Pain within the left posterior back may be caused by muscle strain, lumbar disc herniation and urological diseases, etc., and you should consult a doctor in time to find out the cause. Specifically as follows: 1. Muscle strain. If the patient’s left lumbar muscles for a long time or frequent bending labor, then it may lead to muscle strain at the left lower back, which will lead to the patient’s left lower back pain. 2. Lumbar disc herniation. When the patient suffers from lumbar disc herniation, the protruding disc will stimulate the nerves in the spinal canal, so it will also cause the patient to experience pain in the left posterior lumbar region. 3. Urinary diseases. When the patient suffers from left kidney stones or left ureteral stones, it will also stimulate the patient to have pain in the left posterior lumbar. Therefore, there are many causes of left posterior intramedullary pain, when the patient has left posterior intramedullary pain, should consult the doctor in time to find out the cause of the disease, and if necessary, give the appropriate treatment, so as not to delay the condition.