The 'AC' Joint (Acromioclavicular)

Many rugby viewers will recognize the commentator's statement : “Aaah…… looks like his AC joint Murray”. Just what is the “AC joint”, and how is this common injury best managed.

Injury to the collarbone (clavicle) and acromioclavicular joint are a common consequence to falls directly onto the shoulder or and outstretched hand. The force is transmitted up the arm to our shoulder girdle where something has to 'give'. The collarbone absorbs this force and acts almost like a crush zone.  Its either fractures along its shaft, or the clavicle springs where it joins to the shoulder blade. The latter injury involves damage to the ligaments and capsule fo the acromio clavicular joint.

Acromio clavicular joint sprains can be classified broadly into 3 levels of severity.

Type I - Is a relatively mild sprain to the joint with no visable displacement (or visual bump) of the bone end.  There will be some swelling tenderness and pain on arm movements, especially reaching the arm across the body.

Type II -  Involves a tear or rupture to one of the three parts of the joint, ligaments, as well as swelling there may be some displacement upwards of the end of the clavicle, known as the 'step' deformity.

Type III - Involves a rupture to all three associated ligaments and results in a significant 'step' deformity.

Severe acromio clavicular joint sprains are the most commonly seen in high impact sports - rugby, mountain biking, skiing, motor biking etc - But less severe sprains can result from falls in everyday life.

As with all joint sprains your first treatment should be R.I.C.E.

Rest by avoiding raising your arm into painful positions. An ice pack should be applied for 10-20 minutes at 2-4 hourly intervals for the first 24 hours. Compression and Elevation of this joint are difficult to apply, rest with your arm in a sling is probably the best you can do.

With a Type I injury, after a few days of rest, gentle movement can be resumed. For Type II and Type III injuries it may take up to six to eight weeks to regain full range and pain free movement.

Rehabilitation can be assisted by physiotherapy.  This will include exercises to regain full movements of your arm, graduated strengthening to build up the muscles that surround the joint and possibly strapping to support the site of damage while full activity are resumed.

Occassionally the 'step' deformity in a Type II or III injury persists after the joint has healed. Such joints may still function perfectly well and be painfree.  In some grade III injury situations, if pain and instability continues to be a problem, surgery may be required.

Jeannie Brown is a Physiotherapist at the Oamaru Physiotherapy Clinic. She has a wealth of physiotherapy experience in the management of orthopaedic and musculoskeletal conditions.

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