Transitional Stiffness Intramedullary Stems to Reduce Periprosthetic Pain

Abstract

The intramedullary canal presence of a stemmed prosthetic component can be expected to change the distribution of stress from the joint loading to the adjacent skeleton. The reconstructed skeletal stiffening that results for relatively rigid prosthetic components can result in periprosthetic stress shielding. The abrupt change in reconstruction stiffness that can occur at the implant stem terminus can be associated with periprosthetic pain. A stem end “clothes pin” slot, intended to make a stem end more flexible, produces a substantially asymmetric and abrupt alteration of stem stiffness. The present work is directed to analyzing ways that the structural stiffness of the terminus region of a prosthetic stem can be controlled to provide a symmetrical transitional region of controllable load transfer to the surrounding bone. It is hypothesized that through implant design, prosthesis-to-bone interface pressure and periprosthetic bone stress levels at a prosthetic stem terminus can be reduced and that this will be associated with a reduced occurrence and severity of “end of stem pain” in a variety of prosthetic applications.