Figure 2.

Illustrations of the rectus femoris muscle (top panels) and its moment arm at the knee averaged over 20–60 degrees of knee flexion (bottom panels). The moment arms of the models (black bars) are compared with moment arms measured experimentally (grey bars) by Delp et al. (1994) in cadaver specimens in the (a) preoperative condition, after (b) transfer to the sartorius, and after (c) transfer to the iliotibial band. The muscle insertions shown in models (b) and (c) are effective insertions used to calculate moment arms (see Methods). The muscle’s knee extension moment arm in the (d) scarred transfer model is compared to its moment arm calculated from in vivo measurements of the muscle’s displacement in the patient from Asakawa et al. (2002) with the minimum reduction in knee extension moment arm after rectus femoris transfer.