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Rheumatoid arthritis is a painful and debilitating disease which often afflicts the key joint of the hand, the metacarpophalangeal joint. In the worst cases the diseased joint has to be replaced with an artificial joint or prosthesis. The development of the Durham metacarpophalangeal prosthesis as it was taken from prototypes through to production samples, is described in this thesis. Testing of several Durham prostheses to over 70 million cycles has been carried out on a finger function simulator and consistent wear factors of the order of 0.4 x 10(^-) (^6)mm(^3)/Nm have been measured. These wear factors for the prosthesis were also significantly lower than any found previously. Production samples of the prosthesis have been manufactured together with appropriate surgical instrumentation. Tests of the prosthesis material, cross-linked polyethylene, rubbing against itself, have been undertaken on reciprocating pin on plate rigs and again show total wear factors of the order of 0.4 x lO(^-6)mm(^3)/Nm. Interestingly, it was found that pin wear was very much less than plate wear. The pin on plate tests were extended to include ultra-high molecular weight polyethylene (UHMWPE) rubbing against UHMWPE, as well as both polyethylenes against hard counterfaces and the results are reported. A new finger function simulator has been designed, manufactured and a validation test undertaken. Having written the necessary protocol, in conjunction with clinicians and the prosthesis manufacturer, ethical approval was obtained from the local research ethics committee and the Medical Devices Agency, to permit implantation of the prosthesis in human subjects. Lastly a hand strength measurement device for pre and post operation assessment of patients has been developed and manufactured.