Feasibility of computer-assisted surgery for trapeziometacarpal prosthesis: a preliminary experimental study

The main complication of trapeziometacarpal replacement is trapezial cup loosening due to an imperfect positioning of the trapezial component. This problem is quite similar to those related to other arthroplasties. Hip surgery was progressed toward computer-assisted surgery (CAS) for the improvement of acetabular cup positioning. In this study, we propose an analysis of the feasibility of CAS in trapeziometacarpal replacement. We implanted the hand of a cadaver with a trapeziometacarpal prosthesis (Elektra, by SBI). The surgical procedure and the analysis of motion with CAS were carried out in 6 steps: incision, bone morphing preparation and initialisation, trapezial and metacarpal recordings, first kinematic analysis, prosthesis insertion, and second kinematic analysis. The evaluation of the results was carried out as the comparison of the 2 curves sequences before and after prosthesis insertion. We did not notice any dislocation of the prosthesis. The comparison of 2 curves showed differences regarding motion. For instance, as for abduction-adduction movements, before prosthesis insertion, an opposed-phase automatic rotation was clearly observed whereas after prosthesis insertion, no rotation was observed. CAS makes it possible to analyze the trapeziometacarpal joint motion in terms of biomechanics rather than in terms of anatomy. Such progress should result in measurement standardization that in turn should improve the positioning of prostheses and perhaps the lengthening of their life expectancy by decreasing the rates of prosthesis loosening.