What could be the cause of a bony prominence on my shoulder?

Causes of Bony Prominence on the Shoulder

The most likely causes of a bony prominence on your shoulder include acromioclavicular joint osteoarthritis, an os acromiale (unfused acromial bone), or a bony Bankart lesion, with acromioclavicular joint osteoarthritis being the most common cause in adults. 1

Common Causes and Evaluation

Anatomical Variants

• Os acromiale: An unfused accessory bone at the tip of the acromion process, present in 7-15% of the population 2
  • Only diagnosed after age 25 when ossification of the acromion should be complete
  • Must be differentiated from an acromion fracture

Degenerative Changes

• Acromioclavicular joint osteoarthritis: Most common cause of a visible or palpable bony prominence 1
  • Often associated with pain that worsens with overhead activities
  • May develop osteophytes (bone spurs) that create visible prominences

Traumatic Conditions

• Bony Bankart lesion: Fracture of the anteroinferior glenoid rim 3
  • Occurs in up to 22% of first-time anterior shoulder dislocations
  • More common in young male athletes playing contact sports
  • Can lead to shoulder instability if untreated

Other Considerations

• Acromion shape variations: The acromion can be flat (10.2%) or curved (89.8%) 2
• Acromial spur: Often mistaken for a "hooked" acromion type 2
• Malunited clavicle fracture: Can create a visible bump along the clavicle

Diagnostic Approach

Initial Imaging

• Plain radiographs: Recommended as the first imaging study 1
  • Should include anteroposterior (AP) view, Grashey view, axillary view, and scapular Y view
  • Can identify most bony abnormalities, fractures, and degenerative changes

Advanced Imaging (if needed)

• CT scan: Better for detailed bone assessment 4, 1

  • Particularly useful for evaluating bone loss or complex fractures
  • Metal reduction protocols available if hardware is present

• MRI: Preferred for soft tissue evaluation 1

  • Better for assessing associated rotator cuff tears or labral injuries
  • Normal X-rays do not rule out soft tissue pathology

Management Approach

Conservative Management

• First-line treatment for most bony prominences, especially those related to mild AC joint osteoarthritis 1

• Pain management options:

  • Local thermal interventions (heat or cold)
  • NSAIDs for pain control
  • Activity modification to avoid painful movements
  • Ice, heat, and soft tissue massage

• Corticosteroid injections:

  • May provide short-term improvement
  • Should be limited (typically no more than 3-4 per year) to avoid potential tendon weakening 1

Physical Therapy

• Phased rehabilitation approach 1:
  1. Pain control, gentle range of motion exercises
  2. Progressive ROM exercises, light strengthening for rotator cuff and periscapular muscles
  3. Progressive resistance training and activity-specific training

Surgical Considerations

• Consider surgical consultation if:
  • No improvement after 3 months of appropriate rehabilitation
  • Patient is under 30 years with high athletic demands
  • Evidence of significant mechanical symptoms 1

Follow-up and Monitoring

• Initial follow-up 1-2 weeks after treatment initiation
• Clinical reassessment at 6 weeks to evaluate progress
• Consider imaging or surgical consultation if symptoms worsen or don't improve by 3 months 1

Important Caveats

• Bony prominences may be normal anatomical variants and not pathological
• Pain associated with a bony prominence warrants further investigation
• Traumatic causes should be ruled out in patients with a history of injury or dislocation
• Young athletes with shoulder instability may have underlying glenoid bone deficiency 5