The presence of veins at the knuckles may be caused by physiological reasons such as thinness or pathological reasons such as thrombosis of the veins of the upper extremities and venous valve dysfunction. 1. Physiological reasons: If the body type is thin and the skin of the fingers is fair, it can cause the fat content of the hand to decrease, resulting in the veins showing obviously, which is manifested as the phenomenon of bruises at the knuckles. 2. Pathological reasons: if the upper extremity venous thrombosis and other factors, can lead to venous return obstruction, and then cause the expansion of blood vessels at the knuckles; such as upper extremity venous valve dysfunction can lead to varicose veins of the upper extremity, there may be the phenomenon of blood vessel expansion at the knuckles, which is manifested as bruises at the knuckles. If there are other uncomfortable symptoms, you need to go to the hospital in time, to clarify the cause of the disease, under the guidance of the doctor for standardized treatment.