Mechanical and kinematic alignment in total knee arthroplasty: A comparative study on sizing discrepancies

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Knee biomechanics

Background:

• Total knee arthroplasty (TKA) aims to restore knee function.
• Kinematic alignment (KA) seeks to replicate pre-arthritic anatomy, contrasting with mechanical alignment (MA) which follows the mechanical axis.
• Accurate prosthesis sizing is vital for optimal TKA outcomes, but MA-based systems may pose challenges for KA.

Purpose of the Study:

• To investigate discrepancies in femoral and tibial prosthesis sizing between KA and MA in primary TKA.
• To determine if inherent differences in alignment philosophies affect component selection.

Main Methods:

• Retrospective analysis of 324 primary TKA cases.
• Categorization into KA and MA groups.
• Comparison of predicted versus implanted component sizes, analyzing discrepancies.

Main Results:

• KA demonstrated a higher incidence of smaller femoral components relative to tibial components (10.7% vs. 1.4%) and equal-sized components (51.1% vs. 28.8%) compared to MA.
• MA resulted in a greater proportion of larger femoral components (69.9% vs. 38.2%).
• KA was associated with smaller femoral implants, with predicted sizes exceeding actual sizes more frequently (68.7% vs. 53.6%).

Conclusions:

• Femoral component sizing distributions differ significantly between KA and MA techniques.
• Alignment strategy must be considered in TKA component design and selection.
• Recognizing these sizing variations is essential for optimizing implant selection and improving TKA outcomes as KA adoption grows.