Fig. 2
A three-dimensional model of the proximal interphalangeal joint (PIPJ) using the rolling contact joint mechanism. a Contours of the proximal (green) and middle (blue) phalangeal bones and the base (Σb), proximal (Σp), and middle (Σm1) coordinate frames in full extension of the PIPJ. b The ith radiographic image and homogenous transformation (HT) matrices. c The average center of rotation (ACR) based on the HT matrices obtained from multiple radiographic images