Causes
The 2 main causes are embolism and thrombosis. Other causes to consider are trauma and dissection:
Embolism
An embolus is a piece of blood clot or atheroma which moves from one place in the arterial tree to another. When it lodges in the smaller arteries, it causes ischaemia of the tissues supplied by that artery. The commonest source of an embolus is the heart - either due to valve disease (as in rheumatic heart disease) or due to abnormal heart rhythms (such as atrial fibrillation). The embolus may also travel to the brain causing a stroke or TIA. If it travels to the arteries supplying the gut, the bowel may die.
Thrombosis
This may result from reasons involving the arterial wall, the flow of blood or the constituents of the blood. If an atheromatous plaque cracks, a blood clot may form. If the blood flow is very slow for some reason, again the blood may clot - this is more of a problem in the venous circulation and leads to deep vein thrombosis. Changes in blood constituents refers to increases in the cells (e.g. polycythaemia, leukaemia, thrombocytosis etc.) or increased viscosity of the plasma (e.g. in myeloma and profound dehydration) which make the blood 'thicker' and more likely to clot.
A past history of intermittent claudication is more likely to indicate previous arterial disease and therefore the greater likelihood of thrombosis.
Trauma
This may be due to blunt trauma to the artery causing it to block or the artery may be divided completely - the ends tend to retract and clot. Investigation and treatment are essential.
Dissection
This is uncommon. The artery wall is damaged and allows the blood to flow in a channel in the wall itself. This can cause the artery to clot. It can occur following needle insertion into the artery for angiograms.