Intraoperative Measurement of Pivot Shift by Electromagnetic Sensors

The pivot-shift test is commonly used for assessing dynamic instability in anterior cruciate ligament (ACL)-insufficient knees and is related to subjective knee function, unlike static load-displacement measurement. Residual pivot shift after ACL reconstruction is a crucial factor related to poor clinical outcome. However, no method exists that can be used to evaluate pivot shift quantitatively and noninvasively. Conventional measurements of 3-dimensional position displacement cannot assess such dynamic instability in vivo and produce comparable parameters. Not only 3-dimensional (3D) position displacement but also its 3D acceleration should be measured for quantitative evaluation of the pivot-shift test. We developed a new noninvasive in vivo measurement system by using an electromagnetic sensor, which can be used to measure the 6 degrees of freedom of the knee during the pivot-shift test with a high sampling rate (60 Hz). It enables monitoring of instantaneous 3D position displacement and calculates a 3D acceleration of the motion. These measurements can be used for quantified evaluation of dynamic instability demonstrated by the pivot-shift test.