Abstract
Introduction
Implant contamination prior to cement application has the potential to affect the cement-implant bond. the consequences of implant contamination were investigated in vitro using static shear loading with bone cement and titanium dowels of differing surface roughness both with, and without contamination by substances that are likely to be present during surgery. Namely; saline, fat, blood and oil, as a negative control.
Methods
Fifty Titanium alloy (Ti-6Al-4V) dowels were prepared with two surface finishes comparable to existing stems. The roughness (Ra and Rq) of the dowel surface was measured before and after the pushout test. Four contaminants (Phosphate Buffered Saline (PBS), ovine marrow, ovine blood, olive oil) were prepared and heated to 37°C. Each contaminant was smeared on the dowel surface completely and uniformly approximately 4 minutes prior to implantation. Samples were separated into ten groups (n=5 per group) based on surface roughness and contaminant. Titanium alloy dowels was placed in the center of Polyvinyl chloride (PVC) tubes with bone cement, and equilibrated at 37°C in PBS for 7 days prior to mechanical testing. The push out test was performed at 1 mm per minute. The dowel surface and cement mantel were analyzed using a Scanning Electron Microscopy (SEM) to determine the distribution and composition of any debris and contaminates on the surface.
Results
All contaminants decreased stem-bone cement interfacial shear strength. Saline produced the greatest decrease, followed by blood. The effect of fat was less pronounced and similar to that of oil likely due to the strong lipid solvent properties of the methacrylate monomer. For rough dowels, there were differences in ultimate shear strength between control and contaminated groups (p<0.001). Blood and saline groups had lower ultimate shear strength compared to fat and oil (p<0.05) (fig. 1). The ultimate shear strength for smooth samples was not significantly affected by contamination. Increasing surface roughness increased the interfacial bonding strength, even in the presence of contaminants. In control, fat and oil groups, the effect of roughness are significant (p<0.001, p<0.05 and p<0.001 respectively) (fig. 1). Scanning Electron Microscopy (SEM) showed that contaminants influence the interfacial bond by different mechanisms. Although rough surfaces were associated with higher bond strength, they also generated more debris, which could negatively affect the longevity of the implant bond (fig. 2 and fig. 3).
Conclusion
The results of this study underscores the importance of keeping an implant free from contamination, and that if contamination does occur, a saline rinse may further decrease the stability of an implant. Contaminants did not significantly affect the bond strength between bone cement and smooth Ti stem, although a trend of improved properties was seen in the presence of lipid based contaminants. Therefore, the influence of contaminants is more important to the shape-closed type stem. Increasing surface roughness dramatically improved the load carrying capability of the implant-cement interface even with contaminants.
