Improving TKA pain outcome when joint gap targets are achieved throughout flexion

The definition of ideal balance in TKA remains elusive. Traditionally, surgeons have used instruments to measure balance at 0 and 90 degrees, while using their ‘feel’ to gauge balance in between. Now, with the OMNIBotics^® BalanceBot^TM, ligament balance can be measured throughout full range of motion, before and after femoral preparation. By recording these measurements, and comparing to patient’s overall pain measurements, we investigated the optimal joint balance throughout flexion for maximising patient outcomes¹.

Methods:

135 patients were enrolled and joint gaps were measured under a controlled tension from 10°– 90° flexion. Correlations between joint gaps and one-year KOOS outcomes were investigated. KOOS pain sub-scores were used to define clinically relevant joint gap target thresholds in extension, mid-flexion, and flexion. Gap thresholds were then combined to investigate the synergistic effects of satisfying multiple targets.

Knee gap assessment with BalanceBot™

Defining medial-lateral gap difference

Joint gap thresholds of an equally balanced or tighter medial compartment in extension, medial laxity ±1mm compared to the final insert thickness in mid-flexion, and a mediolateral imbalance of less than 1.5mm in flexion generated subgroups that reported significantly improved KOOS pain scores at one year. The greatest improvement, however, was observed when all three targets were satisfied (median Δ = 11.2, p = 0.002).

KOOS pain scores relative to gap differences

KOOS pain scores with all targets factored

Balance targets were successfully quantified at three distinct flexion angles throughout the complete range-of-motion. Improvements in KOOS pain scores were realised for patients whose TKA was balanced to any one of these targets and, importantly, further improvements were realised when multiple targets were achieved within a single procedure. These conclusions are limited based on the data from patients who received an ultra-congruent insert after a PCL-sacrificing, total knee procedure. The concept, however, of quantifying balance targets throughout the range of motion and linking that to improvements in pain scores is of universal importance and made possible with technologies like the BalanceBot and the Predictive Balance technique. 

The OMNIBotics Predictive Balance technique uses intraoperative ligament balance assessments to determine how implant position effects final ligament balance. By understanding the ligament targets from this study, we aim to predict optimal implant positions to maximise patient outcomes.   

Click the link to learn more:  https://link.springer.com/article/10.1007/s00167-021-06482-2

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Corin Clinical Team

References:

1. 1. Wakelin, E.A., Shalhoub, S., Lawrence, J.M. et al. Improved total knee arthroplasty pain outcome when joint gap targets are achieved throughout flexion. Knee Surg Sports Traumatol Arthrosc (2021).