Young, J Arthroplasty 2025 - The John N. Insall Award: Functional versus Mechanical Alignment in Total Knee Arthroplasty: A Randomized Controlled Trial

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The John N. Insall Award: Functional versus Mechanical Alignment in Total Knee Arthroplasty: A Randomized Controlled Trial

Young, Bayan, et al.·J Arthroplasty·2025·36 citations·RCT

Free Full Text·DOI·PubMed

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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.

Copyright remains with the authors and publisher.

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The John N. Insall Award: Functional versus Mechanical Alignment in Total Knee Arthroplasty: A Randomized Controlled Trial

Young, Bayan, et al.·J Arthroplasty·2025·36 citations·RCT

Free Full Text·DOI·PubMed

|

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.

Copyright remains with the authors and publisher.

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