title: High Altitude Is an Independent Risk Factor for Postoperative Symptomatic Venous Thromboembolism After Knee Arthroscopy: A Matched Case-Control Study of Medicare Patients.
abstract: OBJECTIVE
  To use a national database of Medicare patients to evaluate the association of uncomplicated knee arthroscopy performed at high altitude with the incidence of postoperative venous thromboembolism (VTE).
  
  
  METHODS
  The 100% Medicare Standard Analytical File database was queried for all patients undergoing isolated arthroscopic partial meniscectomy and/or chondroplasty from 2005-2012. Patients with more complex open or additional arthroscopic knee procedures, a personal history of VTE, or any hypercoagulable state were excluded. The result of this query was then stratified by the altitude of the hospital ZIP code in which the procedure was performed. The appropriate patients were placed into a high-altitude group (≥4,000 ft) and matched to patients who underwent the same procedures at an altitude less than or equal to 100 ft on the basis of age, sex, and medical comorbidities. The rate of VTE was then assessed for both the high-altitude and matched low-altitude patients within 30 days and 90 days postoperatively.
  
  
  RESULTS
  The rate of combined VTE (deep venous thrombosis [DVT] and/or pulmonary embolism [PE]) (odds ratio [OR], 2.0; P = .0003), the rate of PE (OR, 2.5; P = .0099), and the rate of DVT (OR, 1.7; P = .0066) within 30 days were all significantly higher in patients with procedures performed at high altitude compared with matched patients with the same procedures performed at low altitude. At 90 days postoperatively, similarly elevated risks of VTE, PE, and DVT were found in patients with procedures performed at high altitude.
  
  
  CONCLUSIONS
  In this study of knee arthroscopy in Medicare patients, a procedure performed at an altitude ≥4,000 ft was a significant risk factor for the development of postoperative VTE compared with matched patients undergoing the same procedure at an altitude less than or equal to 100 ft.
  
  
  METHODS
  Level III, retrospective case-control study.
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia Health System, Charlottesville, Virginia, U.S.A.
authors.forename: Jourdan M
authors.initials: JM
authors.lastname: Cancienne
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia Health System, Charlottesville, Virginia, U.S.A.
authors.forename: David R
authors.initials: DR
authors.lastname: Diduch
authors.affiliation: Department of Orthopaedic Surgery, University of Virginia Health System, Charlottesville, Virginia, U.S.A.. Electronic address: bcw4x@virginia.edu.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Werner
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000531:Altitude; D001182:Arthroscopy / Q000009:adverse effects*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000601:surgery*; D008297:Male; D006278:Medicare; D011183:Postoperative Complications / Q000453:epidemiology; D012189:Retrospective Studies; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D054556:Venous Thromboembolism / Q000453:epidemiology* / Q000209:etiology*