Shoulder Pain: What Could Be Causing It?

Why the Shoulder Is So Vulnerable to Pain

The shoulder is the most mobile joint in the body. That mobility comes at a cost: the glenohumeral joint sacrifices bony stability for range of motion, relying instead on the rotator cuff muscles, the labrum, the bursa, and surrounding ligaments to keep the humeral head centered. Any structure in that system can break down.

Anatomy in 60 Seconds

The shoulder complex includes three bones (humerus, clavicle, scapula), four joints (glenohumeral, acromioclavicular, sternoclavicular, scapulothoracic), four rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis), and the subacromial bursa. Pain can originate in any of these, or arrive from a distant structure entirely.

How Clinicians Think About Shoulder Pain

The standard diagnostic approach categorizes pain as:

• Intrinsic, arising from the shoulder joint and its local structures
• Extrinsic or referred, arriving from the cervical spine, brachial plexus, chest, abdomen, or diaphragm
• Systemic, driven by inflammatory arthritis, infection, or malignancy

A 2023 systematic review published in the BMJ found that failure to distinguish referred from intrinsic pain is among the leading causes of misdiagnosis and delayed treatment in primary care shoulder presentations. [1]

Rotator Cuff Disorders: The Most Common Culprit

Rotator cuff pathology is the single most frequent explanation for shoulder pain, responsible for approximately 70% of all shoulder complaints seen in primary care. [2] It covers a spectrum from mild tendinopathy to full-thickness tears requiring surgical evaluation.

Rotator Cuff Tendinopathy and Impingement

Subacromial impingement occurs when the supraspinatus tendon is compressed between the humeral head and the acromion during overhead movement. Pain typically peaks between 60 and 120 degrees of arm elevation (the "painful arc"). Night pain when lying on the affected side is a hallmark feature.

A large UK pragmatic randomized controlled trial published in The Lancet (CSAW trial, N=313) found that supervised exercise therapy produced clinically meaningful pain reduction at 12 months comparable to both arthroscopic subacromial decompression and a sham procedure, with mean Oxford Shoulder Score improvements of 11.8 (exercise) versus 11.7 (surgery). [3] Physical therapy first. Surgery later, if at all.

Full-Thickness Rotator Cuff Tears

Full-thickness tears are more common after age 60. Many are asymptomatic. A large cadaveric and imaging study (N=411) found that 22.1% of subjects had a full-thickness rotator cuff tear, rising to 51% in those over age 80. [4]

Symptoms that suggest a full-thickness tear rather than tendinopathy include:

• Sudden weakness during external rotation or abduction
• A "drop arm" sign on clinical examination
• Pain persisting beyond 6 weeks of physical therapy

MRI detects full-thickness tears with approximately 91% sensitivity and 86% specificity. [5] Ultrasound is a practical alternative, with sensitivity around 79% for full-thickness tears.

Biceps Tendinopathy and SLAP Tears

The long head of the biceps tendon runs through the shoulder joint and is frequently involved alongside rotator cuff disease. Pain localizes to the anterior shoulder and is reproduced by Speed's test and Yergason's test. Superior labrum anterior-to-posterior (SLAP) tears cause a deep, clicking pain and are more common in overhead athletes and workers under age 40.

Frozen Shoulder (Adhesive Capsulitis)

Frozen shoulder is defined by progressive, painful restriction of both active and passive shoulder motion without another structural explanation. It affects 2 to 5% of the general population and up to 20% of people with type 1 or type 2 diabetes. [6]

Three Clinical Phases

The condition moves through three overlapping phases:

1. Freezing (2 to 9 months): Increasing pain, especially at night; motion begins to decrease.
2. Frozen (4 to 12 months): Pain partially subsides; stiffness dominates; external rotation is typically lost first.
3. Thawing (5 to 24 months): Gradual spontaneous return of motion.

Treatment Options

Corticosteroid injection into the glenohumeral joint provides faster early pain relief than physical therapy alone. A Cochrane review (2012, updated evidence 2021) found that intra-articular corticosteroid injection produced greater short-term improvement in pain (standardized mean difference -0.90) and function at 6 weeks compared with no treatment, though differences narrowed by 6 months. [7]

Hydrodilatation (injection of saline plus corticosteroid under fluoroscopic guidance) may accelerate recovery in the frozen phase. Manipulation under anesthesia or arthroscopic capsular release is reserved for cases failing 12 months of conservative management.

Acromioclavicular (AC) Joint Problems

The AC joint sits at the top of the shoulder where the clavicle meets the acromion. It is a common pain generator that is easy to overlook.

AC Joint Osteoarthritis

AC joint arthritis produces pain directly over the joint that worsens with cross-body adduction (reaching across the chest). The "cross-body adduction test" has a reported sensitivity of 77% for AC joint pathology. [8] Radiographic changes correlate poorly with symptoms: many people with marked arthritic changes on X-ray report no pain.

First-line treatment includes activity modification, NSAIDs such as naproxen 500 mg twice daily, and targeted physical therapy. A single corticosteroid injection into the AC joint offers 60 to 70% short-term symptom relief. [9] Surgical resection of the distal clavicle (Mumford procedure) is effective for refractory cases.

AC Joint Sprains (Separations)

High-energy injuries (falls, collision sports) can disrupt the AC and coracoclavicular ligaments. Grading runs from Type I (sprain only) through Type VI (severe displacement). Types I and II are managed conservatively. Type III management remains debated. Types IV through VI typically require surgical stabilization.

Glenohumeral Osteoarthritis

Primary glenohumeral osteoarthritis is less common than knee or hip arthritis but still affects an estimated 16 to 20% of adults over age 65. [10] Pain is diffuse, deep within the joint, and worsens with end-range motion in all directions. Patients often describe a grinding sensation.

Plain X-ray showing joint space narrowing, subchondral sclerosis, and osteophyte formation is usually sufficient to confirm the diagnosis. Treatment follows a stepwise approach: NSAIDs, intra-articular corticosteroids, physical therapy for periscapular strengthening, and eventually total shoulder arthroplasty for severe cases. Five-year outcomes after total shoulder arthroplasty are favorable, with 90% implant survival and significant pain reduction reported in registry data. [11]

Cervical Radiculopathy: Shoulder Pain from the Neck

Not all shoulder pain originates in the shoulder. Cervical nerve root compression, most often at C5 or C6, produces pain that radiates from the neck into the shoulder, upper arm, and sometimes the forearm and hand. The distinction matters because treating the shoulder will not help if the neck is the actual source.

Clinical Clues Pointing to the Cervical Spine

• Pain that worsens with neck flexion or rotation rather than shoulder movement
• Neurological findings: numbness or tingling in a dermatomal pattern (C5: lateral deltoid; C6: thumb and index finger)
• Spurling's test positive (axial compression with ipsilateral neck rotation reproducing arm pain)
• Shoulder range of motion preserved or near-normal

A prospective study (N=255) found that Spurling's test carries a specificity of 93% for cervical radiculopathy when compared with MRI-confirmed root compression. [12]

Management

Conservative management (physical therapy, cervical traction, selective nerve root block) resolves symptoms in roughly 75% of patients within 12 weeks. Surgical decompression is indicated for progressive neurological deficits or intractable pain beyond 6 to 12 weeks of conservative care.

Referred Pain from the Heart, Lungs, and Abdomen

Some shoulder pain is a warning sign of a life-threatening condition elsewhere in the body. Diaphragmatic irritation from subphrenic pathology refers pain to the ipsilateral shoulder tip via the phrenic nerve (C3, C5). Left shoulder pain combined with chest tightness or pressure can signal acute myocardial ischemia.

Cardiac Red Flags

The American Heart Association notes that atypical MI presentations, including isolated shoulder or jaw pain, occur more often in women, older adults, and people with diabetes. [13] Any shoulder pain accompanied by:

• Chest discomfort, pressure, or heaviness
• Diaphoresis or nausea
• Dyspnea at rest
• Pain that does not change with shoulder movement

...requires immediate emergency evaluation. Do not wait for a primary care appointment.

Diaphragmatic Irritation

Ruptured ectopic pregnancy, splenic rupture, hepatic abscess, or free intraperitoneal air can all cause ipsilateral shoulder tip pain without any local shoulder finding. Clinicians call this "Kehr's sign" when left shoulder pain results from splenic hemorrhage.

Inflammatory and Systemic Causes

Rheumatoid Arthritis

Rheumatoid arthritis (RA) affects the glenohumeral joint in up to 90% of patients with longstanding disease. [14] Unlike osteoarthritis, RA presents with prolonged morning stiffness (greater than 30 minutes), bilateral involvement, and systemic features such as fatigue and low-grade fever. Synovial fluid analysis showing inflammatory markers confirms the diagnosis. Disease-modifying antirheumatic drugs (DMARDs) such as methotrexate remain the backbone of treatment per the 2022 ACR guideline. [15]

Polymyalgia Rheumatica

Polymyalgia rheumatica (PMR) should be considered in any patient over age 50 presenting with bilateral shoulder and hip girdle pain and stiffness lasting more than 4 weeks. Erythrocyte sedimentation rate (ESR) is typically above 40 mm/hr, often above 80 mm/hr. Low-dose prednisolone (10 to 20 mg/day) produces a dramatic response within 24 to 72 hours; a failure to respond should prompt reconsideration of the diagnosis. [16]

Septic Arthritis

Shoulder joint infection is rare but is among the most urgent diagnoses in shoulder pain. Risk factors include IV drug use, recent joint injection, immunosuppression, and adjacent skin infection. The joint becomes hot, swollen, exquisitely tender, and any passive range of motion is severely limited. Joint aspiration showing white cell count above 50,000 cells/mm3 with predominantly neutrophils confirms septic arthritis. Surgical washout within 24 hours reduces cartilage destruction. [17]

How Shoulder Pain Is Diagnosed

A structured history and physical examination remain the foundation of diagnosis, before any imaging is ordered.

History

Key questions:

• Onset: Traumatic versus gradual. A pop followed by immediate weakness suggests tendon rupture.
• Location: Anterior (biceps, AC joint, glenohumeral); lateral (rotator cuff, impingement); posterior (labral tear, posterior capsule).
• Radiation: Into the arm (cervical or brachial plexus); into the neck (AC joint); to the hand (C6, C7 radiculopathy).
• Modifying factors: Worse with overhead activity (impingement); worse with lying on the shoulder (rotator cuff, bursitis); worse with neck movement (cervical origin).

Physical Examination Tests

No single test is definitive. Combining three or more positive tests improves diagnostic accuracy substantially. Commonly used tests and their properties:

| Test | Target Pathology | Sensitivity | Specificity | |------|-----------------|-------------|-------------| | Neer's sign | Subacromial impingement | 72% | 66% | | Hawkins-Kennedy | Subacromial impingement | 79% | 59% | | Empty can (Jobe) | Supraspinatus tear | 69% | 66% | | Drop arm sign | Full-thickness tear | 35% | 98% | | External rotation lag | Infraspinatus/teres minor tear | 56% | 98% | | Speed's test | Biceps tendinopathy | 54% | 81% | | Spurling's | Cervical radiculopathy | 50% | 93% |

Data synthesized from multiple systematic reviews. [18]

Imaging

• X-ray: First-line for trauma, suspected arthritis, or calcific tendinitis.
• Ultrasound: Excellent for dynamic assessment of the rotator cuff; operator-dependent.
• MRI: Best overall for soft-tissue detail; sensitivity approximately 91% for full-thickness cuff tears. [5]
• MRI arthrography: Preferred for labral pathology (SLAP, Bankart tears); sensitivity rises to 89% for labral tears when gadolinium is injected. [19]
• CT: Best for fracture characterization and pre-surgical planning for severe arthritis.

Treatment Principles by Cause

The table below summarizes the primary treatment pathway for each major diagnosis. This decision framework was developed by the HealthRX medical team and reviewed against current AAOS, ACR, and British Elbow and Shoulder Society (BESS) guidelines.

| Diagnosis | First-Line (0 to 6 weeks) | Second-Line (6 to 12 weeks) | Escalation (beyond 12 weeks) | |-----------|----------------------|--------------------------|------------------------------| | Impingement / tendinopathy | Activity modification, NSAIDs, PT | Subacromial corticosteroid injection | Arthroscopic decompression (if conservative care fails at 6 months) | | Full-thickness rotator cuff tear | PT (if low-grade weakness) | MRI, orthopedic referral | Surgical repair for active patients <65 or significant weakness | | Frozen shoulder | NSAIDs, gentle PT, glenohumeral steroid injection | Hydrodilatation | Manipulation under anesthesia or arthroscopic capsular release | | AC joint arthritis | Activity modification, NSAIDs | AC joint steroid injection | Distal clavicle resection | | Glenohumeral OA | NSAIDs, PT, steroid injection | Viscosupplementation (limited evidence) | Total shoulder arthroplasty | | Cervical radiculopathy | NSAIDs, cervical PT, soft collar | Nerve root block | Surgical decompression (ACDF or foraminotomy) | | PMR | Prednisolone 10 to 20 mg/day | Taper over 12 to 24 months | Rheumatology referral for relapse | | Septic arthritis | Emergency washout + IV antibiotics | Organism-guided oral antibiotics | Repeat washout if inadequate response |

Physical therapy dosage matters. Studies supporting PT for shoulder conditions typically use 6 to 12 weeks of supervised therapy at 2 to 3 sessions per week, not sporadic home exercises alone.

When to Seek Emergency or Urgent Care

Most shoulder pain is not an emergency. These presentations are:

• Go to the emergency department now: Chest pain plus left shoulder pain; severe trauma with visible deformity; signs of joint infection (fever, hot swollen joint); acute severe weakness after hearing a pop (possible tendon rupture or proximal humerus fracture).
• Urgent appointment within 24 to 48 hours: Progressive arm weakness or new hand numbness; pain unresponsive to any position including rest; significant trauma in a patient over age 65 (high fracture risk).
• Routine appointment within 1 to 2 weeks: Gradual onset pain without neurological symptoms; pain that is mechanical and position-dependent; chronic ache without red flags.

The American College of Emergency Physicians recommends that any shoulder pain occurring at rest, not reproduced by shoulder movement, and accompanied by cardiovascular risk factors be evaluated for cardiac etiology before being attributed to musculoskeletal disease. [20]