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Scientific Articles   |    
Which Factors Determine the Wear Rate of Large-Diameter Metal-on-Metal Hip Replacements?Multivariate Analysis of Two Hundred and Seventy-six Components
A.J. Hart, MA, MD, FRCSG(Orth)1; S. Muirhead-Allwood, FRCS(Orth)2; M. Porter, FRCS(Orth)3; A. Matthies, BSc, MBBS1; K. Ilo, BSc, MBBS1; P. Maggiore, BSc, MBBS1; R. Underwood, PhD4; P. Cann, PhD4; J. Cobb, FRCS(Orth)1; J.A. Skinner, FRCS(Orth)2
1 Department of Musculoskeletal Surgery, Imperial College (Charing Cross Hospital Campus), Fulham Palace Road, London SW7 2AZ, UK. E-mail address for A.J. Hart: a.hart@imperial.ac.uk
2 Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK
3 Wrightington Hospital, Hall Lane, Wigan, Lancashire WN6 9EP, UK
4 Department of Mechanical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
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Investigation performed at the London Implant Retrieval Centre, a Collaboration Between Imperial College London, London, and the Royal National Orthopaedic Hospital NHS Trust, Middlesex, United Kingdom

A commentary by Joshua J. Jacobs, MD, and Markus A. Wimmer, PhD, is linked to the online version of this article at jbjs.org.



Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Copyright © 2013 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2013 Apr 17;95(8):678-685. doi: 10.2106/JBJS.J.01447
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Abstract

Background: 

Determining the relationship between clinical factors and engineering analysis of retrieved hip implants can help our understanding of the mechanism of device failure. This is particularly important for metal-on-metal hip arthroplasties because the most common cause of failure is unexplained. We sought to understand the variation in wear rates in a large series of retrieved metal-on-metal hip arthroplasty components.

Methods: 

We prospectively recorded preoperative, intraoperative, and postoperative data to study the effect on both head and cup wear rates of the following variables: patient sex, cause of failure, manufacturer type, resurfacing or modular design, blood cobalt and chromium levels, edge-loading, femoral head size, and cup inclination angle. We analyzed 276 components (138 femoral head and acetabular cup couples) retrieved from failed metal-on-metal hip replacements.

Results: 

We found a high rate of edge-loading (64%), but only forty-three (31%) of 138 hips had a cup inclination angle of >55°. Multivariate analysis showed that the most important factor responsible for the variation in wear rate was the presence or absence of edge-loading, even when adjusted for cup inclination angle. Strong positive correlations were found between acetabular cup and femoral head wear rates and between wear rates and both blood cobalt and chromium ion levels.

Conclusions: 

Multivariate analysis of nine factors found that edge-loading was the most important predictor of wear rate and occurred in two-thirds of failed metal-on-metal hip replacements. The majority did not have excessive cup inclination angles: 68% had an inclination angle of ≤55°. This finding, together with the relatively low median wear rate of the components in our study, suggests that cup position and/or wear rate may not be the only outcome related to failure of metal-on-metal hip replacements.

Level of Evidence: 

Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

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    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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