Some factors influencing 3-D modeling of the human finger

Abstract

Modeling of the human finger requires reliable data sampling, both numeric and anatomical. Most data are obtained from anatomical specimens in different stages of flexion and extension, and presented as 2-D models in lateral or dorsal views of the finger. These models are inadequate, however, since they merely represent projections of the model in sagittal, resp. frontal planes. 3-D data derived from serial cross sections should be corrected for differences in slice thickness and for specimen distortion. In our studies, high resolution MRI is used to reconstruct the 3-D structure from three scans in perpendicular planes, and to determine the exact position of the anatomical elements in the human finger. At the level of the proximal interphalangheal (PIP) joint of an extended finger, the position of the extensor assembly coincides approximately with the frontal plane. The extensor assembly is maintained in this position by strong collateral ligaments. During flexion of the finger, however, the ligaments shift alongside the throchlea to more palmar positions, thus enabling the lateral bundles of the extensor complex also to move to more palmar positions. In a flexed finger the positions of the lateral bundles of the extensor assembly coincide more or less with sagittal planes at the level of the PIP joint. These positional changes of tendons and ligaments should be taken into account in 3-D modeling of finger kinematics.