Knee arthroscopy is a common, minimally invasive surgical procedure used both for diagnosis and treatment of knee conditions. It is increasingly carried out in day surgery using various types of anaesthesia. Some people are at increased risk of developing deep vein thrombosis (DVT) because of factors including a previous history, immobilization, smoking, obesity, varicose veins and increasing age. Different approaches are available for preventing DVT (thromboprophylaxis), both mechanically and with drug medication. The characteristic symptoms of DVT are limb pain and swelling (edema) but often there are no obvious signs or symptoms. DVT at or above knee level (proximal) is associated with an increased risk of pulmonary embolism (which can be fatal) but isolated calf DVT (distal) rarely causes symptoms and is asymptomatic. Arthroscopy patients are often young and soon become mobile again. The incidence of DVT is reported to be from 0.6% when diagnosed clinically to 17.9% using the most sensitive imaging techniques (venography).
This review reports that low molecular weight heparin reduces the incidence of distal DVT diagnosed but the clinical benefits of this are uncertain. The review authors identified four completed studies from three countries that randomly assigned a total of 527 adults to low molecular weight heparin (LMWH) or no intervention or placebo. The mean age of participants ranged from 31 to 44 years and nearly three quarters were male. The relative risk (RR) of thrombotic events was 0.16 (range 0.05 to 0.52). The number needed to treat to prevent one thrombotic event was 17. All the blood clots were distal and were mainly diagnosed by sonogram. Adverse events were most common in the intervention group. The most common complication was minor bleeding with a RR of 2.23 (range 0.99 to 4.99). The number needed to harm was 20. No completed studies were found that looked at mechanical devices such as graduated elastic stockings or intermittent pneumatic compression, for patients immobilized in bed.