What is the pathophysiology and management of acromial (AC) bursitis?

Pathophysiology and Management of Acromial (AC) Bursitis

Acromial bursitis is primarily an inflammatory condition of the subacromial bursa caused by mechanical irritation, with treatment focused on corticosteroid injections and physical therapy for optimal outcomes and reduced recurrence rates.

Pathophysiology

The pathophysiology of acromial (AC) bursitis involves several key mechanisms:

1. Anatomical Basis:

   • The subacromial bursa is located between the superior surface of the supraspinatus tendon and the overlying coraco-acromial ligament and acromion 1
   • It functions as a cushioning structure to reduce friction during shoulder movement

2. Inflammatory Process:

   • Contrary to traditional belief, histological studies show that true inflammatory cell infiltration with polymorphonuclear cells is uncommon in most cases 2
   • Instead, the pathology typically involves:
     • Numerical increase in cells throughout the bursal wall
     • Proliferation of endothelial cells in vascular channels
     • Dense intermediate filaments in cell cytoplasm
     • Lipid droplet accumulation in cases with rotator cuff tears 2

3. Causative Factors:

   • Mechanical impingement from:
     • Acromioclavicular joint degeneration with osteophyte formation
     • Distally projecting osteophytes
     • Tight coraco-acromial ligament 1
   • Cytokine involvement, particularly interleukin-1 beta, which plays a prominent role in the inflammatory cascade 3
   • Secondary to rotator cuff pathology or calcific tendinitis 2

Diagnostic Approach

1. Clinical Evaluation:

   • Pain localized to the lateral aspect of the shoulder
   • Pain aggravated by pressure from shoes/clothing
   • Pain relief when pressure is removed 4
   • Tenderness lateral to the Achilles tendon (similar mechanism in trochanteric bursitis) 4

2. Imaging Studies:

   • Radiographs: First-line imaging to identify bony abnormalities like osteophytes or calcifications 4
   • Ultrasound: Highly effective for evaluating bursitis and associated soft tissue abnormalities 4
     • Can detect joint effusions, bursal collections, capsular thickening, and synovitis
     • Useful for guiding injections
   • MRI: Usually appropriate for questionable bursitis or tenosynovitis 4
     • Both MRI and ultrasound are rated as equivalent (9/9 rating) for evaluation of bursitis 4
     • Can assess peritrochanteric structures including muscles, tendons, and bursa 4

Management

Non-surgical Management

1. First-line Treatments:

   • Activity modification to reduce mechanical irritation
   • NSAIDs for pain and inflammation control 4, 5
   • Ice application for acute symptoms 5

2. Corticosteroid Injections:

   • Highly effective for acute symptom relief 6
   • Technique:
     • Should be image-guided (ultrasound preferred) for accuracy 4
     • Avoid injecting directly into tendons
     • Can be combined with local anesthetic for diagnostic confirmation 4

3. Physical Therapy:

   • Therapeutic exercise programs (8-week duration recommended) 6
   • Focus on strengthening the rotator cuff and scapular stabilizers
   • Stretching exercises to improve range of motion

4. Combined Approach:

   • Corticosteroid injection combined with physical therapy shows superior outcomes to physical therapy alone for pain relief and improved shoulder function 6
   • However, physical therapy alone shows the lowest recurrence rate (7.5%) compared to corticosteroid injection alone (36.1%) or combined treatment (17.1%) 6

Surgical Management

Surgical intervention is indicated for refractory cases that fail to respond to conservative measures:

1. Indications:

   • Persistent symptoms despite 6-8 weeks of conservative treatment 4
   • Large, distally projecting osteophytes with AC joint degeneration 1

2. Procedures:

   • Arthroscopic subacromial decompression
   • Resection of the prominent posterior superior aspect of the calcaneus and inflamed bursa (similar approach to Haglund's deformity) 4
   • When AC joint pathology is present:
     • Distal clavicular resection
     • Beveling of the AC joint
     • Excision of marginal osteophytes 1

Treatment Algorithm

1. Initial Presentation:

   • Confirm diagnosis with clinical exam and imaging (radiographs + ultrasound)
   • Start NSAIDs, activity modification, and ice

2. First 6 Weeks:

   • Corticosteroid injection under ultrasound guidance
   • Initiate physical therapy program focusing on therapeutic exercises
   • Monitor for symptom improvement

3. At 6-8 Week Assessment:

   • If improved: Continue physical therapy until symptoms resolve
   • If no improvement: Consider repeat injection or surgical consultation

4. Persistent Symptoms Beyond 3 Months:

   • Surgical evaluation for subacromial decompression and/or AC joint procedures

Key Considerations and Pitfalls

1. Differential Diagnosis:

   • Must distinguish bursitis from arthritis, fracture, tendinitis, and nerve pathology 5
   • AC joint pathology may coexist with or mimic subacromial impingement 1

2. Injection Technique:

   • Avoid multiple repeated injections as they may lead to tendon weakening
   • Use image guidance to ensure accurate placement and avoid tendon injection

3. Recurrence Prevention:

   • Physical therapy has the lowest recurrence rate and should be included in all treatment plans 6
   • Address underlying biomechanical issues to prevent symptom return

4. Monitoring:

   • Follow patients for at least 4 weeks after treatment to assess response 6, 3
   • Consider alternative diagnoses if symptoms persist despite appropriate treatment

By understanding the pathophysiology and following a structured management approach, most patients with AC bursitis can achieve significant symptom relief and improved shoulder function.