Summary

HCO for severe KOA with K-L grade 4 may have good long-term outcomes with a large correction that sets the postoperative WBLR more than 70%.

Abstract

Background

Medial opening-wedge high tibial osteotomy (OWHTO) for severe medial compartment osteoarthritis of the knee with varus deformity (KOA) has been pointed out several problems such as worsening postoperative cartilage degeneration of the patellofemoral joint and increased tibial posterior tilt angle. To resolve those issues, recently, distal tibial tuberosity osteotomy (DTO) has been reported. Among several techniques of DTO, Hemicallotasis (HCO) is a unique bone-lengthening procedure in which the medial osteotomized gap is gradually opened to the planned corrective angle using a unilateral external fixator attached to the medial aspect of the lower leg. However, there is a lack of studies evaluating the long-term results of this procedure. The aim of this study was precisely to evaluate the long-term survival of HCO for severe KOA. The secondary objective was to identify independent predictors of conversion to total knee arthroplasty (TKA). The hypothesis is that multiple factors such as age, body mass index, and the various radiological parameters including degree of correction angle may influence the long-term survivorship of HCO.

Methods

This was a prospective study carried out on a total of 322 knees in 313 patients underwent HCO between March 2009 and March 2016. Of all subjects, 56 knees in 47 patients had KOA with Kellgren-Lawrence grade 4 were available for more than 7-years follow-up, whom recruited in this study. The mean age at surgery was 62 years-old, and the mean follow-up period was 10 years (ranged from 7 to 14 years). Clinical assessment using Knee Society Score (KSS) and radiographic measurements were performed preoperatively, one year postoperatively and at the final examination. Standing long antero-posterior radiographs of both lower limbs were used to determine various parameters including the Hip-Knee-Ankle Angle (HKA), a weight-bearing line ratio (WBLR), the mechanical lateral distal femoral angle (mLDFA), the mechanical medial proximal tibial angle (mMPTA). One-way ANOVA and post hoc pairwise comparisons using Tukey's tests were used to determine the significance of change of KSS between follow-up periods. Multiple regression analysis was used to assess the effect of any factors on HCO survival. P-value < 0.05 was considered to be statistically significant for all the statistical tests.

Results

The mean pre-op KSS was 59 which improved to 94 at one year postoperatively (p<0.01). At the final survey, the mean KSS was 85 which was a significant deterioration compared with that at one year postoperatively (p<0.01). Four of the 56 HCOs (7%) were converted to TKA, and survival rate at a mean 10-year follow-up was 93%. The mean preoperative WBLR was 11% which improved to 66% at one year postoperatively (p<0.01). The WBLR at the final examination had decreased by an average of 5% compared with those at 1-year postoperatively. There were 22 knees (40%) with a decrease of more than 5% WBLR at the final survey (∆WBLR>5%), whose one-year WBLR was less than 70%. In multiple regression analysis, two factors of preoperative HKA (p=0.017) and mLDFA (p=0.013) among the patients’ demographic data and radiological parameters showed a correlation with ∆WBLR, which indicated inadequate correction in cases with preoperative large varus deformity and large mLDFA.

Conclusions

In OWHTO, it is well documented that precise correction of deformity and maintenance of correction achieved is important to ensure long-term good results. The results of this study suggest that HCO for severe KOA with K-L grade 4 may have good long-term outcomes with a large correction that sets the postoperative WBLR more than 70%. This is higher than the previously known WBLR value of 62.5%.