Radiographic Technique for Routine Clinical Measurement of Postoperative Total Knee Extension

Introduction: We propose a novel clinical technique to easily obtain a radiographic measurement for terminal passive knee extension based upon a weight-bearing lateral radiograph. Materials and Methods: Lateral radiographs were obtained with the patient in the standing position. The leg was positioned with slight hip flexion and full passive extension of the knee by instructing the patient to bear partial weight through their heel, with simultaneous use of a wooden wedge to dorsiflex the foot to neutral and to aid in balance. A Terminal extension was measured radiographically with digital imaging software. Fifty postoperative knee radiographs were used in assessing inter-observer and intra-observer reliability. Results: Inter-observer reliability yielded an Intraclass Correlation Coefficient of 0.973. The correlation coefficient for intra-observer reliability was 0.980. Conclusion: With the use of weight-bearing extension radiographs and our measurement technique, we present a method that can easily be applied across any setting in total knee arthroplasty to obtain accurate, objective data on patient knee extension.