Summary

Increasing joint line obliquity during medial open wedge high tibial osteotomy does affect subsequent total knee arthroplasty and its outcomes.

Abstract

Introduction

A valgus producing high tibial osteotomy(HTO) can offload the medial compartment in those with isolated medial compartmental disease, but can cause an increase in joint line obliquity(JLO) depending on the degree of metaphyseal deformity present. In the event of progressive, symptomatic osteoarthritis subsequently, a total knee arthroplasty(TKA) is the definitive surgical option. To the best of our knowledge, the effect of JLO created at the time of HTO on clinical outcomes post subsequent conversion TKA has not yet been studied.

Our aims were to study the effect of a)JLO created at the time of HTO on achievement of JLO post TKA, b)JLO after TKA on clinical outcomes, and c)maintaining neutral JLO both at HTO and TKA on clinical outcomes.

Methods

We retrospectively identified 110 TKAs with a prior valgus producing HTO performed at a single center. All patients had a minimum 1 year follow-up(mean 5.8 years). Utilizing the Coronal Plane Alignment of the Knee(CPAK) classification, JLO was calculated as the sum of mechanical medial proximal tibial angle (MPTA) and mechanical lateral distal femoral angle(LDFA) with patients grouped as distal(<177°), neutral(177-183°) and proximal(>183°) categories based on their JLO. Thus, a valgus producing osteotomy would typically lead to an increase in JLO. We compared clinical outcomes using Western Ontario and McMaster University Osteoarthritis Index(WOMAC) score. The inter-observer(>0.9) and intra-observer(>0.9) reliability was excellent for Hip Knee Ankle angle (HKA), MPTA and LDFA. Statistical analysis was performed using analysis of variance test, with p<0.05 significant.

Results

a) Prevalence of proximal JLO post TKA was higher(p=0.004) in those with proximal JLO pre TKA(40%) as compared to those with neutral JLO pre TKA(13.4%).
The Odds Ratio of having a proximal JLO post TKA was 4 [(95% CI 1.4424 to 11.0930) p= 0.008] in those with a proximal JLO pre TKA.

b) Based on post TKA JLO there were no differences(p>0.05) in age, sex, level of constraint, pre and post TKA HKA alignment, pre and post TKA WOMAC between the three groups.

c) To study the effect of maintaining a neutral JLO at both HTO and TKA, the patients were divided into three groups a)neutral JLO pre and post TKA, b)proximal JLO pre TKA and neutral JLO post TKA, and c)proximal JLO pre and post TKA. There were no differences(p>0.05) in sex, level of constraint used, pre TKA HKA, pre TKA WOMAC and its subcomponents between the groups. There was a statistical difference in post TKA HKA alignment(p=0.04) but these were not clinically relevant(-1.11°, 0.08°, 1.28° respectively). Postoperatively, the mean total WOMAC and its stiffness and function subcomponent were significantly better(p<0.05) in the group which had a neutral JLO both pre and post TKA. These differences were considerably higher than the mean clinically important difference defined for WOMAC, and thus clinically relevant.

Conclusion

Proximal JLO created at time of HTO has an increased risk (Odds Ratio 4) of having a proximal JLO post TKA. By maintaining neutral JLO at HTO and TKA, patients seem to have higher clinical scores post TKA but further research is required.