Summary

Pre-resection balancing with robotic arm assisted technology is an accurate and reproducible technique, with balance achieved prior to bony cuts being maintained at the completion of the procedure despite the posterior osteophytes remaining in situ at the time of initial balancing.

Abstract

Introduction

Total knee arthroplasty (TKA) traditionally relied on the surgeon’s judgement to determine soft tissue balance. Recent papers have shown inaccuracies in these subjective techniques when compared to objective measurements of soft tissue tension using technology.

Robotic-assisted TKA (RATKA) allows for prediction of soft tissue balance prior to bony resection in addition to the ability to accurately execute a surgical plan. This study aims to determine the accuracy this pre-resection balancing technique.

Methods

A consecutive prospective cohort of 2028 TKAs utilising Triathlon Knee system with the Mako robotic-assistance (Stryker, Kalamazoo, MI) was assessed.

Following removal of medial and lateral osteophytes and optimisation of component position, virtual gap measurements were recorded at 10° and 90° of flexion. Soft tissue releases were performed if imbalance of greater than 2mm observed. Balance was re-assessed post implantation. The final values were then compared to the pre-resection values to determine the accuracy of this pre-resection balancing technique.

Results

Of the 2028 TKAs performed 50.1% were female, with a mean age of 67 and BMI of 31. In terms of alignment philosophy 83.1% utilised functional alignment (FA), and 16.9% adjusted mechanical alignment(aMA).

The pre-resection technique achieved virtual balance in extension within 1mm by alteration of virtual component position in 83% of cases (86% of FA and 69% of aMA) and 95% had <2mm difference in extension balance. 99% of TKAs had final extension balance within 2mm. Of those that were able to be virtually balanced within 1mm, 98% of TKAs maintained balance within 1mm at the completion of the procedure without soft tissue release. Being unable to virtually balance a TKA prior to bone resection resulted in a significantly greater requirement for soft tissue release (p<0.001).

The absolute values of the final gaps achieved were a mean of 1.3mm greater than virtual gaps predicted for both medial and lateral gaps in both flexion and extension. There were no clinically significant differences in ability to maintain pre-resection balance post execution based on alignment philosophy with FA having a mean absolute difference in extension balance of 0.3mm and MA resulting in 0.5mm.

Discussion

Pre-resection balancing with robotic arm assisted technology is an accurate and reproducible technique in this patient cohort. Balance achieved prior to bony cuts is maintained at the completion of the procedure despite the posterior osteophytes remaining in situ at the time of initial balancing. Both aMA and FA-TKAs can be accurately performed by this technique.