DVT after knee arthroscopy

The question about whether to give prophylaxis to reduce the risk of serious DVT depends on how likely DVT is in the first place. After some major orthopaedic surgery, estimates of DVT incidence are quite high, perhaps occurring in four of every five patients. In that case, prophylaxis with low molecular weight heparin would seem to be sensible.

Most, though not all, patients who have knee arthroscopy are relatively young, and deep venous thrombosis is rarely a complication, with more serious pulmonary embolism even rarer. But DVT can have sequelae that are far from pleasant, including painful swellings, ulceration, and in extreme cases amputation.

So what is the DVT rate after knee arthroscopy? A new meta-analysis [1] has put a number on it.

This was a single search for English-language studies to the end of 2004, together with examination of bibliographies of relevant articles. For inclusion studies had to be prospective, include patients without antithrombotic prophylaxis, involve universal screening if the lower extremities using diagnostic venography or ultrasound, and involve only arthroscopic knee surgery without ligament surgery or open procedures.

Six studies were found, two using venography (dark symbols in Figure 1), and four ultrasound (light symbols). The average age in these studies was 38-46 years, with more men than women.

Individual results for total DVT incidence ranged from 3.1% to 18% in the studies, and in the 684 patients overall it was 10% (95% confidence interval 8-12%). The venography studies picked up 11 cases of proximal DVT, for an overall rate of 2%. No cases of pulmonary embolism were reported.

Including only studies with prospective screening using trusted methods gives confidence in the results, and while there was variability between the studies, this was only to be expected given their relatively small size. The overall result of a 10% DVT rate is interesting. It is probably too low for prophylactic use of low molecular weight heparin, but too high to be ignored.

Some of the individual studies looked for risk factors, useful for picking those patients having arthroscopy who should receive antithrombotic prophylaxis. Individually they were too small to provide great insight, but those suggested include older age (over 65 years), obesity, smoking, previous DVT, venous insufficiency and use of HRT or oral contraceptives. Not finding any cases of pulmonary embolism means we can be 95% confident that it occurs less frequently than 1 time in 230 cases, which is probably what we know anyway. The actual pulmonary embolism rate after knee arthroscopy is not known with certainty.

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