Design of a surface replacement prosthesis for the proximal interphalangeal joint

A surface replacement finger joint prosthesis was designed specifically for the proximal interphalangeal joint (PIPJ). The two-piece design consisted of a bi-condylar proximal phalangeal head and a conforming bi-concave middl e phalangeal base. The bearing surfaces were designed as close to the origi nal anatomy of the PIPJs as possible, using detailed information obtained f rom a previous anatomical study of 83 PIPJs by the present authors. Four sizes of prosthesis were designed with maximum head diameters of 7, 8, 9 and 10 mm. Fixation of the joint prosthesis was achieved by an interfere nce fit between the stems of semicircular cross-section and the phalangeal bone shafts. The main considerations for the stem designs were the offset f rom the centre of rotation, angle of inclination, length, and cross-section al shape and size. It is proposed that the two components will be made from cross-linked polyethylene (XLPE) because it can be injection moulded to pr oduce the complex shapes of the joint prosthesis. In addition, XLPE against itself has shown comparable wear rates with stainless steel against ultra- high molecular weight polyethylene from previous work by Joyce et al.