Young SW, Tay ML, Kawaguchi K, van Rooyen R, Walker ML, Farrington WJ, Bayan A. The John N. Insall Award: Functional Versus Mechanical Alignment in Total Knee Arthroplasty: A Randomized Controlled Trial.
J Arthroplasty 2025:S0883-5403(25)00193-7. [PMID:
40023458 DOI:
10.1016/j.arth.2025.02.065]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/21/2025] [Revised: 02/19/2025] [Accepted: 02/20/2025] [Indexed: 03/04/2025] Open
Abstract
BACKGROUND
Mechanical alignment (MA) in total knee arthroplasty is regarded as a gold standard; however, some patients report dissatisfaction postsurgery. Functional alignment (FA) is a potential alternative, integrating kinematic alignment (KA) principles with preresection bone balancing within defined boundaries. The use of FA aims to improve outcomes by restoring native joint lines and optimizing soft-tissue balance. However, comparative evidence is limited.
METHODS
This prospective, randomized controlled trial compared MA (n = 121) and FA (n = 123) in robotic-assisted total knee arthroplasty. For MA, components were positioned perpendicular to the limb mechanical axis, with soft-tissue releases to achieve balance. For FA, initial virtual component positioning was used to match native knee anatomy, with adjustments for soft-tissue balance before bone cuts. The primary outcome was the forgotten joint score (FJS). Outcomes were compared with a mixed-model analysis of variance.
RESULTS
At the 2-year follow-up, the mean FJS was comparable (MA: 64.4 ± 30.1 versus FA: 70.1 ± 25.6, P = 0.10). The MA cases had more soft-tissue releases than FA (65 versus 16%, P < 0.001). Compared to MA patients, FA patients had higher Knee Injury and Osteoarthritis Outcome (KOOS) Symptoms (86.6 ± 12.9 versus 82.5 ± 14.0, P = 0.01) and KOOS-Quality of Life scores (76.1 ± 20.3 versus 70.7 ± 22.7, P = 0.03). More FA patients "would recommend" the procedure (94 versus 82%, P < 0.01). For patients who had preoperative Coronal Plane Alignment of the Knee Type I, FA had higher FJS (71.3 ± 24.8 versus 56.8 ± 31.6, P = 0.02) and KOOS-Quality of Life (76.4 ± 21.7 versus 64.2 ± 19.2, P = 0.02) than MA. No other differences were seen in patient-reported outcomes (Oxford Knee Score, KOOS, EuroQol-5 Dimensions, Pain Visual Analog Scale), clinical outcomes (length of stay, functional physio tests), reoperations, or implant survivorship (FA: 1 versus MA: 0 revisions).
CONCLUSIONS
While FA required fewer soft-tissue releases compared to mechanical alignment, at 2 years patient-reported and clinical outcomes were similar. The use of FA may provide improved outcomes for a specific subgroup of patients based on their preoperative alignment.
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