http://upload.orthobullets.com/topic/3036/images/shoulder_ax.jpg
http://upload.orthobullets.com/topic/3036/images/os acromiale drawing..jpg
http://upload.orthobullets.com/topic/3036/images/os acromiale xray axillary.jpg
Introduction
  • An unfused secondary ossification center 
    • most common location is the junction of meso- and meta-acromion  
    • important to distinguish an os acromiale from fractures of the acromion
  • Epidemiology
    • incidence 8%
    • bilateral in 60%
    • more common in males
    • more common in African American
  • Associated conditions
    • shoulder impingement
    • rotator cuff disease
      • meso-acromion is associated with rotator cuff tendonitis and full thickness tears (in 50%)
  • Prognosis
    • poorer outcomes after rotator cuff repairs in patients with meso-os acromiale 
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
 

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Questions (1)

(OBQ07.156) A 22-year-old man presents with shoulder pain. Radiographs are shown in Figure A and B. What is the most likely cause? Review Topic

QID:817
FIGURES:
1

Acute acromial fracture

0%

(0/226)

2

Type IV acromioclavicular separation

0%

(1/226)

3

Deltoid avulsion

0%

(1/226)

4

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

22%

(50/226)

5

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

77%

(173/226)

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

By age 17, the acromion has consolidated to form three separate ossification centers along the periphery: the 1) PRE-ACROMIAL center which serves as the attachment for the coracoacromial ligament and the anterior tendinous origin of the deltoid; the 2) MESO-ACROMIAL center which anchors the middle tendinous fibers of the deltoid; and the 3) META-ACROMIAL center from which the posterior deltoid fibers originate. These three centers consolidate over the next year and ossify medially toward the clavicular facet by the time that the individual is eighteen years old (see illustration). The most common form of symptomatic os acromiale is failure of fusion between the meso-acromion and meta-acromion. Treatment is challenging and includes nonoperative management, ORIF of the fragment, open fragment excision or arthroscopic fragment decompression. All treatment modalities are fraught with benefits and disadvantages.

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