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Functional alignment in total knee arthroplasty best achieves balanced gaps and minimal bone resections: an analysis comparing mechanical, kinematic and functional alignment strategies

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Knee Surgery, Sports Traumatology, Arthroscopy Aims and scope

Abstract

Purpose

Key concepts in total knee arthroplasty include restoration of limb alignment and soft-tissue balance. Although differences in balance have been reported amongst mechanical alignment (MA), kinematic alignment (KA) and functional alignment (FA) techniques, it remains unclear whether there are differences in gap imbalance or resection thicknesses when comparing different constitutional alignment subgroups.

Methods

MA (measured resection technique), KA (matched resections technique) and FA (technique based on the restricted KA boundaries) were compared in 116 consecutive patients undergoing 137 robotic-assisted cruciate-retaining total knee arthroplasties. The primary outcome was the proportion of balanced gaps (differential laxities ≤ 2 mm) for extension, flexion, medial and lateral gap measurements. Manual pre-resection laxity measurements were obtained for MA and KA and manual post-resection measurements were obtained for FA in 10° and in 90° of knee flexion. Secondary outcomes were resection depths and implant alignment. All outcomes were analysed per constitutional coronal alignment and joint line obliquity subgroups.

Results

The proportions of balance in all four gap measurements were 54.7%, 66.4% and 96.5%, with MA, KA and FA, respectively. Across all constitutional alignment types, FA achieved the highest proportion of balance. MA resected the least amount of bone from the medial tibial plateau. KA had femoral components in most valgus and most internally rotated, tibial components in most varus and was the most bone-preserving for the posteromedial femoral condyle. FA had the most externally rotated femoral components and was most bone-preserving for the distal femoral resections.

Conclusion

The study shows that implant alignment to the mechanical axis or joint line anatomy (equal resections) alone does not guarantee a balanced total knee arthroplasty. FA resulted in the highest proportion of balanced knees across all analysed subgroups. Future research will consider whether one alignment philosophy leads to superior outcomes for different constitutional alignment subgroups.

Level of evidence

Level II.

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Data availability

De-indentified data that support the findings of this study are available on request from the corresponding author.

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Acknowledgements

We would like to express our gratitude to Christina Esposito for her contributions to the final manuscript, which enhanced the quality and clarity of our work.

Funding

No funding was received for this study.

Author information

Authors and Affiliations

  1. Sydney Knee Specialists, Suite 201, 131 Princes Highway, Kogarah, Sydney, NSW, 2217, Australia

    Victor A. Van de Graaf, Darren B. Chen, Richard J. Allom, Jil A. Wood & Samuel J. MacDessi

  2. CPAK Research Group, Suite 201, 131 Princes Highway, Kogarah, Sydney, NSW, 2217, Australia

    Darren B. Chen & Samuel J. MacDessi

  3. University of NSW, Medicine and Health, St George and Sutherland Campus, Clinical Sciences (WR Pitney) Building, St George Hospital Clinical School, Short Street, Kogarah, Sydney, NSW, 2217, Australia

    Samuel J. MacDessi

Authors
  1. Victor A. Van de Graaf
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  4. Jil A. Wood
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Contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by [VAG, DBC, RJA, JAW and SJM]. The first draft of the manuscript was written by [VAG and SJM] and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Samuel J. MacDessi.

Ethics declarations

Conflict of interest

SM and DC report receiving research support (Stryker, Smith & Nephew, Zimmer Biomet (Research fellowship funding); Ramsay Hospital Research Fund (support for unrelated study), reimbursement for presentations (Stryker, Smith and Nephew) and paid consultations (Stryker, Amplitude SAS).

Ethical approval

Ethics approval was provided by Ramsay Health Care Research Ethics and Governance (2023/ETH/0029).

Informed consent

Informed consent was obtained from all individual participants included in the study.

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Van de Graaf, V.A., Chen, D.B., Allom, R.J. et al. Functional alignment in total knee arthroplasty best achieves balanced gaps and minimal bone resections: an analysis comparing mechanical, kinematic and functional alignment strategies. Knee Surg Sports Traumatol Arthrosc 31, 5118–5127 (2023). https://doi.org/10.1007/s00167-023-07567-w

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