What Causes AC Joint Injuries?

The acromioclavicular (AC) joint unites the shoulder's cap (acromion), which is part of the shoulder blade and the collar bone (clavicle), holding them together with the help of the strong AC and coracoclavicular (CC) ligaments. Even though the joint is durable, its location leaves it vulnerable to injuries that can result in sprains or separations

AC joint injuries are most frequent in individuals under 35, with males being 5 times more prone. Injuries can result from overuse and trauma, especially in the case of sports requiring repeated overhead motions or high-impact collisions:

  • Football 
  • Lacrosse
  • Hockey
  • Baseball
  • Tennis 
  • Swimming

AC joint injuries can also occur due to falling improperly on an outstretched arm during sports involving high velocities like skiing, ice skating, and cycling, or non-athletic causes like falling off a ladder. AC joint injuries can also be sustained due to overuse in non-athletic occupations such as construction work or from the gradual deterioration caused by aging. 

AC Joint Injury Diagnosis

When AC injuries occur and the symptoms are evident, some individuals may dismiss them as discomfort common with contact sports or a normal part of the aging process. Ignoring symptoms and leaving them untreated may worsen the injury and produce long-term consequences like arthritis, collarbone fracture or displacement, severe shoulder separation, and damage to adjacent structures like the rotator cuff.

Regardless of the injury's cause, AC joint injuries share similar symptoms: 

  • Pain in the shoulder or arm
  • Tightness and loss of mobility
  • Weakness in the shoulder or arm
  • Visible bruising or swelling
  • Popping sound during shoulder movement

Differential diagnosis is required to assess the damage and rule out other potential injuries like rotator cuff tears, arthritis, biceps tendonitis, or scapulothoracic bursitis. X-ray imaging and physical examination are usually sufficient to determine the extent of AC joint injuries, ranging from I to VI depending on severity. 

  • Types I, II, and III involve low to medium damage to the AC and CC ligaments, which can be treated non-surgically with healing times ranging from a few weeks to months.
  • Types IV, V, and VI involve a higher level of joint and ligament damage that requires invasive surgery