Introduction: Trapeziometacarpal prosthesis allows to reach faster mobility and usefull thumb than trapeziectomy. But successfull Implantation of the trapezium cup depends on the bone stock and the jig. An anatomical and biomechanical study is presented followed by a prospective clinical evaluation of the impllantation af a screwed trapezium cup to define the best way to reach the center of the trapezium.

Matériel et méthodes: Cadaver study: 11 screwed trapezium implant have been implanted on cadaver (age > 70 yo, alcool conservation). 5 implants with 5 spires and 6 implants with 3 spires have been tested. Extraction tests have been performed after Xray evaluation of the position of the implant. 2 series of test were done in the subgroup of trapezium with 3 spires. Ergonomic and dynamometric jig to implant the trapezium cup has been invented to avoid fracture during implantation.

Clinical study: 58 trapezium cup have been implanted in 6 months with evaluation of the position of the implant in the center of the trapezium.

Résultats: Best bone stock was identified on medial border of trapezium. Only 1/5 trapezium cup with 5 spires was extracted (120N). In the subgroup of trapezium with 3 spires, if only 2 spires were screwed (first serie of test) the extraction load reached 103, 24N (57–133). If 3 spires were screwed (second serie of test) the extraction load reached 89,5 N (45–137). Trapezium was stronger in male than in female No trapezium fracture have been pointed, but slight fissuration of the lateral border were observed in 4 cases after é series of test. The multicenter study allowed to validate the the operative technique of implantation: key point were reported as: optimal view on the borders of the trapezium, implantation of a pin in the center of the trapezium under Xray control and preparation of the bone with approproate jig around the well positionned pin. 2 fractures of the trapezium were observed explained by the implantation of the trapezium cup without help of the Xray control. Each time the surgeon has pinned with no fluoroscopic assistance, the pin was never in the center of the trapezium.

Discussion: The two main complication of trapezio metacarpal prosthesis remain the instability with dislocation and loosening. Such implant is not recommended if trapezium is less than 8 mm. The key point of such procedure remain the implantation of the cup in the trapezium. Bone stock is more important on medial side and implantation of the cup in the center of the bone needs fluorocopic even if the surgeon is an experimented one. 3 spires in the bone of the tested screwed cup remain efficient to reach sufficent extraction load.

Purpose: We reviewed a series of pollicizations in children with congenital thumb malformations. The purpose of this study was to assess the influence of anatomic or technical factors on functional and cosmetic outcome.

Material: The series included 33 operations in 26 children. The Blauth classification was: grade IIIA (n=1), grade IIIB (n=8), grade IV (n=8), grade V (n=13), mirror hand (n=8). We noted the type of skin incision, technique used to fix the metacarpal head on the carpus, and tendon shortenings. Results were assessed at mean 4 years follow-up on the basis of the cosmetic aspect (parent satisfaction) and functional outcome measured with the Kapandji index and flexion-extension of inter-phalangeal joint, thumb finger opposition, and sensitivity.

Results: Mean age at surgery was 32 months. Fixation was achieved with sutures in 24 cases and pinning in nine. Tendon shortening was performed in 16 cases on the extensor system and in one case on the deep flexor system. Mean follow-up was four years. There was no significant difference between groups A and B for cosmetic outcome. The main factor influencing objective functional outcome was the association of a grade III or IV radial club hand. In these patients, the final outcome was compromised by the stiffness or deformation of the radiocarpal joint and the stiffness of the preoperative Kapandji index which was 7 (mean) in group A and 4.75 in group B.

Discussion and conclusion: The following technical aspects did not have a significant effect on the final functional result in our series: type of skin incision, type of carpal fixation, shortening the extensor or flexor system. Technical aspects which must be performed with particular care include reconstruction of the thenar muscles using interosseous muscles, curettage of the growth cartilage of the head of the second metacarpus, and hyper-extension of the head of the second metacarpus during fixation onto the carpus. Careful technique avoids future complications such as excessive growth of the neometa-carpus or Z-thumb.