A finger function simulator and surface replacement prosthesis for the metacarpophalangeal joint

Abstract

Joint replacement surgery in the treatment of arthritic disease is now commonplace and on the whole very successful. Research into the design and development of prostheses has made major advances since the 1940s resulting in complex devices for almost all articulating joints of the body. In this thesis, a programme of work to design and test a surface replacement prosthesis for the metacarpophalangeal joint is presented. The anatomy and kinematics of the MCP joint are discussed for both normal and abnormal joint function and, based on these considerations, the design of a new surface replacement prosthesis is described. Various materials are explored with respect to their biocompatibility, durability and ease of fabrication with special attention being paid to one material - a new cross linked ultra-high molecular weight polyethylene - which is tested for wear and assessed for durability in long-term prototype tests. A finger function simulator is detailed which was designed and developed during this research programme, and results of tests on bone replicas, Swanson Silastic implants and prototypes of the new design are presented. The simulator can be easily modified to accept any MCP joint prosthesis for bench testing. Finally the stress response of the prototype design is studied using finite element analysis and modifications to the implant design and bone preparation are suggested.