Constitutional and postoperative joint line obliquity can predict serial alignment change after opening-wedge high tibial osteotomy: analysis using coronal plane alignment of the knee classification.

Purpose: The purposes of this study were (1) to clarify the distribution of the Coronal Plane Alignment of the Knee (CPAK) phenotype in patients who underwent medial opening-wedge high tibial osteotomy (OWHTO) and (2) to identify the predictive factors for postoperative serial alignment changes after OWHTO by analyzing constitutional phenotypes.

Methods: Patients who underwent OWHTO between March 2014 and December 2019 were retrospectively evaluated. Those who completed a minimum follow-up of 3 years were divided into three groups based on the direction of alignment changes from postoperative 3 months to the final follow-up: Group 1 (varus direction) when the weight-bearing line ratio (WBLR) change was less than - 4%, Group 2 (maintained) when the WBLR change was between - 4% and 4%, and Group 3 (valgus direction) when the WBLR change was greater than 4%. The following parameters were assessed serially and compared between the groups: (1) radiologic parameters of coronal limb alignment such as joint line obliquity (JLO), (2) CPAK phenotypes, and (3) clinical outcomes.

Results: In total, 163 knees were included, and the average duration of follow-up was 4.8 ± 1.6 years. More apex distal JLO was observed in the order of Group 1, 2, and 3 at all times (all p < 0.05). The most common CPAK type was type (I + II) (constitutional: apex distal JLO) + type (V + VI) (postoperative 3 months: neutral JLO) in Group 1 (29.4%; p = 0.000); otherwise, the most common CPAK type was type (IV + V) (constitutional: neutral JLO) + type (VIII + IX) (postoperative 3 months: apex proximal JLO) in Group 3 (11.7%; p = 0.000). Clinical outcomes did not differ between the groups.

Conclusion: Constitutional and postoperative JLO were predictive factors of postoperative alignment changes after OWHTO. Constitutional apex distal and postoperative neutral JLO had a tendency for varus alignment progression, whereas constitutional neutral and postoperative apex proximal JLO had a tendency for valgus alignment progression.

Level Of Evidence: Retrospective cohort study; Level III.