High tibial osteotomy (HTO) utilizing a medial opening wedge has become a common and effective surgical technique for treatment of isolated medial compartment knee osteoarthritis secondary to varus malalignment. To reduce the risk of under- or overcorrection, accurate preoperative planning is important. This is a radiographic study to evaluate the reliability of preoperative measurement on full-length weight-bearing X-rays (FLWBXr) compared to post-operative X-rays after healing. In addition, we calculated if the intraoperative opening wedge performed was consistent with the preoperative calculation and the postoperative correction. Three independent observers measured preoperative and postoperative FLWBXr at three different times. The angle of varus deformity; the angle to correct and the wedge needed to achieve desired alignment: the angle achieved postoperatively, and the postoperative mechanical axis deviation were measured. Intra- and inter-rater reliability showed high values for all the investigated parameters. The discrepancy between the calculated wedge and the wedge actually used in surgery ranged from 1 mm of over-correction to 3 mm of undercorrection, averaging -1.3 mm. The mechanical axis crossed the tibial plateau an average of 53% ±12.7. Clustering the data by the plate type statistically significant differences were found for preoperative varus alignment, advocated correction, intraoperative correction and post-op alignment. The Dugdale method can be considered highly reliable. Possible factors affecting the final correction are: surgeon's desire not to overcorrect in young patients and minimal osteoarthritis; measurement errors; variability in the method the FLWBXr is performed. In addition, the under correction could be the result of some collapse with time or the correction could be affected by the fixation system. Further investigation should include complete post-operative evaluation of outcomes and assess the role of these potential factors and their relationship to correction. Level of Evidence: Level III, Retrospective study.
Keywords: genu varum; high tibial osteotomy; mechanical axis correction; opening wedge.