Outlet (subacromial) Impingement

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Topic updated on 01/06/14 9:43am
Introduction
  • Outlet impingement is the first stage of rotator cuff disease which is a continuum progressing from partial to full-thickness to massive rotator cuff tears, and finally to rotator cuff tear arthropathy
  • Epidemiology
    • incidence
      • rotator cuff disease, inclusive of impingement, affects millions of individuals
  • Associated conditions
    • hook-shaped acromion
    • os acromiale 
    • posterior capsular contracture
    • scapular dyskinesia 
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) 
    • Type I - flat
    • Type II - curved
    • Type III - hooked
Presentation
  • Symptoms
    • insidious onset of pain exacerbated by overhead activities
    • night pain
      • poor indicator of successful nonoperative management
  • Physical exam
    • impingement tests (see complete physical exam of shoulder) 
      • Neer impingement test
        • positive if passive forward flexion >90° causes pain
      • Neer impingement sign
        • positive if a subacromial injection relieves pain associated with passive forward flexion >90°
      • 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
      • 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
        • os acromiale 
  • MRI
    • useful in evaluating the degree of rotator cuff pathology
Treatment
  • Nonoperative
    • physical therapy, oral anti-inflammatory medication, subacromial injections
      • indications
        • subacromial impingement syndrome
      • 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 
  • Operative
    • 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 
Technique
  • Acromioplasty
    • modified Neer 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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(OBQ05.208) Arthroscopic subacromial decompression with acromioplasty has been shown to yield lower subjective satisfaction scores in patients with which of the following preoperative factors? Topic Review Topic

1. Dominant arm involvement
2. Males
3. Workers' compensation
4. Smokers
5. Age <60

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