Comparison of Cutaneous and Transosseous Electromagnetic Position Sensors in the Assessment of Tibial Rotation in a Cadaveric Model

Abstract

Background Recent studies have highlighted the growing interest in validating anatomic anterior cruciate ligament reconstructions. A simple method of measuring tibial rotation is necessary to provide an objective clinical assessment of restoration of normal knee kinematics after various anterior cruciate ligament reconstructive techniques. Objective To validate a new method of measuring tibial rotation by comparing cutaneous with transosseous electromagnetic position sensors during a simulated standard knee examination. Study Design Controlled laboratory study. Methods Eight thawed, fresh-frozen cadaveric knee specimens with skin and soft tissues preserved were mounted on the femoral side in neutral rotation by a rigid clamp, allowing 6 degrees of freedom of the knee joint. With the knee fixed at 30° of flexion, a series of maximal manual internal and external tibial rotations were performed and measured with an electromagnetic tracking system that measures 6 degrees of freedom in a Cartesian coordinate system. During each series of measurements, a cutaneous transmitter was fixed overlying the tibial tuberosity. Simultaneously, a second transducer was rigidly fixed to a transosseous pin placed just distal to the tibial tubercle. Measurements were repeated at 90° of flexion. Differences in measurements were assessed. Results No significant differences were found with maximal internal and external rotation between cutaneous and transosseous measurements at 30° of knee flexion (13.0° vs 14.5°, P = .4) or at 90° of flexion (11.2° vs 12.9°, P = .5). Correlation ( R) between cutaneous and transosseous measurements at 30° was .97 ( P = .00009) and at 90° was .99 ( P < .00001). The accuracy of cutaneous measurements using transosseous as the known was 1.6° ± 1.3°. Repeatability of cutaneous measurements was 0.8° ± 0.4°. The repeatability of transosseous measurements was 1.0° ± 0.5°. Conclusion No significant differences were found at either 30° or 90° of flexion when measuring tibial rotation using cutaneous versus transosseous electromagnetic position sensors. Clinical Relevance The ability to measure knee rotation using cutaneous electromagnetic position sensors represents a promising new method for assessing various clinical conditions and surgical outcomes.