Related Experiment Video
Updated: Sep 15, 2025
In Vitro Application of a Wireless Sensor in Flexion-Extension Gap Balance of Unicompartmental Knee Arthroplasty
Published on: May 5, 2023
Are current total knee arthroplasty implants tested and approved for personalised alignment?
Sabrina Böhle1, Leandra Bauer2, Matthias Woiczinski2
1Orthopaedics, University Hospital Jena, Campus Eisenberg, Waldkliniken Eisenberg, Friedrich-Schiller-University Jena, Jena, Germany.
Purpose:
Total knee arthroplasty (TKA) traditionally aims for neutral mechanical alignment (MA) to ensure implant longevity. However, this approach ignores individual knee variations, potentially leading to soft-tissue imbalances and suboptimal functional outcomes. As an alternative, personalised alignment techniques (PAT) have emerged that aim to restore bony anatomy, potentially improve soft tissue balance and thus accelerate recovery. Despite promising short-term results, long-term outcomes and regulatory approval remain unclear. This study investigates the extent to which TKA systems from various manufacturers are approved for kinematic alignment and allowable deviations from neutral MA.
Methods:
TKA systems were identified using the 2020 Endoprosthesis Registry Germany (EPRD). Manufacturers were systematically contacted to determine if their implants were approved for deviations from neutral MA and the maximum permissible deviations. Follow-ups in 2021 and 2022 resulted in responses from 11 of 13 manufacturers, with an additional update in 2023 and 2025.
Results:
Seven of twelve responding manufacturers either stated that their prostheses were not approved for MA deviations or did not specify details. Among the others, approval varied between implant systems. Two allowed deviations for specific implants without defined limits, while three specified allowable deviation ranges (Triathlon from Stryker with their Mako System 6° varus to 3° valgus; ATTUNE CR FB from Johnson & Johnson deviation 7° varus to 3° valgus°; ATTUNE PS FB and ATTUNE RP ± 3°; Primary system from Zimmer Biomet 0 ± 5° with their ROSA system). Revision systems universally restricted axis deviation due to mechanical constraints.
Conclusion:
Only a limited number of manufacturers have conducted rigorous testing of their systems for deviations from MA, and consequently, are able to specify limits to such deviations. Additionally, practical limitations arise from the complexity of PAT, patient-specific factors and prosthesis suitability. To safeguard patient safety and ensure implant longevity, manufacturers should systematically evaluate alignment deviations through standardised tests or computational simulations.
Level Of Evidence:
N/A.
