An Evaluation of Anatomic Referencing for Femoral Component Sizing Using Computed Tomography-Based Computer Modeling

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Medical device design

Background:

• Traditional femoral component sizing in total knee arthroplasty used anterior referencing (AR) and posterior referencing (PR) due to size variability.
• Smaller increments in femoral component sizes have led to the development of anatomic referencing.

Purpose of the Study:

• To validate the concept of anatomic referencing for femoral component placement.
• To demonstrate that 2mm incremental femoral sizes can achieve anterior cortical flushness and restore posterior condylar offset (PCO).

Main Methods:

• Created digital surface models of 515 femurs from CT scans.
• Performed virtual bone resections, component sizing (2mm increments), and placement.
• Assessed component positioning against the anterior cortex and measured posterior condylar gaps.

Main Results:

• Anatomic referencing with 2mm increments allowed femoral components to be placed flush with the anterior cortex, restoring PCO.
• The average medial gap was 0.6mm, and the overall average condylar gap was 1.02mm.
• The medial condyle was the limiting factor in 73% of cases.

Conclusions:

• Anatomic referencing with 2mm incremental sizing is a viable alternative to AR and PR for total knee arthroplasty.
• This method ensures accurate anterior flange alignment and PCO restoration without compromising fit.
• It eliminates the need to choose between AR or PR when between standard femoral sizes.