The shoulder is a highly mobile ball-and-socket joint, allowing the arm an extensive range of motion that comes at the cost of stability. This structural trade-off means the joint is susceptible to a variety of mechanical injuries and degenerative changes. Left shoulder pain, specifically, presents a diagnostic challenge because its origin can be local, stemming from the joint itself, or distant, referred from structures in the chest or abdomen. Understanding the potential source is the first step toward appropriate care for the discomfort.
Common Musculoskeletal Injuries
The majority of left shoulder complaints arise from the overuse or acute injury of the surrounding soft tissues. The rotator cuff, a group of four muscles and their tendons, is the most frequently involved structure, responsible for stabilizing the upper arm bone within the shoulder socket and initiating movement. A rotator cuff tear can range from a minor strain to a complete disruption of the tendon, causing sharp pain and weakness, especially when lifting the arm overhead or reaching behind the back. This pain often worsens at night, particularly when lying on the affected side.
Tendinitis, or inflammation of a tendon, commonly affects the supraspinatus tendon within the rotator cuff or the long head of the biceps tendon. Repetitive motions, such as those involved in swimming or painting, can cause friction and irritation, leading to acute tendinitis. The pain is typically localized to the front or side of the shoulder and is aggravated by specific movements that load the inflamed tendon. Bursitis, the inflammation of the bursa (a small, fluid-filled sac that cushions bone and soft tissues), often accompanies tendinitis.
The subacromial bursa, located just beneath the bony arch of the shoulder, is most often affected, and its inflammation is frequently associated with shoulder impingement. Impingement occurs when the bursa and rotator cuff tendons get pinched between the upper arm bone and the acromion when the arm is raised, causing a painful arc of motion. Bursitis pain is often described as a deep ache in the shoulder area that can radiate toward the neck or down the arm.
Chronic Structural Issues and Nerve Impingement
Pain that persists over a long period often points toward degenerative changes within the joint or nerve compression originating outside the shoulder. Osteoarthritis, the “wear-and-tear” form of arthritis, occurs when the protective cartilage on the ends of the bones, particularly in the acromioclavicular joint, wears down. This loss of cartilage results in bone-on-bone friction, causing pain, stiffness, and a noticeable grinding or clicking sensation with movement. The pain from osteoarthritis tends to develop slowly and worsens over time.
Another condition marked by progressive stiffness is adhesive capsulitis, commonly known as frozen shoulder. This occurs when the connective tissue capsule surrounding the shoulder joint thickens and tightens, severely restricting range of motion. People with diabetes or those who have had a shoulder immobilized for a period are at higher risk for developing this condition.
Pain can also originate from the cervical spine in a condition called cervical radiculopathy. This happens when a nerve root is compressed as it exits the spinal cord, often due to a herniated disc or degenerative changes. Because the nerves that supply the shoulder and arm originate in the neck, this compression causes pain that radiates down the nerve pathway into the shoulder and arm. The pain is typically described as sharp or burning and can be accompanied by numbness, tingling, or weakness in the arm or hand.
Referred Pain from Internal Organs
The left shoulder is a significant site for referred pain, meaning the sensation of pain is felt here but originates from a distant internal organ. The most concerning source of referred left shoulder pain is the heart, as a heart attack (myocardial infarction) or angina (chest pain from reduced blood flow) can manifest this way.
In cardiac events, the pain is often felt across the left chest and jaw, but it can radiate down the medial aspect of the left arm and into the shoulder. This referred pain is a symptom, particularly when accompanied by shortness of breath, nausea, or sweating. The diaphragm, the muscle separating the chest and abdomen, is another source of referred pain via the phrenic nerve, which connects to the same spinal segments that supply sensation to the shoulder area.
Irritation of the left side of the diaphragm can cause pain at the tip of the left shoulder, a sign known as Kehr’s sign. This irritation can be caused by conditions in the abdomen, such as a ruptured spleen or pancreatitis, where internal bleeding or inflammation contacts the underside of the diaphragm. The pain is usually poorly localized and described as a deep, dull, or vague ache, distinct from the sharp, mechanical pain of a joint injury.
When Immediate Medical Attention is Necessary
While most left shoulder pain is musculoskeletal and not life-threatening, certain accompanying symptoms require immediate emergency evaluation. A sudden onset of severe, crushing chest pain or pressure that radiates to the left shoulder, neck, or jaw is a medical emergency that may signal a cardiac event.
Severe pain following a significant traumatic injury, like a fall, which results in a visible deformity or the complete inability to move the arm, suggests a fracture or dislocation. Any shoulder pain combined with systemic signs, such as a high fever, redness, and swelling around the joint, requires prompt attention to rule out a serious infection. A sudden loss of sensation, profound weakness, or numbness and tingling extending into the arm and hand can also indicate acute nerve or vascular compromise.