[Descriptive anatomy and biodynamic study of the medial collateral ligament of the trapezio-metacarpal articulation of the thumb].

The trapezoid articular surface is classically compared to a saddle. The movements of the thumb obey to two centers of rotation. The one is proximal and determined by the convexity of the saddle; the other is distal and determined by its convexity. The authors have realised 15 dissections and 20 cinematic studies; they bring precision to the collateral medial trapeziometacarpal ligament and show the fundamental role of its anchorage point on the medial metacarpal tubercle: the distal center of rotation and the anchorage point are practically superimposed. The movements from this center are realised in indifferent pronosupination. The proximal center of rotation and the anchorage point are distant. The movements from this center are necessarily accompanied by pronation or supination. Statement report of the mechanism of this double rotation.