We know that blood clots after surgery are a very real problem. One risk-factor for blood clots after surgery is immobilization. And usually, people who have foot surgery will remain in a boot and need to stay off their foot for at least several weeks. So, it makes sense that clots after foot surgery will occur frequently. Unfortunately, data are scarce and formal guidance is even harder to come by.
How Common are Clots after Foot Surgery?
The bottom line is that we probably don’t really know.
There are not many reports of the incidence of blood cots after foot surgery. Still, a few small single-center reports mainly from the early 2000’s exist. All included a low number of patients. And all reported a low incidence of deep vein thrombosis after foot surgery.
So, can we gain some understanding by looking at foot injury? It turns out that reports of blood clots after foot and ankle injury are also uncommon. In one study that analyzed nearly 300,000 foot and ankle fractures, only 0.56% of people developed a clot. Another small study is worth mention. Here, researchers compared three approaches to managing foot and ankle injury. They reported an incidence of deep vein thrombosis or pulmonary embolism of 2.2%-4.8%, depending on the approach they took to treatment.
Still, remember, that when you think about these figures, you should understand that these were not post-operative clots. Also, an interesting fact is that they allowed chemoprophylaxis for patients that they considered “high-risk” for developing clots. In practice, this means patients with co-morbid conditions, history of clotting or complex injury.
As you can see, there are no real data specifically about the epidemiology of clots after foot (or ankle) surgery.
Preventing Clots after Foot Surgery
Assuming we agree that venous thrombosis can happen after foot surgery, we should be thinking about prevention. One strategy to prevent clots in general is to avoid immobility. But after foot (and ankle) surgery that is a problem. Often, a patient will need to wear a cast or a boot for a minimum of 6 weeks. So we need to decide if we should prescribe aspirin or a blood thinner such as rivaroxaban for prevention.
First, a study examined active toe motion as a method to prevent clots. This did not work. Intermittent pneumatic compression is not relevant in these patients, because typically the there is a cast or boot over the calves. So they are out as well.
So, we are left with chemoprophylaxis. This might be the correct approach in some patients. One meta-analysis reported a lower incidence of venous thromboembolism with low-molecular weight heparin prophylaxis in patients treated with below the knee cast for foot and ankle trauma. Bleeding was rare. Indeed, in a more modern retrospective analysis of nearly 15,000 ankle injuries, using prophylaxis with low-molecular weight heparin was associated with fewer clots.
I should note that while all the data surround low-molecular weight heparin, in practice, we often prescribe low-dose rivaroxaban or low-dose apixaban for prophylaxis. This is because we extrapolate from other indications, such as hip or knee surgery.
Treatment if a Clot Develops
One a clot develops, we need to decide about the best treatment. I actually took part in a study that examined this question. We showed that patient who underwent hallux valgus surgery and who develop a clot, usually receive anticoagulation. Most will take the blood thinner for a limited duration. After stopping the blood thinner, recurrence is uncommon.
My practice is to treat patients for a limited time. Usually, this means treating for about 3 months. Obviously, you have to individualize decisions for each patient. For instance, if a patient still can’t walk on their foot or still requires a boot or splint after 3 months, I may recommend to treat for longer. On the other hand, patients who are back to normal mobility, especially if their bleeding risk is higher, should not receive longer treatment.
What do the Guidelines Say?
As you can imagine, guidelines have little to say on the matter. Current guidelines focus more on major orthopedic surgery including spine, hip and knee surgery. There are non-guidelines supported publications that suggest risk-stratifying patients. Thus, if a patient has a higher risk for clotting, they may need prophylaxis, even if the procedure is considered lower risk than “major” surgery.