title: Incidence of contralateral THA after index THA for osteoarthritis.
abstract: BACKGROUND
  Currently more than 200,000 THAs are performed annually in the United States. In patients with bilateral disease, the chance of subsequent contralateral THA reportedly ranges from 16% to 85%. Factors influencing contralateral THA are not completely understood.
  
  
  OBJECTIVE
  We therefore determined (1) the 10-year probability free of progression to contralateral THA after index THA, (2) whether demographics differed between those who did and did not ultimately undergo contralateral THA, and (3) whether initial clinical symptoms and/or degree of radiographic osteoarthritis affects progression.
  
  
  METHODS
  We retrospectively identified 332 patients with minimum 24-month followup and primary osteoarthritis who underwent unilateral THA between 2001 and 2008. There were 150 men and 182 women with a mean age of 61 years (range, 27-93 years) and a mean BMI of 29.6 kg/m(2) (range, 17.6-49.2 kg/m(2)). We reviewed clinical, radiographic, and demographic data at index THA and last followup and classified patients as low, indeterminate, or high risk of undergoing contralateral THA.
  
  
  RESULTS
  Seventy-four of the 332 patients (22%) underwent contralateral THA, resulting in an 83% 10-year probability free of progression to the contralateral hip. Low-risk patients had a less than 1% chance of progression, indeterminate-risk patients had a 16% to 24% chance of progression, and high-risk patients had a 97% chance of progression.
  
  
  CONCLUSIONS
  Indeterminate-risk patients may be managed nonoperatively and deserve further study with a larger multicenter analysis. We defined high- and low-risk patients who may be candidates for bilateral THA or may rarely need a contralateral THA.
  
  
  METHODS
  Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Center for Joint Preservation and Replacement, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore, 2401 West Belvedere Avenue, Baltimore, MD 21215, USA.
authors.forename: Siraj A
authors.initials: SA
authors.lastname: Sayeed
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Johnson
authors.forename: David E
authors.initials: DE
authors.lastname: Jaffe
authors.forename: Michael A
authors.initials: MA
authors.lastname: Mont
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip; D015142:Baltimore / Q000453:epidemiology; D018450:Disease Progression; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D015994:Incidence; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000601:surgery*; D016016:Proportional Hazards Models; D011859:Radiography; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D012720:Severity of Illness Index; D013997:Time Factors; D016896:Treatment Outcome