The left back and shoulder region includes the glenohumeral joint, the shoulder blade (scapula), the upper section of the thoracic spine with their corresponding ribs, and various muscles, tendons, ligaments and nerves. Pain in the left back and posterior shoulder is caused by injuries, poor posture, arthritis and congenital anomalies such as scoliosis.
Muscle Strain
Muscle strains prove a common cause of pain in the left upper back and posterior shoulder. Muscles become strained when they are stretched beyond normal limits, causing the muscle fibers and small blood vessels to become partially ripped, or when they are violently contused from a blow, causing minor crushing of the fibers and blood vessels. Both types of strains result in inflammation, redness, soreness and sometimes discoloration/bruising. The muscles most commonly strained in this region include the rhomboids, levator scapulae, supraspinatus, posterior deltoids, trapezius and left paraspinal group. The rotator cuff tendons, which surround the shoulder can also become strained and create pain in the shoulder blade area.
Joint Sprains
Joint sprains are another common cause of upper back and posterior shoulder pain, and usually the most painful. The joints most commonly misaligned or "jammed" in this region include the left thoracic facet joints and the costovertebral joints (where the ribs attach to the spine). This type of joint pain feels sharp and stabbing in nature. The glenohumeral (shoulder proper) joint can become dislocated or compacted, which would create posterior shoulder and upper back pain of a deep and achy nature. The labrum (cartilaginous shock absorber) of the glenohumeral joint can become ripped, which would create severe, deep pain, especially with movement.
Degenerative and Inflammatory Arthritis
Degenerative arthritis, or osteoarthritis, can affect the left glenohumeral joint creating a grinding feeling and an achy stiffness. Degeneration and bone spur formation can also occur in the thoracic spine, which can sometimes irritate the thoracic nerve roots and cause a tingling or burning pain. Inflammatory conditions, such as rheumatoid arthritis, can also affect the glenohumeral joint and thoracic spine. If the capsule of the glenohumeral becomes inflamed, then a condition called "frozen shoulder" might result, which would create some posterior shoulder and upper back pain.
Scoliosis
Scoliosis is an abnormal lateral curvature of the spine, which most commonly affects the thoracic spine, ribs and scapula. If the curvature is dramatic enough, thoracic and costovertebral joints become chronically sprained and all the related muscles become chronically strained and sore.
Serious, but Rare Causes
Primary cancer or metastasis can affect the thoracic and posterior 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 addition, heart attacks and angina pain can be perceived in the left back and posterior shoulder region in some cases, but anterior chest pain and weakness or pain down the left arm are more characteristic symptoms and areas of pain.
References
- "Orthopedic Physical Assessment"; David J. Magee, Ph.D.; 1997
- "Atlas of Human Anatomy"; Frank H. Netter, M.D.; 1994
- "Chiropractic Management of Spine Related Disorders"; Meridel I. Gatterman, D.C.; 2002
- American Academy of Family Physicians: Shoulder Diagnoses
- Spine Universe: Take Charge of Your Upper Back Pain
