AC Joint Injury
What is an AC Joint Injury?
(Acromioclavicular Joint Injury)
An acromioclavicular (AC) joint injury is commonly referred to as "shoulder separation" and should not be confused with a shoulder dislocation.
Your acromioclavicular joint (or AC Joint) is the joint at the top of your shoulder between your clavicle (collarbone) and your scapula (shoulder blade). The AC joint is important in allowing overhead and across the body movements of your arm, as well as transmitting forces from the arm to the rest of the body during activities such as pushing, pulling and lifting. There are a number of ligaments which help to stabilise this joint.
An acromioclavicular joint sprain refers to an injury where the ligaments supporting the acromioclavicular joint are overstretched. The degree of AC joint ligament damage can vary from a mild strain of one or more of the surrounding ligaments to complete ligament tears and deformity.
What is the AC Joint?
The shoulder joint is formed at the junction of three bones: the collarbone (clavicle), the shoulder blade (scapula), and the arm bone (humerus). The scapula and clavicle form the socket of the joint, and the humerus has a round head that fits within this socket. The end of the scapula is called the acromion, and the joint between this part of the scapula and clavicle is called the acromioclavicular joint.
When the acromioclavicular joint is disrupted, it is called a shoulder separation and can form a "step" if displaced. Another name for this injury is an acromioclavicular joint separation, or AC separation or an AC joint sprain.
The ligaments that hold the joints together are the acromioclavicular, coracoacromial and coracoclavicular (trapezoid and conoid) ligaments.
What Causes an AC Joint Injury?
Direct forces can injure your AC joint when a person collides with a solid object or surface such as a fall from a bicycle or during a football tackle where the shoulder hits the ground.
You acromioclavicular joint may also be injured indirectly when a person falls on an outstretched arm. The contact force is transmitted up through the arm, which forces a separation of the acromion and clavicle. The ligaments are overstretched and damaged in the process.
AC Joint Injury Symptoms
Your physiotherapist will suspect an acromioclavicular ligament sprain when you report:
AC joint injury is graded by severity from Grade I (minimal joint disruption) to Grade III (severe injury). If the injury is the more severe, Grade III, a bump caused by the separated AC joint may be seen or felt at the tip of the shoulder bones. The diagnosis of shoulder separation is often quite apparent from hearing a story that is typical of this injury, and a simple physical examination.
X-rays should be performed to ensure there is no fracture of these bones. Clavicle fractures from falls are particularly common.
If the diagnosis is unclear, X-rays while holding a weight in your hand may be helpful. When this type of X-ray is performed, the force of the weight will accentuate any AC joint instability and better show the effects of the separated shoulder.
AC Joint Injury Treatment
Most patients with acromioclavicular joint injury start to feel better within a few days or a week of the injury. However, full ligament healing will take at least six weeks. During this time it is important to protect your AC joint ligaments from overstretching the immature scar tissue. It can be helpful to use a sling, taping or a shoulder brace that de-loads your AC joint.
Your physiotherapist's treatment will aim to:
In severe cases, some patients choose to undergo AC joint surgery to pin the AC joint or repair the damaged ligaments surrounding the AC joint.
Post-operative rehabilitation is one of the most important, yet too often neglected, aspects of surgery. The quickest and most successful outcomes result from the guidance and supervision of an experienced shoulder physiotherapist.
Your rehabilitation following shoulder surgery focuses on restoring full shoulder motion, strength, power and endurance. You will also require proprioception and functional-based retraining that is individualised towards your specific needs.
Risks of surgery include infection, persistent instability and pain, stiffness, and difficulty returning to your previous level of activity.
Return to Sports with an AC Joint Injury
When returning to your sport, it is important that you undergo a graduated transition to avoid the risk of injury recurrence. This includes the completion of a full individually designed rehabilitation program aimed at improving strengthening, flexibility and proprioception in your upper limbs.
For more information, please ask the advice of your physiotherapist.
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