Shoulder Impingement Syndrome (Subacromial Impingement)

**Shoulder impingement syndrome** occurs when the rotator cuff tendons (primarily supraspinatus) and subacromial bursa become compressed in the **subacromial space** — the narrow gap between the humeral head and the acromion. With shoulder elevation, this space normally narrows; in impingement, it becomes pathologically constricted, causing tendon irritation, inflammation, and progressive damage. **The Neer Classification (3 stages):** **Stage 1 — Reversible Edema and Hemorrhage:** - Typical age <25 - Acute inflammation from overuse - Fully reversible with rest and rehab - Common in young athletes (swimmers, throwers, painters) **Stage 2 — Fibrosis and Tendinitis:** - Typical age 25-40 - Chronic inflammation leads to tendon thickening and bursal fibrosis - Partially reversible with structured rehabilitation - Mechanical impingement worsens with continued overuse **Stage 3 — Rotator Cuff Tear, Bone Changes:** - Typical age >40 - Partial or full-thickness rotator cuff tears - Acromial spurs and bony remodeling - May require surgical intervention **Two main types:** - **Primary (Outlet) Impingement**: Mechanical narrowing from acromial shape, bone spurs, or AC joint arthritis - **Secondary (Non-outlet) Impingement**: Functional narrowing from glenohumeral instability, scapular dyskinesis, or rotator cuff weakness — far more common in younger patients The condition exists on a spectrum with [rotator cuff tendinitis](/condition/rotator-cuff-tear), bursitis, and rotator cuff tears — all related to the same underlying mechanical problem.

## Root Causes **Extrinsic (Mechanical) Factors — Primary Impingement:** - **Acromial shape**: Type III (hooked) acromion increases impingement risk 2-3x; Type II (curved) is intermediate; Type I (flat) lowest risk - **Acromial spurs**: Develop with age, narrowing the subacromial space - **AC joint osteoarthritis**: Inferior osteophytes encroach on the subacromial space - **Os acromiale**: Failure of acromial fusion (5-15% of population) **Intrinsic (Functional) Factors — Secondary Impingement:** - **Rotator cuff weakness**: Allows superior migration of the humeral head into the acromion - **Scapular dyskinesis**: Abnormal scapular movement reduces subacromial space dynamically - **Posterior capsule tightness**: Forces the humeral head superiorly during elevation - **Glenohumeral instability**: Especially in throwing athletes — internal impingement - **Postural dysfunction**: Forward head, rounded shoulders, and thoracic kyphosis decrease subacromial space **Activity-Related Risk Factors:** - Overhead occupations (painters, electricians, construction workers) - Overhead sports (swimming, tennis, baseball, volleyball) - Sudden increase in shoulder activity (weekend warriors) - Heavy lifting with poor mechanics

## Conservative Treatment (First-Line — 60-80% Success) **1. Activity Modification:** - Reduce overhead activities for 4-6 weeks - Avoid sleeping on the affected side - Modify ergonomics for work and exercise **2. Physical Therapy (Most Important):** *Phase 1 (Weeks 1-2): Pain Reduction* - Pendulum exercises for gentle mobilization - Pain-free range of motion work - Posterior capsule stretching (cross-body stretch, sleeper stretch) - Ice 15-20 minutes after activity *Phase 2 (Weeks 3-6): Strengthening* - **Rotator cuff strengthening** — external rotation and internal rotation with resistance bands - **Scapular stabilization** — rows, scapular squeezes, prone Y-T-W raises - Closed-chain exercises (wall pushups progressing to standard pushups) - **Avoid empty can exercises** in early phase — these can perpetuate impingement *Phase 3 (Weeks 6-12): Functional Return* - Sport or activity-specific exercises - Plyometrics for athletes - Progressive loading toward overhead activities **3. Medications:** - NSAIDs (ibuprofen, naproxen) for 2-3 weeks during acute flares - Topical NSAIDs as alternative for those who can't tolerate oral medications **4. Corticosteroid Injection:** - Subacromial bursa injection provides 70-80% short-term relief - Should be combined with physical therapy — injection alone has poor long-term outcomes - Limit to 2-3 injections per year to avoid tendon weakening **5. Postural Correction:** - Address forward head and rounded shoulder posture - Strengthen middle and lower trapezius, rhomboids - Stretch pectoralis minor and major ## Surgical Treatment (10-15% of Cases) **Indicated for:** - Failed 6+ months of structured conservative treatment - Stage 3 disease with rotator cuff tears - Type III acromion with significant outlet stenosis **Subacromial decompression** (arthroscopic): - Removes acromial spurs and bursal tissue - Releases the coracoacromial ligament - Often combined with rotator cuff repair if tears present - Recovery: 3-6 months for full return; success rate 70-85%