SUBACROMIAL IMPINGEMENT SYNDROME
Shoulder Pain | Rotator Cuff Pathology | Conservative First | Surgery for Refractory Cases
NEER STAGES
Critical Must-Knows
- Primary impingement = structural narrowing (acromion, AC joint) vs Secondary impingement = rotator cuff weakness/instability
- Neer test (passive forward flexion) and Hawkins-Kennedy test (IR at 90° flexion) - highest sensitivity when combined
- Conservative treatment for 3-6 months before considering surgery - includes NSAIDs, physiotherapy, subacromial injection
- Subacromial decompression = arthroscopic acromioplasty + bursectomy - controversial efficacy vs sham surgery
- Imaging - X-ray for bone abnormalities (acromion shape, spurs), MRI for rotator cuff tears and inflammation
Examiner's Pearls
- "Most common cause of shoulder pain in adults over 40 years
- "Combination of Neer and Hawkins-Kennedy tests increases diagnostic sensitivity to over 90%
- "CSAW trial (2018) showed no benefit of arthroscopic decompression over placebo surgery - controversial
- "Bigliani classification of acromion shape (Type I flat, II curved, III hooked) - Type III highest impingement risk
Clinical Imaging
Imaging Gallery
Critical Subacromial Impingement Exam Points
Primary vs Secondary Impingement
Primary = structural narrowing (acromion morphology, spurs, AC joint arthritis). Secondary = rotator cuff weakness or instability causing superior humeral head migration. Treatment differs - address underlying cause.
Neer Staging System
Stage I (under 25 years) = edema/hemorrhage, reversible. Stage II (25-40 years) = fibrosis/tendinitis. Stage III (over 40 years) = bone spurs, tears, irreversible. Guides prognosis and treatment.
Clinical Tests Hierarchy
Neer test (90% sensitive) + Hawkins-Kennedy (87% sensitive) combined approach 95% sensitivity. Neer impingement test (subacromial lidocaine injection eliminates pain) confirms diagnosis.
Surgery Controversy
CSAW trial (2018) showed arthroscopic decompression no better than sham surgery at 1 year. UKUFF trial confirmed findings. Current consensus: surgery only after failed conservative treatment, patient selection critical.
Quick Decision Guide
| Patient Scenario | Stage | First-Line Treatment | Key Pearl |
|---|---|---|---|
| Young athlete (under 30), acute onset, normal X-ray | Stage I - Acute inflammation | Rest, NSAIDs, early physio | Rule out instability - may be secondary impingement |
| 40-year-old, chronic pain, failed 2 months physio | Stage II - Fibrosis/tendinitis | Subacromial steroid injection + structured rehab | Need 3-6 months total conservative trial before surgery |
| Over 60, chronic pain, Type III acromion, small cuff tear | Stage III - Structural changes | Consider surgery if failed conservative | Manage cuff tear if present - may need repair not just decompression |
SCABSubacromial Space Anatomical Boundaries
Memory Hook:The SCAB forms when impingement causes inflammation - think of the inflamed bursa!
FINSNeer Impingement Provocation Test Technique
Memory Hook:FINS help the fish swim UP (forward flexion) - Neer test moves arm upward!
FCHBigliani Acromion Classification
Memory Hook:FCH = From Curve to Hook - progressive impingement risk increases!
HNPClinical Impingement Tests
Memory Hook:HNP tests Hunt for Neer's Pathology!
EFTNeer Staging of Impingement
Memory Hook:Edema, Fibrosis, Tears - impingement progresses with age!
Overview and Epidemiology
Subacromial impingement syndrome (SIS) is the most common cause of shoulder pain in adults, accounting for 44-65% of all shoulder pain complaints. The condition results from mechanical compression of the rotator cuff tendons and subacromial bursa within the subacromial space during shoulder elevation.
Why This Topic Matters
SIS represents a spectrum of pathology from acute reversible inflammation to chronic irreversible tendon degeneration and tears. Understanding the distinction between primary (structural) and secondary (functional) impingement is critical for appropriate treatment selection. Recent high-quality RCTs have challenged traditional surgical approaches, making this a high-yield exam topic for evidence-based discussion.
Demographics
- Age: Peak incidence 40-60 years
- Gender: Slightly more common in females (1.2:1)
- Occupation: Overhead workers, athletes (swimmers, throwers)
- Dominant arm: More commonly affected (60%)
Impact
- Work loss: Average 6-12 weeks for manual laborers
- Function: Significant disability in ADLs and sleep
- Progression: 5-10% develop full-thickness rotator cuff tears annually
- Economic: $3 billion annual healthcare costs (US data)
Anatomy
Critical Concept: Subacromial Space Dimensions
The subacromial space measures approximately 7-14mm in height. Any reduction below 7mm significantly increases impingement risk. This narrow corridor contains the supraspinatus tendon, long head biceps, subacromial bursa, and rotator cuff interval. Understanding this confined anatomy explains why even small changes (1-2mm bone spurs, bursal thickening) cause significant symptoms.
Primary Impingement (Extrinsic Compression)
Structural factors that narrow the subacromial space:
| Anatomical Factor | Mechanism | Prevalence | Clinical Significance |
|---|---|---|---|
| Acromion morphology (Bigliani Type III) | Hooked acromion reduces clearance by 3-5mm | 20-30% of population | Highest impingement risk - often requires acromioplasty |
| Acromial spurs (anterior-inferior) | Osteophyte formation narrows outlet | 30-40% over age 50 | Common in Stage III disease - visible on X-ray |
| AC joint arthritis with osteophytes | Inferior osteophytes encroach on space | 25-35% over age 60 | May require AC joint excision (Mumford procedure) |
| Os acromiale (unfused apophysis) | Mobile anterior acromion segment | 3-8% of population | Can be unstable - may need open fixation or excision |
Secondary Impingement (Functional)
Rotator Cuff Weakness
- Mechanism: Weak cuff cannot depress humeral head during elevation
- Superior migration: Head translates upward 2-4mm
- Cycle: Impingement causes pain → disuse → further weakness
- Treatment: Address weakness, not surgical decompression
Glenohumeral Instability
- Mechanism: Subtle instability (microinstability) causes abnormal kinematics
- Population: Young athletes, especially overhead sports
- Presentation: Positive apprehension/relocation tests alongside impingement signs
- Treatment: Stability rehabilitation, not acromioplasty
Pathophysiology
Pathological Cascade (Neer Stages)
Progressive Pathology
Pathology: Acute inflammatory response to mechanical irritation. Bursal edema, microhemorrhage in supraspinatus tendon.
Reversibility: Completely reversible with rest and conservative treatment.
Clinical: Acute onset pain, positive impingement tests, full strength initially.
Pathology: Chronic inflammation leads to bursal thickening (3-5mm), tendon fibrosis, early degeneration.
Reversibility: Partially reversible - fibrosis persists but symptoms can resolve.
Clinical: Chronic pain, night pain common, weakness developing, positive impingement tests.
Pathology: Anterior-inferior acromial spurs, greater tuberosity changes, partial or full-thickness rotator cuff tears.
Reversibility: Irreversible structural changes - symptom management only.
Clinical: Chronic pain, weakness, limited ROM, crepitus, positive impingement and cuff tear tests.
Classification Systems
Neer Classification of Impingement Stages
Historical but still clinically relevant staging system based on pathological changes and age.
| Stage | Age Range | Pathology | Treatment Approach |
|---|---|---|---|
| Stage I | Under 25 years | Reversible edema, hemorrhage, inflammation | Conservative only - rest, NSAIDs, physio |
| Stage II | 25-40 years | Fibrosis, tendinitis, bursal thickening | Conservative first; surgery if failed 6 months |
| Stage III | Over 40 years | Bone spurs, rotator cuff tears, irreversible | Often surgical - may need cuff repair not just decompression |
Clinical Application
While age ranges are guidelines, pathological stage matters more than chronological age. A 30-year-old overhead athlete may have Stage III disease, while a 50-year-old office worker may have Stage I. MRI and clinical exam determine stage, not just age.
Clinical Assessment
History
- Pain location: Anterolateral shoulder, radiates to deltoid insertion
- Aggravating factors: Overhead activities, reaching behind back, sleeping on affected side
- Onset: Gradual (chronic) vs acute (after injury/overuse)
- Occupation/sport: Overhead work (painters, carpenters), swimming, tennis, throwing
- Night pain: Common - suggests more advanced disease (Stage II-III)
- Weakness: Difficulty lifting, reaching - suggests cuff involvement
Examination Sequence
- Look: Muscle atrophy (supraspinatus, infraspinatus wasting), asymmetry
- Feel: Tenderness anterolateral acromion, AC joint, greater tuberosity
- Move: Painful arc 60-120° abduction, loss of active elevation
- Special tests: Impingement tests (Neer, Hawkins-Kennedy), cuff tests (Jobe, external rotation)
- Neurovascular: Exclude cervical radiculopathy, thoracic outlet syndrome
Key Special Tests
| Test | Technique | Positive Finding | Sensitivity | Specificity |
|---|---|---|---|---|
| Neer Impingement Test | Passive forward flexion in IR, scapula stabilized | Pain at terminal flexion | 79-90% | 31-53% |
| Hawkins-Kennedy Test | 90° forward flexion, passive IR | Pain with IR movement | 74-92% | 25-58% |
| Neer Impingement Injection Test | 10ml lidocaine subacromial injection, repeat Neer test | Complete pain relief confirms impingement | 75-95% | 40-70% |
| Painful Arc | Active abduction 0-180° | Pain between 60-120° (most 70-110°) | 33-98% | 10-81% |
Test Interpretation Pearl
Single test specificity is poor - Neer and Hawkins-Kennedy have high sensitivity (good for ruling OUT) but low specificity (many false positives). Combination approach: If BOTH Neer AND Hawkins-Kennedy are positive, combined specificity increases to 70-80%. Impingement injection test is most specific - complete pain relief confirms diagnosis and predicts good response to treatment.
Beware the Cervical Mimic
C5 radiculopathy can present with shoulder pain, weakness, and positive impingement tests. Always check: Spurling test (cervical compression), reflexes (biceps, brachioradialis), dermatomal sensation. Key distinction: Cervical pathology causes pain with neck movement, not just shoulder movement. MRI cervical spine if diagnostic doubt.
Investigations
Imaging Protocol
Views: AP, axillary lateral, outlet view (scapular Y with 10° caudal tilt)
Findings:
- Acromion shape: Bigliani Type I/II/III on outlet view
- Acromial spurs: Anterior-inferior undersurface
- AC joint: Arthritis, inferior osteophytes, distal clavicle hypertrophy
- Greater tuberosity: Sclerosis, cysts, cortical irregularity (chronic impingement)
- Os acromiale: Unfused acromial apophysis (axillary view best)
- Calcific tendinitis: Calcium deposits in rotator cuff
Limitations: Cannot visualize soft tissues (cuff, bursa). Normal X-ray does NOT rule out impingement.
Advantages: Real-time visualization during movement, operator-dependent, low cost
Findings:
- Bursal thickening: Normal under 2mm; pathological greater than 3mm
- Subacromial space: Measure distance during abduction (normal 6-14mm)
- Rotator cuff: Partial tears, full-thickness tears, tendinosis
- Dynamic assessment: Observe impingement during active elevation
Sensitivity/Specificity: 67-98% for cuff tears (operator-dependent)
Indications: Suspected cuff tear, failed conservative treatment, pre-operative planning
Findings:
- Subacromial space: Fluid, bursal thickening (bright T2), fibrosis
- Rotator cuff: Partial/full-thickness tears, tendinosis, muscle atrophy
- Acromion: Bone marrow edema adjacent to cuff (chronic impingement)
- AC joint: Cartilage loss, osteophytes, joint effusion
- Labrum/capsule: Associated instability (secondary impingement)
Sensitivity: 84-100% for full-thickness tears, 44-91% for partial tears
Imaging Decision Algorithm
Under 40 years, acute onset, normal exam strength: X-ray only, trial conservative treatment. Over 40 years, chronic pain, weakness: X-ray + MRI to exclude cuff tear (5-10% annual tear risk in this population). Pre-operative planning: Always MRI to assess cuff integrity - do not offer isolated acromioplasty if significant cuff tear present (may need repair).
Management Algorithm
Conservative treatment is first-line for ALL patients and successful in 80-90% of cases. Minimum 3-6 month trial before considering surgery.
Conservative Management
Initial Management Goals
Primary objectives: Reduce pain and inflammation, maintain ROM, prevent stiffness
Treatment Protocol
- Avoid: Overhead activities, repetitive reaching, heavy lifting
- Modify: Work ergonomics (desk height, computer position)
- Sleep: Avoid lying on affected side; use pillow support
- Duration: 2-4 weeks strict avoidance, then gradual return
- NSAIDs: Ibuprofen 400mg TDS or naproxen 500mg BD for 10-14 days
- Ice therapy: 15-20 minutes TDS-QID (acute inflammation)
- Analgesics: Paracetamol 1g QID for additional pain relief
- Avoid: Prolonged immobilization (risk of frozen shoulder)
- Pendulum exercises: Passive ROM to prevent stiffness (days 1-7)
- Gentle ROM: Pulley exercises, wand exercises (weeks 1-3)
- Scapular stabilization: Early focus on periscapular muscles
- Avoid: Painful range, overhead strengthening too early
Frozen Shoulder Risk
Over-aggressive rest (complete immobilization) increases frozen shoulder (adhesive capsulitis) risk by 2-3 fold. Maintain gentle ROM from week 1. If passive ROM is restricted (external rotation less than 50% of normal), suspect early capsulitis and intensify stretching.
Conservative Treatment Outcomes
Surgical Management
Surgery Indications - Strict Criteria
Absolute requirements for surgical consideration:
- Failed conservative treatment for minimum 3-6 months (optimal 6 months)
- Persistent symptoms significantly affecting quality of life
- Positive impingement signs on clinical exam
- Positive impingement injection test (confirms subacromial pathology)
- Structural abnormality on imaging (Type III acromion, spurs) - primary impingement
- Excluded secondary causes (instability, cuff weakness without structural lesion)
Contraindications: Secondary impingement, poor rehabilitation compliance, cervical pathology, significant cuff tears (may need repair).
Arthroscopic Acromioplasty and Bursectomy
Procedure: Arthroscopic removal of anterior-inferior acromion (5-7mm) and subacromial bursa.
Surgical Steps
Position: Beach chair or lateral decubitus
Portals: Posterior viewing, lateral working, anterior accessory
Diagnostic: Arthroscopy glenohumeral joint first - exclude labral pathology, cuff tears from articular side
Entry: Scope enters subacromial space via posterior portal
Bursa removal: Arthroscopic shaver debrides thickened, inflamed bursa
Visualization: Clear subacromial space to identify undersurface of acromion, CA ligament, and rotator cuff
Identify anterior-inferior acromion: The impinging prominence
Resection: Arthroscopic burr removes 5-7mm of bone, creating flat undersurface
Check: Ensure smooth undersurface, no residual spurs
CA ligament: Partial or complete release (controversial - can cause instability)
Hemostasis: Check for bleeding, irrigate
Closure: Simple portal closure
Immobilization: Sling for comfort only (24-48 hours)
Rehabilitation: Early ROM day 1, strengthening week 2-4
Surgical Controversy - CSAW and UKUFF Trials
CSAW Trial (2018, BJSM, n=313): Arthroscopic subacromial decompression vs sham surgery (skin incisions only) vs active monitoring. Result: No difference in pain or function at 1 year. UKUFF Trial (2019, Lancet, n=503): Confirmed no benefit of decompression over investigational shoulder arthroscopy. Conclusion: Questions routine use of acromioplasty. Current practice: Highly selective surgery for patients with clear structural impingement and failed conservative treatment. In exam, acknowledge controversy and evidence.
Complications
Conservative Treatment Complications
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Frozen shoulder (adhesive capsulitis) | 2-5% | Prolonged immobilization, diabetic patients | Maintain ROM exercises from onset, aggressive stretching if develops |
| Tendon degeneration from repeated injections | Rare with under 3 injections/year | Greater than 3 steroid injections annually | Limit to 3 injections maximum per year, space 3 months apart |
| Progression to full-thickness cuff tear | 5-10% annually | Age over 50, chronic impingement, partial tear | Regular review, MRI if worsening weakness |
Surgical Complications
| Complication | Incidence | Risk Factors | Prevention/Management |
|---|---|---|---|
| Persistent pain (no improvement) | 10-15% | Secondary impingement, missed cuff tear, inadequate rehab | Exclude at outset - don't operate on secondary impingement |
| Frozen shoulder (postoperative stiffness) | 3-8% | Prolonged immobilization, poor compliance with PT | Early ROM from day 1, supervised physiotherapy |
| Deltoid dysfunction | 2-5% | Axillary nerve injury (open), detachment (open) | Limit deltoid split to less than 5cm from acromion, careful dissection |
| Infection | Less than 1% | Diabetes, immunosuppression, steroid injection pre-op | Antibiotic prophylaxis, aseptic technique, delay surgery 3 months post-injection |
| Anterosuperior instability | 1-3% | Excessive CA ligament release, over-resection of acromion | Preserve CA arch integrity, limit resection to 5-7mm |
Prevention of Failed Surgery
Most common cause: Operating on secondary impingement (rotator cuff weakness, instability). These patients have positive impingement signs but surgery does not address the underlying functional problem. Prevention: Thorough preoperative assessment to distinguish primary (structural) from secondary (functional) impingement. Young athletes with instability signs should NOT have acromioplasty.
Outcomes and Prognosis
Conservative Treatment Outcomes
| Treatment | Short-term (3-6 months) | Long-term (1-2 years) | Notes |
|---|---|---|---|
| Physiotherapy alone | 60-70% improvement | 50-60% sustained | Best for Stage I, younger patients |
| Physio + NSAIDs | 70-80% improvement | 60-70% sustained | Standard first-line approach |
| Physio + steroid injection | 75-85% improvement | 65-75% sustained | Injection benefits mainly short-term (under 12 weeks) |
Surgical Outcomes
| Outcome Measure | Traditional Series | CSAW Trial (2018) | Interpretation |
|---|---|---|---|
| Pain improvement at 1 year | 75-85% significant improvement | No difference vs sham surgery | Questions whether improvement is due to surgery or placebo/natural history |
| Function improvement | 70-80% return to work/sport | Similar improvement in all 3 groups (surgery, sham, conservative) | Suggests natural improvement over time regardless of treatment |
| Patient satisfaction | 80-85% satisfied | High satisfaction in all groups including sham | Highlights powerful placebo effect of surgery |
Prognostic Factors
Good Prognosis Indicators
- Age under 50 years: Better outcomes with both conservative and surgical treatment
- Short symptom duration (less than 6 months): Responds better to conservative treatment
- Positive injection test: Predicts good surgical outcome (if structural impingement)
- Type III acromion with spur: Clear structural abnormality (if primary impingement)
- Good rehabilitation compliance: Critical for both conservative and surgical success
Poor Prognosis Indicators
- Secondary impingement: Surgery fails (instability or cuff weakness not addressed)
- Workers' compensation claims: Associated with worse outcomes (psychological factors)
- Chronic symptoms (over 2 years): Lower success rates
- Significant cuff tear: Need cuff repair, not just decompression
- Smoking, diabetes: Delayed healing, higher complication rates
Critical Evidence Discussion
Pre-CSAW (before 2018): Surgical outcomes quoted as 75-85% good-excellent results based on traditional case series. Post-CSAW (2018 onward): High-quality RCT showed no benefit over sham surgery, challenging these historical results. Current consensus: Surgery may still benefit highly selected patients (failed prolonged conservative treatment, clear structural abnormality, positive injection test), but expectations should be moderated given trial evidence. Quote realistic outcomes: "50-75% chance of significant improvement, but this may occur with continued conservative treatment as well."
Postoperative Care and Rehabilitation
Rehabilitation Timeline
- Immobilization: Sling for comfort only (not mandatory)
- Pain control: Ice, analgesics, limit opioids
- Early ROM: Pendulum exercises day 1, passive forward flexion to tolerance
- Goal: Prevent stiffness, control pain
- ROM: Active-assisted ROM all planes, wand exercises
- Sling: Discontinue when comfortable (usually 3-5 days)
- Avoid: Resisted exercises, heavy lifting
- Goal: Full passive ROM by week 2
- Strengthening: Begin rotator cuff and scapular exercises (isometric, then theraband)
- ROM: Full active ROM by week 4-6
- Functional: Light ADLs, desk work
- Goal: Restore muscle balance, endurance
- Advanced strengthening: Progressive resistance, sport-specific exercises
- Return to work: Manual labor by week 8-12 (depending on demands)
- Return to sport: Overhead athletes week 12-16
- Goal: Full function, return to activities
Postoperative Milestones
Week 2: Full passive ROM expected. Week 6: Full active ROM expected. Week 12: Return to overhead sports. Failure to achieve these milestones suggests complication (frozen shoulder, re-impingement) - investigate and intensify physiotherapy.
Evidence Base and Key Trials
CSAW Trial - Subacromial Decompression vs Sham Surgery
- Multicenter RCT: 313 patients with subacromial pain, randomized to arthroscopic decompression vs arthroscopy only (sham) vs active monitoring
- Primary outcome (Oxford Shoulder Score at 6 months): No significant difference between decompression and sham (both improved)
- Secondary outcomes: No difference in pain, function, or quality of life at 1 year
- All three groups showed improvement over 6 months (natural history + placebo effect)
UKUFF Trial - Decompression for Rotator Cuff Disease
- RCT: 503 patients with shoulder impingement, randomized to arthroscopic decompression vs diagnostic arthroscopy vs conservative treatment
- At 2 years: No difference in pain between decompression and diagnostic arthroscopy
- Conservative treatment group also showed similar outcomes
- Conclusion: Decompression no better than placebo surgery or conservative treatment
Bigliani Acromion Classification and Impingement Risk
- Cadaveric study: 140 shoulders examined for acromion morphology and rotator cuff pathology
- Type I (flat) 17% prevalence, 13% had cuff tears
- Type II (curved) 43% prevalence, 24% had cuff tears
- Type III (hooked) 40% prevalence, 70% had cuff tears
- Statistically significant association between Type III and cuff pathology
Corticosteroid Injection for Subacromial Impingement - Cochrane Review
- Meta-analysis of 26 RCTs evaluating subacromial corticosteroid injection
- Short-term benefit (up to 9 weeks): Small improvement in pain and function vs placebo
- Long-term benefit (beyond 6 months): No difference from placebo
- Similar efficacy to NSAIDs at short-term; injection may work faster
- No benefit of repeated injections over single injection
Conservative vs Surgical Treatment for Subacromial Impingement - Systematic Review
- Systematic review of 5 RCTs comparing surgery vs conservative treatment
- Short-term (3-6 months): Surgery showed faster improvement
- Long-term (1-2 years): No significant difference in outcomes
- 80-90% success rate with conservative treatment at 1 year
- Surgery benefits highly selected patients with persistent symptoms and structural abnormalities
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Classic Presentation - Initial Assessment (2-3 min)
"A 52-year-old painter presents with 6 months of progressive right shoulder pain. He has difficulty working overhead and has night pain. Examination shows positive Neer and Hawkins-Kennedy tests, painful arc 70-110°, full strength on rotator cuff testing. X-ray shows a Type III acromion with small anterior-inferior spur. How would you assess and manage this patient?"
Scenario 2: Young Athlete - Secondary Impingement (3-4 min)
"A 28-year-old competitive swimmer presents with 4 months of shoulder pain during training. She has positive impingement signs. You also note positive apprehension and relocation tests. MRI shows subacromial bursal fluid but no cuff tear, normal labrum. How would you approach this case?"
Scenario 3: Failed Conservative Treatment - Surgical Decision (2-3 min)
"A 58-year-old manual laborer has failed 9 months of conservative treatment for subacromial impingement. He's had physiotherapy, 2 steroid injections with temporary relief only. X-ray shows Type III acromion with prominent spur. MRI shows bursal thickening, no rotator cuff tear. He's requesting surgery. How do you counsel him about surgical options and evidence?"
MCQ Practice Points
Anatomy Question
Q: The subacromial space is bounded superiorly by which structure? A: Coracoacromial arch (anterior acromion, coracoid process, and coracoacromial ligament). The inferior boundary is the superior surface of the rotator cuff (supraspinatus primarily). Normal subacromial space height is 7-14mm.
Classification Question
Q: According to Bigliani classification, which acromion type has the highest association with rotator cuff tears? A: Type III (hooked acromion) - 70% association with rotator cuff tears vs 24% for Type II (curved) and 13% for Type I (flat). Type III represents 40% of the population.
Diagnostic Test Question
Q: What is the most specific test for diagnosing subacromial impingement syndrome? A: Neer impingement injection test - 10ml lidocaine injected into subacromial space. Complete pain relief (greater than 50% reduction) on repeat provocative tests confirms subacromial pathology. Sensitivity 75-95%, specificity 40-70%. Also predicts response to surgical decompression.
Treatment Evidence Question
Q: The CSAW trial (2018) compared arthroscopic subacromial decompression to what control? A: Sham surgery (arthroscopic portal incisions without decompression) and active monitoring. Result: No significant difference in outcomes at 6-12 months. This Level 1 evidence challenged routine use of acromioplasty and emphasized conservative treatment.
Conservative Management Question
Q: What is the minimum duration of conservative treatment recommended before considering surgery for subacromial impingement? A: 3-6 months of structured conservative treatment (physiotherapy, NSAIDs, ± steroid injection). 6 months is optimal. 80-90% of patients respond to conservative treatment within this timeframe. Premature surgery (less than 3 months) is a common cause of poor outcomes.
Surgical Complication Question
Q: What is the most common cause of failed arthroscopic subacromial decompression? A: Operating on secondary impingement (functional impingement due to rotator cuff weakness or instability). These patients have positive impingement signs but no structural narrowing - surgery does not address the underlying problem. Always distinguish primary (structural) from secondary (functional) impingement before recommending surgery.
Australian Context and Medicolegal Considerations
Australian Guidelines
- RACS Guidelines: Conservative management for minimum 3 months before surgical referral recommended
- PBS: NSAIDs (ibuprofen, naproxen) on PBS for musculoskeletal pain
- Wait times: Public system 6-12 months for non-urgent shoulder surgery - often symptoms improve during wait
Medicolegal Considerations
- Informed consent: MUST discuss CSAW/UKUFF trial findings - arthroscopic decompression no better than sham
- Documentation: Record conservative treatment timeline, injection response, patient expectations
- Failure to improve: Not a complication if adequately counseled (10-15% expected)
- Alternative options: Document discussion of continued conservative management vs surgery
Consent Documentation Requirements
Specific points to document in consent discussion:
- Success rate: 75-85% good-excellent results, but 10-15% no improvement (based on older data; CSAW suggests lower benefit)
- Recent evidence: CSAW trial showed no benefit over sham surgery - explain why still offering surgery (structural factors, failed conservative treatment, individual patient selection)
- Complications: Infection (less than 1%), stiffness (3-8%), persistent pain (10-15%), nerve injury (rare, less than 1%)
- Recovery: 3-6 months to full function, early physiotherapy critical
- Alternative: Continued conservative treatment is a valid option even after failed initial trial
Medicolegal claims often arise from failure to discuss realistic expectations and recent evidence.
SUBACROMIAL IMPINGEMENT SYNDROME
High-Yield Exam Summary
Key Anatomy
- •Subacromial space = 7-14mm height (under 7mm = impingement risk)
- •Boundaries: Superior = coracoacromial arch, Inferior = rotator cuff (supraspinatus)
- •Bigliani Type III (hooked) acromion = 70% cuff tear association (vs 13% Type I flat)
- •Structures at risk: Supraspinatus tendon, long head biceps, subacromial bursa
Classification
- •Neer Stage I (under 25) = edema/hemorrhage = reversible = conservative only
- •Neer Stage II (25-40) = fibrosis/tendinitis = conservative first, surgery if failed 6 months
- •Neer Stage III (over 40) = spurs/tears = often surgical
- •Primary (structural: acromion, spurs, AC joint) vs Secondary (functional: cuff weakness, instability)
Clinical Tests
- •Neer test (passive forward flexion) = 79-90% sensitive
- •Hawkins-Kennedy (IR at 90° flexion) = 74-92% sensitive
- •Combined Neer + Hawkins-Kennedy = greater than 90% sensitivity
- •Neer injection test (10ml lidocaine subacromial) = 75-95% sensitive, 40-70% specific = BEST diagnostic test
Treatment Algorithm
- •ALL patients: Conservative first - NSAIDs, physio (cuff/scapular strengthening), activity modification
- •Failed 4-6 weeks: Add subacromial steroid injection (short-term benefit only, max 3/year)
- •Failed 3-6 months (optimal 6): Consider surgery IF positive injection test + structural abnormality
- •Surgery: Arthroscopic decompression (acromioplasty + bursectomy) - 75-85% success but CSAW trial showed no benefit over sham
Surgical Pearls
- •Resect 5-7mm anterior-inferior acromion (excessive = instability risk)
- •Complete bursectomy for visualization
- •Assess cuff from articular side first (exclude tears needing repair)
- •Early ROM day 1 postop (prevent stiffness), strengthen from week 2