AC Joint Dislocation

What is the AC or Acromio-Clavicular Joint?

The Acromio-Clavicular Joint is a small joint between the outer end of the clavicle and the acromial process of the scapula. Its full name is commonly abbreviated as the AC Joint. Although a small amount of movement occurs at the AC Joint it’s more important role is to help stabilise the scapula or shoulder blade on the chest wall. This in turn helps to provide a stable foundation for the entire shoulder joint.

AC Joint Dislocation

Dislocation of the AC Joint most often follows a heavy fall on to the point of the shoulder. Common injury mechanisms include a fall from a ladder or bicycle. Direct shoulder to shoulder contact in sports such as football may also dislocate the AC Joint.

Stability of the AC Joint is provided by:

  • AC Joint Capsular Ligaments
  • Coraco-Clavicular Ligaments
  • Deltoid and Trapezius muscle attachments

The extent of tearing of these stabilising structures will determine the Grade of Dislocation. The Grade of the injury will serve as a guide to selection of the best treatment option.

Type I Type I

Type II Type II

Type III Type III

Diagnosis of AC Joint Dislocation?

The injury is diagnosed by:

  • Clinical Assessment
  • X-rays

Lesser Grades of injury may have just slight swelling and local tenderness over the AC Joint. Higher grades of injury will have a more obvious clinical deformity. There will be a tender bony lump on top of the shoulder. It may look as though the outer end of the clavicle is sitting too high. But what has really happened is that the entire shoulder and arm are drooping downwards under the effect of gravity, thus leaving the clavicle behind.

X-rays will show that the outer clavicle is not aligned with the acromion. Comparison with an X-ray of the non-injured shoulder may help. Simultaneous X-rays of both shoulder in a standing position while hold a weight in each hand will make the separation more obvious. (Weight Bearing X-rays)The amount of shift will help to understand the degree of ligament injury.

 Weight Bearing X-rays of AC Joints Weight Bearing X-rays of AC Joints

Treatment of AC Joint Dislocation

Low grade injuries such as Grade I and Grade II may recover well with rest, analgesics and anti-inflammatory medication. The soreness tends to resolve slowly over approximately 6 to 8 weeks.

Physiotherapy may be required later in the recovery process to address any shoulder stiffness or muscle weakness. There may be a slight residual prominence of the AC joint but rarely any ongoing pain or shoulder dysfunction. Lesser grade injuries may predispose to AC Joint Arthritis in later life.

Higher grade AC Joint Dislocations may result in ongoing shoulder symptoms. As such a Surgical Treatment may be indicated for high grade injuries. Ongoing symptoms are likely to be of more significance in younger patients with an active physical lifestyle. Factors such as overhead sporting pursuits, occupation and involvement of the dominant shoulder may also be considerations. Possible ongoing symptoms may include:

  • AC Joint pain
  • AC Joint Clicking
  • Inability to lie on the shoulder
  • Aching due to loss of shoulder suspension
  • Significant Cosmetic Deformity

AC Joint Reconstruction

The strategy of AC Joint Reconstruction is the hold the Acromion and Clavicle in their correct anatomical alignment while the ligaments and other soft tissues that maintain stability of the joint heal. Many techniques have been described for achieving AC Joint stability. Mr Lyons will discuss in detail the relative merits of different techniques and the rehabilitation process after surgery.