There are many factors that cause decubitus ulcers. First of all, considering the mechanical factors, there are three main physical mechanical factors that cause pressure sores, as follows: 1. pressure, when a bedridden patient does not change his or her position for a long time and the local tissues are under continuous pressure for more than two hours, it can cause irreversible tissue damage; 2. friction, improper placement of the deck liner, unevenness or some debris inside the cast, when the patient is bedridden for a long time or in a wheelchair, the skin can The skin can be rubbed by the retrograde resistance of the surface, causing decubitus ulcers; 3. Shear force, closely related to body position, is generated by the progressive relative friction and pressure summed up by sliding between two adjacent tissue surfaces. Secondly, physicochemical factors, stimulation can cause decubitus ulcers. Long-term pressure on the skin is often stimulated by sweat, urine, fecal fluid various exudates and drainage fluid, the sebaceous layer is damaged, and skin tissue damage, breakage and infection induce decubitus ulcers. Systemic nutrition is very important, and pressure sores are likely to occur in bedridden patients, such as elderly patients who are malnourished, febrile and comatose for a long time and unable to eat, and paralyzed patients with poor nutrition. Finally patients with restrictions, such as paraplegics and post-operative fracture patients, with improper padding for fractures, plaster bandages, deck and traction elasticity, can cause localized decubitus ulcers.