With its extreme mobility and limited stability and power, the shoulder joint is vulnerable to injuries in sport and activities, requiring expert management to recover entirely to normal. The shoulder joint proper is known as the glenohumeral joint and above this lies the acromioclavicular joint. Frequent reasons for injuring this joint are falls from skiing or bicycling and most contact sports. The joint is made up of the acromion, the end of the scapula, and the lateral end of the collar bone or clavicle and is vulnerable to forceful injuries.
There are a number of ligaments which strengthen the joint and they may be sprained or ruptured by an injury which may appear as an obvious disruption of the joint. Complications may occur in the presence of fractures at either side of the joint which can result in arthritic changes developing later in the joint. If athletic individuals consult a doctor for a shoulder injury then acromioclavicular joint injuries are the most likely cause with shoulder dislocations coming next. Smaller degrees of sprain with partial ligament tearing is much more common than complete joint separation, all occurring most frequently in young males.
The acromion and the lateral end of the clavicle make up the joint, which is held by four relatively small ligaments and surrounded by a fibrous bag called a joint capsule. These joint ligaments mostly stop the joint from being separated in a forwards and backwards direction while another ligament group adds to stability in an upwards and downwards direction. These ligaments pass from another part of the scapula and attach just inwards from the acromioclavicular joint. Depending which group of ligaments are torn will alter the picture of the injury sustained.
When someone falls onto the tip of their shoulder it is forced downwards compared to the remainder of the shoulder, making injury to the ligaments or a fracture a possibility as the collar bone stays where it was. The ligaments may be sprained or torn completely which makes the joint very unstable and loses its function. The severity of the injury is graded in the classification of these injuries. A type 1 sprain is the result of lesser trauma and may involve sprain of the joint ligaments, with the joint staying stable and appearing normal although a source of pain.
A type 2 sprain involves some disruption of the acromioclavicular ligaments but leaves the others which attach to the other part of the scapula uninjured. The far end of the clavicle or collar bone may now show a little prominently above the joint line as the supports have been damaged. In type 3 sprains both sets of ligaments are completely ruptured and the collar bone is obviously separated from the acromion, forming a visible and palpable lump towards the outside of the upper shoulder area. More severe injuries may involve fractures and complete disruption and malposition of the bony elements.
A patient with pain over the point of the shoulder should be suspected of having an acromioclavicular joint injury and be examined accordingly. Falling onto the tip of the shoulder is most common whilst the arm is close to the trunk. Many other ways of injuring this joint exist such as the frequently occurring fall on an outstretched hand. Patients may initially complain of rather generalised symptoms with pain and swelling around the area, with a few days needing to go by before local pressure over the joint confirms the diagnosis of an acromioclavicular joint sprain.
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.