Peritonitis is defined as inflammation of the peritoneum. The inflammatory response involves vasodilation, exudation of protein-rich fluid, cellular infiltration, pain and, chronically, formation of fibrous adhesion. The disease can be classified into primary and secondary cases.
It begins in the venous plexus along the medial side of the foot, and it runs up the medial side of the leg and knee, alongside the saphenous nerve. In the thigh, the long saphenous vein continues up the medial surface, accompanying the medial femoral cutaneous nerve.
The small saphenous vein pierces the popliteal fascia of the popliteal fossa to enter the diamond, and empty into the popliteal vein. In the popliteal fossa, the deepest structure is the popliteal artery. It is a continuation of the femoral artery, and travels into the leg to supply it with blood.