Purpose: High tibial osteotomy (HTO) has gained more importance in the treatment of cartilage damage or osteoarthritis of the medial compartment with concurrent varus deformity. Concerning the extent of axis correction, various different views exist. The aim of this study was to evaluate the effect of the size of axis correction on functional outcome in patients undergoing a valgus HTO.
Methods: From 2005 to 2013, 156 patients with an underlying varus deformity and cartilage damages or unicompartimental osteoarthritis of the medial compartment were treated by HTO. Retrospectively patients were allocated into three different groups according to the degree of axis correction. For this purpose, three adjacent areas, respectively, comprising 5% of the tibial plateau were defined. Limits of those areas were set as follows: with the medial border representing the 0% point and the lateral border representing the 100 point, the three areas were separated according to their limiting intersection points (group A 50-55%, group B 55-60%, group C > 60%). For comparison of the functional outcomes, standardized measures and scores were used (pre-OP: VAS, Lysholm; post-OP: VAS, Lysholm, KOOS). Analysis of the pre- and post-operatively recorded X-rays was effected by means of a planning software (mediCAD, Hectec GmbH, Germany), and statistical analysis was carried out using SPSS Statistics 21.0 (IBM Corp., Armonk, USA). A p value of 0.05 was considered statistically significant.
Results: Thirty-nine patients were allocated to group A, 50 patients to group B and 67 to group C. Pre-operatively, patients in each group were of a homogenous constitution. In the groups A-C, HTO proved to reduce the VAS score and to increase the Lysholm score (p < 0.001). Regarding outcome parameters, group A showed significantly better results in terms of increased Lysholm (p = 0.049) and KOOS pain score (p = 0.043). In patients treated by HTO and ACI implantation for medial compartment lesions, the best results were achieved in group A which was of statistical significance in comparison of the Lysholm (p = 0.006) and VAS score (p = 0.045) of groups A and C. In this subgroup, the size of the post-operative valgus angle significantly correlated with the final VAS score (PC 0.364; p = 0.013), final Lysholm score (PC - 0.390; p = 0.007) and KOOS4 (PC - 0.356; p = 0.014).
Conclusion: HTO for varus deformity in patients with concomitant cartilage damage or osteoarthritis of the medial compartment is a reliable treatment option with satisfying functional outcome. Precise pre-operative planning regarding individual factors in each patient is mandatory; a pathology-based extent of correction leads to a favourable clinical outcome and to a significant reduction in pain.
Level of evidence: Retrospective cohort study, Level III.
Keywords: Cartilage defect; Correction angle; High tibial osteotomy; Osteoarthritis; Varus deformity.