The concavity in the middle of the back of the waist may be caused by normal physiological curvature, spinal deformity, old injury and other pathological reasons. 1. Normal physiological curvature: the normal human body due to the lumbar spine is anteriorly convex, in the human body lumbar back side can appear in the middle of the concave in, generally speaking, women are more obvious than men, belong to the human body’s normal physiological phenomenon. 2. Spinal deformity: such as scoliosis and other deformities, the patient will be due to the lumbar spine forward protruding deformity, the back of the waist in the middle of the concave phenomenon. 3. Stale injury: due to trauma and other reasons lead to local fracture, after the fracture healing, the local soft tissue or muscle contracture, the patient may appear in the middle of the lumbar back concave in. There may be other reasons for the concavity in the middle of the back, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.