Distal Femur Morphology of Iranian Population and Correlation With Current Prostheses

Maintaining proper size and rotation of components of total knee arthroplasty is mandatory for optimal longevity. Ethnical differences may affect the fitness of prostheses that were manufactured mainly based on Caucasian dimensions.

To evaluate the distal femur morphology of the Iranian population at the level of standard cuts simulated via computed tomography.

During 2013, 150 consecutive patients (96 males and 54 females) from the outpatient Department of Orthopedic Surgery of Rasoul Akram Hospital with knee CT scans were studied. We entered cases with apparent normal extremity alignment and bone maturity. Exclusion criteria were history of fracture or conditions affecting knee profile. Standard cuts were simulated on the CT scan using the Marco Pacs program. For each bone, anteroposterior (AP), mediolateral (ML), and aspect ratio (ML/AP) were measured. Values were compared with the sizing of four currently available prostheses.

The mean age of the patients was 43 years (range: 17 to 80). All isolated parameters were higher in men significantly (P < 0.001). However, the aspect ratio did not show any significant difference (1.51 ± 0.11 vs 1.46 ± 0.1), suggestive of a similar configuration of distal femur profiles between genders. Ultimately, close correlations were observed among simulated cuts and size-matched femoral components of the prostheses. For females, however, components were mostly overhang mediolaterally except for one gender-specific subset. Decrement in the aspect ratio for larger knees was another mismatch with current prostheses that preserve an almost constant ratio throughout all sizes.

Our findings may be applied by manufacturers to design prostheses more compatible with Asian populations. Alterations to the shape of components should be considered to provide optimal coverage.