Experimental Measurement of Rotatory and Translatory Instability of the Knee Joint

Abstract

In the evaluation and treatment of knee ligament injuries and for comprehensive understanding of knee ligament function, it is important to know where in the movement of extension-flexion the different types of instability released by wellknown ligament injuries occur. An apparatus was developed to record anterior– posterior tibial displacement, valgus–varus instability, and axial tibial rotation instability on knee preparations, continuously, in the extension–flexion movement, when the tibia was submitted to a well-defined constant torque or force. Osteoligamentous knee preparations were suspended in the femur and a lever was fixed to the tibial segment. The lever was fitted with strain gauges to measure the torque in three planes. Potentiometers recording extension–flexion, anterior–posterior tibial displacement, valgus–varus, and axial rotation angulations were mounted. The lever was moved manually, and signals from strain gauges and potentiometers passed through an amplifier and a data acquisition system to a microcomputer, which stored the results of the measurements. The final movement curves were calculated and plotted at a regional computer service centre. Tests for reproducibility of measurements at different ligament status demonstrated a high level of reproducibility.