There are several reasons for the long bag on the back of the foot: 1, the most common tendon sheath cyst in daily life, the tendon sheath around the back of the foot has mucus appearing due to long-term friction and tendon friction, and its treatment is mainly surgical removal. 2, lipoma refers to the accumulation of fat, forming a bulge with a smooth surface and good mobility, and there is no obvious pressure and pain when pressing the bulge. Lipoma is benign and does not need to be treated if it does not obviously affect normal life, but if it presses on the nerve, it needs to be removed surgically. 3, sebaceous cysts, sebaceous cysts are sebaceous glands secrete sweat, due to sebaceous duct obstruction can not be discharged, long-term accumulation will lead to sebaceous cysts, thus forming a bulge, the solution is to carry out surgery. In short, the back of the foot long bag to identify the cause, and then according to the cause of symptomatic treatment.