Shoulder Pain: Possible Causes

Shoulder pain possible causes are more varied than most people realize. The shoulder is the most mobile joint in the human body — capable of movement in virtually every plane — but that mobility comes at a cost. It is also one of the most inherently unstable joints, relying heavily on muscles, tendons, and soft tissue structures for stability. This combination makes it vulnerable to injury, overuse, and degeneration across all age groups. Understanding the specific cause of shoulder pain matters because different conditions require fundamentally different treatments — and some presentations signal urgent medical problems that cannot wait.

The Shoulder: Why It’s Built for Mobility but Vulnerable to Pain

The shoulder is not a single joint but a complex of four articulations working together: the glenohumeral joint (the main ball-and-socket between the humeral head and the glenoid of the scapula), the acromioclavicular (AC) joint (between the clavicle and the acromion), the sternoclavicular joint (where the clavicle meets the sternum), and the scapulothoracic articulation (the gliding of the scapula over the rib cage).

The glenohumeral joint provides the greatest range of motion of any joint in the body. Because the glenoid socket is relatively shallow — sometimes described as a golf ball sitting on a tee — stability depends almost entirely on surrounding soft tissue structures: the rotator cuff muscles, the glenohumeral ligaments, the joint capsule, and the fibrocartilage labrum that deepens the socket. The rotator cuff consists of four muscles known by the acronym SITS: Supraspinatus, Infraspinatus, Teres minor, and Subscapularis. Together they compress and center the humeral head in the glenoid during arm movement. The supraspinatus — which passes through the narrow subacromial space between the humeral head and the overlying acromion — is the most commonly injured.

Shoulder Pain Possible Causes: Rotator Cuff Conditions

Rotator Cuff Tendinopathy and Impingement Syndrome

Rotator cuff tendinopathy — degeneration or irritation of the rotator cuff tendons, particularly the supraspinatus — is the single most common diagnosis in adults presenting with shoulder pain. It often coexists with subacromial impingement, where the rotator cuff tendons are mechanically compressed between the humeral head and the acromion during arm elevation.

The hallmark symptom is a painful arc: pain that occurs during arm elevation roughly between 60 and 120 degrees (the range during which the supraspinatus is passing beneath the acromion) and then resolves as the arm reaches overhead. The pain is typically felt in the outer shoulder or upper arm rather than at the joint itself. Night pain — particularly when lying on the affected shoulder — is a consistent and often disabling feature. Activities involving reaching overhead, reaching behind the back, or lifting with the arm away from the body reproduce the pain.

Risk factors include age-related tendon degeneration (the condition becomes more prevalent from the 40s onward), overhead occupational or recreational activities (painters, swimmers, tennis players, overhead press athletes), and poor scapular control. Clinical examination typically shows a positive Neer impingement sign (pain on passive forward elevation with the arm internally rotated) and a positive Hawkins-Kennedy test (pain on forced internal rotation at 90 degrees of forward elevation), though neither test alone is diagnostic — they are screening tools that guide further assessment.

The majority of rotator cuff tendinopathy responds to a combination of activity modification, physiotherapy focusing on rotator cuff and scapular strengthening, and short-term NSAIDs. Subacromial corticosteroid injection provides effective short-term (4–8 weeks) pain relief that facilitates engagement with rehabilitation but does not alter the underlying tendon pathology. Repeated injections should be limited given evidence of potential tendon damage with frequent corticosteroid exposure.

Rotator Cuff Tear (Partial and Full-Thickness)

Rotator cuff tears range from partial-thickness fraying to complete full-thickness disruption of one or more tendons. They can be acute — occurring with a sudden forceful movement, fall on an outstretched arm, or direct trauma — or degenerative, developing gradually as tendons weaken with age.

Acute tears present with sudden severe pain, often with an audible or palpable pop, followed by significant weakness in arm elevation and external rotation. Degenerative tears often have a more insidious onset, with progressive pain and weakness developing over months to years, sometimes following a period of tendinopathy. Night pain is prominent in both types.

An important clinical reality: full-thickness rotator cuff tears are present on MRI or ultrasound in approximately 20% of adults over 60 and 50% of adults over 80, with many being entirely asymptomatic. This means that imaging findings of a “rotator cuff tear” must be interpreted in clinical context — the tear may not be the cause of the current symptoms. Conversely, large or massive tears (involving multiple tendons) in active individuals are more likely to be clinically significant.

Treatment depends on tear size, patient age, activity demands, and degree of functional limitation. Physiotherapy rehabilitation is effective for many partial tears and smaller full-thickness tears in older, less active patients. Surgical repair (arthroscopic or mini-open) is typically recommended for acute full-thickness tears in active individuals, large or massive tears with significant functional deficit, and cases failing adequate conservative management.

Frozen Shoulder (Adhesive Capsulitis)

Frozen shoulder — medically termed adhesive capsulitis — is a condition characterized by progressive pain and global restriction of glenohumeral range of motion in all planes, caused by fibrosis and contracture of the joint capsule. It is one of the most disabling and poorly understood shoulder conditions, with a natural history spanning one to three years.

Frozen shoulder affects approximately 2–5% of the general population and up to 10–20% of people with diabetes. It is more common in women and typically occurs between ages 40 and 60. Risk factors include diabetes mellitus (both Type 1 and Type 2, with poorly controlled diabetes carrying higher risk), thyroid disorders, prior shoulder injury, prolonged immobilization of the shoulder (such as after a fracture or surgery), and cardiac surgery. The cause in most cases is idiopathic — no precipitating event is identified.

The condition progresses through three recognizable phases:

• Freezing phase (2–9 months): Increasing shoulder pain, often severe and worse at night, with gradual onset of stiffness. Pain typically precedes the stiffness. This is often the most painful phase.
• Frozen phase (4–12 months): Pain begins to decrease but stiffness reaches its maximum. Activities of daily living — dressing, reaching behind the back, reaching overhead — become significantly limited.
• Thawing phase (5–24 months): Gradual spontaneous recovery of range of motion. Most patients recover near-full function, though approximately 40% have some residual symptoms or stiffness.

Management is primarily conservative: physiotherapy, analgesics, corticosteroid injections (most effective early in the freezing phase to reduce pain and facilitate rehabilitation), and hydrodilatation (injection of saline and corticosteroid under imaging guidance to distend the capsule). Surgical options (arthroscopic capsular release) are reserved for refractory cases.

Shoulder Bursitis

The subacromial bursa is the largest bursa in the body and sits between the rotator cuff tendons and the overlying acromion and deltoid muscle. Its function is to reduce friction and allow smooth rotator cuff movement beneath the acromion. Inflammation of this bursa — subacromial bursitis — produces pain that is often diffuse across the outer shoulder and upper arm, worsened by overhead activities and by lying on the affected shoulder at night.

Subacromial bursitis rarely exists in isolation — it most commonly occurs alongside rotator cuff tendinopathy and impingement syndrome as part of the same subacromial pain syndrome. Distinguishing isolated bursitis from tendinopathy on clinical examination alone is difficult; MRI or ultrasound can identify bursal thickening and fluid. Management follows the same pathway as impingement and tendinopathy: physiotherapy, NSAIDs, and subacromial corticosteroid injection when appropriate.

Acromioclavicular (AC) Joint Problems

AC Joint Sprain

The acromioclavicular joint — the small joint at the top of the shoulder where the clavicle meets the acromion — is frequently injured in contact sports, cycling falls, and falls onto the point of the shoulder. AC joint injuries are graded I through VI using the Rockwood classification, based on the degree of ligament disruption and clavicular displacement:

• Grade I–II: Partial tear of AC ligaments; no or minor clavicular displacement. Conservative management with sling, analgesia, and physiotherapy.
• Grade III: Complete AC ligament tear with some clavicular displacement. Management is controversial — most cases do well with conservative treatment, but some surgeons recommend surgical stabilization in active individuals or manual workers.
• Grade IV–VI: Severe displacement with disruption of additional ligaments. Surgical stabilization is typically required.

The clinical presentation is localized tenderness directly over the AC joint, with a visible step deformity in higher-grade injuries. Pain is reproduced by cross-body adduction (bringing the arm across the chest — “crossover sign”) and by placing the hand on the opposite shoulder.

AC Joint Osteoarthritis

Degenerative osteoarthritis of the AC joint is common, particularly in adults over 40 and in those with a history of prior AC joint injury or heavy overhead loading (weight trainers, manual laborers). Symptoms are localized to the top of the shoulder: a dull ache that is worsened by overhead activities, reaching across the body, and sleeping on the affected side. The crossover test reproduces pain specifically at the AC joint. Management includes NSAIDs, physiotherapy, AC joint corticosteroid injection, and in refractory cases, surgical resection of the distal clavicle (Mumford procedure).

Shoulder Instability and Dislocation

Because the glenohumeral socket is so shallow, the shoulder relies heavily on the labrum, ligaments, and rotator cuff for stability. When these structures are overwhelmed by force, dislocation occurs. The glenohumeral joint is the most frequently dislocated joint in the body, accounting for approximately 50% of all joint dislocations.

Anterior dislocation — where the humeral head displaces forward beneath the coracoid process — accounts for 95–97% of cases and typically results from a fall on an outstretched arm or a contact sports impact with the arm in abduction and external rotation. The shoulder has a visibly abnormal contour and the patient holds the arm in slight abduction and external rotation, resisting internal rotation. Associated injuries include Bankart lesions (avulsion of the anterior labrum from the glenoid), Hill-Sachs lesions (compression fracture of the posterior humeral head), and in older patients, rotator cuff tears.

The most important clinical reality of shoulder dislocation is the high recurrence rate, particularly in young athletes. After a first-time dislocation in a patient under 20, the recurrence rate approaches 80–90%. For this reason, many sports medicine physicians now recommend early surgical stabilization (Bankart repair) for young active patients rather than conservative management alone.

SLAP (Superior Labrum Anterior to Posterior) tears involve the superior labrum and the attachment of the long head of the biceps tendon. They are seen in overhead athletes (throwers, swimmers, racket sports) and after traction injuries. Symptoms include a deep, poorly localized shoulder pain, mechanical symptoms (catching, clicking), and pain with overhead activities.

Biceps Tendinopathy and Rupture

The long head of the biceps tendon is a frequent and often overlooked source of anterior shoulder pain. It originates from the superior glenoid labrum, runs through the shoulder joint, and passes down through the bicipital groove in the anterior humerus before joining the biceps muscle belly. This intra-articular course makes it vulnerable to mechanical irritation, particularly when combined with rotator cuff pathology.

Biceps tendinopathy presents as anterior shoulder pain localized to the bicipital groove, worsened by overhead activities, lifting, and forearm supination against resistance. Clinical tests include Speed’s test (pain on shoulder flexion against resistance with the elbow extended and forearm supinated) and Yergason’s test (pain on supination against resistance with the elbow at 90 degrees). Biceps tendinopathy frequently coexists with rotator cuff pathology and often improves with treatment directed at the rotator cuff and subacromial space.

Proximal biceps tendon rupture — complete tear of the long head tendon — typically occurs in men over 40 with pre-existing tendon degeneration, often with relatively minor provocation. The characteristic finding is the “Popeye deformity” — the biceps muscle belly bunches distally on the forearm, creating a visible asymmetric bulge. Pain is often surprisingly brief after the initial event. Because the short head of the biceps is intact, most patients retain approximately 80% of biceps strength, and the cosmetic deformity is the main residual issue. Surgical repair is generally reserved for young, active patients or those who require maximum supination strength.

Other Shoulder Pain Causes Worth Knowing

Calcific Tendinitis

Calcific tendinitis of the shoulder involves the deposition of calcium hydroxyapatite crystals within rotator cuff tendons, most commonly the supraspinatus. It affects approximately 3% of adults and is often found incidentally on plain X-rays in asymptomatic individuals. However, when the calcium deposit enters the resorptive phase, the acute presentation can be one of the most severe and abrupt pain syndromes in musculoskeletal medicine: sudden, excruciating shoulder pain of rapid onset, often waking the patient from sleep, with near-complete loss of shoulder movement and extreme tenderness to even light touch. This acute phase is sometimes misdiagnosed as septic arthritis or a fracture.

The acute phase is self-limiting as the calcium resorbs, but can last days to weeks. NSAIDs, short-term oral corticosteroids, and subacromial injection provide pain relief during the acute phase. For chronic symptomatic calcific tendinitis, ultrasound-guided barbotage (needling and lavage of the calcium deposit) is effective and is supported by randomized controlled trial evidence.

Glenohumeral Osteoarthritis

Primary osteoarthritis of the glenohumeral joint is less common than hip or knee osteoarthritis but still affects a significant proportion of older adults — prevalence on imaging reaches 16–27% in those over 60, though symptomatic disease is less common (approximately 3–4%). Secondary glenohumeral OA develops after prior injury, dislocation, or inflammatory arthritis. Symptoms include deep shoulder pain with all movement (not position-dependent like impingement), progressive stiffness affecting the end range of movement in all planes, and crepitus (grinding or grating sensation with movement). Unlike frozen shoulder, which has a characteristic pattern of global restriction, glenohumeral OA tends to preferentially restrict external rotation and forward elevation. Management escalates from analgesics and physiotherapy through corticosteroid injection to total shoulder arthroplasty (shoulder replacement) for advanced cases with severe functional limitation.

Referred Pain: Cardiac, Cervical, and Other Sources

Not all shoulder pain originates in the shoulder. Several important conditions refer pain to the shoulder region and must be considered, particularly when the clinical picture does not fit a mechanical shoulder diagnosis.

Cardiac referred pain is among the most critical: ischemic heart disease can refer pain to the left shoulder and arm via the same C8-T1 dermatome that serves the medial arm. Any patient presenting with new left shoulder pain accompanied by chest tightness, breathlessness, diaphoresis (sweating), nausea, or jaw pain must be assessed urgently for myocardial infarction.

Cervical radiculopathy (C5 root) refers pain from the neck to the lateral shoulder and outer upper arm, closely mimicking intrinsic shoulder pathology. Key distinguishing features: neck movements (extension, ipsilateral rotation) reproduce or worsen the arm pain; there is no restriction of shoulder range of motion; and there may be associated biceps weakness and reduced biceps reflex.

Diaphragmatic irritation refers pain to the tip of the shoulder (C3-4 dermatome) via the phrenic nerve. Causes include subphrenic abscess, ruptured ectopic pregnancy, splenic injury, and pneumothorax. Tip-of-shoulder pain in the context of abdominal or thoracic pathology requires urgent evaluation.

Pancoast tumour (apex lung carcinoma) invades the brachial plexus and causes shoulder and arm pain with progressive weakness and numbness, often accompanied by Horner syndrome (ptosis, miosis, anhidrosis) from involvement of the cervical sympathetic chain. This diagnosis should be considered in any patient with shoulder pain and upper limb neurological symptoms, particularly smokers.

Shoulder Pain Red Flags: When to Seek Urgent or Emergency Care

Self-Care Basics for Shoulder Pain

For most mechanical shoulder pain conditions, self-care measures are appropriate as a first-line approach. The following are supported by clinical evidence.

Activity modification — reducing or temporarily avoiding the specific activities that provoke pain (overhead reaching, lifting with the arm extended, sleeping on the affected side) while maintaining general movement. Total rest and immobilization are not recommended and lead to worse outcomes, particularly for frozen shoulder where early immobilization worsens the stiffness.

Ice and heat — ice (15–20 minutes every 2–3 hours) is useful in the first 48 hours after acute injury for reducing local inflammation. Heat is more appropriate for chronic muscle tension and stiffness. Both can be alternated based on symptom pattern and patient preference.

Analgesics — NSAIDs (ibuprofen, naproxen) are preferred over paracetamol for acute shoulder pain. Topical NSAIDs (diclofenac gel) applied directly to the shoulder are effective and have a better systemic safety profile, particularly for older adults.

Pendulum exercises — gentle gravity-assisted shoulder movement (leaning forward and letting the arm swing in small circles) decompresses the joint and maintains movement without active muscle contraction. Particularly useful for frozen shoulder and post-injury stiffness.

When to escalate: if pain is severe, persistent, or accompanied by any of the red flag features above, self-care is not sufficient. Physiotherapy assessment is indicated for rotator cuff pathology, instability, and frozen shoulder. A corticosteroid injection is often the most effective short-term intervention for subacromial bursitis and early frozen shoulder and can be arranged through a GP or musculoskeletal clinic.

Related Articles on Horizon Health Guide

• Neck Pain: Common Causes and Self-Care Basics
• Joint Pain: Common Causes and When to Seek Care
• Back Pain: Causes, Symptoms, and Prevention
• Bone Pain: What Adults Should Know
• Muscle Pain: Common Causes and Warning Signs

Frequently Asked Questions

What is the most common cause of shoulder pain?

Rotator cuff pathology — including tendinopathy (degeneration and irritation of the rotator cuff tendons), impingement syndrome (mechanical compression of the tendons under the acromion), and rotator cuff tears — accounts for approximately 65–70% of all shoulder pain presentations in primary care. The supraspinatus tendon is most commonly involved. Most cases of rotator cuff tendinopathy respond well to physiotherapy and do not require surgery, though full-thickness tears in active individuals often benefit from surgical repair.

How do I know if my shoulder pain is serious?

Most shoulder pain is mechanical in origin and resolves with conservative management. However, certain features indicate a serious underlying problem requiring urgent evaluation: left shoulder pain accompanied by chest tightness, breathlessness, or sweating may indicate a heart attack; a hot, swollen, extremely painful shoulder with fever suggests septic arthritis; visible shoulder deformity after trauma suggests dislocation or fracture; progressive arm weakness or neurological symptoms suggest nerve involvement. Shoulder pain with unexplained weight loss, night sweats, or in a patient with a known cancer history also requires prompt assessment.

Can shoulder pain be referred from the neck?

Yes — cervical radiculopathy from C5 nerve root compression is a common cause of shoulder and upper arm pain that can closely mimic intrinsic shoulder pathology. Key distinguishing features: neck movements (particularly extension and rotation toward the painful side) reproduce or worsen the arm pain; passive shoulder range of motion is usually preserved; and there may be associated biceps weakness and reduced biceps reflex. MRI of the cervical spine will reveal the disc herniation or foraminal stenosis responsible. Treatment is directed at the cervical spine, not the shoulder.

What is the difference between frozen shoulder and a rotator cuff tear?

Both conditions cause significant shoulder pain and restricted movement, but they differ in important ways. Frozen shoulder causes global restriction — movement is limited in all directions (forward elevation, external rotation, and internal rotation), and the stiffness develops progressively over months through characteristic phases. Rotator cuff tears cause pain and weakness but typically do not restrict passive range of motion — the shoulder can still be moved through its full range by an examiner, though the patient cannot lift it actively against resistance. The distinction matters because management differs substantially: frozen shoulder requires patience (1–3 years natural history), mobilization, and often injection; rotator cuff tears may require surgical repair.

How long does shoulder pain typically last?

Duration depends on the underlying cause. Simple muscle strain typically resolves in 2–4 weeks. Rotator cuff tendinopathy often improves over 4–12 weeks with appropriate physiotherapy. Frozen shoulder has a natural history of 1–3 years. First-time shoulder dislocation recovers quickly (weeks) if managed well, though the underlying instability persists without surgical repair. Calcific tendinitis in the acute phase typically resolves over days to weeks as the calcium resorbs. Degenerative conditions (osteoarthritis, large rotator cuff tears) are generally not self-resolving and require ongoing management.

Is it safe to exercise with shoulder pain?

For most mechanical shoulder conditions, gentle movement and appropriate exercise are beneficial and should be continued. Complete rest leads to muscle weakness, loss of range of motion, and — particularly for frozen shoulder — worsening stiffness. The principle is to maintain movement within comfortable range and gradually progress loading. Avoid activities that provoke sharp or severe pain. A physiotherapist can design a shoulder rehabilitation program matched to the specific diagnosis. However, if there is a suspected acute fracture, dislocation, or septic arthritis, exercise should not be started until these have been evaluated and excluded.

When does shoulder pain need surgery?

The majority of shoulder conditions — including rotator cuff tendinopathy, bursitis, early frozen shoulder, and AC joint sprain grades I–III — do not require surgery and respond to conservative management. Surgery is indicated for: acute full-thickness rotator cuff tears in active individuals; large or massive tears causing significant functional deficit after adequate conservative management; shoulder dislocation with Bankart lesion in young athletes with high recurrence risk; AC joint injuries grade IV–VI; glenohumeral osteoarthritis causing severe functional limitation not controlled by non-surgical measures; and refractory frozen shoulder after failure of physiotherapy, injection, and hydrodilatation. The decision should involve a shared discussion with an orthopaedic or shoulder specialist.

References

1. Luime JJ, et al. Prevalence and incidence of shoulder pain in the general population. Scand J Rheumatol. 2004;33(2):73-81.
2. Tempelhof S, Rupp S, Seil R. Age-related prevalence of rotator cuff tears in asymptomatic shoulders. J Shoulder Elbow Surg. 1999;8(4):296-299.
3. Zuckerman JD, Rokito A. Frozen shoulder: a consensus definition. J Shoulder Elbow Surg. 2011;20(2):322-325.
4. Tashjian RZ. Epidemiology, natural history, and indications for treatment of rotator cuff tears. Clin Sports Med. 2012;31(4):589-604.
5. Hovelius L, et al. Nonoperative treatment of primary anterior shoulder dislocation in patients forty years of age and younger. J Bone Joint Surg Am. 2008;90(5):945-952.

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This article is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for evaluation and treatment of shoulder pain, particularly if red flag symptoms are present.