Are current total knee arthroplasty implants tested and approved for personalised alignment?

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Implantology

Background:

• Traditional total knee arthroplasty (TKA) focuses on neutral mechanical alignment (MA) for implant longevity.
• This approach may overlook individual knee anatomy, potentially causing soft-tissue imbalances and suboptimal functional outcomes.
• Personalised alignment techniques (PAT) aim to restore bony anatomy, potentially improving soft tissue balance and recovery.

Purpose of the Study:

• To investigate the regulatory approval status of TKA systems for kinematic alignment and deviations from neutral MA.
• To determine the extent of manufacturer approval for personalized alignment techniques.

Main Methods:

• TKA systems were identified from the 2020 Endoprosthesis Registry Germany (EPRD).
• Manufacturers were contacted to ascertain approval for MA deviations and permissible limits.
• Data were updated through follow-ups in 2021, 2022, 2023, and 2025.

Main Results:

• Seven of twelve responding manufacturers lacked approval or specific details for MA deviations.
• Approval for deviations varied among systems; some allowed specific implants without defined limits.
• Specific deviation ranges were provided by some manufacturers (e.g., Stryker, Johnson & Johnson, Zimmer Biomet); revision systems universally restricted axis deviation.

Conclusions:

• Limited manufacturers have rigorously tested TKA systems for MA deviations, restricting the specification of limits.
• Practical challenges include PAT complexity, patient factors, and prosthesis suitability.
• Manufacturers should systematically evaluate alignment deviations via standardized tests or simulations for patient safety and implant longevity.