The purpose of this study was to determine the coordinates of the origin and insertion, muscle volumes, lengths, lines of action, and effective moment arm of the quadriceps muscles in vivo using magnetic resonance imaging (MRI) and radiography for a pilot study involving musculoskeletal modeling. Two magnetic resonance scans were performed, and axial images were obtained for the left thigh of a female subject in the anatomical position to measure muscle volume, coordinates of the origin and insertion, and muscle belly length at the anatomical position of each quadriceps muscle. Six knee radiographs were used to determine the effective moment arm of the quadriceps force at different knee flexion angles. A combination of MRI and radiography data was used to compute the muscle lengths at different knee flexion angles. The coordinates of the vastus lateralis, muscle volumes of individual quadriceps muscles, and effective moment arms were clearly different from the corresponding values from cadaver data reported in the literature. These comparisons demonstrate the advantages of using personalized muscle parameters instead of those collected from cadavers and dry-bone specimens.
J.W. Chow was with the Department of Exercise Science at the University of Iowa at the time of the study and is now with the Department of Kinesiology at the University of Illinois, Urbana, IL 61801. W.G. Darling is with the Department of Exercise Science at the University of Iowa, Iowa City, IA 52242. J.C. Ehrhardt is with the Department of Radiology at the University of Iowa.