Fixation of a surface replacement endoprosthesis of the metacarpophalangeal joint

Surface replacement of the metacarpophalangeal joint would provide many benefits over current conservative treatment or the use of hinged spacers in excision arthroplasty. One of the main problems in surface replacement is securing adequate fixation of the prosthesis, especially if cement is not to be used. The direction and size of the forces that cause loosening have been described and a series of experiments in cadaveric bone have been used to elucidate the best shape of the component and stem to resist these forces. A 5 mm square section stem of 30 mm length gave the best overall result when combined with a flat on the palmar aspect of the inner bearing surface.