[Biomechanics of the carpus and the wrist]

Over the last decade, the classical concept of the single block carpus has been radically transformed to a more dynamic concept of a "carpus with variable geometry". This conceptual revolution is the result of progress in a number of fields: precise information concerning the situation and, more particularly, the variability of "instantaneous axes", a better understanding of the anatomy of ligaments and their role, allowing their grouping into functional units: the anterior and posterior ligamentous straps and the cuneiform sling which determines its stability and basic movements. The role of the articular disk of the inferior radio-ulnar joint involves not only the stability of the inferior radio-ulnar joint, but also the suspension of the ulnar side of the carpus. The extensor retinaculum, considered to be extra-articular slings, also has a similar role: the anterior ligament controls the concavity of the carpal groove and the dorsal ligament stabilises the posterior ulnar tendon. The essential progress consists of the concept of the first row of carpal bones as an intercalated structure, in particular the concept of "useful space" or "useful distance" between the antebrachial joint cavity and the second row of carpal bones, filled in by the elementary movements of the bones of the first row. This discovery leads directly to concepts of "internal coherence of the carpus " or spatial coherence and the "variable geometry" of the carpus. This approach reveals the internal components of the movements associated in the global movements of the wrist. The last essential concept is that of self-locking and facilitation of the fist row of carpal bones as a result of the interosseous ligaments, which clarifies new syndromes of internal instability of the carpus.