The venous drainage of the lower limb is of enormous clinical and surgical significance. The venous blood of the lower limb is emptied against gravity. Yet, a number of variables help ease its drainage (vide infra). If these variables don’t assist the drainage, the stagnation of venous blood in the superficial veins cause varicose veins and in the deep veins result in deep vein thrombosis.
Variables Helping the Venous Drainage of the Lower Limb.
- The contraction of the calf muscles (main variable) contracts the blood upward along the deep veins. Notice the calf muscles serve as “calf pump (peripheral heart)”.
- Carried pulsations from the adjacent arteries.
- Presence of valves in the perforating veins prevents the reflux of blood into the superficial veins during contraction of the calf muscles.
- Presence of valves in the deep veins supports the column of blood and keeps unidirectional upward flow of the blood.
- Negative intrathoracic pressure becomes more negative during inspiration and yawning.
- In recumbent position, the “vis-a-tergo” is generated by the contraction of the heart and suction action of the diaphragm.
Categorization of The Veins
The veins of the lower limb are classified anatomically and functionally into the following 3 types:
- Superficial veins.
- Deep veins.
- Perforating veins.
The superficial veins basically contain the great and small saphenous veins, which represent pre-axial and post-axial veinsof the developing lower limb, respectively. They be located in the superficial fascia on the surface of the deep fascia and are thick walled mainly because of the presence of the smooth muscle. They possess valves, that are more numerous in their own distal part than in the proximal part. A large percentage of their blood is emptied into the deep veins via the perforating veins.
The deep veins contain the anterior tibial, posterior tibial, peroneal, popliteal, and femoral veins. They’re surrounded and supported by the strong muscles. They possess more valves. They accompany the arteries. Below the knee, they’re ordered as a set of venae comitantes along the arteries but above the knee, they create single large vein. All the veins from muscles draining into deep veins also possess valves with the exception of those in the soleus where they’re ordered in the create of venous sinuses (soleal sinuses).
The perforating veins (perforators) pierce the deep fascia and attach the superficial veins with the deep veins. Their valves allow only 1-way flow of the blood, from the superficial veins to the deep veins. There are about 5 perforators along the great saphenous vein, and 1 perforator along the small saphenous vein.
The venous blood of the thigh and leg flows from the superficial to deep veins (being steered by the valves of perforating veins). Yet, in foot, the venous blood flows from the deep veins (in the sole) to the superficial veins (on the dorsum of the foot).