Shoulder Pain: Causes, Swelling and When to Worry

How the shoulder works

The shoulder is the most mobile joint in the body. A shallow socket holds the ball of the upper arm bone, kept in place by the rotator cuff, four tendons and muscles that wrap around the joint, and by the labrum, a rim of cartilage. A fluid-filled sac, the subacromial bursa, cushions the cuff under the bony roof of the shoulder (the acromion). This mobility comes at the cost of stability, which is why tendon problems and dislocations are common.

Common causes of shoulder pain

Rotator cuff problems

Rotator cuff problems cause most shoulder pain in adults. The pain is felt on the outer side of the upper arm rather than at the top of the shoulder. Typically there is a "painful arc", pain when lifting the arm between about 60 and 120 degrees, and difficulty sleeping on that side. Tears become common with age and may cause weakness.

Frozen shoulder

Frozen shoulder (adhesive capsulitis) thickens and tightens the joint capsule. It goes through a painful "freezing" phase, a stiff "frozen" phase and a "thawing" phase over 1 to 3 years. People with diabetes and thyroid disease are at higher risk.

Referred pain

Pain felt in the shoulder can come from elsewhere:

• the neck (a pinched nerve)
• the heart, especially left shoulder or arm pain with chest symptoms
• the gallbladder or liver (right shoulder blade)
• the diaphragm, irritated by blood or air in the belly (shoulder-tip pain)
• the top of the lung (Pancoast tumor, rare)

Shoulder pain with swelling

True swelling of the shoulder is less common than pain alone, because the joint is deep under muscle. When it happens, consider:

• Bursitis: a swollen subacromial bursa, from overuse, inflammatory arthritis or gout.
• Injury: a dislocation, fracture or AC joint separation causes swelling and bruising within hours.
• Septic arthritis: a hot, swollen, very painful joint with fever. This is an emergency, especially in older adults, people with diabetes or after an injection.
• Inflammatory arthritis and gout or pseudogout: warm, swollen joint.
• Myositis: inflamed muscles cause aching and weakness in the shoulders and thighs, sometimes with mild swelling. Severe weakness or dark urine needs urgent assessment.
• Arm swelling: if the whole arm swells with shoulder pain, a clot in the arm vein or lymphedema is possible.

Shoulder pain then a lump in the upper arm

A common story is months of front-of-shoulder pain, followed by a sudden pop and a new bulge in the lower half of the upper arm. This is a typical rupture of the long head of the biceps tendon. The muscle slides down and bunches into a lump (the "Popeye sign"), often with bruising. It usually happens in people over 40 with existing tendon wear, and pain often improves after the rupture. Most people regain good function without surgery, though some lose a little strength in turning the forearm. It can coexist with a rotator cuff tear, so an assessment is worthwhile.

Other lumps around the shoulder and upper arm:

• Lipoma: a soft, painless, slow-growing fatty lump.
• Ganglion or AC joint cyst: a firm lump on top of the shoulder, sometimes with a rotator cuff tear.
• Bursitis: a soft, fluid-filled swelling.
• Sarcoma: rare. Features that need prompt imaging are a lump that is growing, larger than 5 cm (about the size of a golf ball), deep to the muscle, or painful.

How doctors diagnose shoulder pain

A doctor will ask which movements hurt, whether you had an injury, about night pain, neck symptoms and other joints. The exam tests range of movement, strength of each rotator cuff muscle and specific provocation tests. Imaging may include:

• X-ray: arthritis, fractures, dislocation, calcium deposits
• Ultrasound: rotator cuff tears, bursitis, biceps problems, lumps
• MRI: detailed view of tendons, labrum and soft tissue masses
• Blood tests: inflammation markers for polymyalgia rheumatica or infection, and a joint fluid test for suspected infection or gout

Treatment and home care

• Relative rest: avoid painful overhead activities, but keep the shoulder moving gently to prevent stiffness. Slings should be used only briefly unless prescribed.
• Ice or heat: ice for 15 minutes after activity for acute pain; heat for stiffness.
• Pain relief: acetaminophen (paracetamol) or an NSAID such as ibuprofen, following the label dose. Avoid NSAIDs if you have stomach ulcers, kidney disease or heart failure.
• Physical therapy: the main treatment for rotator cuff problems and frozen shoulder. Strengthening exercises over 6 to 12 weeks help most people.
• Steroid injections: short-term relief for bursitis, impingement and frozen shoulder.
• Surgery: for acute traumatic rotator cuff tears in active people, recurrent dislocation, severe arthritis (shoulder replacement) or failure of other treatment.
• Sleep position: sleep on the other side with a pillow supporting the painful arm.

Frequently asked questions

What causes shoulder pain without injury?

The most common causes are rotator cuff tendinopathy and impingement, frozen shoulder, arthritis and pain spreading from the neck. In people over 50, morning stiffness in both shoulders may be polymyalgia rheumatica. Left shoulder pain with chest symptoms can be heart-related and needs urgent care.

Why is my shoulder painful and swollen?

Shoulder swelling usually means bursitis, an injury such as a dislocation or fracture, inflammatory arthritis, gout or infection. A hot, red, swollen shoulder with fever needs same-day care because joint infection can damage the joint quickly.

What is a sudden lump in my upper arm after shoulder pain?

A sudden bulge in the lower upper arm after months of shoulder pain, often after a pop, is typically a ruptured long head of the biceps tendon. Pain often improves afterward. See a doctor to confirm it and check for a rotator cuff tear. A lump that grows steadily needs imaging.

Why does my shoulder hurt more at night?

Night pain is typical of rotator cuff problems and frozen shoulder. Lying on the affected side compresses the inflamed tendons, and lying flat changes the position of the joint. Sleeping on the other side with a pillow hugging the arm can help.

When should I worry about shoulder pain?

Get emergency care for shoulder pain with chest pain, breathlessness or sweating, a deformed shoulder after a fall, or a hot, swollen joint with fever. See a doctor for pain lasting over 2 weeks, weakness, numbness or a growing lump.