Summary

Primary indications for single-level MOWHTO are symptomatic constitutional varus and small intra-articular varus deformities preferably with a tibial bony varus component in combination with mild-moderate overall preoperative varus malalignment.

Abstract

Purpose

Clinical medial open-wedge high tibial osteotomy (MOWHTO) studies often analyse a mixture of varus entities without differentiating for its primary varus-inducing component. This study wants to verify the most prevalent preoperative varus malalignment phenotypes with their respective radiological and clinical outcomes before and after MOWHTO. Our hypothesis was that tibial bony varus deformities with or without a moderate intra-articular (IA) varus component would have favourable clinical and radiological outcomes.

Methods

Accurate MOWHTO (180-184°) cases with preoperative varus malalignment >3° and minimal 2 year clinical follow-up were retrospectively selected from a knee osteotomy database (2016-2019). Based on the preoperative medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA) and joint line convergence angle (JLCA), subjects were allocated to one out of six predefined varus cohorts: (1) constitutional (MPTA 85-90°, LDFA 85-90°, JLCA <2°), (2) intra-articular (MPTA 85-90°, LDFA 85-90°, JLCA >2°), (3) tibial (MPTA <85°, LDFA 85-90°, JLCA <2°), (4) tibial with IA (MPTA <85°, LDFA 85-90°, JLCA >2°), (5) femoral (MPTA 85-90°, LDFA >90°, JLCA <2°), (6) femoral with IA (MPTA 85-90°, LDFA >90°, JLCA >2°). Cohort 2 was subdivided in three groups based on preoperative alignment and osteoarthritis (OA) severity. Clinical outcomes consisted of NRS and KOOS at 1,2 and 4.5 years. Inter-observer correlation (IOC) and One-way ANOVA testing was performed for cross-cohort outcome comparison.

Results

A total of 119 cases (age 53.4 ± 9.3, female 32.8%) were selected. Excellent IOC (r=0.85) was found for radiological data. For the postoperative MPTA, cohort 6 (95.7° ±2.2) differed significantly from cohort 1-4 (p<0.001) while cohort 3 (90.2 ±1.7°) differed from cohort 2 (92.9° ±1.8) and 5 (93.5° ±2.2) (p<0.001). Cohort 6 (7.3° ± 1.9) had significantly higher postoperative JLO values than cohort 1-5 (mean <5°) (p<0.001). Clinically, no significant differences between varus cohorts were found from baseline up to 4.5 years follow-up, however at 4.5y, large numerical differences were observed in favour of cohort 1, 3 and 5.

Conclusion

Primary indications for single-level MOWHTO are symptomatic constitutional varus and small intra-articular varus deformities preferably with a tibial bony varus component in combination with mild-moderate overall preoperative varus malalignment. From a radiological perspective, large intra-articular and primarily femoral varus deformities seem less appropriate for single-level MOWHTO since postoperative MPTA and JLO can be excessively high.