The quasistatic and fatigue performance of the implant/bone‐cement interface

Abstract

Loosening is a major cause of failure in total arthroplasties. The efficacy of the fixation systems depends not only on the bulk properties of the components but also on the interfaces through which they interact. This study was initiated to examine the implant/bone-cement interface for four of the most commonly used implant materials, Co-Cr-Mo, Ti-6A1-4V, 316SSLVM and ultrahigh molecular weight polyethylene (UHMWPE). The surface preparation, specimen design, joining, and testing techniques were studied and then standardized in a manner which accurately represents current clinical procedures. The interfaces were tested for both their quasistatic and fatigue properties. Finite-element and fracture toughness analyses of the quasistatic shear specimens were performed in order to provide results of an absolute nature which could be subsequently compared to bulk material properties of bone cement. The interfaces were tested "dry" (i.e., at room temperature and 50% R.H.) and in physiological saline at 37°C. The interfaces demonstrated both fracture toughness and fatigue properties far inferior to those of bone cement. A predominantly interfacial type failure was observed using SEM fractography. The ultimate compressive strength (U.C.S.) of bone cement was measured after prolonged exposure to saline at 37°C and showed no decrease in U.C.S. suggesting that the reasons for the interface strength reductions were interfacial rather than bulk in nature. The "wetting" ability of bone cement was measured using contact angles at various cure times on the four implant materials. These measurements showed that intimate interfacial contact is impossible with current clinical methods. This study indicates that failure of the implantibonecement interface is likely only a short period after implantation and therefore may be a major contributor to implant loosening.

Residual stress due to curing can initiate damage in porous bone cement: experimental and theoretical evidence

“…6:9 MPa for ultimate tensile strength (Raab et al, 1981), and could be expected to accelerate interfacial debonding upon cyclic loading of the specimen. This interface was difficult to observe in the specimens due to increased opacity, created mainly by shadows from the high density of pores in this region, and so no definitive assessment of interface integrity could be made.…”

Effect of metal surface topography on mechanical bonding at simulated total hip stem-cement interfaces

“…Instead of using only average surface roughness (R a ) to correlate with the interfacial strength as was done by Raab et al, 9 Keller and Lautenschlager, 16 and Bundy and Penn, 17 the correlation between interfacial shear strength and other surface parameters was also investigated. For the surfaces that were made by the same machining method but with different R a (e.g., fine ground/rough ground, or fine turned/rough turned, the interfacial shear strength increased with the increase of R a .…”

“…However, for cemented hip replacement, debonding between the bone cement and prosthesis is regarded as a major contributor to the initiation of hip replacement failure. 9,10 Clinical support for this argument is given by Stauffer. 11 This 10-year follow-up of 300 patients who had total hip replacement showed that the incidence of femoral component loosening happened at the cement-stem interface in most cases.…”

“…The clinical investigations of Mohler et al 12 drew a similar conclusion. Recent studies of the bone cement and prosthesis interface explored this phenomenon 9,10,[13][14][15] ; however, the precise mechanism of loosening is not clearly established.…”

“…The surface topography of the prosthesis has proved to be an important factor affecting the interfacial strength between the bone cement and prosthesis 9,16,17 and average surface roughness, R a , alone is insufficient to describe a prosthesis surface. 17,18 However, less work has been found in which the prosthesis surface is described more comprehensively and a comparison made on the effect of different surface topographies on the prosthesis fixation strength.…”