INDICATIONS FOR TOTAL KNEE ARTHROPLASTY IN THE VALGUS KNEE – IS THE SIGNIFICANCE OF INSTABILITY TRULY UNDERSTOOD?

Abstract

Indications for Total Knee Arthroplasty (TKA) include pain and disability. Correction of instability is essential to post operative outcome as instability is often a component of pre-operative functional disability, particularly in patients with valgus deformity. Soft tissue balancing is essential to the success of TKA. Anecdotally, patients with valgus deformity seemed to complain more of instability than pain. The aim of this study was to identify the role and significance of instability and determine whether patients with instability benefit more from TKA as it is useful to determine which patient characteristics will predict success in TKA.

Five hundred and two patients aged 45–90 years underwent 522 Kinemax TKAs, performed by seven surgeons in five centres between October 1999 and December 2002. Soft tissue releases were recorded and objective soft tissue balance recorded using a ‘balancer’ device. Independent observers assessed patients using 3 outcome measures including the American Knee Society Score (AKSS) for a minimum of 12 months. Pre-operative alignment was divided into 6 groups according to the degree of varus or valgus deformity (mild, moderate, severe varus or valgus). Specific components of the AKSS including pain scores, knee scores and medio-lateral stability scores were specifically analyzed.

There is a significant difference in the improvement of the knee scores between the severely valgus knees and all varus knees (ANOVA p=0.000). Significant differences were found between pre-operative pain scores, knee scores and medio-lateral stability between severely varus and severely valgus knees (ANOVA p=0.029, p=0.000 & p=0.000 respectively).

Knees with severe valgus deformities have significantly worse pre operative scores and show greater improvement with equivocal post-operative outcome, when compared to those with severe varus deformity. We believe that this significant improvement is due to the fact that both key issues in the severely deformed valgus knee, namely pain and instability, have been addressed.