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Updated: Oct 20 2023

Internal Impingement

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  • Summary
    • Internal impingement is a cause of shoulder pain in overhead athletes caused by repetitive impingement between the undersurface of the rotator cuff and the posterosuperior glenoid.
    • Diagnosis is may clinically with worsening posterior shoulder pain during maximal abduction and external rotation (position of late cocking) associated with decreased internal rotation and supplemented with MRI showing posterior rotator cuff and posterior labral pathology.
    • Treatment with physical therapy and posterior capsule stretching is effective for most patients. Arthroscopic surgery is indicated for patients who fail conservative management.
  • Epidemiology
    • Demographics
      • major cause of shoulder pain in throwing and overhead athletes
  • Etiology
    • Pathophysiology
      • mechanism
        • 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 by the biceps
      • pathoanatomy
        • caused by repetitive impingement of the posterior under-surface of the supraspinatus tendon and the posterior superior aspect of the glenoid
        • pathologic micromotion of the humeral head allows the rotator cuff to become impinged between the humral head and glenoid.
          • 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 the articular side of the posterior rotator cuff (supraspinatus-infraspinatus interval)
          • posterior and superior labral lesions
          • hypertrophy and scarring of posterior capsule glenoid (Bennett lesion)
          • cartilage damage at posterior glenoid
      • etiology
        • tightness of posterior band of IGHL
        • anterior micro-instability
    • Associated conditions
      • associated with GIRD
      • SLAP tears
      • SICK scapula and dyskinesia
  • Anatomy
    • 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
    • Rotator cuff
      • primary function is dynamic stability and centering the humeral head within the glenoid via balancing the force couples about the glenohumeral joint in both coronal and transverse planes, creating a stable fulcrum
        • coronal plane
          • the inferior rotator cuff (infraspinatus, teres minor, subscapularis) balances the superior moment of the deltoid
        • transverse plane
          • the anterior cuff (subscapularis) balances the posterior moment of the posterior cuff (infraspinatus and teres minor)
        • the goal of treatment in rotator cuff tears is to restore this equilibrium in all planes
  • Classification
    • No formal classification scheme
  • Presentation
    • Symptoms
      • shoulder pain, sometimes loalized posteriorly
        • diffuse pain in posterior shoulder along the posterior deltoid
        • shoulder pain worse with throwing
          • especially during late cocking and early acceleration
    • Physical exam
      • inspection
        • may see retroversion of proximal humerus
        • pain with palpation along infraspinatus
      • ROM
        • increased external rotation
        • decreased internal rotation
          • loss of > 20° of IR at 90° compared to contralateral shoulder
            • must stabilize the scapula to get true measure of glenohumeral rotation
        • preservation of the total arc of motion
      • strength
        • often can demonstrate rotator cuff weakness
      • provocative tests
        • Whipple test
          • performed to test for partial suprapinsatus tears
          • performed by ranging shoulder in forward flexion, adduction and scapular retraction
          • positive when pain is reproduced on resistance
        • Apprehension test
          • positive for internal impingement
          • performed by bringing shoulder into maximum ER, abduction and extension
          • positive if posterior shoulder pain reproduced in this position and relieved when arm brought into neutral extension/flexion
  • Imaging
    • Radiographs
      • recommended views
        • complete shoulder series
      • findings
        • usually unremarkable
        • AP may show a Bennett lesion (exostosis of posteroinferior glenoid)
    • MRI or MR arthrogram
      • findings
        • can show pathology of the rotator cuff and/or labral pathology
          • such as partial articular-sided supraspinatus-infraspinatus tendon avulsion (PASTA), fraying, or tear
          • signal at greater tuberosity and/or posterosuperior labrum
      • optional views
        • ABER positioning reproduces position of impingement showing dynamic process on the humerus and glenoid sides
  • Treatment
    • Nonoperative
      • PT, cessation from throwing, posterior capsule stretching
        • indications
          • first-line of treatment
          • most internal impingement can be treated non-operatively
          • Operative treatment should only be considered if patient has failed adequate physical therapy for an extended period of time as results folliwing operative intervention are unpredictable
    • Operative
      • arthroscopic debridement of rotator cuff and/or labrum
        • indications
          • failure of nonoperative treatment and
            • partial thickness rotator cuff tear (PASTA) that compromise the integrity of the rotator cuff
              • partial rotator cuff tears <50%
            • Bennett lesions
            • peel-back labral lesion
      • Arthroscopic vs mini-open rotator cuff and/or labral repair
        • indications
          • partial tears >50% tendon thickness or full thickness tears
          • unstable labral tears
      • Posterior capsule release vs anterior capsular stabilization
        • indications
          • persistent posterior capsule contracture or anterior shoulder instability in addition to any of the above pathology
  • Techniques
    • PT, cessation from throwing, posterior capsule stretching
      • cessation
        • break from throwing until pain subsided, followed by supervised return to throwing focusing on proper mechanics
      • therapy
        • posterior capsular stretching program (i.e. sleeper stretches), rotator cuff strength balancing, scapular stabilization, kinetic chain coordination
        • stretching for 6 months
      • outcomes correlated with compliance to therapy regimen
    • Arthroscopic debridement of rotator cuff tear and/or labrum
      • diagnostic arthroscopy
        • perform meticulous exam under anesthesia to assess range of motion
        • diagnostic arthroscopy intra-articular and subacromial
      • debridement
        • arthroscopic shaver to debride loose tissue edges
      • allows accelerated rehab and return to throwing
      • shorter post-op immobilization time
    • Arthroscopic vs mini-open rotator cuff repair
      • approach
        • arthroscopic has advantage of addressing labral and other intra-articular pathology
      • acromioplasty
        • bursectomy performed to visualize bursal-side of tendon
        • acromioplasty is not indicated if no bursal-sided pathology seen
      • cuff repair
        • abrasive preparation of the greater tuberosity footprint
        • portal of Wilmington usually necessary
        • partial-thickness tears
          • in-situ trans-tendinous repair
            • pulley technique utilizing suture anchors to reduce tendon to tuberosity
            • will functionally shorten the tendon length
        • complete partial tear followed by anatomic repair technique
          • single or double-row repair
      • labrum
        • prepare glenoid rim and repair of unstable labral tear
    • Posterior capsular release vs anterior stabilization
      • posterior release
        • done adjunctively with above procedures
        • cautery wand or arthroscopic shaver to release synovium and capsular tissues
        • risk of axillary nerve injury
      • anterior stabilization
        • done adjunctively with the above procedures
        • capsular plication most common
  • Complications
    • Progression to full-thickness rotator cuff tear
      • small risk of partial tears treated with debridement alone
    • Delayed Rate of Return to Play
      • worse rates following rotator cuff repairs in throwing athletes
    • Axillary nerve injury
      • at risk during posterior release at the inferior border of infraspinatus
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