Effects of Alignment Strategies on Bone Cuts in Neutral Knee Phenotypes for TKA

Overview

This simulation study evaluated how different alignment strategies—mechanical, anatomical, and kinematic—affect bone resections and joint line orientation in neutral knee phenotypes undergoing total knee arthroplasty (TKA). It demonstrated that although overall neutral limb alignment is maintained, bone cuts and joint line obliquities vary significantly depending on the specific knee phenotype and alignment approach.

Background

Total knee arthroplasty alignment strategies remain debated, with mechanical alignment (MA) traditionally used to achieve neutral limb alignment and even load distribution. However, dissatisfaction with functional outcomes has prompted exploration of phenotype-based and kinematic alignment techniques that aim to restore pre-arthritic knee kinematics. Knee phenotypes vary in femoral and tibial joint line obliquities, and a one-size-fits-all alignment strategy may not be optimal. This study focuses on neutral limb alignment phenotypes to assess how different alignment methods influence bone cuts and joint line orientation.

Data Highlights

Neutral alignment defined as HKA 180° ± 1.5°, FMA 93° ± 1.5°, TMA 87° ± 1.5°. Varus and valgus defined outside these ranges. Joint line convergence angle (JLCA) changes of 1° correspond to 1 mm distal condyle offset.

Key Findings

• Mechanical alignment (MA) aims for perpendicular femoral and tibial cuts to achieve neutral HKA of 180° ± 3°.
• Anatomical alignment (AA) targets an oblique joint line of 2–3° from perpendicular to better replicate native anatomy.
• Neutral limb alignment phenotypes exhibit variable femoral and tibial joint line obliquities, affecting bone resection patterns.
• Bone cuts differ significantly between phenotypes despite similar overall neutral limb alignment.
• Maintaining neutral overall alignment does not guarantee identical joint line orientation across phenotypes.
• Personalized alignment strategies may better accommodate individual knee phenotypes than uniform mechanical alignment.

Clinical Implications

Surgeons should consider the specific neutral knee phenotype when planning bone cuts in TKA, as uniform mechanical alignment may alter joint line obliquity and affect knee kinematics. Personalized alignment approaches that account for femoral and tibial joint line angles could improve functional outcomes by preserving native knee biomechanics. Understanding phenotype-specific bone resection patterns can guide implant positioning to optimize longevity and patient satisfaction.

Conclusion

This study highlights that in neutral knee phenotypes, different alignment strategies produce distinct bone resection patterns and joint line orientations despite maintaining neutral overall limb alignment. Personalized alignment approaches tailored to individual phenotypes may enhance TKA outcomes.

References

1. Hirschmann et al. 2019 -- Coronal Knee Phenotypes and Alignment Strategies
2. Study Source -- Effects of Various Alignment Approaches on Bone Cuts for Neutral Knee Phenotypes in Total Knee Replacement Surgery