The left back and shoulder region includes many structures that can cause pain, including your shoulder joint, ribs, shoulder blade and various muscles, tendons, ligaments and nerves. Pain in the left back and posterior shoulder can caused by injuries, including joint sprains and muscle strains. Pain in this area may also be caused by medical conditions such as arthritis or cancer. See your doctor for an accurate diagnosis if you experience pain in these areas.
Muscle strains commonly cause pain in the left back and shoulder. Muscles are strained when they are stretched beyond normal limits, causing the muscle fibers to tear slightly. Muscle injury can also occur with direct trauma to the back and shoulder. Both types of strains may cause inflammation, redness, soreness and or bruising. Trigger points -- or knots -- may develop in these muscles, also contributing to this pain. Moist heat, massage, gentle stretching and temporary rest may help decrease pain caused by muscle strains.
Joint sprains are another common cause of back and shoulder pain. The joints in your back that are most commonly affected are between the bones in your spine, and the areas where your ribs attach to your spine. Pain caused by sprains of these joints is typically sharp and stabbing, and worsens when you move.
Your shoulder joint can also be sprained, causing shoulder and upper back pain. This pain is often deep or achy at rest, and sharp with movement of your arm. It may also wake you at night. Joint sprains can be often be treated with moist heat, antiinflammatory medications, temporary rest and gentle stretching.
Osteoarthritis, caused by breakdown of the padding between bones in your joints, can cause pain in your shoulder and the left side of your back. This pain is often sharp with arm movement, and may cause aching while you are resting or attempting to sleep. Osteoarthritis may also develop in the upper back between the bones of your spine. This condition typically starts gradually and worsens with time. Although osteoarthritis can affect multiple joints, it frequently affects one side of the body.
Rheumatoid arthritis -- a condition that causes your body to mistakenly attack healthy joint tissue -- can also cause left shoulder and back pain. Unlike osteoarthritis, this condition typically affects multiple joints of your body at the same time. Pain caused by both types of arthritis may decrease with temporary rest, antiinflammatory medications and moist heat. In severe cases, surgery may be required.
Primary cancer or metastasis can affect the back and shoulder region and create pain, but this proves very rare. Lung cancer can refer pain to the left upper back, but only in rare instances. In some cases, a heart attack may cause pain in the left back and shoulder region. Seek immediate medical attention if you experience this pain along with chest pain or pressure, pain in your arm or jaw, shortness of breath, nausea or vomiting or sudden fatigue.