Measurement of anterior-posterior displacement of the knee. A comparison of the results with instrumented devices and with clinical examination.

Thirteen subjects who had normal knees and fifteen patients who had a chronic rupture of the anterior cruciate ligament were tested in order to compare the measurements of tibiofemoral displacement as recorded by four commercial devices: the Acufex knee-signature system, the Genucom knee-analysis system, the Medmetric KT-1000 arthrometer, and the Stryker knee-laxity tester. Anterior and posterior displacement were measured at forces of eighty-nine newtons (twenty pounds) and 133 newtons (thirty pounds). We found significant differences in reproducibility of measurement among the devices. The Acufex, Medmetric, and Stryker devices had more reproducible measurements, and they could be used to identify 80 to 90 per cent of the normal subjects and anterior cruciate-deficient patients. The Genucom device had poorer reproducibility of measurement, and it tended to register greater differences in displacement between the right and left knees of normal subjects.