How long it takes for a knee wound to scab off depends on the severity of the wound itself and the entire treatment process. If the wound is a superficial skin abrasion and is disinfected to avoid infection, and the knee joint is braked to promote healing as much as possible, it will fall off on its own in about 10-15 days. During this process, be careful not to pick at it yourself. However, if the skin damage is more serious and the area is larger, some even have muscle leakage, the scab will not be able to fall off by itself. It is necessary to go through the hospital to clear the wound and trim the scabbed part to expose the fresh tissue, and further consider the surgical treatment of skin implantation, and to regularly observe the changes of the whole scab, there may be a situation of infection under the scab.