What are the pathomechanics and treatment options for thrower's shoulder?

Pathomechanics and Treatment of Thrower's Shoulder

The pathomechanics of thrower's shoulder involve repetitive stress leading to atraumatic microinstability, rotator cuff dysfunction, and secondary impingement syndrome, requiring treatment focused on rest, rehabilitation of rotator cuff and scapular stabilizers, and proper mechanics restoration. 1

Pathomechanics

Biomechanical Forces

• During throwing, extreme forces are generated at the shoulder:
  • Internal rotation torques up to 67 N-m during arm cocking phase 1
  • Internal rotation velocities approaching 7000° per second during acceleration 1
  • Distraction forces equal to body weight during deceleration 1
  • Compressive forces up to 1090 N directed posteriorly during deceleration 1

Pathologic Cascade

• The initial event is thickening and contracture of the posteroinferior capsule from repetitive tensile forces during deceleration, known as "the essential lesion" 2
• This leads to glenohumeral internal rotation deficit (GIRD) 2
• Changes in glenohumeral contact points create a series of adaptations that initially enhance throwing performance 2
• The "thrower's paradox" requires the shoulder to be lax enough for excessive external rotation but stable enough to prevent symptomatic humeral head subluxations 3

Common Pathologies

1. Rotator Cuff Dysfunction:

   • In youth throwers: undersurface tears from overuse and eccentric stress 1
   • Pain typically occurs at release and during deceleration/follow-through phases 1
   • Mechanism involves repetitive eccentric stress on supraspinatus, external rotators, and scapular stabilizers 1

2. Secondary Shoulder Impingement:

   • Results from difficulty maintaining humeral head centered in glenoid fossa during motion 1
   • Caused by rotator cuff weakness combined with ligamentous laxity 1
   • Pain located in anterior/anterolateral shoulder during cocking and acceleration phases 1

3. Scapular Dyskinesis:

   • Poor coordination of scapular upward rotation and posterior tilting during arm elevation 1
   • Contributes significantly to rotator cuff injury 1, 2

4. Proximal Humeral Epiphysiolysis (in youth):

   • Known as "Little League shoulder" 1
   • Torsional overload of proximal humeral epiphysis 1
   • Radiographic widening of proximal humeral physis 1

Clinical Evaluation

Key Signs and Symptoms

• Pain during throwing, especially during release and deceleration phases 1
• Decreased velocity and precision 1
• Focal weakness with decreased range of motion during abduction with external or internal rotation 1, 4
• Muscle atrophy in rotator cuff and deltoid regions 4
• Scapular dyskinesis (abnormal scapular movement) 1, 4

Physical Examination

• Assess for tenderness over proximal humerus 1
• Evaluate range of motion, comparing with contralateral side 4
• Look for glenohumeral internal rotation deficit (GIRD) 2
• Assess scapular movement during arm elevation 1, 4

Treatment Approach

Non-operative Management

1. Rest Period:

   • Complete rest from throwing until asymptomatic 1
   • For youth with proximal humeral epiphysiolysis: minimum 6 weeks elimination of throwing, followed by 6 weeks without throwing during strengthening phase 1

2. Rehabilitation Program:

   • Strengthen rotator cuff muscles 1
   • Enhance scapular stabilizers 1
   • Improve core and lower-body strength 2
   • Re-establish proper mechanics of shoulder and spine 1
   • Restore range of motion 1
   • Improve proprioception and neuromuscular control 3

3. Gradual Return to Throwing:

   • Implement a structured throwing program emphasizing proper mechanics 1
   • Progress over 1-3 months depending on injury severity 1
   • Return to competition only after completing a functional, progressive throwing program without symptoms 1

Surgical Management

• Consider when non-operative treatment fails 2
• Surgical options should target specific pathologies in the cascade causing dysfunction 2
• For throwers with posterior instability and rotator cuff tears, arthroscopic capsulolabral repair with rotator cuff debridement has shown good outcomes 5

Prevention Strategies

• Implement pitch count and rest restrictions 1
• Avoid pitching with fatigue (36× higher risk of injury requiring surgery) 1
• Limit innings pitched (>100 innings/year increases injury risk 3.5×) 1
• Delay introduction of breaking pitches (sliders and curveballs increase shoulder pain) 1
• Focus on proper biomechanics and sequential timing 6
• Address kinetic chain deficits through core and hip strengthening 6
• Incorporate balance training 6

Key Pitfalls to Avoid

• Failing to recognize early warning signs (pain, decreased velocity, decreased control) 1
• Returning to throwing before adequate rest and rehabilitation 1
• Ignoring scapular dyskinesis when treating rotator cuff injuries 1, 4
• Not addressing the entire kinetic chain in rehabilitation 2, 6
• Overlooking the "thrower's paradox" balance between mobility and stability 3