Subacromial Decompression (Arthroscopic)

Subacromial Space Anatomy

The subacromial space is the potential space between:

• Superiorly: Undersurface of acromion, coracoacromial ligament, AC joint
• Inferiorly: Superior surface of rotator cuff (supraspinatus, infraspinatus)
• Contents: Subacromial bursa (largest bursa in body)

Normal dimensions:

• Acromiohumeral interval: 9-10mm (reduced to less than 7mm = impingement)
• Acromion thickness: 8-10mm (minimum 8mm must be preserved)

Bigliani Classification of Acromion Morphology

Bigliani's original cadaveric work found Type III (hooked) acromions disproportionately associated with full-thickness cuff tears. Importantly, the direction of causation is debated: the hook may be a traction enthesophyte forming within the coracoacromial ligament as a CONSEQUENCE of cuff disease and altered loading, rather than the primary cause of impingement. This mechanistic uncertainty underpins the disappointing results of acromioplasty in the placebo-controlled trials.

Coracoacromial (CA) Arch

• Coracoid process - medial attachment of CA ligament
• CA ligament - thick fibrous band running from coracoid to anterolateral acromion undersurface
• Acromion - lateral attachment of CA ligament

Function: Provides superior constraint to humeral head. In massive cuff tear, CA arch is the only remaining superior stabilizer - preventing anterosuperior escape.

Key Distances

• Axillary nerve: 5cm distal to acromion (lateral portal must be less than 4cm)
• Deltoid origin: Anterior and lateral acromion edges (preserve 5mm from edges)
• Safe acromion thickness: Minimum 8mm must remain after acromioplasty

Patient Position Options:

Beach Chair Position (most widely used globally):

• Patient 65-80 degrees upright
• Head secured in padded head ring
• Arm in pneumatic arm holder allowing full ROM
• Advantages: Easier conversion to open if needed, familiar orientation
• Disadvantages: Risk of hypotensive events (cerebral hypoperfusion)

Lateral Decubitus Position:

• Patient 90 degrees lateral
• Axillary roll placed under dependent axilla
• Arm in traction (5-10 pounds) with abduction 45 degrees, forward flexion 15 degrees
• Advantages: Better distraction for cuff repair
• Disadvantages: Unfamiliar orientation, difficult to convert to open

Examination Under Anaesthesia:

• Document ROM (may reveal stiffness not apparent when awake)
• Assess stability (instability may change diagnosis)

Anatomic Landmark Marking:

• Acromion borders (anterior, lateral, posterior)
• Clavicle and AC joint
• Coracoid process
• Portal sites (posterior, lateral, anterior if needed)

Preparation:

• Confirm arthroscopy equipment functional
• Ensure fluid pump, shaver, burr available
• Check epinephrine in irrigation (1:1,000,000 for haemostasis)

Step 1: Portal Establishment - Posterior Portal

Establish posterior viewing portal first:

Technique:

• Mark posterior portal site: "Soft spot" 2cm inferior and 2cm medial to posterolateral acromion corner
• Make 5mm skin incision with #11 blade
• Blunt dissect through deltoid with artery forceps
• Insert trocar aimed toward coracoid (neurovascular structures are medial)
• Feel "pop" as capsule penetrated
• Insert 30-degree arthroscope
• Inflate joint with fluid (pump pressure 40-60 mmHg)

Step 2: Systematic Glenohumeral Arthroscopy

Perform systematic glenohumeral joint inspection before subacromial work:

Inspection Checklist:

1. Biceps tendon - tendinitis, subluxation, tears (consider tenotomy if more than 50% torn)
2. Rotator interval and coracohumeral ligament
3. Subscapularis - tears especially upper portion (hidden lesions)
4. Labrum (anterior, superior, posterior) - instability, SLAP tears
5. Glenoid and humeral head articular surfaces
6. Inferior recess - adhesive capsulitis, loose bodies
7. Articular side of rotator cuff - partial thickness tears

Step 3: Enter Subacromial Space

Redirect arthroscope from glenohumeral joint to subacromial space:

Technique:

• Withdraw scope slightly from GH joint (do not exit skin)
• Angle scope posteriorly and superiorly
• Enter subacromial bursa (space between acromion and cuff)
• Inflate space with fluid
• Expect thickened inflamed bursa in chronic impingement (versus thin filmy normal bursa)

Step 4: Lateral Working Portal Establishment

Establish lateral working portal using outside-in technique:

Technique:

• Visualize lateral acromion edge from inside
• Use spinal needle to localize portal position under direct vision
• Optimal position: 3-4cm distal to lateral acromion edge (NEVER more than 4cm = axillary nerve risk)
• Make skin incision, blunt dissect through deltoid
• Insert cannula under direct vision

Step 5: Subacromial Bursectomy

Thorough bursectomy is essential for visualization:

Technique:

• Insert shaver (4.0-5.5mm aggressive cutter) through lateral portal
• Systematically resect inflamed bursa starting posteriorly
• Work from posterior to anterior, medial to lateral
• Continue until clearly visualizing:
  • Undersurface of acromion (entire surface)
  • Bursal surface of rotator cuff
  • CA ligament anteriorly
  • AC joint medially
  • All acromion borders

Step 6: Identify Anatomic Landmarks

Before bone work, clearly identify acromion boundaries:

Technique:

• Use spinal needle from outside to localize borders
• Mark borders with electrocautery on bone surface
• Identify:
  • Anterior edge (CA ligament attaches here)
  • Lateral edge (deltoid origin)
  • Posterior edge (at posterior portal level)
  • Medial edge (AC joint - do not violate)

Acromion morphology assessment:

• Type I flat: Minimal resection needed
• Type II curved: Remove curved undersurface
• Type III hooked: Remove anterior hook (most bone work)

Step 7: Acromioplasty - Bone Resection

Flatten undersurface of acromion to Type I morphology:

Technique:

• Insert arthroscopic burr (5.5mm acromionizer) through lateral portal
• Work from POSTERIOR (safe) to ANTERIOR (danger zone)
• Use lateral edge as reference plane - resect undersurface to this level
• Remove:
  • Curved undersurface (Type II)
  • Anterior hook (Type III)
  • Anterior/anterolateral osteophytes
• Extend medially to AC joint (do not violate)

Typical bone removal:

• Anterior: 5-8mm
• Lateral: 2-5mm
• Posterior: Minimal

Critical safety margins:

• Stay 5mm from anterior edge (deltoid origin)
• Preserve 8mm minimum acromion thickness (prevents fracture)

Step 8: CA Ligament Management

CA ligament release versus preservation is controversial:

Option 1: Release (Traditional)

• Release CA ligament from anterior acromion using electrocautery or basket forceps
• Allows more aggressive anterior decompression
• Most published studies used this approach

Option 2: Preservation (Modern Trend)

• Stop acromioplasty 5-8mm from anterior edge
• Preserves CA ligament attachment
• Maintains superior constraint
• Recommended if massive cuff tear present

CONTRAINDICATION to release:

• Known massive irreparable cuff tear
• Significant cuff tear with superior migration
• Would lead to anterosuperior escape (loss of superior stability)

Step 9: Assess Adequacy of Decompression

Verify adequate decompression before finishing:

Adequacy Tests:

1. Visual assessment: Smooth flat undersurface, no residual hook/osteophytes
2. Arthroscope rotation test: Rotate scope 360 degrees from lateral portal - should not contact acromion
3. Instrument passage: Shaver/burr should pass freely under acromion
4. Fluoroscopy (if available): Lateral outlet view shows flat profile

Common areas of incomplete decompression:

• Anterolateral corner (difficult to reach)
• Extreme anterior hook (fear of deltoid detachment)
• Medial near AC joint

Step 10: AC Joint Assessment

Assess AC joint and treat if contributing to impingement:

Assessment:

• Visualize AC joint from posterior or anterior portal
• Look for inferior osteophytes impinging on cuff
• AC joint arthritis with synovitis
• AC joint instability

If AC pathology present: Perform concurrent distal clavicle excision (Mumford procedure):

• Resect 1.0-1.5cm of distal clavicle from inferior
• Preserve superior AC capsule and ligaments (stability)
• 1.0cm minimum (prevent bone healing across joint)
• 1.5cm maximum (prevent instability)

Step 11: Rotator Cuff Assessment

After decompression, thoroughly inspect rotator cuff:

Assessment:

• Bursal surface of supraspinatus, infraspinatus
• Identify tears (partial or full thickness)
• Assess tear pattern: Crescent, L-shaped, U-shaped, massive
• Determine reparability: Can edges reach footprint without tension?

If repairable tear found:

• Proceed with arthroscopic cuff repair (separate procedure)
• SAD provides optimal environment for cuff healing

If irreparable tear:

• Document and counsel patient
• Options: Debridement, superior capsular reconstruction, patch, reverse TSA for massive with pseudoparalysis

Step 12: Haemostasis and Final Inspection

Achieve haemostasis before closure:

Technique:

• Reduce pump pressure to 40mmHg (identify bleeding vessels)
• Cauterize bleeding points with electrocautery
• Final systematic inspection from multiple portals
• Ensure no instrument breakage or loose bodies
• Document with arthroscopic images

Step 13: Portal Closure

Close arthroscopic portals:

Technique:

• Remove cannulas under direct vision
• Allow fluid to drain (compress gently)
• Portal closure: Interrupted absorbable sutures or Steri-strips for small portals
• Apply sterile absorbent dressing (significant fluid leakage expected 24-48 hours)
• Cold therapy device or ice pack
• Sling for comfort (NOT immobilization)

Step 14: Post-operative Protocol

Early ROM is critical for isolated SAD (no healing constraint):

Immediate (Day 1):

• Pendulum exercises
• Passive ROM
• Sling for comfort only (wean quickly)

Week 1-2:

• Active-assisted ROM all planes
• Continue passive stretching
• Discontinue sling

Week 4-6:

• Begin strengthening
• Resistance exercises

Week 6-12:

• Advance strengthening
• Return to normal activities
• Sports by 8-12 weeks

Note: If concurrent cuff repair, protocol modified to protect repair (restricted ROM first 6 weeks).

Week 1:

• Pendulum exercises, passive ROM
• Sling for comfort only (discard by end of week)
• Portal wound care (expect significant fluid drainage)
• Ice, elevation, analgesia

Weeks 1-4:

• Progress to active-assisted then active ROM
• Full ROM target by 4 weeks
• Swimming/water exercises excellent

Weeks 4-8:

• Begin resistance exercises
• Rotator cuff and periscapular strengthening
• Progressive return to activities

Weeks 8-12:

• Advance strengthening
• Return to sports and heavy labour
• Full recovery expected by 3 months

Follow-up:

• 2 weeks: Wound check, ROM assessment
• 6 weeks: Progress check, may discharge if doing well
• 3 months: Final outcome assessment

Expected Outcomes:

• Historical case series (e.g. Ellman 1987) reported around 80-90% satisfactory results, but these were uncontrolled
• Placebo-controlled RCTs (CSAW 2018, FIMPACT 2018) show NO clinically important benefit over sham arthroscopy for subacromial pain with an intact cuff
• 2019 BMJ Rapid Recommendation: strong recommendation AGAINST subacromial decompression for subacromial pain syndrome
• Most reliable role today is as an adjunct within rotator cuff repair, not as an isolated procedure

Global Epidemiology

• Subacromial (rotator cuff related) pain is the most common cause of shoulder pain presenting to primary care worldwide, accounting for a large share of all shoulder consultations.
• Arthroscopic subacromial decompression was, until the late 2010s, among the fastest-growing orthopaedic operations in several high-income health systems despite limited efficacy evidence.

Major Guidelines, Side by Side

The international consensus is now consistent: physiotherapy-led non-operative care is first line, and isolated decompression should not be offered for subacromial pain with an intact cuff.

Where the Procedure Still Has a Role

• As an ADJUNCT during rotator cuff repair (clearing a mechanical block, smoothing a genuine anterolateral acromial spur, improving visualisation and the healing environment).
• Os acromiale or AC-joint osteophyte genuinely impinging on the cuff, addressed alongside the underlying problem.
• It should NOT be offered as a stand-alone treatment for atraumatic subacromial pain with an intact cuff.

Global Practice Variation

• Rates of decompression fell substantially in the UK and parts of Europe after CSAW, FIMPACT and the 2019 guideline, and after commissioning bodies restricted funding for low-value procedures.
• In lower-resource settings, where access to supervised physiotherapy is limited, the relative cost-effectiveness balance differs but the efficacy evidence against isolated decompression still applies.

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