title: Bilateral total knee replacement: staging and pulmonary embolism.
abstract: BACKGROUND
  When a bilateral total knee replacement is indicated, it is not clear whether it is preferable to operate on both knees during the same hospitalization (simultaneously) or to stage the procedures in two separate hospital stays. A greater risk of pulmonary embolism after simultaneous total knee replacement has been reported by some authors, but little national data are available.
  
  
  METHODS
  We reviewed the records of 122,385 United States Medicare enrollees who had had a total knee replacement in 2000. We noted whether they had had a unilateral procedure or two procedures and, if they had had two procedures, whether both had been done during the same hospitalization or whether the operations had been performed during two separate hospital stays. Age, sex, race, residence, Medicaid eligibility (a proxy for low income), and the Charlson comorbidity score were documented for each patient as were the total numbers of total knee replacements performed in the year 2000 by the hospital and the surgeon. The probability of a symptomatic pulmonary embolism developing in the first three months after surgery was calculated for the simultaneous, staged, and unilateral procedures.
  
  
  RESULTS
  Simultaneous procedures were much more likely to be performed in high-volume hospitals and by high-volume surgeons than were staged procedures. Men had proportionately more simultaneous procedures than did women. Hospitals in the northeastern United States were the most likely to perform simultaneous procedures. A pulmonary embolism developed in the first three months in 0.81% of the patients who had had a single procedure compared with 1.44% of the patients who had undergone a simultaneous procedure (adjusted hazard ratio 1.81; 95% confidence interval, 1.49, 2.20).
  
  
  CONCLUSIONS
  The systematic differences in patient gender, hospital and surgeon volume, and geographic region between those who undergo simultaneous total knee replacements and those who undergo staged procedures should be borne in mind when outcomes are being compared. The adjusted risk of pulmonary embolism is about 80% higher in the three months after a simultaneous procedure than in the three months after a single procedure, which suggests that the sum of the risks associated with the two operations of a staged procedure may equal or exceed the risk of simultaneous total knee replacement.
authors.affiliation: Department of Medicine, Dartmouth Medical School, 46 Centerra Parkway, Evergreen Building, Suite 300, Lebanon, NH 03766, USA. jane.a.barrett@dartmouth.edu
authors.forename: Jane
authors.initials: J
authors.lastname: Barrett
authors.forename: John A
authors.initials: JA
authors.lastname: Baron
authors.forename: Elena
authors.initials: E
authors.lastname: Losina
authors.forename: John
authors.initials: J
authors.lastname: Wright
authors.forename: Nizar N
authors.initials: NN
authors.lastname: Mahomed
authors.forename: Jeffrey N
authors.initials: JN
authors.lastname: Katz
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000379:methods* / Q000706:statistics & numerical data; D005260:Female; D006276:Health Facility Size; D006801:Humans; D008297:Male; D006278:Medicare; D011655:Pulmonary Embolism / Q000453:epidemiology*; D012189:Retrospective Studies; D012737:Sex Factors; D014481:United States / Q000453:epidemiology; D016526:Workload