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Primary Total Knee Arthroplasty Using a Functional Alignment Concept With Kinematic Versus Inverse Kinematic
Joseph D Henningsen1, Wyatt T Ware1, John E Whitaker1
1Department of Orthopaedic Surgery, University of Louisville, Louisville, Kentucky.
The Journal of Arthroplasty
|April 3, 2026
Summary
The kinematic technique (FA(k)) in total knee arthroplasty (TKA) resulted in greater tibial varus and higher Forgotten Joint Scores (FJS), indicating less patient awareness of the implant. The inverse kinematic technique (FA(ik)) also showed significant improvements in patient outcomes.
Area of Science:
- Orthopedic Surgery
- Biomedical Engineering
- Robotics in Medicine
Background:
- Functional alignment (FA) is increasingly utilized in total knee arthroplasty (TKA).
- Two primary techniques exist: kinematic (FA(k)) and inverse kinematic (FA(ik)).
- Comparing these FA techniques in TKA is crucial for optimizing patient outcomes.
Purpose of the Study:
- To compare the clinical outcomes of kinematic versus inverse kinematic techniques for functional alignment in primary TKA.
- To evaluate the impact of each technique on component alignment and patient-reported outcome measures (PROMs).
Main Methods:
- Retrospective review of robotic-assisted TKA cases with 1-year follow-up.
- Exclusion criteria included BMI > 45 and valgus deformity (CPAK classification).
- Comparison of 166 FA(k) cases and 146 FA(ik) cases using intraoperative and postoperative outcome data (FJS, VAS, KOOS JR).
Main Results:
- FA(ik) demonstrated significantly less tibial varus (3.0° vs. 4.5°) and final HKA varus (0.92° vs. 2.6°) compared to FA(k).
- Both techniques showed significant improvement in Forgotten Joint Scores (FJS), with FA(k) yielding higher scores (indicating less awareness of the knee).
- No significant differences were observed in postoperative KOOS JR or VAS pain scores between the groups.
Conclusions:
- Both FA(k) and FA(ik) techniques improve patient-reported outcome measures in TKA.
- The FA(k) technique is associated with greater varus alignment and higher FJS, suggesting patients are less aware of their knee prosthesis.
- The choice between FA(k) and FA(ik) may influence alignment and patient awareness post-TKA.
