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https://upload.orthobullets.com/topic/3041/images/cuff tear arthropathy.jpg
https://upload.orthobullets.com/topic/3041/images/os acromiale supraspinatus outlet view.jpg
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Introduction
  • Subacromial impingement is the first stage of rotator cuff disease which is a continuum of disease from
    • impingement and bursitis
    • partial to full-thickness tear
    • massive rotator cuff tears
    • rotator cuff tear arthropathy
  • Epidemiology
    • incidence
      • subacromial impingement is the most common cause of shoulder pain
      • accounts for 44-65% of shoulder disorders
  • Pathophysiology
    • subacromial impingement is thought to be a combination of
      • extrinsic compression 
        • of the rotator cuff between the humeral head and 
          • anterior acromion
          • coracoacromial ligaments 
          • acromioclavicular joint
      • intrinsic degeneration
        • supraspinatus
          • attrition of the supraspinatus leads to inability to balance the humeral head on the glenoid causing superior migration and narrowing of the subacromial space
    • inflammatory process
      • inflammation of the subacromial bursa due to abutement between the humerus and rotator cuff, and acromion and associated ligaments 
  • Associated conditions
    • hook-shaped acromion
    • os acromiale 
    • posterior capsular contracture
    • scapular dyskinesia 
    • tuberosity fracture malunion
    • instability
Anatomy
  • Acromion
    • 3 ossification centers unite to form the acromion 
      • meta-acromion (base)
      • meso-acromion (mid)
      • pre-acromion (tip)
    • failure of the ossification centers to fuse results in an os acromiale 
Classification
  • Bigliani classification of acromion morphology (based on a supraspinatus outlet view) 
    • classification types
      • Type I - flat
      • Type II - curved
      • Type III - hooked
    • studies have shown classification system has poor inter observer reliability
Presentation
  • Symptoms
    • pain
      • insidious onset
      • exacerbated by overhead activities and lifting objects away from body
      • night pain
        • poor indicator of successful nonoperative management
  • Physical exam
    • strength
      • usually normal
    • impingement tests (see complete physical exam of shoulder) 
      • positive Neer impingement sign
        • positive if passive forward flexion >90° causes pain
      • positive Neer impingement test
        • if a subacromial injection relieves pain associated with passive forward flexion >90°
      • positive Hawkins test
        • positive if internal rotation and passive forward flexion to 90° causes pain
      • Jobe test
        • pain with resisted pronation and forward flexion to 90° indicates supraspinatus pathology
      • Painful Arc Test
        • pain with arm abducted in scapular plane from 60° to 120°   
      • Yocum Test
        • positive if pain reproduced with elbow elevation while ipsilateral hand placed on contralateral shoulder 
        • sensitive but nonspecific  
      • Internal Impingement test
        • positive if pain is elicited with abduction and external rotation of the shoulder
Imaging
  • Radiographs
    • recommended views
      • true AP of the shoulder 
        • useful in evaluating the acromiohumeral interval 
          • normal distance is 7-14 mm
      • 30° caudal tilt view
        • useful in identifying subacromial spurring
      • supraspinatus outlet view
        • useful in defining acromial morphology
    • findings
      • common radiographic findings associated with impingement
        • proximal migration of the humerus as seen in rotator cuff tear arthropathy  
        • traction osteophytes
        • calcification of the coracoacromial ligament
        • cystic changes within the greater tuberosity
        • Type III-hooked acromion
          • associated with impingment
        • os acromiale 
          • best seen on axillary lateral
  • MRI
    • useful in evaluating the degree of rotator cuff pathology
    • subacromial and subdeltoid bursisits often seen
  • CT arthography
    • can also accurately image the rotator cuff tendons and muscle bellies
  • Ultrasound
    • can also accurately image the rotator cuff tendons and muscle bellies
Studies
  • Histology
    • tendinopathy histology shows
      • disorganized collagen fibers
      • mucoid degeneration
      • inflammatory cells
    • inflammation of the subacromial bursa
      • high levels of metalloproteases and other inflammatory cytokines 
Treatment
  • Nonoperative
    • physical therapy, oral anti-inflammatory medication, subacromial injections 
      • indications
        • first line and mainstay of treatment of subacromial impingement alone without rotator cuff tear
      • techniques
        • aggressive rotator cuff strengthening and periscapular stabilizing exercises
        • an integrated rehabilitation program is indicated in the presence of scapular dyskinesia which aims to regain full shoulder range of motion and coordinate the scapula with trunk and hip motions
        • platelet-rich plasma injections
          • most recent meta-analysis showing insufficient evidence to support use
  • Operative
    • subacromial decompression / acromioplasty  
      • indications
        • subacromial impingement syndrome that has failed a minimum of 4-6 months of nonoperative treatment
      • outcomes
        • poor subjective outcomes have been observed after acromioplasty in patients with 
          • workers' compensation claims   
          • anxiety and depression
Technique
  • Subacromial decompression and acromioplasty
    • acromioplasty
      • two-step procedure performed open or arthroscopically
        • an anterior acromionectomy is performed first
          • the anterior deltoid origin determines the extent of the acromionectomy when performed arthroscopically and must remain intact
        • an anteroinferior acromioplasty to smooth the undersurface of the acromion follows as the second step of the procedure
          • a bone rasp is used if performed open 
          • a shaver or burr is used if performed arthroscopically
        • the deltoid is meticulously repaired to bone in open procedures
    • treatment of an os acromiale
      • a two-stage procedure may be required with the presence of an os acromiale to avoid deltoid dysfunction caused by direct excision
        • the os acromiale is first fused with bone graft and allowed to heal 
        • an acromioplasty is then performed as a separate second procedure
Complications
  • Deltoid dysfunction
    • resulting from a failed deltoid repair following an open acromioplasty or an excessive acromionectomy during an arthroscopic procedure
    • secondary to direct excision of an os acromiale
  • Anterosuperior escape
    • avoid acromioplasty and CA ligament release to preserve the coracoacromial arch in patients with massive, irreparable rotator cuff tears
 

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