**2. Chronic venous disorders**

Chronic venous disorder occurs due to improper functioning of venous system, especially in the lower extremity, which makes it difficult for the venous reflux to return to the heart from the legs [7, 8]. Patients suffering from such disorders have poor quality of life due to consistent pain, limited mobility, physical function, depression, social isolation and high treatment cost [9]. It has been estimated that 1% of the general population (age group: 18–64) is suffering from chronic venous disorders [10]. This rate is further increased to 4% in people over the age of 65 [11]. Furthermore, it has been anticipated that the rate will increase significantly in future due to changing lifestyle and the growing aging population.

Chronic venous disorders such as varicose veins, deep vein thrombosis, oedema, ulcers, lymphoedema, etc., happen primarily in lower limbs when the veins are not able to pump enough blood back to the heart. This improper functioning is the result of venous hypertension [12]. In most cases, venous hypertension is caused by reflux through incompetent valves, but other causes include venous outflow obstruction and failure of the calf-muscle pump owing to obesity or leg immobility. Deep vein thrombosis is the condition where the blood clots (thrombus) inside the veins, which obstructs the smooth flow of blood toward the heart [13]. The blood trying to pass through these blocked veins can increase the blood pressure in the vein, which, in turn, will overload the valves. This can lead to damage to the valves, which can further worsen the problem as these incompetent values will not be able to prevent backflow of blood. This may result in pooling of blood in the surrounding tissues, which will cause swelling (also termed as oedema). Over time, this can worsen the condition and result in venous ulceration (Figure 1).

**Figure 1.** Different forms of chronic venous symptoms in lower leg (varicose veins, venous oedema and venous leg ulcers; from left to right)
