Despite 46 years clinical experience with ceramic-on-ceramic (COC) hip bearings, there is no data on what constitutes a successful long-term wear performance. There have been many studies of short-term failures (Dorlot, 1992; Nevelos, 2001, Walters, 2004). One retrieval study using optical-CMM technology (OCM) documented volumetric wear-rates ranging up to 7mm³/year on femoral heads (Esposito 2012). It was noted that 83% of these revisions showed stripe damage within 3–4 years. The supposition would appear to be that these were bearing-related failures.

Our selected COC case for this study was particularly interesting, a female patient having her index surgery performed at age 17 and revised at age 49 (following onset of hip pain). This patient led an active lifestyle, went dancing multiple times per week, and was mother to three children. The 38mm Autophor^TM THA (left hip) was eventually revised due to the cup painful migrating (Fig. 1: 32-years follow-up). Radiographs showed cup inclination at approximately 19^°. Impingement marks were noted on the CoCr neck and collared stem (Fig. 2). Implant geometry and form factors were analyzed by standard contour measurement (CMM) while SEM and EDS imaging provided wear topography and evidence of metal contaminants. Linear and volumetric wear in head and cup were studied by OCM at Redlux (Southampton, UK).

The head's main wear-pattern consisted of two overlapping circular areas (Fig. 3). The narrowest margin made by the wear-pattern was used to define the superior aspect of the head. By light microscopy, the superior main-wear zone covered 1490–1680mm² area while the total bi-lobed area covered larger 2170mm² area. OCM analysis delineated the same bi-lobed appearance of head wear with the superior worn area assessed at 1365mm². The cup revealed a more extensive wear pattern that circumnavigated its surface. The black staining identified by EDS imaging in the cup revealed Co and Cr elements. By OCM technique the head volumetric wear was 179 mm³ and the cup was 214mm³ (Fig. 4), i.e. 20% greater than head. Volumetric wear-rate averaged 12.3mm³ per year for this pioneering alumina ceramic.

This first demonstration of long-term, COC volumetric wear provides the foundation for retrieval and simulator studies alike. Our patient represented a “worst-case” scenario for hip-replacement surgery, due to extreme youth and long-term sporting life. While the superior wear pattern was not totally contained within the cup (Fig. 3), her implant positioning was clearly adequate. Nevertheless both cup edge-wear and CoCr contamination indicated this patient experienced habitual impingement, i.e. alumina cup rim wearing against CoCr femoral neck (Fig. 2). The head wear-pattern was distinctly bi-lobed but OCM images showed the majority of wear was in the superior hemisphere as noted in MOM retrievals (Clarke, 2013). The head wear-rate in this pioneering “Mittelmeier” THA averaged 5.6mm³/year over 32-years of follow-up. This appeared directly comparable to ceramic head wear measured with the same OCM-technique in modern ceramic THA (Esposito, 2012: 0.1 to 7mm³/year). This indicated to us that COC wear rates of the order 10–14mm³/year represented an acceptable “normal” level of performance in young and active individuals.

This study reports the mid-term results of a large bearing uncemented metal on metal total hip replacement (MOMHTHR) matched series using the Synergy stem and Birmingham modular head in 36 hips (mean follow up 61 months). All patients underwent clinical, metal ion and MRI assessment. Wear analysis was performed on retrieved heads using Redlux non-contact optical profilometry.

Seven patients (19%) have undergone revision surgery. All revisions had two or more of either symptoms, high metal ions or an MRI suggestive of an adverse reaction to metal debris (ARMD). There was no evidence of component malposition or impingement. Frank staining of tissues together with high volume dark brown fluid collections were found in all cases. All stems and cups were well fixed. In 4 cases pubic and ischial lysis (adjacent to the inferior fins) was observed. All 7 cases had radiological, intraoperative and histological evidence of ARMD (Figure 1). The failure cohort had significantly higher whole blood cobalt ion levels and OHS (p = 0.001), but no significant difference in cup size (p = 0.77), gender predominance, stem offset or cup position (p = 0.12). Sleeves had been used in all revision cases

Wear analysis (n = 4) demonstrated increased wear at the trunnion/sleeve interface in a distribution compatible with micromotion (Figure 2). There was normal wear at the articulating surface.

This series further demonstrates unacceptable failure rates in LHMOMTHR in a series where a compatible stem for the BHR modular head was used. Use of a CoCr sleeve within a CoCr head taper appears to contribute to abnormal wear and therefore potential ARMD and subsequent failure.

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal articulating surface wear has focussed attention on the trunnion / taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in form and surface finish of the head taper as well as quantitative assessment of wear volume. This study aimed to assess and compare qualitatively tapers from small and large diameter MOMTHR's. Tapers from 3 retrieval groups were analysed. Group 1: 28mm CoCr heads from MOMTHRs (n=5); Group 2: Large diameter CoCr heads from LHMOMTHRs (n=5); Gp 3 (control): 28mm heads from metal on polyethylene (MOP) THRs; n=3). Clinical data on the retrievals was collated. RedLux profiling of tapers produced a taper angle and 3D surface maps. The taper angles were compared to those obtained using CMM measurements. There was no difference between groups in mean 12/14 taper angles or bearing surface volumetric and linear wear. Only LHMOMs showed transfer of pattern from stem trunnion to head taper, with clear demarcation of contact and damaged areas.3D surface mapping demonstrated wear patterns compatible with motion or deformations between taper and trunnion in the LHMOM group. These appearances were not seen in tapers from small diameter MOM and MOP THRs. Differences in appearance of the taper surface between poorly functioning LHMOMTHRs and well functioning MOP or MOM small diameter devices highlight an area of concern and potential contributor to the mode of early failure.

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal wear at the articulating surfaces has focussed attention on the trunnion / taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in the form and surface finish of the head taper as well as a quantitative assessment of wear volume. This study aimed to assess and compare qualitatively the tapers from well functioning small diameter, with poorly functioning LHMOMTHR's using the above technique.

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal wear at the articulating surfaces has focussed attention on the trunnion/taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in form and surface finish of the head taper as well as a quantitative assessment of wear volume. This study aimed to assess and compare qualitatively the tapers from small diameter with LHMOMTHR's. 3 groups of retrieval tapers were analysed (Group 1: 28mm CoCr heads from MOMTHRs (n=5); Group 2: Large diameter CoCr heads from LHMOMTHRs (n=5); Group 3: 28mm heads from metal on polyethylene (MOP) THRs; n=3). Clinical data on the retrievals was collated. Both bearing surfaces and head tapers were measured for wear using the Redlux profiling non contact measurement system. Measurements included taper angle and 3D surface maps. Taper angles obtained with the Redlux method were compared to those obtained using CMM measurement on 3 parts. The Redlux profiling, including imprints, was also repeated 3 times to gauge potential errors. There was no difference in mean 12/14 taper angles between groups. There was no difference in volumetric and linear wear at the bearing surface between groups. Only the LHMOMs showed transfer of pattern from the stem to the internal head taper, with clear demarcation of the contact and damaged area between head taper and stem trunnion. 3D surface mapping demonstrated wear patterns compatible with motion or deformations between taper and trunnion in the LHMOM group alone. Discussion: Differences in appearance of the taper surface between LHMOMTHRs and MOP or MOM small diameter devices highlight an area of concern and potential contributor to the mode of early failure. Further work is required to fully qualify the Redlux method capabilities.

Retrieval analysis offers a direct insight into in vivo wear mechanisms. However, the 3D measurement of wear patch characteristics on spherical highly reflective bearings has been difficult. An instrument based on an optical technique has been developed over the past 3 years. It is capable of scanning metallic head and cup in a single measurement, within minutes, at a resolution of 20 nm. From the cloud of 3D points obtained during scanning (typically 35,000 To 1,000,000), a 3D image of the measured part can be obtained. The associated computer program allows for sphericity, roughness, radius and local radius to be calculated, and surface maps of the 3D model can easily be plotted.

Both head and cup of two failed MoM resurfacing devices, a wear simulator test couple and intact components were analysed using the new technique. A successful McKee Farrar head (20 years in vivo) was also scanned. Results were compared with traces obtained on a Mitutoyo RA 300 roundness machine (resolution 0.01 microns).

3D maps of the bearing surfaces of MoM devices were obtained. The maximum linear wear values on heads were 2.5 microns, 99 microns 53.5 microns and 298 microns for the simulator sample, the McKee Farrar head and the two failed resurfacing devices respectively. The corresponding maximum linear wear values on cups were 11 microns, 529 microns and 645 microns for the simulator sample and the two failed resurfacing devices respectively. These results were in good agreement with results obtained on the Mitutoyo machine. Contrary to other worn samples, the two latter cups showed that the cup had worn on the edge of the bearing surface. This resulted in an oval shaped wear patch on the head. For the McKee Farrar device and the simulator device, the wear patch was away from the edge and the outline of the wear patch was circular in shape.

This novel technique has allowed for high resolution 3D mapping of the full bearing surfaces on successful McKee Farrar device and on more recent resurfacing devices. Further studies are required. However, the results suggest that component positioning is paramount to wear performance of metal on metal devices.