Is trapezius muscle weakness common in Facioscapulohumeral Muscular Dystrophy (FSHMD) resulting in winging of the scapula?

Trapezius Muscle Weakness in FSHMD and Scapular Winging

No, trapezius muscle weakness is NOT the cause of scapular winging in Facioscapulohumeral Muscular Dystrophy (FSHMD)—the winging results from selective weakness of the thoracoscapular muscles (serratus anterior, rhomboids, and levator scapulae) while the trapezius and deltoid muscles are typically preserved. 1, 2

Mechanism of Scapular Winging in FSHMD

The pathophysiology of scapular winging in FSHMD differs fundamentally from other causes of winging:

• Selective muscle involvement: FSHMD causes preferential weakness of the periscapular stabilizing muscles (serratus anterior, rhomboids, levator scapulae) while relatively sparing the trapezius and deltoid muscles 1, 2

• Muscle imbalance pattern: This selective weakness creates a characteristic imbalance where the scapula lifts off the chest wall during shoulder movements because the weakened thoracoscapular muscles cannot maintain scapular position against the pull of the preserved deltoid 1

• Functional consequence: Despite having adequate deltoid strength for shoulder elevation, patients cannot effectively use this strength because the unstable scapular base prevents force transmission 2, 3

Clinical Presentation

Patients with FSHMD and scapular winging typically present with:

• Severely limited shoulder elevation: Preoperative active shoulder flexion averages 57-71° and abduction 53-68° despite preserved deltoid muscle strength 4, 3, 5

• Visible scapular winging: The scapula prominently lifts away from the thoracic cage during attempted arm elevation 1, 4

• Preserved deltoid function: The deltoid muscle remains functional but cannot generate effective shoulder motion without scapular stability 1, 2

• Progressive functional limitation: Patients become unable to perform overhead activities and basic activities of daily living 3, 5

Diagnostic Confirmation

When evaluating suspected FSHMD with scapular winging:

• Clinical examination: Assess for the characteristic pattern of facial weakness, shoulder girdle weakness with scapular winging, and relatively preserved deltoid strength 1, 2

• Muscle strength testing: Document shoulder elevation <90° as a key criterion for considering surgical intervention 3

• Genetic testing: Confirm FSHMD diagnosis through genetic testing, as this is essential for definitive diagnosis 6

• Serum CK levels: Check creatine kinase, though levels vary by muscular dystrophy subtype 6

Treatment Approach

Surgical Intervention: Scapulothoracic Arthrodesis

Scapulothoracic arthrodesis is the definitive treatment for FSHMD patients with severe scapular winging and preserved deltoid muscle strength, consistently improving shoulder elevation by 50-60° and significantly enhancing quality of life. 2, 3

Patient Selection Criteria

Surgical candidates must meet specific criteria:

• Preserved deltoid strength: Adequate deltoid and supraspinatus muscle function is essential for postoperative improvement 2, 5

• Shoulder elevation <90°: Patients with preoperative elevation less than 90° are ideal candidates 3

• Significant functional limitation: Inability to perform activities of daily living due to scapular instability 3, 5

• Multidisciplinary evaluation: Assessment by neurologists, geneticists, and orthopedic surgeons is required for optimal patient selection 2

Expected Outcomes

Based on the largest case series with long-term follow-up:

• Shoulder elevation improvement: Increases from mean 61° preoperatively to 124° postoperatively (63° improvement) 3

• Shoulder abduction improvement: Increases from mean 53° preoperatively to 99° postoperatively (46° improvement) 3

• Functional scores: Quick DASH scores improve from 34.7 to 13.3, indicating substantial functional gains 3

• Durability: Improvements are maintained long-term, with mean follow-up of 71 months showing sustained benefits 3

• Fusion rates: Scapulothoracic fusion is achieved in >98% of cases 3

Complications and Management

Pulmonary complications occur in approximately 11% of cases but typically resolve spontaneously with conservative management. 3

Common complications include:

• Pulmonary issues (11%): Pneumothorax, pleural effusion, and atelectasis may occur but usually resolve without long-term sequelae 3

• Scapular-related complications (16%): Include rib fractures, implant irritation, nonunion, and scapular fractures, with 11% requiring revision surgery 3

• Overall complication rate: Approximately 27%, but most resolve with appropriate management 3

• Pulmonary function: No long-term decline in pulmonary function tests after surgery 3

Critical Pitfalls to Avoid

• Misattributing winging to trapezius weakness: The trapezius is typically preserved in FSHMD; weakness of the thoracoscapular stabilizers causes the winging 1, 2

• Operating on patients with weak deltoid muscles: Preserved deltoid strength is essential for functional improvement after scapulothoracic arthrodesis 2, 5

• Inadequate postoperative analgesia: Effective pain control reduces pulmonary complications 2

• Delaying cardiac evaluation: Cardiac complications must be monitored in muscular dystrophies, as they significantly increase mortality risk 7, 6