Computational Comparison of One Piece Metacarpo-Phalangeal/Phalangeal-Phalangeal Total Joint Replacements

Abstract

Trauma, osteoarthritis and rheumatoid arthritis can destroy the articulating cartilage in small and large joints, especially in the metacarpo [tarso] phalangeal (MCP/MTP) and phalangeal-phalangeal (PIP) joints. Single piece finger prosthetic designs can reduce pain and correct aesthetic issues, with problems on contemporary designs including decreased stability, lack of fixation and loss of functionality. The examined implants are representative models of currently available total joint replacement (TJR) designs for MCP replacement, such as the Swanson one piece implant. These implants have been shown clinically to have a high failure rate (up to 90%), but the cause of failure is unknown. Compressive studies using a 50 N force and medial-lateral loads of 50 N perpendicular to the longitudinal axis of the arms of the implant were individually applied. Due to material failings, lower values had to be used in some cases. Maximum stress values were found for flexion loading; the Swanson approximation had a peak stress of 8.71 GPa at the interface of the joint arm and the flexion center, Neuflex had 0.188 GPa peak stress at the fixation center of the arm, and in the center of the joint, and the Avanta design had a 5.20 GPa peak stress at the flexion center. The location and concentration of stresses on the models correspond to literature searches for clinical data, showing that the main failure mechanism for these implants is due to primary flexion-extension natural movement of the joint.