Arthroscopy of the knee is the single most common orthopedic operation done in this country. Even so, the risk of blood clots in the legs, also known as DVT (deep vein thrombosis) and subsequent pulmonary embolism has been hard to pin down. A recent study by Dahm and colleagues examined the files of 12,595 patients at their institution having knee arthroscopy over a 20 year period and identified 43 patients with symptomatic clots. Of these, 5 had a PE, or a clot which travels from the leg lodging in the lung (these can be fatal.) 3 of the 43 would develop a PE at a later date. The overall incidence of so called VTE, venous thrombotic events, was 0.34 percent.
"Classic risk factors" for post operative VTE include:
Age greater than 65 years
BMI (body mass index) above 30
use of oral contraceptives or hormone replacements
chronic venous insufficiency
previous episode(s) of VTE
history of malignancy (cancer)
Although it may seem counter intuitive, the type of procedure performed on the knee did not seem to be a factor nor was the presence of coronary artery disease, diabetes, or type of anesthesia. Also noteworthy, contrary to what was taught to me for years, the length of procedure or duration of leg tourniquet (wrapped around the thigh and inflated at the beginning of the operation to control bleeding and keep a clear visual field) did not seem to play a role.
The take home here, as noted by Dr. Dahm in performing a retrospective study, is that "we are most certainly underestimating the true incidence of VTE." So if you may be considering a scope and have one or more of the above risk factors, especially if you have two risk factors, you should consider chemoprophylaxis post op. This is already done after hip or knee replacement routinely and should be discussed by you and your physician.
I can tell you first hand that getting paged to the ICU a couple days after what you and the patient both feel was a highly successful ACL reconstruction to find her with an IV drip in her arm and the diagnosis of pulmonary embolism is surprising to say the least. The time to figure this out is before the arthroscopy.
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