Injuries to the Acromioclavicular Joint - Part One



Posted: Tuesday, March 09, 2010

by Jonathan Blood Smyth

The shoulder is a very vulnerable joint in many functional and sporting situations and needs careful treatment and management to recover back to its normal abilities. The main joint in this region is the shoulder joint proper, known as the glenohumeral joint, but above the shoulder itself lies the acromioclavicular joint which is vulnerable to sporting injuries. Contact sports, falling off bicycles, skiing and falls are common reasons for suffering an injury to this joint. Above the shoulder the end of the clavicle or collar bone and part of the scapula, the acromion, come together to make up the acromioclavicular joint.

The acromioclavicular joint is strengthened and supported by a group of ligaments, injury to which can result in joint sprains up to visible deformity of the joint. Either side of the joint may suffer from a fracture which adds to the complexity of the situation and may cause joint arthritis to develop with time. Medical consultation by athletes for shoulder injuries is most commonly for acromioclavicular joint damage with second place going to shoulder dislocations. It is more likely that patients will have more limited sprains and ligamentous tears rather than joint deformity, all more likely in young men.
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The acromioclavicular joint is composed of the lateral end of the collar bone and a part of the shoulder blade called the acromion, surrounded by four minor ligaments and the joint capsule, a fibrous bag. The ligaments prevent the two joint surfaces from moving frontwards or backwards in respect to each other whilst upward and downward stability is maintained by a different ligament group. These latter ligaments attach to the clavicle on the inward side of the acromioclavicular joint and come from part of the scapula. The presentation of the injury will vary depending on which group of ligaments has been damaged to what degree.

Falling onto the shoulder pushes the tip of the shoulder downwards compared to the rest of the shoulder girdle area, potentially injuring the ligaments or causing a fracture as the clavicle remains in its original position. A sprain may result or the ligaments may be completely torn, making the joint unstable and unable to perform its primary function. Sprains of this area are classified as to their severity. A type 1 sprain results from a relatively minor force and results in some spraining of the ligaments but no change in the joint position, which looks normal despite being painful.
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A disruption of the ligaments around the acromioclavicular joint itself, not involving the other ligament group, indicates a type 2 sprain. A small prominence of the lateral end of the clavicle may be noticeable as the supporting ligaments have been damaged. If both the major ligament groups are completely ruptured then the surfaces of the joint are no longer in contact and a type 3 sprain is present, showing an easily palpable and visible bony lump at the side of the shoulder. Injuries can be more serious with increased forces causing fractures, disruption of the joints and bony separations.

If a patient complains of pain over the top of the elbow then an acromioclavicular joint injury should be suspected and screened for. A fall directly onto the point of the shoulder is the most common injury mechanism, with the arm usually held close to the body at the time. There can be many other methods of injuring this joint including the very common fall on an outstretched hand. Initial symptoms may not be localised to the acromioclavicular joint itself with a more generalised pain and swelling of the shoulder area, but once a few days have elapsed then it may be more apparent that there is tenderness on pressure over the acromioclavicular joint.
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If injured, weight training athletes may find difficulty with exercises which stress the acromioclavicular joint such as bench pressing. Night pain is common as it is difficult to eliminate shoulder stresses during the night and patients may wake when they roll over onto the point of the shoulder. Examination reveals pain over the joint itself which is very localised, and if the injury is more severe there may be obvious deformity of the lateral end of the collar bone, it typically being prominent upwards. Patients will have limited movement in the shoulder and be unwilling to lift the arm beyond horizontal.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about  Physiotherapist, back pain, orthopaedic conditions, neck pain, injury management and  physiotherapists in Manchester. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
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