[In vivo cinematic study of the trapezometacarpal joint].

The aim of this study was to assess the trapeziometacarpal joint kinematics from in vivo measurements, both quantifying the ranges of motion and suggesting a suitable joint model. A motion analysis system has been used to collect the spatial trajectories of markers, glued respectively on the thumb and on the hand's palm. A rigorous protocol was set up to make sure of the trapezoid bone's fixity relatively to the hand, and then to be able to characterize the movement of the first metacarpus with respect to the trapezium. The ranges of motion have been measured on two distinct movements: circumduction and flexion-extension, and different types of joints: healthy, pathological and prosthetic. The joint axes of rotation (for flexion-extension and ante-retroposition movements) have been determined on healthy subjects. The computation of rotation amplitudes and positions of joint axes was based upon the finite helical axis concept, which degenerates into finite rotation axis when translations can be neglected. Both the measurement protocol and the calculation method have been validated by comparing the computed joint center with that measured on a radiography, in the case of a spherical prosthesis. The ranges of motion obtained on the healthy subject series were consistent with values published by other authors. Comparisons have been realized between these reference joints and different cases: arthrodesis, arthrosis and prosthesis. The determination of rotation axes of a normal joint has lead to a generalized cardan joint, i.e. two non perpendicular converging rotation axes.