Mechanical effects on measuring displacement of the knee joint with the knee arthrometer KT1000 and KT2000]

The KT2000 knee ligament arthrometer manufactured by the MEDmetric Corporation is used in the field of orthopedics to establish quantitatively the size of the anterior and posterior draw phenomena of the knee joint. The basis for the measurement is the Lachman test in which a force is applied to the tibia relative to the femur. The resulting displacement is limited by the cruciate ligaments. The measurements obtained for a potentially injured knee are compared with those of the healthy knee and empirical threshold values, and serve as a basis for deciding whether to operate on patients with cruciate ligament insufficiency. The subject of the present study is a design shortcoming of the KT2000 that may falsify the measured results when the device is not correctly employed. A simple mechanical modification of the KT2000 can reduce this error. In the present study, the error is quantified and we show how the modification can keep it within tolerable limits.