[Longevity factors in total trapezometacarpal prostheses]

We report the long term outcome of the trapeziometacarpal prosthesis in a personal series of 13 cases with a follow-up ranging from 12 to 17 years. This ball and socket prosthesis with a metal on polyethylene pairing is cemented. Several modifications were performed along the years: such as increased range of motion, better fit between the metacarpal medullary canal and the proximal part of the stem and addition of a versatile, intermediate component in order to re-establish length of the first ray. The status of the metacarpo-phalangeal joint is critical. Natural hyperextension of this joint has been seen in about two-third of th normal individuals. If the metacarpal component become loose, the thumb column become shorter and hyperextension of the metacarpophalangeal joint is followed by an adduction contracture of the metacarpal which produces a shear force component on the cup and finally the loosening of the cup (sequential loosening). Keeping or re-establishing the length of the first ray is the major principle in the trapeziometacarpal prosthesis. On the other hand, metacarpophalangeal arthrodesis is a contraindication for a trapeziometacarpal prosthesis. Trapeziometacarpal prosthesis should only be used as a last resort when there is severe pain. If the dominant hand is involved, intensive use is a contraindication. The trapezium must be large enough to accommodate the cup. The author recommends a posterior approach which preserve the anterior ligaments and allows a proper bone resection and a good positioning of the cup.