Incidence of Symptomatic Venous Thromboembolism After Elective Knee Arthroscopy

Background: Knee arthroscopy is the most commonly performed orthopaedic procedure in the United States and is usually considered to be a low-risk procedure. The purposes of this study were to describe the incidence of symptomatic deep venous thrombosis, symptomatic pulmonary embolism, and mortality after elective knee arthroscopy performed without thromboembolic prophylaxis, as well as to investigate the association of age, sex, procedure type, and oral contraceptive use with the odds of developing a venous thromboembolism. Methods: A retrospective cohort study of elective arthroscopic knee procedures during a twenty-seven-month period (January 1, 2006, through March 31, 2008) was performed with use of the administrative database of a large health maintenance organization. Use of ICD-9-CM (International Classification of Diseases, Ninth Revision, Clinical Modification) procedure codes for arthroscopic surgery identified 21,794 arthroscopic knee procedures. The occurrence of a symptomatic deep venous thrombosis or pulmonary embolism within ninety days after surgery was identified by reviewing administrative and electronic medical record data for inpatient, outpatient, urgent care, and emergency encounters. Mortality and the cause of death were captured with use of electronic medical records, Social Security Administration Death Master Files, and county death certificates. Patient charts were reviewed for confirmation of the deep venous thrombosis, pulmonary embolism, or death. Patients who had a history of a venous thromboembolism or who had received anticoagulation therapy within fourteen days prior to the index surgery were excluded. Results: The study cohort comprised 20,770 patients who met the inclusion criteria. Fifty-one patients (0.25%; 95% confidence interval, 0.18% to 0.31%) developed a deep venous thrombosis, and thirty-five (0.17%; 95% confidence interval, 0.11% to 0.22%) developed a pulmonary embolism. The incidence of venous thromboembolism was higher in patients who were fifty years of age or older (0.51% compared with 0.34% in younger patients), and the incidence in female patients was higher if they had been prescribed oral contraceptive medication (0.63% compared with 0.30% in female patients with no such prescription). No differences in the incidence of deep venous thrombosis or pulmonary embolism on the basis of sex or arthroscopic procedure code were noted. Nine patients (0.04%) died within ninety days of surgery, although only one death was confirmed to have resulted from a pulmonary embolism. Conclusions: The ninety-day incidence of symptomatic venous thromboembolism after elective knee arthroscopy was relatively low, with a 0.25% incidence of deep venous thrombosis and a 0.17% incidence of pulmonary embolism. The overall ninety-day mortality after arthroscopic knee surgery was 0.04%. Level of Evidence: Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.