Extreme differences in properties of successful bone cements

Abstract

In clinical registries, use of two acrylic bone cements correlates especially highly with longevity of total hip replacement: Palacos R and Simplex P. However, the cements are markedly different. Palacos R is based on a high molecular weight starting powder that is chemically sterilised, while Simplex P employs a different polymer formulation of much lower molecular weight that is radiation-sterilised. In the lab, Palacos R is high in strength, toughness and fatigue resistance, and Simplex P is not. In a long-term clinical retrieval study, Palacos R molecular weight declined but remained high, while Simplex P molecular weight began low and continued to decline. Lower molecular weight cements are inherently more prone to creep and stress relaxation. It seems clear that the basis for excellent clinical performance of each of these cements must be different. Our analysis implies that cements which emphasise strength and durability may be the best choice for hip stems designed to provide interlock, and cements which emphasise controlled creep and stress relaxation may be preferable with stems designed to allow subsidence. © 2005 Springer Medizin Verlag Heidelberg.