Extensive porosity at the cement–femoral prosthesis interface: A preliminary study

Abstract

This study is the first description of the extensive porosity which is preferentially located at the cement-prosthesis interface of cemented femoral components of total hip replacements. The observation is important because the interfacial porosity may decrease the strength of the cement-femoral prosthesis interface and jeopardize the mechanical integrity of the cement mantle. We examined the cement-metal interfaces from a multiplicity of in vivo and in vitro specimens using both optical and scanning electron microscopy. These samples included several stem designs, implants made from either Co-Cr or Ti alloy, implants made with a variety of surface finishes and both centrifuged and uncentrifuged cement. All in vivo and in vitro samples had marked porosity in the cement focally concentrated at the cement-metal interface. The amount of porosity at the interface greatly exceeded the amount of general porosity found throughout the bulk cement. Centrifuging did not affect the interfacial porosity, and neither did alloy nor surface finish. The presence of these pores may be explained by the rheological characteristics of the cement.

Acrylic Cement Creeps but Does Not Allow Much Subsidence of Femoral Stems

“…In addition, subsidence may be promoted by cement-stem interfacial porosity which can be as much as 50%, even when advanced mixing procedures are used. 17 Obviously, cement cracks may allow substantial subsidence. The effects of creep on the cement stresses were analysed by considering the maximal and average cement stress values.…”

Interface gap after implantation of a cemented femoral stem in pigs

“…Davies and Hams (1995) showed that porosity reduction by centrifugation did not change the linear dimensions of Simplex P cement and subsequently suggested that linear shrinkage was more important than volumetric shrinkage for fixation of the implant. Several studies have also revealed that extensive porosity is aggregated at the cement-stem interface in retrieved cement mantle and laboratory-prepared specimens (Jasty et al 1991, James et al 1993, Bishop et al 1996. This aggregation of pores could influence the interface bonding between the stem and the cement.…”

Precooling of the femoral canal enhances shear strength at the cement–prosthesis interface and reduces the polymerization temperature

“…6,7 These maneuvers, however, do not diminish pores at the cement-stem interface. 9 The porosity at the interface has been attributed to several factors, such as rheological characteristics of the cement, monomer evaporation, and cement shrinkage. 9,14 In this study, we observed that both precooling the bone and preheating the stem could achieve porosity reduction at the cement-stem interface.…”

“…9 The porosity at the interface has been attributed to several factors, such as rheological characteristics of the cement, monomer evaporation, and cement shrinkage. 9,14 In this study, we observed that both precooling the bone and preheating the stem could achieve porosity reduction at the cement-stem interface. We believe that cement shrinkage during polymerization plays an important role in the development of interfacial porosity.…”

“…3,4 Modern cementing techniques, such as vacuum mixing, centrifugation, pressurization, and retrograde filling with a cement gun, have been emphasized to reduce porosity and improve mechanical strength of the cement mantle, [5][6][7][8] but these efforts do not reduce porosity at the cementstem interface. 9 The probable cause for the preferential formation of voids at the interface is cement shrinkage during curing. 10 With a stem implanted at room temperature, polymerization of bone cement initiates at the warmer cement-bone interface, causing bone cement to shrink away from the prosthetic stem and create pores at the last region to solidify.…”