Abstract
Introduction
Infection following total joint arthroplasty is a major and devastating complication. After removal of the initial prosthesis, an antibiotic-impregnated cement spacer is inserted for approx. three months. Treatment is completed by a second stage revision arthroplasty.
Up to now, spacers are produced from conventional bone cements that contain abrasive radio-opaque substances like zirconium dioxide or barium sulphate. As long as spacer wear products (cement particles containing these hard substances) are not fully removed during the final revision surgery they may enter the articulating surfaces of the revision implant leading to third body wear.
In order to reduce the formation of reactive wear particles, a special cement (Copal(r) spacem) without abrasive zirconium dioxide or barium sulphate was developed.
To date, no comparative tribological data for cement spacers have been published. Hence, we carried out a study on the wear properties of Copal(r) spacem (with and without gentamicin) in comparison to conventional bone cements (Palacos(r) R and SmartSet(r) GHV).
Material and Methods
In order to assure reproducible forms of the femoral and tibial components, silicon rubber moulds were produced and filled with the respective cement. Force-controlled simulation was carried out on an AMTI knee simulator (Figure I). The test parameters were in accordance to ISO 14243-1 with a 50% reduced axial force (partial weight bearing). Tests were carried out at 37 °C in closed chambers filled with circulating calf serum. Tests were run for 240,000 cycles (representing the average step rate during 6-8 weeks) at a frequency of 1 Hz. For wear analysis, digital photographs of the spacer were taken at the beginning and at the end of the testing period. The areas of wear scars were measured by the means of a digital image processing software.
Results
At the end of wear test none of the cement specimens showed cracks or failures. Pairwise comparison between the cement types revealed significant differences: Larger wear scars were observed for Copal(r) spacem compared to Copal(r) spacem + gentamicin (TUKEY test, p=0.025), whereas smaller wear scars were measured compared to Palacos(r) R (Figure 2), (TUKEY test, p<0.001). Copal(r) spacem + gentamicin showed the smallest wear scars with significance to all tested cements (Copal(r) spacem (TUKEY test, p=0.025), Palacos(r) R (TUKEY test, p<0.001), and SmartSet(r) GHV (TUKEY test, p=0.006).
Discussion
Copal(r) spacem without and especially with gentamicin showed considerably smaller wear scar areas at 240,000 cycles compared to the well established cements Palacos(r) R and SmartSet(r) GHV (Figure 2). This finding is due to the soft calcium carbonate in Copal(r) spacem, which is clearly less abrasive against the surfaces of the sliding partners when compared to bone cements containing zirconium dioxide as radio contrast agents.
Summarising these results, Copal(r) spacem provides a new and interesting approach to produce enhanced spacers with decreased wear. This concept should be further investigated from a mechanical, material-scientific and clinical point of view. Whether the favourable properties of Copal(r) spacem are applicable in order to improve survival of the revision implant needs to be investigated in a long-term study.
