Acromioclavicular Joint Injuries – Part One

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.

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.

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.

If the acromioclavicular ligaments themselves are disrupted but the other ligaments from the scapula are unaffected them the injury is a type 2 sprain. There may be a small prominence of the far end of the clavicle due to the damage to the restraining ligaments. Type 3 sprains result from complete rupture of both ligament groups so that the two joint surfaces have become separated from each other and the lateral clavicle forms an easily visible lump at the edge of the shoulder. Even more serious injuries may occur with fractures, complete joint disruption and bony malalignment.

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.

Injuries to this joint may cause athletes who train with weight to find it is difficult to perform certain exercises such as the bench press. Typically the shoulder is painful at night as finding a non-stressful position for the shoulder is difficult and the joint pain may wake someone as they roll over onto it. On examination the pain complaint is very localised to the small joint area itself and if the injury is a bad one there may be a significant deformity of the outward end of the clavicle as it has moved upwards. Limitation of shoulder movement is common with pain making lifting above the horizontal uncomfortable.

Jonathan Blood Smyth is the Superintendent of Physiotherapy at an NHS hospital in the South-West of the UK. He writes articles about back pain, neck pain, and injury management. If you are looking for physiotherapist Manchester visit his website.