Summary
Functional alignment may improve clinical outcomes after total knee arthroplasty in certain pre-operative alignment subgroups.
Abstract
Introduction
Mechanically-aligned (MA) total knee arthroplasty (TKA) is considered a gold standard, however some patients report dissatisfaction following surgery. Functional alignment (FA) is a potential alternative in TKA, aiming to restore patients’ native joint line and minimise compromise of the soft tissue envelope, potentially leading to improved clinical outcomes.
Methods
This prospective, randomised controlled trial compared patient-reported and clinical outcomes of FA (n=122) and MA (n=121) in TKA. Robotic-arm assisted technology was used for all cases. MA components were positioned perpendicular to the limb mechanical axis, with soft tissue releases performed to achieve balance. FA components were positioned to match individual patient anatomy, then adjusted virtually to achieve balance prior to bony cuts being made. Primary outcome was forgotten joint score (FJS) at 1 year. Outcomes were compared using t-tests, Chi-squared tests, and logistic regression.
Results
We found no difference in FJS between groups at one year (MA Mean 55.4 +/- SD29.9, FA 58.1 +/- 29.6, p=0.5). At one year, 86% of FA patients vs 81% of MA patients reported ‘high’ or ‘very high’ satisfaction (p=0.5). FA patients reported higher net promoter score (NPS) at six months (FA 86% ‘high’ or ‘very high vs. MA 78%, p=0.01), and were less likely to undergo manipulation under anaesthetic post-TKA (FA 1 patient (0.8%) vs. MA 5 patients (4.1%), OR 0.19 (0.02-1.64)). At 1-year, no other differences were seen in patient-reported outcomes (Oxford Knee Score, Knee Injury and Osteoarthritis Outcome Score, EuroQol-5Dimensions, Pain Visual Analog Scale), clinical outcomes (range of motion, length of stay) or implant survivorship (FA n=1 revision vs. MA 0 revisions). In patients classified as pre-operative coronal plane alignment of the knee (CPAK) Type 1, MA had lower mean FJS than FA (MA Mean 38.1 +/- SD23.9 vs FA 55.4 +/- 32.0, p=0.02)
Conclusions
Overall, we found no patient-reported, clinical or survivorship differences at 1-year when comparing functional versus mechanical alignment in robotic-arm assisted TKA. However, functional alignment may improve clinical outcomes in certain pre-operative alignment patient subgroups.