Comparison of cutaneous and transosseous electromagnetic position sensors in the assessment of tibial rotation in a cadaveric model

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 degrees 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 degrees 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 degrees Vs 14.5 degrees, P =.4) or at 90 of flexion (11.2 degrees Vs 12.9 degrees, P =.5). Correlation (R) between cutaneous and transosseous measurements at 30 degrees was .97 (P =.00009) and at 90 degrees was .99 (P <.00001). The accuracy of cutaneous measurements using transosseous as the known was 1.6 degrees +/- 1.3 degrees. Repeatability of cutaneous measurements was 0.8 degrees +/- 0.4 degrees. The repeatability of transosseous measurements was 1.0 degrees +/- 0.5 degrees. Conclusion: No significant differences were found at either 30 degrees or 90 degrees 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.