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Published on: February 27, 2018
Discrepancy between anatomical axis and stem position of various femoral components in Japanese
M Ueno1, Ken Urabe, Mamou Fujita
1Department of Orthopedic Surgery, Kitasato University Hospital, Kitasato University School of Medicine, Sagamihara, Kanagawa, Japan.
Insights
Femoral component stems in knee replacements often misalign with the natural femur axis in Japanese patients. Current implants may require modification or new designs for optimal fit and function in this population.
Area of Science:
- Orthopedic surgery
- Biomedical engineering
- Radiology
Background:
- Accurate alignment of femoral components is crucial for successful total knee arthroplasty (TKA).
- Anatomical variations in different ethnic populations can influence implant fit and performance.
- Previous studies have not fully characterized the relationship between femoral component stems and the distal femur's anatomical axis in Japanese patients.
Purpose of the Study:
- To evaluate the discrepancy between the anatomical axis of the distal femur and the stem position of five common femoral components in Japanese patients.
- To determine the suitability of existing femoral components for the Japanese population undergoing TKA.
Main Methods:
- Lateral radiographs of 100 Japanese patients (12 men, 88 women; mean age 59 years) with rheumatoid arthritis were analyzed.
- The anatomical axis of the distal femur was compared with the stem position of five femoral components (Nexgen LCCK, Press-Fit Condylar, Scorpio, Total Stabilizer, Rotating Hinge) using template superimposition.
- Measurements quantified the angular and positional discrepancies between the femur's natural axis and the implanted stem.
Main Results:
- Significant variation was observed in both the distal femur's anatomical axis and the stem positions of all tested femoral components among Japanese patients.
- All five component designs exhibited a tendency for stems to be positioned more posteriorly than the anatomical axis.
- The Nexgen LCCK and Press-Fit Condylar components showed the smallest discrepancies, while three other models exceeded 3 mm. In 35% of cases, no prosthesis could be optimally positioned, suggesting a need for smaller implant sizes.
Conclusions:
- The stem position relative to the anatomical axis is a critical factor in selecting appropriate femoral components for Japanese patients.
- Current femoral components may not be optimally designed for the unique anatomy of Japanese patients, potentially leading to malalignment.
- Development of novel femoral prostheses with stems specifically designed for the anatomical characteristics of Japanese patients with rheumatoid arthritis is recommended.
Purpose:
To evaluate the discrepancy between the anatomical axis of the distal femur of Japanese patients and the stem position of 5 types of femoral components.
Methods:
Lateral radiographs of 12 men and 88 women aged 31 to 83 (mean, 59) years with rheumatoid arthritis were evaluated. The discrepancy between the anatomical axis of the distal femur and the stem position of 5 types of femoral components (Nexgen LCCK, Press-Fit Condylar, Scorpio, Total Stabilizer, and Rotating Hinge) was determined by superimposing the template of each model over each lateral radiograph.
Results:
The anatomical axis varied widely among our patients, as did the stem position of the 5 femoral components. Stems of all 5 femoral components tended to be more posterior than the anatomical axis. The discrepancy was smallest in the Nexgen LCCK, followed by the Press-Fit Condylar components. It was >3 mm in the other 3 models. In 35% of the patients, none of the prosthesis could be placed in an appropriate position. Smaller-size prostheses appear necessary for the Japanese.
Conclusion:
The stem position should be an important factor guiding selection of the appropriate model. The currently available femoral components may not be appropriate for the Japanese. Prostheses with appropriately positioned stems for Japanese patients with rheumatoid arthritis should be developed.
