Single flexion-axis selection influences femoral component alignment and kinematics during knee simulation

Area of Science:

• Biomedical Engineering
• Orthopedic Surgery
• Medical Device Design

Background:

• Improper femoral flexion-axis selection during total knee replacement (TKR) surgery can negatively affect implant function.
• This can lead to significant anterior/posterior (A/P) and proximal/distal (P/D) displacements of the femoral component.
• Improving TKR alignment consistency is crucial for accurate biomechanical simulations.

Purpose of the Study:

• To investigate how implant geometry and alignment influence surface displacement in TKR.
• To demonstrate a method for improving the consistency of TKR alignment in knee simulations.
• To analyze the impact of femoral axis alignment on P/D and A/P displacements.

Main Methods:

• Utilized four multi-axis femoral components from two manufacturers (NKII and 3DKnee).
• Employed a custom-built instrument for femoral alignment and surface measurement.
• Optimized single femoral axis position to minimize P/D displacements and A/P translations for each implant.

Main Results:

• Aligned NKII implants showed mean maximum P/D and A/P contact point shifts of 0.577 +/- 0.078 mm and 2.325 +/- 0.243 mm, respectively (0-60° flexion).
• Aligned 3DKnee implants demonstrated significantly lower mean shifts: 0.415 +/- 0.157 mm (P/D) and 0.800 +/- 0.1512 mm (A/P) (p<0.0001 for both).
• The proposed alignment method successfully minimized displacements for both implant types.

Conclusions:

• Implant geometry and alignment critically affect femoral component displacement in TKR.
• The developed alignment technique enhances the consistency of TKR alignment for biomechanical simulations.
• Further research is required to assess the long-term effects of femoral flexion axis selection on wear, damage, and soft tissue loading.