Abstract
Calcium sulfate bone void fillers are increasingly being used for dead space management in infected arthroplasty revision surgery. The presence of these materials as loose beads close to the bearing surfaces of joint replacements gives the potential for them to enter the joint becoming trapped between the articulating surfaces; the resulting damage to cobalt chrome counterfaces and the subsequent wear of ultra-high-molecular-weight polyethylene is unknown. In this study, third-body damage to cobalt chrome counterfaces was simulated using particles of the calcium sulfate bone void fillers Stimulan® (Biocomposites Ltd., Keele, UK) and Osteoset® (Wright Medical Technology, TN, USA) using a bespoke rig. Scratches on the cobalt chrome plates were quantified in terms of their density and mean lip height, and the damage caused by the bone void fillers was compared to that caused by particles of SmartSet GMV PMMA bone cement (DePuy Synthes, IN, USA). The surface damage from Stimulan® was below the resolution of the analysis technique used; SmartSet GMV caused 0.19 scratches/mm with a mean lip height of 0.03 µm; Osteoset® led to a significantly higher number (1.62 scratches/mm) of scratches with a higher mean lip height (0.04 µm). Wear tests of ultra-high-molecular-weight polyethylene were carried out in a six-station multi-axial pin on plate reciprocating rig against the damaged plates and compared to negative (highly polished) and positive control plates damaged with a diamond stylus (2 µm lip height). The wear of ultra-high-molecular-weight polyethylene was shown to be similar against the negative control plates and those damaged with third-body particles; there was a significantly higher (p < 0.001) rate of ultra-high-molecular-weight polyethylene wear against the positive control plates. This study showed that bone void fillers of similar composition can cause varying damage to cobalt chrome counterfaces. However, the lip heights of the scratches were not of sufficient magnitude to increase the wear of ultra-high-molecular-weight polyethylene above that of the negative controls.
Highlights
Over 140,000 primary arthroplasty procedures are carried out in the National Health Service (NHS) annually[1] with the aim of reducing pain and restoring joint function in patients with osteoarthritis
There were no measurable scratches on the surface of the plates damaged with PGCS, the plates damaged with MGCS had 1.62 scratches per mm which was significantly (p \ 0.05) higher than the number of scratches caused by polymethyl methacrylate (PMMA)
Third-body particles originating from PMMA bone cement and calcium sulfate bone void fillers (BVFs) can damage highly polished cobalt chrome counterfaces, and BVFs of similar composition can cause varying magnitudes of surface damage
Summary
Over 140,000 primary arthroplasty procedures are carried out in the National Health Service (NHS) annually[1] with the aim of reducing pain and restoring joint function in patients with osteoarthritis. Despite an estimated survivorship of greater than 95% at 10 years, failure of metal-on-polyethylene implants most commonly occurs as a result of wear of the ultra-high-molecular-weight polyethylene (UHMWPE) component[2] leading to aseptic loosening. To reduce the potential for aseptic loosening due to wear debris–induced osteolysis, the wear of the UHMWPE component should be minimised. Particle to enter the contact surfaces to cause a single scratch of 2 mm depth to produce a large increase in UHMWPE wear[3] with the wear rate primarily dependent on the scratch lip height.[4] Damage to the cobalt chrome counterface causes a change in the dominant wear mechanism from adhesive to abrasive, which accelerates UHMWPE wear.[5] Clinically, femoral counterfaces can be roughened by bone cement particles, bone particles, and metallic debris, which when trapped between the articulating surfaces can cause damage to the bearing surfaces and accelerate wear.[6] The presence of third-body particles such as bone cement, bone fragments, or porous-coating beads in retrieved devices and surrounding tissue[7] has been widely reported with the particles originating during device implantation, from the device itself, or from failure of the cement mantle.[7,8]
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