What is acromiale?

Os Acromiale: Definition, Classification, and Management

Os acromiale is a developmental anomaly where one or more ossification centers of the acromion fail to fuse with the scapular spine, resulting in a fibrocartilaginous connection rather than bony union. 1

Anatomy and Classification

• Os acromiale represents an unfused accessory center of ossification of the acromion of the scapula, occurring in approximately 8% of the general population 1, 2
• It is more common in Black individuals and males compared to White individuals and females 1
• The Bigliani classification categorizes acromion morphology into three types, with os acromiale representing a failure of fusion of one of these segments 3

Epidemiology and Presentation

• Os acromiale is often an incidental finding on imaging studies and frequently asymptomatic 1, 4
• When symptomatic, it typically presents with shoulder pain that may mimic subacromial impingement syndrome 5
• Pain is often localized to the superior aspect of the acromion and can be exacerbated by overhead activities 5
• Os acromiale has been identified as a potential contributor to shoulder impingement symptoms and rotator cuff tears 1

Diagnosis

• Diagnosis is confirmed through imaging studies, primarily standard shoulder radiographs including anteroposterior, lateral, and outlet or Rockwood views 3, 6
• MRI without contrast or ultrasound may be appropriate for evaluating associated soft tissue pathology 3, 6
• A positive response to local anesthetic injection into the os acromiale site can help confirm it as the source of pain 5

Management

Conservative Treatment

• Initial management should be nonsurgical, including:
  • Therapeutic exercises and physical therapy 7
  • Non-steroidal anti-inflammatory drugs (NSAIDs) 7, 8
  • Subacromial corticosteroid injections 8
• Conservative treatment should be attempted for at least 3-6 months before considering surgical intervention 7, 8

Surgical Options

When conservative management fails to relieve symptoms, surgical intervention may be considered:

1. Excision of the os acromiale:

   • Generally reserved for small to medium-sized fragments (preacromion) 1
   • May also be considered after failed internal fixation 1
   • Caution: Excision of large fragments may result in persistent deltoid dysfunction 1, 8

2. Open reduction and internal fixation (ORIF):

   • Preferred for larger fragments to preserve deltoid function 1
   • Techniques include cannulated screw fixation and tension band wiring 1, 2
   • May be combined with bone grafting to enhance union rates 5, 2
   • Potential complications include nonunion and hardware irritation requiring removal 8

3. Arthroscopic techniques:

   • Arthroscopic subacromial decompression may be considered 8
   • Can be performed with complete or partial resection of unstable fragments 8
   • Advantages include more rapid rehabilitation and shorter surgical times 8
   • Results have been mixed when used for impingement secondary to unstable os acromiale 1

Special Considerations

• The presence of os acromiale should be identified before performing acromioplasty, as simple acromioplasty without addressing the os acromiale may worsen symptoms 5
• Associated rotator cuff tears may be addressed arthroscopically or through an open transacromial approach 1
• The American Academy of Orthopaedic Surgeons notes that simply having an abnormal acromion morphology does not necessitate surgical intervention 3

Outcomes

• Successful surgical treatment typically results in pain relief and improved shoulder function 5
• Union rates are high with appropriate fixation techniques and bone grafting 5, 2
• Tension band wiring with embedded bone grafting has shown reliable results in achieving union 5