High Altitude Is an Independent Risk Factor for Postoperative Symptomatic Venous Thromboembolism After Knee Arthroscopy: A Matched Case-Control Study of Medicare Patients

Abstract

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). 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 (≥4,000ft) and matched to patients who underwent the same procedures at an altitude less than or equal to 100ft 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 30days and 90days postoperatively. 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 30days 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 90days postoperatively, similarly elevated risks of VTE, PE, and DVT were found in patients with procedures performed at high altitude. In this study of knee arthroscopy in Medicare patients, a procedure performed at an altitude ≥4,000ft 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 100ft. Level III, retrospective case-control study.