EXTERNAL IMPINGEMENT
Subacromial Impingement | Neer Stages | Cuff Compression
NEER CLASSIFICATION
Critical Must-Knows
- External impingement = compression of supraspinatus between humeral head and acromion
- Neer stages progress from edema (I) to fibrosis (II) to cuff tear (III)
- Acromial morphology (Type 3 hooked) increases impingement risk
- Non-operative treatment first-line for Stage I-II
- Acromioplasty removes impinging bone but evidence is debated
Examiner's Pearls
- "Bigliani Type 3 (hooked) acromion = higher impingement risk
- "Hawkins and Neer tests assess subacromial impingement
- "Differentiate from internal impingement (posterior/superior, throwers)
- "Subacromial injection test helps confirm diagnosis
Clinical Imaging
Imaging Gallery
Critical External Impingement Exam Points
Neer Stages
Stage I: Edema and hemorrhage (under 25 years, reversible). Stage II: Fibrosis and tendinitis (25-40 years, chronic). Stage III: Rotator cuff tear (over 40 years, often irreversible). Progression is not inevitable.
Acromial Morphology
Bigliani classification: Type 1 (flat), Type 2 (curved), Type 3 (hooked). Type 3 has highest impingement risk. Outlet view X-ray or sagittal MRI shows acromion shape.
External vs Internal
External = subacromial, anterior cuff compression, older patients. Internal = posterior-superior, articular side cuff, throwers/overhead athletes in abduction-ER. Know the distinction.
Acromioplasty Evidence
Recent RCTs (CSAW, FIMPACT) show acromioplasty may not be superior to sham surgery for isolated impingement. This is controversial but important to know for examination.
External vs Internal Impingement
| Feature | External (Subacromial) | Internal (Posterior-Superior) |
|---|---|---|
| Location | Subacromial space, anterior | Posterior-superior, articular |
| Cuff surface | Bursal side | Articular side |
| Age group | Over 35, degenerative | Under 35, throwers/athletes |
| Mechanism | Cuff compressed under acromion | Cuff pinched on glenoid rim in abd-ER |
| Treatment | Physio, injection, acromioplasty | Physio, posterior capsule stretch |
EFTNeer Stages
Memory Hook:EFT = Edema, Fibrosis, Tear - Neer stages progress with age and chronicity!
1-2-3Bigliani Acromion Types
Memory Hook:Bigliani 1-2-3: Flat, Curved, Hooked - Type 3 is trouble!
NHJClinical Tests
Memory Hook:NHJ = Neer, Hawkins, Jobe - key shoulder tests!
Overview and Epidemiology
Why External Impingement Matters
External (subacromial) impingement is one of the most common causes of shoulder pain. Understanding the spectrum from edema to cuff tear, the role of acromial morphology, and the evidence around treatment options is essential for examination and clinical practice.
Demographics
- Over 35 years typical onset
- Occupational overhead workers
- Athletes (overhead sports)
- Degenerative component with aging
- Both genders equally affected
Risk Factors
- Type 3 hooked acromion
- Os acromiale
- Acromioclavicular osteophytes
- Overhead repetitive activity
- Postural factors (kyphosis)
Pathophysiology and Mechanisms
Subacromial Space Anatomy
The subacromial space lies between the acromion/coracoacromial ligament above and the humeral head below. The supraspinatus tendon passes through this space. In external impingement, this space is narrowed, causing mechanical compression of the rotator cuff, particularly during forward flexion and internal rotation.
Causes of Subacromial Narrowing
| Extrinsic (From Above) | Intrinsic (Within Tendon) |
|---|---|
| Type 3 hooked acromion | Tendon degeneration |
| AC joint osteophytes | Tendon calcification |
| Os acromiale | Cuff tear (partial/full) |
| Coracoacromial ligament thickening | Tendon thickening from tendinitis |
Coracoacromial Arch
- Acromion - anterior-superior coverage
- Coracoacromial ligament - connects acromion to coracoid
- Coracoid process - anterior
- This arch forms the "roof" that can impinge
Impingement Zone
- Critical zone of supraspinatus (1cm from insertion)
- Watershed area - relatively avascular
- Bursal surface affected in external impingement
- Articular surface affected in internal impingement
Classification Systems
Neer Classification of Impingement
| Stage | Pathology | Age Group | Treatment |
|---|---|---|---|
| Stage I | Edema and hemorrhage | Under 25 years | Rest, physio, NSAIDs |
| Stage II | Fibrosis and tendinitis | 25-40 years | Physio, injection, +/- surgery |
| Stage III | Rotator cuff tear | Over 40 years | Decompression +/- cuff repair |
Neer's classification emphasizes the progressive nature of impingement syndrome, though progression is not inevitable.
Clinical Assessment
History
- Anterior-lateral shoulder pain
- Night pain (classic)
- Overhead activity exacerbates
- Painful arc during abduction
- Weakness if cuff involved
Examination
- Neer test - forward flex with scapula fixed
- Hawkins test - 90° flex, internal rotate
- Painful arc - 60-120° abduction
- Jobe test - supraspinatus strength
- Injection test - relief with subacromial LA
Clinical Tests Explained
Neer test: Examiner stabilizes scapula, passively forward flexes arm. Positive if reproduces pain (compresses cuff against anterior acromion).
Hawkins test: Flex shoulder/elbow to 90°, then internally rotate forearm. Positive if reproduces pain (compresses cuff against coracoacromial ligament).
Subacromial injection test: Inject LA into subacromial space. If pain relief and improved strength, supports impingement diagnosis.
Investigations
Investigation Protocol
AP, axillary, outlet (Y) views. Assess acromial morphology on outlet view. Look for AC joint arthritis, calcific tendinitis, superior migration of humeral head.
Dynamic assessment. Can visualize cuff tears, bursitis. Operator-dependent. Less detail than MRI.
Best for cuff assessment. Shows tendon pathology, tears, muscle quality. Sagittal views show acromial morphology. Reserve for suspected cuff tear or failed conservative treatment.
Outlet View
The supraspinatus outlet view (scapular Y-view) best demonstrates acromial morphology. Look for Type 3 hooked acromion, subacromial spurs, and os acromiale. This view is essential for impingement assessment.
Management Algorithm
First-Line Treatment
Stage I and most Stage II are treated non-operatively:
1. Activity modification:
- Avoid aggravating overhead activities
- Relative rest (not complete immobilization)
2. Physiotherapy:
- Rotator cuff strengthening
- Scapular stabilization exercises
- Posterior capsule stretching
- Posture correction
3. NSAIDs:
- Short-term for pain relief
- Helps reduce inflammation
4. Subacromial corticosteroid injection:
- Provides temporary relief
- Aids physiotherapy participation
- Max 3 injections per year
- Diminishing returns with repeated use
Success rate for non-operative treatment is 70-90% if compliant with physiotherapy.
Pre-operative Planning
Imaging Review
- Confirm acromial morphology
- Assess for cuff tear (MRI if needed)
- AC joint status
- Exclude other pathology
- Os acromiale evaluation
Surgical Planning
- Beach chair or lateral position
- Standard posterior/lateral portals
- Plan bursectomy extent
- Acromioplasty targets
- Consent includes limited evidence
Surgical Technique
Subacromial Decompression
Surgical Steps
Beach chair or lateral decubitus. Arm in holder with traction if lateral. Standard portals (posterior viewing, lateral working).
First evaluate the glenohumeral joint. Assess rotator cuff (articular side), biceps, labrum. Enter subacromial space.
Remove inflamed bursal tissue with shaver. Visualize undersurface of acromion, coracoacromial ligament, and rotator cuff.
Use burr to flatten anterior-inferior acromion. Remove impinging spurs. Aim for Type 1 (flat) morphology. Do not over-resect.
Release coracoacromial ligament if thickened/impinging. Some preserve to maintain coracoacromial arch integrity.
Avoid Over-Resection
Excessive acromial resection can cause fracture or deltoid detachment. Remove only enough to create flat undersurface. The coracoacromial ligament provides superior restraint - consider preserving if possible.
Complications
| Complication | Incidence | Risk Factors | Prevention/Management |
|---|---|---|---|
| Persistent pain | 10-30% | Patient selection, technique | Proper indication, thorough decompression |
| Acromial fracture | Rare | Excessive resection | Conservative bone removal |
| Deltoid detachment | Rare | Aggressive resection | Protect deltoid origin |
| Stiffness | 5% | Inadequate rehab | Early ROM protocol |
CSAW Trial Implications
The CSAW trial (UK, 2018) showed no significant difference between arthroscopic subacromial decompression and sham surgery at 6 months. This has led to questioning of routine ASD for isolated impingement. Patients should be informed of this evidence during consent.
Postoperative Care and Rehabilitation
Rehabilitation After ASD
Recovery Timeline
Sling comfort only. Begin pendulum exercises. Ice for swelling. May remove sling for exercises.
Active-assisted ROM progressing to active. Begin rotator cuff isometrics. Scapular stabilization.
Progressive strengthening. Rotator cuff and deltoid focus. Return to light activities.
Full return to activity. Sport-specific training. Most recovery by 3 months.
Recovery from isolated ASD is relatively quick compared to cuff repair.
Outcomes and Prognosis
Treatment Outcomes
| Treatment | Success Rate | Notes |
|---|---|---|
| Physiotherapy alone | 70-90% | First-line for Stage I-II |
| Corticosteroid injection | 50-70% at 6 weeks | Temporary benefit, aids PT |
| ASD (isolated impingement) | 65-85% | Debated benefit vs sham |
| ASD + cuff repair | 75-90% | Benefit from cuff repair |
Evidence Controversy
The CSAW (2018) and FIMPACT (2018) trials showed no benefit of ASD over sham surgery at 6-12 months. However, longer-term data may show benefit, and patient selection is key. This is an active debate in orthopaedics - be prepared to discuss in examinations.
Evidence Base and Key Trials
CSAW Trial - ASD vs Sham
- ASD not superior to sham surgery at 6 months
- Both groups improved from baseline
- Placebo effect significant
- Questions routine use of ASD
FIMPACT Trial
- ASD not superior to diagnostic arthroscopy
- Both groups improved
- Non-specific surgical effect
- Finnish population study
Neer Original Description
- Defined impingement syndrome
- Three-stage classification
- Anterior acromioplasty technique described
- Foundation of modern understanding
Bigliani Acromial Morphology
- Three types of acromion described
- Type 3 hooked associated with cuff tears
- Anatomical basis for impingement
- Widely adopted classification
Kuhn Systematic Review - Subacromial Injection
- Corticosteroid injection provides short-term relief
- Benefit peaks at 4-8 weeks
- Not curative, aids physiotherapy
- Limited long-term benefit
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Impingement Assessment (~2-3 min)
"A 45-year-old office worker presents with 6 months of right shoulder pain, worse at night and with overhead activities. How do you assess for subacromial impingement?"
Scenario 2: Treatment Approach (~2-3 min)
"A 50-year-old man has Neer Stage II impingement confirmed clinically. MRI shows thickened supraspinatus tendon without tear. He has failed 3 months of physiotherapy. What is your management?"
Scenario 3: Acromial Morphology (~2 min)
"Describe the Bigliani classification of acromial morphology and its clinical significance."
MCQ Practice Points
Neer Classification Question
Q: What pathology is seen in Neer Stage II impingement? A: Fibrosis and tendinitis - Stage I is edema/hemorrhage (under 25 years), Stage II is fibrosis/tendinitis (25-40 years), Stage III is rotator cuff tear (over 40 years).
Bigliani Question
Q: Which Bigliani acromial type has the highest impingement risk? A: Type 3 (Hooked) - Type 1 is flat (lowest risk), Type 2 is curved (moderate risk), Type 3 is hooked (highest risk and associated with cuff tears).
Clinical Test Question
Q: How is the Neer impingement test performed? A: Forward flex the arm with scapula stabilized - The examiner stabilizes the scapula and passively forward flexes the arm overhead. This compresses the cuff against the anterior acromion. Positive if reproduces the patient's pain.
Hawkins Test Question
Q: How is the Hawkins impingement test performed? A: Flex shoulder and elbow to 90°, then internally rotate - The arm is positioned in 90° of forward flexion and elbow flexion, then the forearm is internally rotated. This compresses the cuff against the coracoacromial ligament.
X-ray View Question
Q: Which X-ray view best demonstrates acromial morphology? A: Outlet view (Supraspinatus outlet/Scapular Y-view) - This view shows the acromial profile and allows classification into Bigliani Types 1, 2, or 3. Also visible on sagittal MRI.
CSAW Trial Question
Q: What did the CSAW trial show regarding arthroscopic subacromial decompression? A: ASD was not significantly better than sham surgery at 6 months for isolated subacromial impingement without rotator cuff tear. This has led to debate about routine ASD for impingement.
Australian Context and Medicolegal Considerations
Australian Practice
- CSAW/FIMPACT evidence widely discussed
- Emphasis on conservative treatment first
- ASD still performed but with informed consent
- PBS covers physiotherapy referrals
- Private practice similar to UK/US trends
Documentation Standards
- Document failed conservative treatment
- Record clinical tests and findings
- Imaging review and acromial type
- Consent must include recent evidence
- Document discussion of limited surgical benefit
Medicolegal Considerations
Key documentation requirements:
- Document failed conservative treatment (type, duration, compliance)
- Record clinical examination with specific tests
- Note imaging findings (acromial morphology, cuff status)
- Consent must discuss: CSAW/FIMPACT evidence (ASD may not be better than sham), alternatives, expected outcomes, risks
- If proceeding to surgery, document patient's informed decision
EXTERNAL IMPINGEMENT
High-Yield Exam Summary
Definition
- •Compression of supraspinatus under acromion
- •External = subacromial (vs internal = posterior-superior)
- •Bursal side cuff affected
- •Degenerative/mechanical etiology
Neer Classification
- •Stage I: Edema/hemorrhage (under 25 years)
- •Stage II: Fibrosis/tendinitis (25-40 years)
- •Stage III: Rotator cuff tear (over 40 years)
Bigliani Acromion Types
- •Type 1: Flat (lowest risk)
- •Type 2: Curved (moderate risk)
- •Type 3: Hooked (highest risk)
- •Seen on outlet view X-ray
Clinical Tests
- •Neer: Forward flex with scapula fixed
- •Hawkins: 90° flex, internal rotate
- •Painful arc: 60-120° abduction
- •Injection test: LA into subacromial space
Treatment
- •Non-operative first (70-90% success)
- •Physio, NSAIDs, injection
- •ASD debated (CSAW/FIMPACT trials)
- •Surgery if cuff tear present
CSAW Trial
- •ASD vs sham surgery comparison
- •No significant difference at 6 months
- •Questions routine ASD for isolated impingement
- •Must discuss in consent