Intraoperative fluoroscopically assessment underestimates the posterior tibial slope in open‐wedge high tibial osteotomy

Purpose: To compare intraoperative and postoperative posterior tibial slope (PTS) measurements and determine whether unintended postoperative changes occur relative to preoperative values. Methods: A total of 79 patients (81 knees) underwent open-wedge high tibial osteotomy (owHTO) using patient-specific instrumentation (PSI) for varus malalignment were included. PTS was assessed pre, intra and postoperatively on short lateral knee radiographs using standardised calibrated software. The hip-knee-ankle angle (HKA) and the medial proximal tibia angle (MPTA) were measured pre and postoperatively on weight-bearing long leg radiographs (LLR). Results: < 0.001). Conclusion: Intraoperative PTS measurements significantly underestimated postoperative PTS, by a mean of 1.8°, indicating that visual intraoperative assessment based on fluoroscopy should be interpreted with caution when used to evaluate postoperative PTS. Level of Evidence: Level IV.