Abstract
INTRODUCTION
Wear, aseptic loosening, dislocation, corrosion and prosthetic joint infection (PJI) are major factors leading to revision of THA. The effect of using ceramic components to address these issues was investigated to determine their behaviour and potential benefit.
METHODS
a) Wear determination in off-normal conditions
A series of CoC articulations (32mm) was evaluated using a hip simulator (ISO 14242) up to 4 million cycles in presence of fine alumina particles (48mg/ml). Wear was measured gravimetrically.
b) Friction moment determination
Friction moments were measured in a hip simulator with 25% newborn calf serum as lubricant. CoC, CoPE, MoPE, MoXLPE and CoXLPE with articulating diameters ranging between 28 and 40mm were used. The cup was inclined to a constant angle of 33° and rotated ±20° sinusoidally around a horizontal axis at 1Hz. Peak friction moments were measured around the cup rotation axis during a constant joint force period of 1700N between 200 and 210 seconds.
c) Infections
Four databases were analysed and additionally data from registers and literature were reviewed to determine the risk of revision for prosthetic joint infection (PJI) dependence on the bearing. Only data for cementless THA were used. Several studies also included analysis of several confounding factors like age at surgery, BMI, pathology, etc. using Cox multivariate analysis.
RESULTS
a) Wear determination in off-normal conditions
Loading the test medium with alumina particles didn't produces detectable wear. Opaque areas appeared only after 3 million load cycles, but the wear-rate remained within the gravimetric measurement detection limit (about 0.1–0.2mg) indicating the still extremely low wear-rate of the tested couplings.
b) Friction moment determination
The highest moments were measured for metal heads; the lowest for CoC bearings. 40mm CoC bearing showed a similar friction moment like 28mm bearings when coupled with a XLPE liner.
c) Infections
The rate of revisions for PJI for 500'749 patients from various studies was in the range of 0.2 to 1.1%. Age at surgery and BMI did not influence septic loosening, while the bearing did; sometimes significant. The trend was identical for all seven sources and ceramic components resulted in a lower incidence of revisions for up to 60%.
CONCLUSION
The wear of CoC articulations is extremely low even in a heavily contaminated environment with fine hard particles. Such high scratch resistance makes CoC the preferable revision solution in THA.
Friction moments with CoC are the lowest, even with large diameter bearings. The low friction moments of ceramics lower the stresses at the modular and also bone interface and can affect the outcome of THA.
Revisions due to infection seem to be also dependent on the bearing couple with a positive influence of ceramic components. Although due to the complex reasons for infections only a trend, CoP and CoC has been identified to mitigate the risk of PJI.
