Shoulder Impingement Syndrome - Detailed 10 Marker

Definition

Anatomy of the Subacromial Space

• Superiorly: Acromion, AC joint, coracoacromial ligament (forming the coracoacromial arch)
• Inferiorly: Humeral head and greater tuberosity
• Contents: Supraspinatus tendon, subacromial bursa, long head of biceps tendon

Types of Acromion (Bigliani/Morrison Classification)

A Type IV (convex) acromion has also been described but is less widely used clinically.

• Genetics play a role in subacromial space shape
• Type III hooked acromions have a reduced supraspinatus outlet and highest rate of rotator cuff pathology
• Acromions with less slope have a propensity toward impingement
• Anterior acromial spurs (traction osteophytes from coracoacromial ligament) can convert a Type I/II into an effectively Type III morphology

Types of Impingement

1. Primary (External) Impingement

• Intrinsic primary: Structures passing beneath the arch enlarge (e.g., rotator cuff thickening, calcium deposits, subacromial bursal thickening) - they abut the arch from below
• Extrinsic primary: Space above the cuff is diminished (subacromial spurring, acromial fracture, os acromiale, AC joint osteophytes, greater tuberosity exostoses)

2. Secondary Impingement

3. Internal Impingement

4. Subcoracoid Impingement

Neer's Stages of Impingement (Pathological Progression)

Aetiology / Risk Factors

• Type III (hooked) acromion
• Acromial osteophytes/spurs
• AC joint osteophytes impinging from above
• Os acromiale
• Subacromial narrowing

• Age-related tendon degeneration: decreased cellularity, fascicular thinning, hypovacularity, dystrophic calcification - likely irreversible
• Degenerative tears associated with narrower subacromial space, larger lateral extension, steeper acromion angulation
• Shear stress from repetitive overhead activities

• Rotator cuff weakness leading to loss of force couples → superior humeral head translation
• Scapular dyskinesia (reduced scapular upward rotation narrows the outlet)
• Kyphosis reducing shoulder elevation
• Overhead sports (swimmers, throwers, racquet sports)

Clinical Features

• Anterolateral shoulder pain, worsened by overhead activity
• Pain at night, difficulty lying on the affected shoulder
• "Painful arc" - pain between 60° and 120° of abduction

• Tenderness over anterolateral acromion and supraspinatus insertion on greater tuberosity
• Painful arc of abduction (60°-120°)
• Weakness in abduction and external rotation (if cuff involved)
• Muscle wasting (supraspinatus/infraspinatus fossa) in chronic cases

Clinical Tests

Clinical pearl (Campbell's): If Hawkins-Kennedy + painful arc + infraspinatus (Jobe) test are ALL positive, likelihood of impingement >95%. If all three are negative, likelihood <24%.

Investigations

• AP and lateral (outlet) views - outlet view best shows acromion type
• Early: normal or hooked acromion
• Late: sclerosis/cysts at anterior acromion and greater tuberosity, narrowed acromiohumeral gap (<7 mm suggests full-thickness tear), superior subluxation of humeral head, anterior acromial traction spur

• Gold standard for soft tissue assessment
• Shows supraspinatus signal changes, partial vs full-thickness tears, bursal thickening
• Arthrogram best for partial-thickness tears

• Dynamic assessment, cost-effective, can detect bursal thickening and cuff tears

Management

Conservative (First Line)

• Rest and activity modification - avoid provocative overhead activities
• NSAIDs - anti-inflammatory analgesia
• Physiotherapy - rotator cuff strengthening, scapular stabilisation, posture correction; evidence shows equivalent outcome to surgery at 1, 2, and 5 years
• Subacromial corticosteroid injection - reduces inflammation, provides short-to-medium term relief; also serves as diagnostic injection
• Patient education - gradual return to activity

Surgical

• Subacromial decompression (acromioplasty): Removal of anteroinferior acromion, resection of coracoacromial ligament, bursectomy. Can be arthroscopic or open. Note: recent evidence questions additional benefit over structured exercise alone for atraumatic tears.
• Rotator cuff repair: For associated full-thickness tears (arthroscopic or mini-open)
• AC joint excision: If AC joint osteophytes contributing

Summary Points for 10 Markers

1. Impingement = encroachment on rotator cuff by coracoacromial arch structures
2. Bigliani's 3 acromion types: flat (I), curved (II), hooked (III) - Type III highest risk
3. Types: primary (intrinsic/extrinsic), secondary (instability), internal (glenoid rim), subcoracoid
4. Neer's 3 stages: oedema → fibrosis → tendon rupture
5. Most common tendon affected: supraspinatus
6. Hallmark symptom: painful arc 60°-120°
7. Best combined tests: Hawkins-Kennedy + painful arc + Jobe (>95% likelihood)
8. Neer's injection test confirms diagnosis
9. MRI is gold standard imaging for soft tissue assessment
10. Conservative physiotherapy = surgery outcomes at 5 years; acromioplasty for refractory cases

Painful Arc Syndrome

Definition

Anatomy and Mechanism

• 0°–60°: The greater tuberosity is still below the acromion - adequate space, no impingement → painless
• 60°–120°: The greater tuberosity and swollen/degenerated supraspinatus tendon are maximally compressed against the undersurface of the acromion → painful arc
• 120°–180°: The greater tuberosity rotates posteriorly, passing beyond the acromion - space opens up again → pain subsides / painless

Diagrams

Types of Painful Arc

Causes / Conditions Producing Painful Arc

1. Chronic supraspinatus tendinitis - most common cause; degeneration of the tendon from deficient blood supply ± degenerative calcification
2. Subdeltoid (subacromial) bursitis - inflamed bursa is compressed during mid-abduction
3. Incomplete (partial thickness) rupture of the supraspinatus tendon
4. Crack (stress) fracture of the greater tuberosity of the humerus
5. AC joint arthritis - produces the higher-range painful arc (120°–180°)
6. Calcific tendinitis - calcium hydroxyapatite deposits within the supraspinatus

Key distinction from other shoulder conditions:

• Acute supraspinatus tendinitis → whole range of abduction is painful
• Chronic supraspinatus tendinitis (painful arc syndrome) → only mid-range (60°–120°) is painful
• Frozen shoulder (acute) → all movements restricted and painful; NOT specific to abduction arc
• Complete supraspinatus rupture → patient shrugs the shoulder at the start of abduction (cannot initiate abduction without deltoid trick movement)

Pathology

• Overuse or repetitive overhead activity
• Deficient blood supply to the "critical zone" of the supraspinatus (1 cm from its insertion - hypovascular zone)
• Age-related changes (most common in males aged 45–60 years)

Clinical Features

• Middle-aged to older adults (typically 45–60 years), males > females
• Pain localized to the anterolateral shoulder, radiating to the deltoid insertion
• Pain specifically during mid-range overhead activity (e.g., reaching to a shelf)
• Night pain - difficulty sleeping on the affected shoulder
• No significant stiffness at rest (distinguishes from frozen shoulder)

• Painful arc of abduction: 60°–120° - the hallmark finding
• Localized tenderness over the supraspinatus insertion at the greater tuberosity and anterior acromion
• Full passive range of motion (no restriction - unlike frozen shoulder)
• Positive impingement tests (Neer, Hawkins-Kennedy)
• Radiograph: may show calcification in the supraspinatus tendon; hooked acromion

Differential Diagnosis Summary

Investigations

• X-ray (AP + outlet view): May be normal early; hooked acromion; calcification in supraspinatus tendon; late - narrowed acromiohumeral interval
• Ultrasound: Supraspinatus tendon thickening, calcification, bursal fluid - dynamic assessment possible
• MRI: Gold standard for soft tissue; differentiates tendinitis from partial/full thickness tears
• Neer's injection test: 10 mL lidocaine into subacromial space - pain abolition confirms subacromial source

Management

Conservative (First Line)

• Rest and activity modification - avoid painful overhead activities
• NSAIDs - ibuprofen/diclofenac for analgesia and anti-inflammation
• Physiotherapy - rotator cuff strengthening, scapular stabilisation, posture; proven equivalent to surgery at 1, 2, and 5 years
• Subacromial corticosteroid injection - methylprednisolone + local anaesthetic; short-to-medium term relief; also diagnostic
• Extracorporeal shock wave therapy (ESWT) - for calcific tendinitis

Surgical (if conservative fails after 3–6 months)

• Arthroscopic subacromial decompression (acromioplasty) - removal of anteroinferior acromion, bursectomy, resection of coracoacromial ligament
• AC joint excision - if AC joint osteophytes are the primary source
• Calcific deposit needling/lavage - for refractory calcific tendinitis

Key Points to Remember

1. Painful arc = 60°–120° - pathognomonic of chronic supraspinatus tendinitis
2. Mechanism: supraspinatus tendon nipped between greater tuberosity and acromion at mid-abduction
3. Extremes of abduction are painless - this distinguishes it from arthritis/frozen shoulder
4. AC joint arc = 120°–180° - higher range, over shoulder level
5. Other causes: subdeltoid bursitis, incomplete rupture, crack fracture of greater tuberosity
6. Age group: 45–60 years, males more common
7. Confirm with Neer's injection test (subacromial lidocaine)
8. MRI is gold standard; X-ray may show calcification or hooked acromion
9. First-line = physiotherapy + NSAIDs ± subacromial injection
10. Surgery: arthroscopic acromioplasty if conservative treatment fails