What is the appropriate management of a subscapularis muscle abscess?

Management of Subscapularis Muscle Abscess

Subscapularis muscle abscesses require urgent surgical drainage combined with empirical intravenous antibiotics covering Staphylococcus aureus (including MRSA), as antibiotics alone are insufficient and delayed intervention leads to rapid clinical deterioration, joint destruction, and potential hematogenous spread to other organs. 1, 2, 3

Immediate Diagnostic Approach

Obtain MRI or CT imaging urgently to confirm the diagnosis and assess extent of involvement, as subscapularis abscesses frequently mimic common shoulder pathologies with subacute shoulder pain and stiffness, leading to diagnostic delays. 3, 4 Key clinical features to identify include:

• Shoulder pain with reduced range of motion worsening over approximately 6-7 days (present in 94% of cases) 3
• Fever and systemic signs of infection including temperature >38.5°C, tachycardia >100 bpm 1, 5
• Anterior shoulder pain that worsens with lifting movements across the chest or internal rotation 3, 6

Blood cultures should be obtained immediately if bacteremia or sepsis is suspected, as subscapularis abscesses can cause severe concomitant infections via hematogenous spread, including bacterial meningitis. 2, 3

Primary Treatment: Surgical Drainage

Surgical drainage is mandatory in all cases and should not be delayed while awaiting culture results or attempting antibiotic therapy alone. 1, 5, 3 The abscess requires open surgical debridement rather than simple needle aspiration due to:

• Complex anatomy with potential spread through subscapular space, subcoracoid recess, and scapulothoracic space 7, 3
• Frequent glenohumeral joint involvement requiring thorough debridement 2, 7
• Need for complete evacuation of infected granulation tissue and loculations 5

Surgical Approach Selection

The deltopectoral approach is the most commonly utilized and recommended initial approach, providing adequate access to the subscapular space via a medial route to the coracoid process. 2, 4 Alternative approaches include:

• Dual anterior approach (deltopectoral plus anterior to latissimus dorsi) for extensive involvement of inferior subscapular spaces and gravity-dependent drainage 7
• Dorsal subscapularis approach when abscess extends from subscapularis muscle to glenohumeral joint 2
• Tendon-sparing approaches can access most locations within the subscapular space 3

Thorough surgical technique must include:

• Complete evacuation of pus and infected granulation tissue 1, 5
• Probing and breaking up all loculations 5
• Curettage of the subscapularis muscle belly if involved 2
• Copious irrigation 2

Antibiotic Therapy

Initiate empirical intravenous antibiotics immediately covering S. aureus including MRSA, as this is the causative organism in the majority of cases. 1, 7, 3 Recommended regimens:

First-line empirical therapy:

• Vancomycin 30 mg/kg/day IV in 2 divided doses 1
• Alternative: Clindamycin 600-900 mg IV every 8 hours (if MRSA susceptibility confirmed) 1, 7

Duration of antibiotic therapy:

• Continue IV antibiotics for 2-6 weeks depending on clinical response and extent of infection 2, 7, 4
• Most cases require 6 weeks of therapy for complete eradication 7
• Transition to oral antibiotics may be considered after clinical improvement with adequate source control 5

Antibiotics are insufficient as monotherapy even with systemic signs of infection, as source control through drainage is essential for resolution. 1, 5

Critical Monitoring and Follow-up

Reassess at 48-72 hours for clinical improvement including decreased pain, fever resolution, and improved range of motion. 5, 8

Patients with ongoing signs of infection beyond 7 days warrant complete diagnostic re-evaluation including:

• Repeat imaging (CT or MRI) to assess for inadequate drainage or recurrent collection 5, 2
• Repeat blood cultures if bacteremia suspected 5
• Consider reoperation if source control inadequate 5

Obtain follow-up imaging at 2 months to confirm no recurrence of infection. 2

Common Pitfalls to Avoid

Do not attempt needle aspiration alone for subscapularis abscesses, as the complex anatomy and frequent joint involvement require open surgical drainage. 5, 3

Do not delay surgical intervention while attempting prolonged antibiotic therapy, as clinical deterioration can be rapid with spread to adjacent structures and joints. 2, 3

Do not underestimate the extent of involvement, as the large musculature and complex communicating spaces can harbor extensive infection not apparent on initial examination. 7, 3

Monitor for nerve complications, as axillary and suprascapular nerve palsies are commonly encountered with extensive collections. 7