title: Revisions of monoblock metal-on-metal THAs have high early complication rates.
abstract: BACKGROUND
  A relatively high percentage of monoblock metal-on-metal total hip arthroplasties (THAs) undergo early revision. Revision of these THAs poses challenges unique to this implant type. The early complications after these revisions remain unreported as do the clinical and demographic factors associated with these complications.
  
  
  OBJECTIVE
  We describe (1) the frequency of early complications after revision of monoblock metal-on-metal THA; and (2) the clinical and demographic factors associated with complications.
  
  
  METHODS
  A review of our institution's total joint registry identified 107 patients who underwent 114 revisions of monoblock metal-on-metal THAs. Mean patient age at revision was 60 years (range, 17-84 years), and 65% of the patients were women. Mean followup after revision was 14 months (range, 0-122 months). Revision diagnoses included metallosis (51%), aseptic loosening (27%), infection (7%), pain (6%), malposition (4%), instability (3%), iliopsoas impingement (2%), and periprosthetic fracture (1%). Major complications (instability, infection, aseptic loosening, and wound complications) were documented and included in the analysis. Minor postoperative complications such as urinary tract infection were excluded.
  
  
  RESULTS
  Twenty-three of 114 procedures (20%) involved at least one early complication after revision of monoblock metal-on-metal THA with 18 (16%) undergoing at least one additional subsequent surgery. The most common complications included aseptic loosening (6%), deep infection (6%), dislocation (4%), and acetabular fracture (3%). Patients who sustained a complication after revision surgery were older on average than those who did not (66 years versus 58 years, p=0.003). There were no differences in complication rate with respect to sex, time to revision, or revision diagnosis.
  
  
  CONCLUSIONS
  Complications and reoperations occur frequently after revision for failed monoblock metal-on-metal THA (20% and 16%, respectively), and older patients appear to be at greater risk for complications after these revisions. Aseptic loosening, deep infection, and instability are all of great concern after revision and surgeons should be aware of these potential complications when undertaking revision of these THAs.
  
  
  METHODS
  Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopedic Surgery, University of Texas Health Science Center, San Antonio, 7703 Floyd Curl Drive, MSC-7774, San Antonio, TX, 78229, USA, stryker@uthscsa.edu.
authors.forename: Louis S
authors.initials: LS
authors.lastname: Stryker
authors.forename: Susan M
authors.initials: SM
authors.lastname: Odum
authors.forename: Thomas K
authors.initials: TK
authors.lastname: Fehring
authors.forename: Bryan D
authors.initials: BD
authors.lastname: Springer
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D061825:Metal-on-Metal Joint Prostheses; D008875:Middle Aged; D011475:Prosthesis Failure; D012086:Reoperation; D055815:Young Adult