The management of venous thrombophlebitis and thromboembolic disease has challenged the medical community for decades. The diagnosis can be elusive because of absent or mild clinical symptoms, and the potential outcome can be catastrophic. Major venous thromboembolic events (VTEs) are uncommon after outpatient knee arthroscopy, although many orthopaedic surgeons are aware of cases of fatal pulmonary embolism (PE) after this “low risk” surgery.
In their paper, Maletis et al. use a large administrative database from the Kaiser Permanente Health Maintenance Organization to analyze the incidence of symptomatic VTE after knee arthroscopy. The records of almost 22,000 patients were retrospectively reviewed to identify ICD-9-CM procedure codes associated with symptomatic deep venous thrombosis (DVT) or PE during a ninety-day postoperative period. The incidence of symptomatic DVT during this period was 0.25% and the incidence of PE was 0.17%. The risk of VTE was 1.5 times higher if patients were over fifty years of age, and the risk in female patients was 2.5 times higher if they were taking prescription oral contraceptive medications. Nine patients (0.04%) died within ninety days of surgery, but only one of these patients had a confirmed PE.
Because of the retrospective nature of this study, there are some significant weaknesses, including the heterogeneous nature of the arthroscopic procedures. Also, the key word in the title is “symptomatic.” I suspect that a large number of patients developed asymptomatic clots, preoperatively as well as postoperatively. Younger patients with larger pulmonary reserves may not have developed the symptoms of an acute PE and would have been missed by the investigators. As the author confirms, they had no ability to stratify risk factors such as type of anesthesia, tourniquet usage, body mass index, duration of surgery, and prior history of VTE. The use of aspirin by patients could also be a confounding variable. The diagnosis of VTE is dependent on the level of clinical suspicion and on how vigorously a physician tests for the condition. All of the patients were enrolled in a managed health care program, and the possibility exists that imaging studies were not ordered to keep the cost of care to a minimum.
The strengths of the study include its large patient database, which comprised the electronic medical records of twenty-seven medical centers. Only 2% of the patients left the health plan within the follow-up period, which represents a small attrition rate.
Maletis et al. believe that the incidence of symptomatic VTE is low after knee arthroscopy, and the data in their paper support this premise. They discourage the use of routine anticoagulation after this procedure (which, as they point out, is in accord with the current recommendation of the American College of Chest Physicians [ACCP]) unless a patient has increased thromboembolic risk factors. The ACCP also encourages early mobilization.
According to Maletis et al., knee arthroscopy is the most commonly performed orthopaedic procedure in the United States. Because anticoagulation is not without risk, orthopaedic surgeons should heed the advice of the authors, who discourage the use of routine anticoagulation after outpatient knee arthroscopy.