Leg Venous System: Anatomy, Function and Diseases

What Is the Leg Venous System?

The leg venous system is the network of veins in the legs responsible for returning deoxygenated blood and metabolic waste products from the leg tissues back to the heart. Unlike the arterial system, which transports blood away from the heart, the venous system must work against gravity – especially when standing upright or walking.

The leg venous system is of great clinical importance, as it is commonly affected by conditions such as varicose veins, deep vein thrombosis (DVT), and chronic venous insufficiency (CVI).

Anatomy of the Leg Venous System

The leg venous system is divided into three functional components:

1. Superficial Venous System (Epifascial System)

The superficial venous system lies directly beneath the skin, above the muscular fascia. It includes two main trunks:

• Great saphenous vein (Vena saphena magna): Runs along the inner side of the leg from the dorsum of the foot to the groin, where it drains into the deep femoral vein. It is the longest vein in the human body.
• Small saphenous vein (Vena saphena parva): Runs along the back of the lower leg and drains into the deep popliteal vein behind the knee.

2. Deep Venous System (Subfascial System)

The deep venous system lies beneath the muscular fascia and carries the majority of venous blood (approximately 80–90%) back to the heart. Key veins include:

• Popliteal vein: Located behind the knee
• Femoral vein: Located in the thigh
• Iliac vein: Located in the pelvis
• Anterior and posterior tibial veins: Located in the lower leg

3. Perforating Veins (Communicating Veins)

Perforating veins are short connecting vessels that link the superficial and deep venous systems. They penetrate (Latin: perforare) the muscular fascia and enable blood to transfer from the superficial to the deep system. Their valves ensure that blood flows in only one direction – from outside to inside and from below upward.

Venous Valves – the Anti-Reflux Mechanism

A key feature of the leg venous system is the venous valves (valvulae venosae). These pocket-shaped structures open when blood flows toward the heart and close when backflow is imminent. This prevents blood from flowing back down due to gravity.

When venous valves become incompetent or fail, venous reflux occurs – the pathological backflow of blood. This is a primary cause of varicose veins and chronic venous insufficiency.

How Venous Return Works

Since blood in the leg veins must travel against gravity toward the heart, several mechanisms facilitate this process:

• Muscle pump: Contraction of the calf muscles during walking and movement squeezes blood upward through the veins. This is commonly referred to as the calf muscle pump.
• Venous valves: Prevent backflow of blood between pump contractions.
• Respiratory pressure changes: Inhalation creates negative pressure in the thoracic cavity, drawing venous blood upward.
• Residual cardiac pressure: A small proportion of venous return is driven by residual pressure from the heart.

Common Diseases of the Leg Venous System

Varicose Veins

Varicose veins are permanently dilated, tortuous superficial veins. They develop due to incompetent venous valves and primarily affect the great saphenous vein and its branches. Symptoms include visibly protruding veins, heaviness, pain, and swelling in the legs.

Deep Vein Thrombosis (DVT)

Deep vein thrombosis occurs when a blood clot (thrombus) forms in the deep venous system, most commonly in the calf or thigh. It can be life-threatening if the clot detaches and causes a pulmonary embolism.

Chronic Venous Insufficiency (CVI)

Chronic venous insufficiency describes a long-term impairment of venous return. It leads to congestion-related conditions such as edema, skin changes, and in advanced stages to venous leg ulcers (venous ulcus cruris).

Spider Veins (Telangiectasias)

Spider veins are fine, web-like visible capillaries just beneath the skin surface. They are generally harmless but can be a cosmetic concern and may indicate underlying venous disease.

Diagnosis of Leg Vein Disorders

The most important diagnostic method for assessing the leg venous system is duplex ultrasound (color-coded Doppler ultrasonography). It allows visualization of blood flow, valve function, and thromboses without radiation exposure. In specific cases, phlebography (X-ray with contrast agent) or MR angiography may also be used.

Treatment and Prevention

Treatment of leg vein disorders depends on the type and severity of the condition:

• Compression therapy: Compression stockings or bandages support venous return and relieve symptoms.
• Exercise and muscle training: Regular physical activity, especially walking, swimming, and cycling, activates the calf muscle pump.
• Sclerotherapy: Injection of a sclerosing agent to close varicose veins and spider veins.
• Surgical procedures: Removal (stripping) or thermal ablation (laser, radiofrequency) of affected vein segments.
• Anticoagulation: In deep vein thrombosis, blood-thinning medications (anticoagulants) are used to prevent clot growth and reduce the risk of pulmonary embolism.

References

1. Rabe, E. et al. - Guidelines on the Diagnosis and Treatment of Varicose Veins. Deutsche Gesellschaft fuer Phlebologie (2022). Available at: https://www.awmf.org
2. Nicolaides, A. N. et al. - Investigation of Chronic Venous Insufficiency: A Consensus Statement. Circulation. 2000;102(20):E126-63. Available at: https://www.ahajournals.org
3. Eberhardt, R. T. and Raffetto, J. D. - Chronic Venous Insufficiency. Circulation. 2014;130(4):333-346. Available at: https://www.ahajournals.org