In this page we see what happens when the DEEP VALVES of the leg fail.

The blood is still pumped up both deep and superficial vein systems on movement (PUMPING).

However when the leg RELAXES, the pumping stops and the blood starts to flow down both deep and superficial vein systems as before.

In the superficial system this back flow of blood causes the valves to snap shut, stopping the blood from flowing back down the leg.

BUT in the deep system, the valves are not working.

Therefore in this case, the blood rushes back from above and gushes into the leg. The blood HITS the vein wall and the smaller veins feeding into the main veins - This causes INFLAMMATION of the tissues surrounding the DEEP veins