Internal Impingement - Shoulder & Elbow

Introduction

Overview
- internal impingement is a cause of shoulder pain in overhead athletes caused by repetitive impingement of the undersurface of rotator cuff
  - treatment with physical therapy and posterior capsule stretching is effective for most
Epidemiology
- major cause of shoulder pain in throwing and overhead athletes
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 posterior under-surface of supraspinatus tendon greater tuberosity
  - pathologic micromotion of the humeral had 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 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