Total Knee Arthroplasty Kinematics Predict Patient-Reported Outcome Measures: Implications for Clinical Kinematic Examinations

Background A core tenet of total knee arthroplasty (TKA) is that achieving more natural kinematics will lead to superior patient outcomes. Yet this relationship has not been proven for large representative cohorts of TKA patients because accurately measuring three-dimensional TKA kinematics is time-consuming and expensive. But advanced imaging systems and machine-learning-enhanced analysis software will soon make it practical to measure knee kinematics pre- and post-operatively in the clinic using radiographic methods. The purpose of this study was to assess the reported relationships between TKA kinematics and outcomes and distill those findings into a proposal for a clinically practical protocol for a clinical kinematic exam. Methods This study reviewed the recent literature relating TKA kinematics to patient outcomes. There were ten studies that reported statistical associations between TKA kinematics and patient outcome scores utilizing a range of functional activities. We stratified these activities by the complexity of the radiographic examination to create a proposed examination protocol, and we generated a list of requirements and characteristics for a practical TKA clinical kinematic examination. Results Given considerations for a clinically practical kinematic exam, including equipment, time and other resources, we propose three exam levels. With basic radiographs, we suggest studying single leg stance in extension, lunge or squat, and kneeling. For fluoroscopic systems with x-ray pulses up to 20 ms, we propose chair-rise or stair ascent to provide additional dynamic information. For fluoroscopic systems with x-ray pulses of less than 10 ms, we propose rapid open-chain knee flexion/extension to simulate the highly dynamic swing phase of gait. Discussion It is our hope that this proposed examination protocol spurs discussion and debate so that there can be a consensus approach to clinical examination of knee and TKA kinematics when the rapidly advancing hardware and software capabilities are in place to do so.