Variation in joint stressing magnitudes during knee arthroscopy

Purpose: When performing knee arthroscopy, joint stressing is essential to increase the operative joint space. Adequate training of joint stressing is important, since high stressing forces can damage knee ligaments, and low stressing might not give sufficient operative space. As forces are difficult to transfer since they cannot be seen, simulators might be suited to train joint stressing as they can visualise the amount of applied stress. This requires the joint stressing thresholds to be validated. The purpose of this study was to measure the variation in the maximum joint stressing forces applied by various surgeons in vivo in a human population and based on that derive thresholds for safe stressing. Methods: From studies on ligament failure properties, we inferred a theoretical maximum stressing force of 78 N. Twenty-one patients were included, and knee arthroscopies were performed by five experienced surgeons. Forces solely performed in the varus and in valgus direction were measured. A load sensor was mounted on a belt, which was rotated along the hip to measure both varus and valgus stressing. The measurements started as soon as the interior of the knee joint was visualised using joint stressing. Results: The average maximum stressing force was 60 N (SD = 28 N). The mean first frame force was 47 N (SD = 34 N). No significant differences were found between varus and valgus stressing. Conclusion: Since variation in stressing forces is high, offering training cases on simulators where the complete range of stressing forces can be experienced is recommended. Abiding to safety levels is essential to increase patient safety.