Your acromioclavicular (AC) joint can be found just above your shoulder, at the outer end of the collar bone (the clavicle) and the top of your shoulder blade (scapula). The job of the AC joint is to suspend your shoulder joint off your clavicle allowing you to swing and rotate your arm in a number of directions. The AC joint plays an important role in stabilizing and facilitating correct movement patterns of the shoulder joint.

There are three major ligaments that hold the two bones of the AC joint together.

  • Acromio-clavicular ligament
  • Trapezoid ligament
  • Conoid ligament

There are two main types of injuries of the AC joint: traumatic and overuse injuries.

When an AC joint injury happens, it causes stress to these ligaments. This often results in some degree of joint separation.

Traumatic AC joint injury

This type of injury occurs when the joint is disrupted. The ligaments are either overstretched or torn due to the shear force that occurs across the joint. Ultimately this results in some degree of joint separation.

Traumatic AC joint injuries are most common in people who fall from a height or with significant force directly onto their shoulder e.g.

  • Rugby player who is heavily tackled.
  • Cyclist who crashes.
  • Builder who falls off a ladder.

Traumatic AC joint injuries can range from a mild to severe grade. Grading is based on the amount of joint separation involved (Grade I-VI). Mild cases can be treated conservatively by a physiotherapist however, more severe cases may require surgery to reduce the separation and repair the ligament damage.

Overuse AC joint injuries

The AC joint is also very susceptible to overuse injuries and osteoarthritis from general wear and tear over time. Years of repeated stress and load to the normal healthy cartilage at the end of the acromion and clavicle bones may become more than it can endure.

What do I feel?

With an AC joint injury, you may experience:

  • Sharp pain over the AC joint when trying to lift arm to the front or side.
  • General ache at rest.
  • Swelling, warmth and tenderness over the AC joint.
  • General loss of shoulder or UL strength.
  • A visible bump or ‘step’ above the shoulder.
  • Piano key sign.
  • Pain when lying on the involved side.
  • Loss of shoulder range of motion.
  • An audible “popping” sound or feeling that your shoulder “catches” with certain movements.
  • Instability.
  • Pain with daily activities that stress the AC joint e.g., lifting overhead, carrying objects by your side, or reaching horizontally across your body.

What can you do?

  • If you have had a heavy fall onto your shoulder, feel significant pain, instability and have a notable ‘bump’ then you should be assessed by a doctor. Diagnostic imaging is required to assess the degree of AC joint injury and the management of this be it surgical or conservative.
  • If you just have pain, swelling and loss of motion then initially you should:
    • Ice in the first 24-48 hours of the injury.
    • Compress area with k-taping techniques.
    • Avoid lying on that side.
    • Relative rest -> avoiding activities that increase your symptoms for the first few days.

If your pain is ongoing then make an appointment with your physiotherapist or hand therapist for more specific details around the management of this injury.  This will likely include the following:

  • Patient education on AC joint injury, relevant anatomy, and biomechanics.
  • Pain management strategies including adjuncts to pain relief such as heat and counter irritants, rest positions and activity modification.
  • Range-of-motion exercises to progress towards full pain free upper limb movement, facilitate normal shoulder joint mechanics, stretch muscles, and reduce adhesions of healing ligaments.
  • Manual therapy to relieve muscle tension from shortened rest positions and address trigger points.
  • Muscle strengthening to progressively strengthen weakened muscle groups around the shoulder secondary to disuse and rest during the recovery of the AC joint injury.
  • Functional training to progressively reintegrate functional movement patterns and tasks for a sustainable return to preinjury level activities e.g. work, sport, and recreation.