Possible causes of left-sided back pain include lumbar muscle strain, lumbar transverse syndrome, lumbar intervertebral disc herniation, and urological diseases. 1. Lumbar muscle strain: lumbar muscle strain is often seen in long-term weight-bearing manual laborers, the patient is mostly manifested as long-term chronic lumbar pain or soreness, and lumbar muscle spasms can be found when pressing, but there is no lower extremity sensory abnormalities, muscle weakness and other nerve compression manifestations. 2. Lumbar three transverse processes syndrome: lumbar three vertebrae transverse processes are the longest one in the lumbar vertebrae, with many tendon ligaments attached, repeated bending is easy to cause friction between tendon ligaments and transverse processes to form chronic inflammation and cause lumbar pain, which mainly manifests itself as chronic lumbar soreness or hidden pain, and pain at the transverse processes of the third lumbar vertebrae on compression. 3. Lumbar intervertebral disc herniation: lumbar intervertebral disc herniation can cause lumbar pain when it stimulates the sinusoidal nerve behind the annulus fibrosus, which can be manifested as lumbar soreness, discomfort and vague pain in the early stage, and the pain becomes more and more obvious with the gradual progress of the disease, and can cause radiating pain in the lower limb nerves when it oppresses the nerve root of lumbar spine. 4. Urological diseases: such as kidney stones, ureteral stones can cause lumbar pain, or kidney tumor, kidney tumor gradually increase can pull the renal peritoneum or surrounding tissues and cause lumbar pain, including renal cancer, renal malformation tumor, renal angiomyolipoma and so on. In addition to the above diseases, lumbar trauma, chronic inflammation of supraspinatus ligament or tendon ligament, osteoporotic fracture of lumbar vertebrae can also cause left-sided lumbar pain, and it is recommended that patients go to the hospital as soon as possible, and identify the cause of the disease in time and then be treated accordingly.