Use of a gyroscope sensor to quantify tibial motions during a pivot shift test

The purpose of this preliminary study was to evaluate the use of a gyroscope sensor to record rotations of the tibia about its long axis during a clinical pivot shift examination. Ten patients with a unilateral ACL injury were tested under anaesthesia prior to surgery. Each ankle was placed in neutral position, wrapped and stabilized with athletic tape, and a small aluminium plate was taped to the bottom of the foot. A data recovery module was attached to the bottom of each plate using a swivel bracket that allowed alignment of the gyro axis with the long axis of the tibia. The module contained a triaxial gyroscope, battery and circuitry for wireless data broadcast to a laptop computer. Ten pivot shift tests were performed on both knees, and the surgeon's clinical grading of the pivot shift was noted for each limb. Mean values (10 trials) of peak tibial rotational velocity and integrated tibial rotation were compared between knees for each patient during the pivot shift reduction event (external tibial rotation during knee flexion). Five patients (50 %) had significantly greater tibial rotation in their injured knee, four showed no difference between knees, and one had significantly greater rotation in the normal knee (p < 0.05). Seven patients (70 %) showed greater peak rotational velocity in their injured knee, and three had no difference between the knees (p < 0.05). Correlations of rotation and rotational velocity with clinical pivot shift grade were weak (r (2) = 0.09 and 0.19, respectively). Foot gyroscope measurements did not correctly identify the injured limb in all patients. Peak rotational velocity during the reduction event was a better indicator of ACL deficiency than the integrated rotation. If this technology is to be more useful clinically, gyroscope data may have to be combined with accelerometer data, perhaps with sensors mounted on both the tibia and femur. Diagnostic case-control study, Level III.