If you’re about to have surgery, particularly if you about to undergo hip and knee replacement surgery, there is a strong risk your blood will clot if no preventive measures are taken.

Up to 50% and 80% of those patients about to have hip and knee surgery respectively are at risk, according to research.

It may be cold comfort to know that your personal profile has a role to play. 

According to Dr David Adler, a specialist physician based in Johannesburg says “some patients are at higher risk of clotting than others, regardless of the risk associated with the actual operation. These include those with a family history of clotting, those who have experienced a previous clot and those with an underlying condition that predisposes them to clotting, such as cancer or HIV.’

He says other risks include obesity, prolonged immobility and age – ‘an unavoidable risk factor’. 

“While clotting is a natural process without which people could bleed to death in the event of injury, clotting excessively has dangerous implications for a person’s health.  A clot in the deep veins of the leg – known as a deep vein thrombosis (DVT) – is potentially fatal if it travels to the lungs causing a pulmonary embolism (PE)” says Rashem Mothilal, Medical Director, Sanofi South Africa 
While a DVT is commonly accompanied by pain, swelling and discolouration of the leg, and PE by chest pain, shortness of breath and the coughing up of blood, both can be asymptomatic. 

If any new leg or lung pain develops soon after surgery, the possibility of clotting should be considered.

‘It’s important for doctors to manage surgical patients in a way that ideally prevents excessive clotting or, failing that, addresses it effectively,’ says Dr Adler. 

‘In many cases, especially in high-risk patients undergoing aggressive surgery, there is a bleeding risk in addition to a clotting one. When taking measures to prevent clots, doctors need to balance those risks against those of bleeding.’

‘Various options exist for preventing clotting after surgery and different surgeries require different periods of prevention,’ he says.

‘Early mobilisation can help prevent clots and may suffice for low-risk procedures like minor ankle surgery,’ says Adler. ‘Compression stockings and calf pumps can be used to promote circulation. Both these measures constitute what is termed ‘mechanical prophylaxis’. 

‘If medication is required, options include a class of drugs known as the low-molecular-weight heparins (LMWHs), of which enoxaparin, an excellent agent given subcutaneously, is the most frequently used as a first-line treatment. 

‘There are also older medications, such as unfractionated heparin and warfarin, and several newer oral agents, such as rivaroxaban and dabigatran. 

‘For a small procedure, a course of enoxaparin while in hospital may suffice. But major hip or knee surgery and cancer surgery, for example, require two to four weeks of preventive treatment after the procedure,’ says Adler.

How long a patient will remain on blood-thinning medication depends on the location, severity of the clot as well as previous episodes and underlying medical issues. 

‘Three months is probably sufficient in the event of a clot following a minor ankle procedure, but lifelong anticoagulation may be required following a severe PE with previous episodes,’ Adler concludes.

In most people, the blood flow is well controlled as it takes oxygen and other nutrients to all parts of the body, with clotting only occurring when necessary - if there’s a wound. But there are those who bleed excessively - for example, those with an inherited condition called haemophilia in which the blood fails to clot and those who clot too much.

Lifestyle factors such as smoking and poor eating habits that play an important role in arterial disease are less important when it comes to clotting, a condition affecting the veins. Learn more about the dangers blood clots