Discrepancy between anatomical axis and stem position of various femoral components in Japanese.
OBJECTIVE
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.


CONCLUSIONS
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.
Ueno
M
M
Department of Orthopedic Surgery, Kitasato University Hospital, Kitasato University School of Medicine, Sagamihara, Kanagawa, Japan.
Urabe
Ken
K
Fujita
Mamou
M
Aikawa
Jun
J
Kobayashi
Akimasa
A
Itoman
M
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000208:ethnology / Q000473:pathology* / Q000601:surgery; D019645:Arthroplasty, Replacement, Knee; D044466:Asian People; D015331:Cohort Studies; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology*; D006801:Humans; D007564:Japan; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D017755:Prosthesis Fitting; D011859:Radiography