Thrombosis
A particularly dangerous complication of pain in the hollow of the knee is thrombotic vascular occlusion of an arterial or venous nature. In most cases, this is a thrombus, i.e. a blood clot that attaches itself to narrow points in the venous system. Such a thrombus has no contact with the vessel wall, and is also called a red (because it is rich in blood platelets) thrombus.
The basis is arteriosclerosis, i.e. hardening of the blood vessels, in combination with little movement, or a narrowing of the vessel. But smoking, insufficient fluid intake, and the contraceptive pill (see: Risk of thrombosis with the pill) can also promote thrombosis. A thrombus also develops when a vessel is injured, when the opened vessel site is to be closed again.
Blood platelets are always circulating in the blood for this purpose. These platelets attach themselves to certain factors that are released when a vessel is injured. This physiological thrombus is known as a white thrombus, or coagulation thrombus.
A thrombosis displaces the vessel, causes blood congestion and makes it swell. In addition to overheating and reddening of the congested tissue, this also leads to pain due to the increased pressure. An acute thrombosis usually develops after long immobilization of the foot, for example on long flights, or after application of a plaster cast.A thrombus can become loose and be flushed with the blood flow to the lungs, where it then separates sections of the lung from the blood supply.
This condition, known as pulmonary embolism, is an acute emergency and requires immediate emergency medical attention, otherwise parts of the lung die. The popliteal artery can also be displaced by a thrombus, which manifests itself as cold, pulseless and numbness in the foot and lower leg. Here the thrombus is not flushed in the direction of the heart, but instead displaces the increasingly thinner vessels that extend in the direction of the foot. One can imagine it rolling along an increasingly narrow tube like a ball: At a certain point it gets stuck and no more blood can pass. Here too, emergency medical care is indicated simply because of the pain.
