Updated: 11/3/2016

Os Acromiale

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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 (3)
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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? Tested Concept

QID: 817
FIGURES:
1

Acute acromial fracture

1%

(15/2061)

2

Type IV acromioclavicular separation

1%

(15/2061)

3

Deltoid avulsion

1%

(12/2061)

4

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

18%

(371/2061)

5

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

79%

(1631/2061)

L 2 C

Select Answer to see Preferred Response

(SAE07SM.92) Figures 26a through 26c show the MRI scans of a 47-year-old man who underwent arthroscopic shoulder surgery 6 months ago and continues to have pain despite a prolonged course of rehabilitation. Management should now consist of Tested Concept

QID: 8754
FIGURES:
1

rotator cuff repair.

28%

(106/374)

2

revision acromioplasty.

25%

(94/374)

3

fragment excision.

17%

(65/374)

4

open reduction and internal fixation.

24%

(90/374)

5

continued rehabilitation.

5%

(19/374)

N/A E

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