Reliability of Intraoperative Knee Range of Motion Measurements by Goniometer Compared with Robot-Assisted Arthroplasty.

Accurate measurement of knee range of motion (ROM) is critical to predict the outcomes of knee surgery and prognosis. We investigated the reliability of knee ROM measurements by goniometer compared with robotic system. Fifty-three patients with medial osteoarthritis who were planning to undergo unicompartmental knee arthroplasty (UKA) with robotic UKA were prospectively enrolled. During the operation, knee ROM measurement was performed in both flexion and extension before and after insertion of the implant using both a goniometer and robotic system. The intraclass correlation coefficient (ICC) of extension measured by the goniometer and robotic system showed good agreement; however, the ICC of flexion did not show good agreement. During passive flexion, the mean values measured before insertion of the implant were significantly lower by goniometer (134.6 ± 6.43) than by robot (145.4 ± 6.80;  = 0.017); likewise, the mean values after insertion of the implant were significantly lower by goniometer (138.6 ± 6.07) than by robotic system (147.0 ± 6.60;  = 0.045). A goniometer can underestimate knee ROM measurements compared with robotic system, especially in flexion. Orthopaedic surgeons should be cautious when measuring the flexion angle with a goniometer.