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  • Internal impingement refers to pathology on undersurface of rotator cuff 
    • in contrast to subacromial or "external" impingement which occurs on bursal side of rotator cuff) 
    • internal impingement covers a spectrum of injuries including
      • fraying of posterior rotator cuff
      • posterior and superior labral lesions
      • hypertrophy and scarring of posterior capsule glenoid (Bennett lesion)
      • cartilage damage at posterior glenoid
  • Epidemiology
    • major cause of shoulder pain in throwing athletes
  • Pathoanatomy
    • caused by impingement of posterior under-surface of supraspinatus tendon on greater tuberosity insertion on the posterosuperior glenoid rim 
      • impingement occurs during maximum arm abduction and external rotation during late cocking and early acceleration phases of throwing  
      • causes"peel-back" phenomenon of posterosuperior labrum
    • thought to be due to combination of
      • tightness of posterior band of IGHL 
      • anterior micro instability
  • Associated conditions
    • associated with GIRD 
  • Glenohumeral joint anatomy 
  • Glenohumeral stability
    • static restraints
      • glenohumeral ligaments
      • glenoid labrum 
      • articular congruity and version
      • negative intraarticular pressure
    • dynamic restraints
      • rotator cuff muscles
      • biceps
      • periscapular muscles
  • Glenohumeral ligaments
    • Superior GHL  
      • restraint to inferior translation at 0° degrees of abduction (neutral rotation) 
    • Middle GHL  
      • resist anterior and posterior translation in the midrange of abduction (~45°) in ER 
    • Inferior GHL  
      • posterior band
        • most important restraint to posterior subluxation at 90° flexion and IR
      • anterior band
        • primary restraint to anterior/inferior translation 90° abduction and maximum ER (late cocking phase of throwing) 
      • superior band
        • most important static stabilizer about the joint
  • Symptoms
    • diffuse pain in posterior shoulder along the posterior deltoid
      • shoulder pain worse with throwing
        • especially during late cocking and early acceleration
  • Physical exam
    • increased external rotation
    • decreased internal rotation 
      • loss of > 20° of IR at 90°
        • must stabilize the scapula to get true measure of glenohumeral rotation
    • often can demonstrate rotator cuff weakness
  • Radiographs
    • recommended views
      • complete shoulder series
    • findings
      • usually unremarkable
      • AP may show a Bennett lesion (glenoid exostosis) 
  • MRI
    • can show associated rotator cuff and/or labral pathology
      • such as partial articular sided supraspinatus tendon avulsion (PASTA) or tear 
      • signal at greater tuberosity and/or posterosuperior labrum 
  • Nonoperative
    • posterior capsule stretching PT for 6 months
      • indications
        • most internal impingement can be treated non-operatively
      • technique 
        • posterior capsule stretching with sleeper stretches
        • rotator cuff stretching and strengthening
  • Operative
    • arthroscopic debridement and/or repair of rotator cuff tear and labrum 
      • indications
        • failed nonoperative treatment
        • partial thickness rotator cuff tear (PASTA) compromises the integrity of the rotator cuff
          • partial rotator cuff tears >50%  
        • Bennett lesions
    • posterior capsule release vs anterior stabilization
      • indications
        • failed nonoperative treatment
        • shoulder instability
      • technique 
        • surgical techniques are controversial
          • some perform a posterior capsule release
          • some perform anterior stabilization
      • complications
        • inferior suprascapular nerve (infraspinatus) is at greatest risk during posterior capsule release

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