least four years' duration had their knee laxity examined with a laxity testing device. Twenty of the 71 patients were tested by two examiners independently. Another 30 patients without previous knee injury were chosen as a reference group and tested. Patients with anterior cruciate-deficient knees had significantly increased anterior and total laxity. If the testing procedure was altered, the laxity changed. Thus, an increase of knee flexion from 15 degrees to 25 degrees resulted in an increased anterior laxity. Changes in the amount and placement of the tibial load also affected laxity. Inter-examiner reproducibility was high if a standardized testing procedure was followed. Sensitivity was 92% if the difference in total laxity between involved and uninvolved knees was determined with a high tibial load (180 N), whereas specificity was 70%. Therefore, the laxity tester has disadvantages as a diagnostic tool, but it is still valuable for evaluation of anterior cruciate ligament ruptures and their treatment.