Affiliations: [a] Graduate School of Science and Technology, Niigata University, Niigata, Japan | [b] Division of Orthopedic Surgery, Department of Regenerative and Transplant Medicine, University Graduate School of Medical and Dental Sciences, Niigata, Japan | [c] Department of Orthopaedic Surgery, Ni-noji Onsen Hospital, Niigata, Japan | [d] Graduate School of Health Sciences, Niigata University, Niigata, Japan | [e] Department of Health and Sports, Faculty of Health Sciences, Niigata University of Health and Welfare, Niigata, Japan
Correspondence:
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Corresponding author: Tomoharu Mochizuki, Graduate School of Medical and Dental Science, Niigata University, 1-757 Asahimachi-dori, Chuo-ku, Niigata City, Niigata 951-8510, Japan. Tel.: +81 25 227 2272; Fax: +81 25 227 0782; E-mail: tommochi121710@gmail.com
Abstract: BACKGROUND:Identifying the time course of rotational knee alignment is crucial for elucidating the etiology in knee osteoarthritis. OBJECTIVE:The aim of this study was to propose new rotational indices for calculating the change in relative rotational angles between the femur and tibia in standing anteroposterior (AP) radiographs. METHODS:Forty healthy elderly volunteers (20 women and 20 men; mean age, 70 ± 6 years) were assessed. The evaluation parameters were as follows: (1) femoral rotational index: the distance between the sphere center of the medial posterior femoral condyle and the lateral edge of the patella, and (2) tibial rotational index: the distance between the medial eminence of the tibia and the lateral edge of the fibula head. The indices were standardized by the diameter of the sphere of the medial posterior femoral condyle. This study (1) identified the relationship between changes in rotational indices and the simulated rotational knee angles in the standing position, (2) proposed a regression equation for the change in relative rotational angles between the femur and tibia in standing AP radiographs, and (3) verified the accuracy of the regression equation. RESULTS:The rotational indices increased in direct proportion to simulated rotational knee angles (femoral index: r > 0.9,p < 0.0001; tibial index: r > 0.9, p < 0.0001). Based on the results, the regression equation with the accuracy of 0.45 ± 0.26° was determined. CONCLUSIONS:The proposed regression equations can potentially predict the change in relative rotational angles between the femur and tibia in a pair of standing AP radiographs taken at different dates in longitudinal studies.
