Wear Performance of Ceramic-On-Metal Hip Bearings
Citation: Reinders J, Sonntag R, Heisel C, Reiner T, Vot L, et al. (
Wear Performance of Ceramic-On-Metal Hip Bearings
Jrn Reinders 0
Robert Sonntag 0
Christian Heisel 0
Tobias Reiner 0
Leo Vot 0
Jan Philippe Kretzer 0
Amir A. Zadpoor, Delft University of Technology (TUDelft), Netherlands
0 Laboratory of Biomechanics and Implant Research, Department of Orthopedics and Traumatology, Heidelberg University Hospital , Heidelberg , Germany
Ceramic-on-metal (CoM) bearings are considered to be a promising alternative to polyethylene-based bearings or hard-on-hard bearings (Ceramic-on-Ceramic (CoC) and Metal-on-Metal (MoM)). Although, CoM shows lower wear rates than MoM, in-vitro wear testing of CoM shows widely varying results. This may be related to limitations of wearmeasuring methods. Therefore, the aim of this study was to improve the gravimetric measurement technique and to test wear behaviour of CoM bearings compared to CoC bearings. Level walking according to ISO-14242 was simulated for four CoM and four CoC bearings. Prior to simulation, errors in measurement of gravimetric wear were detected and improvements in measurement technique incorporated. The results showed no differences in mean wear rates between CoM and CoC bearings. However, the CoM bearings showed wear results over a wide range of wear performance. High reliability of wear results was recorded for the CoC bearings. Material transfer was observed on the ceramic heads of the CoM bearings. Therefore, for level walking a partial mixed or boundary lubrication has to be assumed for this type of bearing. CoM is a highly sensitive wear-couple. The reasons for the observed behaviour cannot be clarified from this study. Simulator studies have to be considered as an ideal loading condition. Therefore, high variations in wear rates as seen in this study, even at low levels, may have an adverse effect on the in-vivo wear behavior. Careful clinical use may be advisable until the reasons for the variation are fully clarified and understood.
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Joint-related disorders of the hip such as persistent pain or
functional disabilities can be successfully treated by total hip
replacement (THR). Following register data, survival rates of
approximately 90% after 10 years are reported [1]. However,
the lifetime of an artificial joint is still limited and wear of the
articulating surfaces remains a major limiting factor in this
respect [2]. Nevertheless, expectations regarding quality of life
and thus on implants are increasing [3]. The performance of
implants therefore has to improve.
New-generation hard-on-hard bearings such as
ceramic-onceramic (CoC) or metal-on-metal (MoM) are technically
promising solutions for the wear problem. Currently, CoC is
considered to be the gold-standard of a low-wearing bearing in
THR with a decreased incidence of osteolysis [4]. However,
breakage (rare incidence of 0-2% depending on the ceramics
used [57]) and squeaking (incidence 0.5-20.9% [5,8]) of
ceramic components are still a concern. For MoM, laboratory
studies have shown low wear [9]. However, concerns exist
regarding interaction of metal wear products with the immune
system, which might take even place at low wear volumes [10].
In this context, cases of high-wear with local effects (metallosis,
necrotic tissue, pseudotumours) [11,12] up to those showing
massive-wear with systemic effects [12] have been reported
and these have alarmed the orthopaedic community.
THR using a metallic liner and a ceramic head (CoM) has
recently been introduced clinically to meet the aforementioned
challenges. It is not known how many CoM bearings have been
implanted to date. One study states that at least 10,000 CoM
bearings have been implanted [13], but it is not clear how this
number was derived. In fact, although CoM bearings are used
clinically there is little knowledge about their in-vivo
performance [14]. Some case reports have shown tremendous
wear of CoM [15,16], but in those cases the technical design
differed from that of modern CoM bearings. Keeping this in
mind, simulator studies may be an important tool for acquiring
knowledge of possible CoM-related risks.
Although some laboratory studies have shown low wear
rates of CoM [1723], there is a high variance between the
results of different research groups. Wear rates from published
studies differ by a factor of 150 [17,20].
Possible reasons for this discrepancy are:
First, CoM is a highly sensitive wear-couple with widely
ranging wear performance.
Second, the wear rate is generally low. Differences are
due to limitations of the methods used to measure wear
(mostly gravimetric).
The aim of this study was therefore to test the wear
behaviour of CoM compared with CoC. To increase the validity
of the results this study focused on improvements in the
gravimetric measurements technique. The results are
supported by continuous screening of the cobalt and chromium
release, as important parameters for the clinical use.
Material and Meth (...truncated)