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

Preoperative (10.3° [7.3-11.7°]) and intraoperative (9.1° [6.7-11.2°]) PTS measurements were significantly lower than postoperative (10.8° [8.5-13.3°]) values (p < 0.001). Intraoperative PTS was also significantly lower than the preoperative one (9.1° [6.7-11.2°] vs. 10.3° [7.3-11.7°]) (p < 0.01). Intraoperative PTS underestimated the postoperative PTS by a mean of 1.8° (95% CI: -2.1° to - 1.5°). Both HKA and MPTA changed significantly postoperatively (-7.4 ± 3.8° vs. 0.4 ± 2.6° p < 0.001, 84.4 ± 2.8° vs. 91.0 ± 2.8° p < 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.