The development of a modular humeral prosthesis locking mechanism

A new modular humeral prosthesis has been developed, incorporating a novel locking mechanism to prevent head-stem disassembly. A series of test protocols was designed to evaluate the integrity of the new locking mechanism and a dedicated test rig was manufactured. Preliminary test results were disappointing and the locking mechanism failed at lower applied loads than predicted. Microscopy studies were conducted to establish the cause of this poor performance and with the aid of statistical analysis, these studies assisted in the development process. Development of the design was directed at the control of the position and angle of contact between bearing surfaces of the locking mechanism. The optimized design was tested under the maximum anticipated loading conditions and performed satisfactorily.