title: Stem Migration and Fretting Corrosion of the Antirotation Pin in the K2/Apex Hip System.
abstract: BACKGROUND
  Many exchangeable neck hip systems have been withdrawn because of fretting corrosion at the neck/stem coupling.
  
  
  METHODS
  Our prospective randomized study evaluating stem stability (Roentgen stereophotogrammetric analysis, dual-energy x-ray absorptiometry) and clinical outcomes between the K2/Apex hip systems was ceased early because of a withdrawal of the stems which had an unfavorably high early revision rate reported in the Australian Orthopaedic Association National Joint Registry (9.3% at 3 years).
  
  
  RESULTS
  At 2 years, there are no clinical differences between the stems. Roentgen stereophotogrammetric analysis has identified a high proportion of potentially concerning subsidence and retroversion in both groups, more marked in the K2 stem, although mostly in asymptomatic patients. Dual-energy x-ray absorptiometry has shown similar bone density around the stems. Retrieval analysis of 3 study patients showed fretting corrosion of the antirotation pin and aseptic lymphocyte-dominated vasculitis-associated lesion, with no relationship to bearing type or size. Analysis of 7 further nonstudy K2/Apex stems confirmed similar corrosion.
  
  
  CONCLUSIONS
  This study shows potentially concerning subsidence of both stems and is the first to describe corrosion at the neck-stem interface and a relationship to metal-related pathology.
authors.affiliation: Perth Orthopaedic Institute, Perth, Western Australia, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Kent
authors.affiliation: Perth Orthopaedic Institute, Perth, Western Australia, Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Edmondson
authors.affiliation: Perth Orthopaedic Institute, Perth, Western Australia, Australia.
authors.forename: Jay
authors.initials: J
authors.lastname: Ebert
authors.affiliation: Perth Orthopaedic Institute, Perth, Western Australia, Australia.
authors.forename: Nils
authors.initials: N
authors.lastname: Nivbrant
authors.affiliation: CITRA (Centre for Implant Technology and Retrival Analysis) Medical Engineering and Physics, Perth, Western Australia, Australia.
authors.forename: Alan
authors.initials: A
authors.lastname: Kop
authors.affiliation: Perth Orthopaedic Institute, Perth, Western Australia, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Wood
authors.affiliation: AOA National Joint Registry, Data Management & Analysis Centre, School of Population Health, University of Adelaide, Adelaide, South Australia, Australia.
authors.forename: Richard
authors.initials: R
authors.lastname: De Steiger
mesh_terms: D006801:Humans; D015502:Absorptiometry, Photon; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation; D001315:Australia; D003343:Corrosion; D006622:Hip Prosthesis / Q000009:adverse effects; D008670:Metals / Q000009:adverse effects; D011446:Prospective Studies; D011474:Prosthesis Design; D011475:Prosthesis Failure / Q000209:etiology; D059869:Radiostereometric Analysis; D012086:Reoperation
chemical_list: D008670:Metals
keywords: ALVAL; RSA analysis; metal pathology; retrieval analysis; revision hip arthroplasty; subsidence