2017 ISAKOS Biennial Congress ePoster #1254

 

How Does Coronal Balancing Of Posterior-Stabilized TKA, Within The Functional Range Of Motion (0-90°), Impact Oxford Knee Score At 1 Year Post Operatively?

Jasan Dannaway, Sydney, NSW AUSTRALIA
Corey Scholes, PhD, Crows Nest, New South Wales AUSTRALIA
Lyn March, Prof., PhD, Sydney AUSTRALIA
David A. Parker, MBBS, BMedSc, FRACS, Sydney, NSW AUSTRALIA

Sydney Orthopaedic Research Institute, Sydney, NSW, AUSTRALIA

FDA Status Not Applicable

Summary

Appropriate coronal balance of a total knee arthroplasty is likely important in order achieve successful outcomes. However in a well balanced cohort it is an insignificant contributor to the Oxford Knee Score at 1 year post op. Other factors (such as patient factors) are more likely greater contributors.

Abstract

Introduction

& aims
Total knee arthroplasty (TKA) is an effective treatment for knee osteoarthritis, although some patients remain unsatisfied. Intraoperative ligament balance in the functional range may influence these results and patient satisfaction. Therefore the aim of this study was to quantify the effect of coronal knee balance (between 0-90°) on the Oxford Knee score (OKS) in TKA patients 1 year post operatively.

Method

Intraoperative navigation data was collected prospectively for 139 patients who underwent cemented posteriorly stabilised TKA. Parameters analysed included: Coronal balance at 30°, 60° and 90°; gradient between 0-90° (marker for consistency of knee balance); and area under the curve between 0-90° (marker for coronal knee laxity). These parameters were all measured pre and post arthroplasty. The change between pre and post arthroplasty balance was assessed with McNemar’s test for proportions (% balanced) and paired t-tests (gradient and area). PLS regression was used to test the predictive relationship of intraoperative navigation measures with the OKS at 1 year follow-up.

Results

There were 89 females and 50 males (70+10yrs; 29+7kg/m2) included in the analysis. Pre arthroplasty, patients were more likely to be in varus alignment (P<0.01) except at 90° of flexion (P=0.21). Patients were more likely to be balanced post arthroplasty (P<0.01) and on average knees were more valgus aligned post arthroplasty. Area under the laxity curve decreased significantly (P<0.01) between pre-operative and post-operative assessments. The gradient 0-90° became significantly more vertical following TKA (P <0.01). Overall, the OKS improved significantly (P<0.01) after TKA by 15 points, however the regression model, while significant (P<0.01) did not accurately predict OKS change, (R2 = 0.28, standard error = 7 pts). The most influential predictors of OKS change were, in order of significance, pre-operative OKS (ß = -0.62), pre-operative gradient (ß = 0.13), and imbalance at 60° pre arthroplasty (ß = 0.11).

Conclusions

TKA significantly improves coronal balance, alignment and total laxity between 0-90° of knee flexion, however these measures have a limited role in explaining the variance in OKS change. It is possible therefore that these objective measures may not explain variability in outcome as much as other factors, and future studies assessing these factors therefore need to consider the relative contribution of surgical technique and patient selection.