title: Clinical and Wear Analyses of 9 Large Metal-on-Metal Total Hip Prostheses.
abstract: BACKGROUND
  Metal-on-Metal (MoM) total hip arthroplasties (THA) are associated with pseudotumor formation and high revision rates. This prospective study analysed the clinical and wear analyses of 9 large Metal-on-Metal (MoM) total hip arthroplasties (THA) to understand the underlying mechanisms of failure. The MoM bearings were revised for multiple reasons; the main reason was pseudotumor formation.
  
  
  METHODS
  From 2006 till 2010 the Reinier de Graaf Hospital implanted 160 large head M2a-Magnum™ (Biomet Inc. Warsaw, Indiana, USA) THAs in 150 patients. The first year, 9 bearings were revised and analysed at the Biomechanics Section, Hamburg University of Technology, Germany. We performed clinical (Harris Hip Score, radiographic analysis, blood cobalt and chromium) and wear analysis (implant, tissue and fluid) of the 9 bearings. Since this study did not fall under the scope of the Medical Research Involving Human Subjects Act in The Netherlands, no ethical approval was necessary. In this prospective study all patient details were anonymized by the corresponding author, all other authors were blinded during the research and wear analyses. Patients with bilateral MoM implants were excluded.
  
  
  RESULTS
  The 9 bearings had a median (IQR) survival of 41.0 (25) months in situ. From these bearings, three showed no noticeable wear. The median (IQR) head wear volume was 3.2 (3.6) mm3 and maximum wear depth 0.02 (0.02) mm. For the cup the median (IQR) wear volume was 0.23 (0.3) mm3 with a maximum wear depth of 0.03 (0.05) mm.
  
  
  CONCLUSIONS
  An early identification of parameters related to failure of the MoM THA, such as pain, decreased range of motion, radiographic changes and high levels of blood cobalt and chromium is of great importance for patient's quality of life. Especially now patients and surgeons face the long term effects of all these bearings still in situ. This study reports the clinical and wear analyses of 9 MoM THA. In the majority of this group the reason for revision was pseudotumor formation. Most bearings showed signs of wear, however with a great diversity in clinical analysis, in inclination angle, serum cobalt and chromium levels as well as wear analysis. For a better understanding of the underlying mechanisms related with failure, more wear analyses of revised MoM bearings are necessary as well as a frequent follow-up of the patients with a MoM bearing.
authors.affiliation: Department of Orthopaedics, Reinier de Graaf Hospital, Reinier de Graafweg 3, 2625 AD, Delft, the Netherlands.
authors.forename: M C
authors.identifier: http://orcid.org/0000-0001-7573-332X
authors.initials: MC
authors.lastname: Koper
authors.affiliation: Department of Orthopaedics, Reinier de Graaf Hospital, Reinier de Graafweg 3, 2625 AD, Delft, the Netherlands.
authors.forename: N M C
authors.initials: NM
authors.lastname: Mathijssen
authors.affiliation: Biomechanics Section, Hamburg University of Technology, Denickestraße 15, 21073, Hamburg, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Witt
authors.affiliation: Biomechanics Section, Hamburg University of Technology, Denickestraße 15, 21073, Hamburg, Germany.
authors.forename: M M
authors.initials: MM
authors.lastname: Morlock
authors.affiliation: Department of Orthopaedics, Reinier de Graaf Hospital, Reinier de Graafweg 3, 2625 AD, Delft, the Netherlands.
authors.forename: S B W
authors.initials: SB
authors.lastname: Vehmeijer
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008422:Materials Testing; D061825:Metal-on-Metal Joint Prostheses; D008875:Middle Aged; D011475:Prosthesis Failure; D014057:Tomography, X-Ray Computed; D055815:Young Adult