Updated: 8/13/2021

Os Acromiale

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  • summary
    • An Os Acromiale is an unfused secondary ossification center of the acromion that can be associated with shoulder impingement and rotator cuff tendonitis.
    • Diagnosis is made with axillary lateral radiographs of the shoulder.
    • Treatment is observation in the majority of cases with operative management reserved for patients who have persistent shoulder impingement or rotator cuff disease that have failed nonoperative management. 
  • Epidemiology
    • Incidence 
      • common
        • 8%
        • bilateral in 60%
    • Demographics
      • more common in males
      • more common in African American
    • Anatomic location
      • most common location is the junction of meso- and meta-acromion
  • Etiology
    • Associated conditions
      • shoulder impingement
      • rotator cuff disease
        • meso-acromion is associated with rotator cuff tendonitis and full thickness tears (in 50%)
  • Anatomy
    • 3 ossification centers
      • meta-acromion (base)
        • origin of posterior portion of deltoid
      • meso-acromion (mid)
        • origin of middle deltoid
      • pre-acromion (tip)
        • origin of anterior deltoid fibers and coracoacromial ligament
    • Blood supply
      • acromiale branch of thoracoacromial artery
  • Presentation
    • History
      • pain
        • from impingement
          • reduction in subacromial space from flexion of the anteiror fragment with deltoid contraction and arm elevation
        • from motion at the nonunion site (painful synchondrosis)
      • incidental finding on radiographs
      • trauma can trigger onset of symptoms from previously asymptomatic os acromiale
  • Imaging
    • Radiographs
      • recommended views
        • best seen on an axillary lateral of the shoulder
    • CT
      • indications
        • to better visualize the nonunion site
        • to detect degenerative changes (cysts, sclerosis, hypertrophy)
  • Treatment
    • Nonoperative
      • observation, NSAIDS, therapy, subacromial corticosteroid injections
        • indications
          • mild symptoms
    • Operative
      • two-stage fusion
        • indications
          • symptomatic os acromiale with impingement
        • technique
          • direct excision can lead to deltoid dysfunction
          • a two-stage procedure may be required
            • first stage - fuse the os acromiale ± bone graft
            • second stage - perform acromioplasty
          • preserve blood supply (acromiale branch of thoracoacromial artery)
          • tension band wires, sutures, cannulated screws
      • arthroscopic subacromial decompression and acromioplasty
        • indications
          • impingement with/without rotator cuff tear (where the os acromiale is only incidental and nontender)
      • open or arthroscopic fragment excision
        • indications
          • symptomatic pre-acromion with small fragment
          • salvage after failed ORIF
        • results
          • arthroscopic has less periosteal and deltoid detachment
          • better excision results with pre-acromion
  • Complications
    • Deltoid weakness
      • from fragment excision
    • Persistent pain/weakness
  • Prognosis
    • Poorer outcomes after rotator cuff repairs in patients with meso-os acromiale
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(OBQ07.156) A 27-year-old man presents with shoulder pain. Radiographs are shown in Figure A and B. What is the most likely cause?

QID: 817
FIGURES:

Acute acromial fracture

1%

(19/2345)

Type IV acromioclavicular separation

1%

(17/2345)

Deltoid avulsion

1%

(14/2345)

Failure of fusion between the meso-acromion and pre-acromion

18%

(427/2345)

Failure of fusion between the meso-acromion and meta-acromion

79%

(1849/2345)

L 2 C

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