High-resolution MRI scans, in conjunction with CAD software, were used to determine the three-dimensional moment arms and force vector direction cosines For 11 structures passing the interphalangeal and metacarpophalangeal joints of the index finger. The results ale presented for five different angles of joint flexion for a single subject. The moment arm data obtained differ from previous studies, where results have been derived from tendon excursion techniques or geometrical models. These dissimilarities have been accounted for by the differences in experimental techniques. (C) 2001 Elsevier Science Ltd. All rights reserved.