Pain inside the left rear shoulder blade especially at night may be caused by infraspinatus strain, fasciitis or cervical spondylosis. 1. Infraspinatus strain: Infraspinatus is a triangular-shaped muscle at the infraspinatus fossa of the scapula at the back of the shoulder, which enables the upper arm to rotate externally. Its injury is mostly caused by chronic strain without obvious trauma history, such as excessive exercise, labor, etc., which can cause soreness and heaviness at the back of the shoulder, and restriction of upper limb activities. 2. Fasciitis: Fasciitis of the shoulder and neck can also occur in the back of the shoulder and neck area of extensive pain, soreness, numbness, limited movement and other symptoms, for a kind of aseptic inflammation of the fascia, which can be caused by the cold, long-term strain, immune factors. 3. Cervical spondylosis: it is a general term for cervical osteoarthritis, hyperplastic cervical spondylitis, cervical nerve root syndrome, cervical disc herniation, which can be caused by long-term strain on the cervical vertebrae and osteophytes. If cervical spondylosis leads to irritation of the peripheral nerves, it may cause pain in the area innervated by that nerve. In order to avoid delays, please go to the hospital if you have pain inside the left posterior scapula, especially at night, and go through a systematic examination to clarify the cause of the disease and treat the cause.