Introduction
This topic covers ulcers and fistulas: what they are, what causes them, and how they are classified. Ulcers and fistulas are common problems in surgical practice and are often the end result of an earlier disease, so the exam answer should link the local lesion to its underlying cause. Gangrene, venous insufficiency and varicose veins, thrombophlebitis and osteomyelitis are covered in neighbouring topics and are mentioned here only where they explain an ulcer or fistula.
Ulcers: definition and general mechanism
An ulcer is a local defect of the skin or a mucous membrane caused by loss of tissue after necrosis of damaged or inflamed tissue. Unlike an acute wound, it does not heal in the normal sequence of repair and tends to persist, usually for more than six weeks. The basic problem is an imbalance between tissue injury and repair. Most chronic ulcers occur where local blood supply is poor, where pressure or friction is repeated, or where sensation is lost, so that minor trauma goes unnoticed.