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The Injured Acromioclavicular Joint Part One

Sporting and normal activities expose the shoulder joint frequently to injury due to its very large range of motion and limited stability and strength, requiring accurate treatment to restore it to a fully functional state. The glenohumeral joint is the shoulder joint itself and the acromioclavicular joint lies above the shoulder, rarely making itself apparent except from injury. The most common injuries result from falls of all kinds including from bicycles and skiing and all contact sports. The acromioclavicular joint consists of the acromion (end of the scapula) and the lateral end of the collar bone or clavicle.

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.

The far end of the clavicle or collar bone and the lateral part of the scapula (the acromion), make up the acromioclavicular joint, held by four small ligaments and enveloped in the fibrous joint capsule. The ligaments prevent the joint from having its joint surfaces moved in a front or back direction against each other, another ligament group taking care of the upward and downward stability of the area. These ligaments originate on another part of the shoulder blade and run up to attach to the collar bone just inwards of the acromioclavicular joint. Which ligaments are injured and how badly will dictate the nature of the presenting injury.

The point of the shoulder is driven downwards compared to the collar bone as a person falls onto the point of their shoulder, incurring a risk of a fracture or a ligamentous injury as the clavicle remains unmoved. Sprains or complete ruptured can occur, leading to an unstable joint with limited function. The classification of acromioclavicular injuries is formed  as to the grades of damage involved. Limited trauma with some ligament spraining may be classified as type 1, with the joint remaining normal although it is painful.

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.

Pain over the point of the shoulder in a patient complaining of upper arm trauma indicates that acromioclavicular joint injury must be considered. The usual mechanism is for the arm to be close to the side while the person falls onto the tip of their shoulder, although many other injuring mechanisms can exist including the very common fall onto an outstretched hand. Presentation in the early stages may include a general pain and swelling around the shoulder area and as the pain settles over a few days it may be possible to diagnose an acromioclavicular joint injury by directly stressing the joint.

Once injured this joint may make it difficult for weight trainers to manage certain exercises such as the bench press. Night pain is a common complaint as it is hard to find a position which does not stress the shoulder at all and when people turn over onto their shoulders the pain will typically wake them. Examination of the joint reveals a very small area of pain directly over the joint itself and a large bony prominence of the outward end of the collar bone in more severe cases. Patients present with limited shoulder movement and are often unwilling to move the arm much above horizontal due to the joint pain this engenders.

Author:  Jonathan Blood-Smyth

 

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