The acromion process is the lateral projection of the scapula spine that extends anteriorly. Fractures of the scapula are uncommon injuries and account for ~3% of all shoulder fractures ^1,2 while isolated acromion fractures occur rarely and account for only 9% of all scapular fractures ³.

Pathology

Mechanisms of injury

Acromial fractures usually occur as the result of direct trauma to the shoulder or superior dislocation of the humeral head ⁴.

Radiographic features

Shoulder radiographs are the first diagnostic investigation and the lateral scapula shoulder or Y view is an excellent projection to evaluate the coracoid and acromion process ⁵.

Computed tomography is sometimes necessary when the shoulder radiographs are normal and when there is high clinical suspicion of acromial injury.

MRI and US exams are also helpful in the assessment of the soft tissues of the shoulder region ^4,6.

Classification

Three types of acromial fracture are defined by Kuhn et al ⁷ which can help to determine whether surgical or non-surgical treatment is appropriate: 

• type I: non- or minimally displaced

  • IA: avulsion fractures

  • IB: true fractures

• type II: displaced but does not reduce the subacromial space

• type III: displaced with narrowing of the subacromial space

  • due to inferior displacement of the acromium; or

  • superior displacement of an associated glenoid neck fracture

Treatment and prognosis

Type I and II acromial fractures are usually managed with non-surgical treatment while type III fractures usually require surgery to prevent secondary impingement. A variety of surgical techniques can be used and include ^7,8:

• tension band wiring

• reconstruction plate

• Kirshner wire

Differential diagnosis

Os acromiale is an unfused acromion accessory ossification center which is relatively common and found in ~8% of the population ^9,10. It is bilateral in ~ 60% of individuals ¹¹.