Design of a knee rotatory kinaesthetic device

The anterior cruciate ligament (ACL) constrains rotatory motion at the knee and is commonly injured during rotational movements in athletic activity. This densely innervated ligament is assumed to play a role in knee proprioception, however, no study has measured proprioception in a manner relevant to either the kinematics of the ligament or the mechanism of injury, partly because of a lack of suitable equipment. The aims of this technical note are to document the development of a novel knee rotatory kinaesthetic device, and to present details of its construction, reproducibility, accuracy and application. The purpose-built device allows rotational movements at the knee to occur with minimal frictional resistance and provides accurate limits to the magnitude of these movements. This allows analysis of subjects' ability to discriminate between movements of differing magnitudes and thus allows calculation of subjects' sensitivity to small differences in magnitude of active knee rotation. Measurements taken with the device had a high level of agreement with those of a calibrated digital inclinometer (ICC=0.99; 95% CI 0.88 to 0.99) with a mean error of 0.24 degrees . The device also demonstrated excellent reproducibility (Pearson's r=1.0). A single case study is presented to detail the clinical application of the device. This novel device allows subjects to perform active knee rotational movements in a closed kinetic chain with discrete, self-paced movement, enabling calculation of movement discrimination. The device is compact and portable enabling testing to be undertaken in remote settings enhancing its clinical applicability.