Abstract
Introduction
Calcium sulfate bone void fillers (CS-BVF) are increasingly being used for dead space management in infected arthroplasty revision surgery. The use of loose beads of CS-BVF close to the articulating surfaces of an implant means there is potential for them to migrate between the articulating surfaces acting as a third body particle. The aim of this study was to investigate the influence of CS-BVF on the third body wear of total knee replacements.
Methods
The influence of CS-BVF on wear was investigated using the commercially available CS-BVF ‘Stimulan’ (Biocomposites Ltd., UK) and posterior stabilised U2 total knee replacement system implants (United Orthopaedic Corp., Taiwan). The experimental wear simulation was performed using a six station ProSim electropneumatic knee simulator (Simulation Solutions, UK) running the Leeds intermediate kinematics input profile [1]. To investigate the damage that could be caused by the third body particles, 5cc of CS-BVF beads (excess) were placed on the tibial component of the implant, the simulator was run dry for 60 cycles before adding lubricant (25% bovine serum supplemented with 0.03% sodium azide) and running for an additional 115,000 cycles representative of the 6–8 weeks the CS-BVF are present in the body prior to their resorption. The surface topography of the cobalt chrome femorals was analysed using contacting profilometry to ascertain whether the third body particles of CS-BVF had damaged the surfaces. To investigate the influence of CS-BVF on the third body wear of the UHMWPE tibials, 3 million cycles (MC) of wear simulation was subsequently carried out. The wear of the UHMWPE tibials was assessed gravimetrically and the wear of implants tested with CS-BVF was compared to the wear against negative controls (initial Ra∼0.02µm) and positive controls (initial Ra ∼0.4µm) damaged with a diamond stylus. N=6 was completed for each condition, statistical analysis was carried out using ANOVA with significance taken at p<0.05.
Results
Light scratching was visible on the surface of the cobalt chrome femorals after the implants were challenged with the CS-BVF, however, there was no significant difference (p>0.05) between the surface roughness of the negative controls and those challenged with CS-BVF for any of the roughness parameters of interest (Table 1 & Figure 1).
3MC of wear simulation showed no significant difference (p>0.05) between implants subjected to the third body wear protocol and the negative controls (Figure 2). To significantly increase the wear of the UHMWPE tibials, the damage to the cobalt chrome femorals had to be above a threshold as in the positive controls scratched with a diamond stylus.
Conclusions
This study showed that the CS-BVF ‘Stimulan’ had no influence on the third body wear or surface topography of total knee replacements compared to negative controls. Therefore, when used close to articulating surfaces of a metal-on-polyethylene joint replacement, CS-BVF may not influence the wear of an implant or be detrimental to its longevity.
