Wear of Mixed Ceramic-on-Ceramic Hip Replacement Bearings under Adverse Edge Loading Conditions Due to Translational Mal-Positioning

Transcription

1 Wear of Mixed Ceramic-on-Ceramic Hip Replacement Bearings under Adverse Edge Loading Conditions Due to Translational Mal-Positioning Mazen Al-Hajjar 1, Silvia Carbone 1, Louise M. Jennings 1, Sabine Begand 2, Thomas Oberbach 2, Daniel Delfosse 3, John Fisher 1. 1 Institute of Medical and Biological Engineering, University of Leeds, Leeds, United Kingdom, 2 Mathys Orthopädie GmbH, Moersdorf, Germany, 3 Mathys AG, Bettlach, Switzerland. Disclosures: M. Al-Hajjar: None. S. Carbone: None. L.M. Jennings: 5; Mathys Orthopadie GbmH, DePuy Synthes Joint Reconstruction, Invibio, Biocomposites. S. Begand: 3A; Mathys Orthopädie GmbH. T. Oberbach: 3A; Mathys Orthopädie GmbH. D. Delfosse: 3A; Mathys AG. J. Fisher: 1; DePuy Synthes Joint Reconstruction. 2; DePuy Synthes Joint Reconstruction. 3A; Tissue Regenix plc. 3B; DePuy Synthes Joint Reconstruction, Tissue Regenix plc, Invibio. 4; Tissue Regenix plc. 5; DePuy Synthes Joint Reconstruction, Invibio, Mathys Medical. Introduction: Ceramic composites have been developed to further improve the mechanical properties, reduce risk of fracture, and increase the survivorship of ceramic-on-ceramic bearings in total hip replacement 1. These composite ceramics have performed very well under adverse edge loading conditions when used in like-on-like configurations, where the femoral head and acetabular cup are of the same material 2. The aim of this study was to determine the wear of pure alumina (Al 2 O 3 ), alumina toughened zirconia (ATZ) and zirconia toughened alumina (ZTA) when used in mixed bearing combinations, under edge loading conditions due to translational malpositioning. Methods: The head-on-cup configurations of three ceramic material (see Table 1), which were supplied by Mathys Orthopädie GmbH (Morsdorf, Germany), were ATZ-on-ZTA, ZTA-on-ATZ, Al 2 O 3 -on-atz, ATZ-on- Al 2 O 3 and Al 2 O 3 -on-zta. They were tested for four million cycles on the Leeds II hip simulator under microseparation 3,4 conditions representing translational mal-positioning. The gait cycle comprised extension/flexion (-15º/+30º), internal external rotation (+/-10º) and a twin peak load with a maximum of 3kN. Microseparation was achieved by applying a 0.5mm dynamic medial/lateral displacement using a spring load resulting in edge loading at heel strike. All femoral heads used had a diameter of 28mm. All cups were mounted at an inclination angle equivalent to an in vivo cup inclination of 55. New-born calf serum (25%) was used as a lubricant. Wear was assessed gravimetrically every one million cycle using a microbalance (Mettler AT201, UK). Statistical analysis was performed using oneway ANOVA (significance taken at p<0.05). Results: The bedding in and steady state wear rates of ATZ-on-ZTA (1.16mm 3 /million cycles bedding in and 0.18mm 3 /million steady state) and ATZ-on-Al 2 O 3 (0.66mm 3 /million cycles bedding in and 0.20mm 3 /million steady state) were lower than that of Al 2 O 3 -on-al 2 O 3 (1.54mm 3 /million cycles bedding in and 0.55mm 3 /million steady state) bearing combination (see Figure 1). However, there was statistically no significant difference (p=0.35) between the wear rates. The wear rates of the other bearings combinations under these adverse microseparation conditions, Al 2 O 3 -on-atz, Al 2 O 3 -on-zta, and ZTA-on-ATZ were very low with no clear bedding in and steady state phases (see Figure 1). This pattern was similar to that of the like-on-like configuration 2 of ZTA-on-ZTA and ATZ-on-ATZ tested under the same adverse simulator conditions. The wear rates of Al 2 O 3 -on-atz, Al 2 O 3 -on-zta, ZTA-on-ATZ including the like-on-like configuration 2 of ZTA-on-ZTA and ATZ-on-ATZ, over the four million cycles of test under adverse microseparation conditions, were all lower than 0.14mm 3 /million cycles with the ZTA-on-ZTA having the highest wear rate of 0.14mm 3 /million cycles and ATZ-on-ATZ having the lowest wear rate of 0.06mm 3 /million cycles. Discussion: Retrievals studies have changed our understanding of preclinical testing as some of the wear mechanisms observed on ceramic-on-ceramic and metal-on-metal bearings did not match wear mechanisms obtained under the standard walking simulator conditions showing the importance of introducing adverse conditions to in vitro methodologies. The mixed material combinations (ATZ-on-ZTA, ATZ-on-Al 2 O 3, Al 2 O 3 -on-atz, Al 2 O 3 -on-zta and ZTA-on-ATZ) tested in this study have shown slightly higher wear rates when compared to ATZ in like-on-like configuration, but superior wear resistance when compared to Alumina BIONIT (Mathys) and BIOLOX forte (CeramTec) Al 2 O 3 -on-al2o 3 bearings tested under the same adverse microseparation conditions. To compare to other bearings materials, the wear rate of metal-on-metal bearings has been reported to be in the range of 2-9 mm 3 /million cycles under microseparation conditions, and the wear rate of metal-on-polyethylene could be 100 times higher than the wear rates of ceramic-on-ceramic bearings. Significance: Ceramic-on-ceramic bearings in mixed material combinations where the head and the cup were of different materials showed stripe wear under edge loading conditions due to translational mal-positioning. However, the wear rates obtained were lower than those of Alumina-on-Alumina bearings Acknowledgments: This study was supported by Mathys Orthopädie GmbH (Moersdorf, Germany). JF is an NIHR Senior Investigator and his research is supported through The NIHR Leeds Musculoskeletal Biomedical Research Unit.

2 References: 1. Begand S., etal. Key Engineering Materials Bioceramics, Al-Hajjar M., etal. JBMR-B, Nevelos J., etal.,arthroplasty, Stewart T., etal., JBMR-B,

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4 ORS 2014 Annual Meeting Poster No: 0942

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