Acromioclavicular (AC) joint dislocation / shoulder separation
The shoulder is the most mobile joint in the body and as such a complex arrangement of structures are required to stabilise the shoulder during movement. The clavicle (collar bone) is an integral part of shoulder stability and function as it helps support the shoulder and the scapula (shoulder blade). The clavicle forms a joint with part of the scapula called the acromion. This joint is termed the Acromioclavicular Joint (ACJ) and permits very small movements between the scapula and clavicle during normal shoulder movement. However, unfortunately this joint can be prone to injury.
To stabilise the ACJ, there is complex arrangement of ligaments. These can be divided into two groups; the acromioclavicular capsular ligaments and the Coroclavicular (CC) ligaments, which in turn consist of the coronoid and trapezoid ligaments. When these ligaments are damaged, an Acromioclavicular Joint (ACJ) dislocation/separation can occur.
An ACJ dislocation, or separation, occurs when the outer end of the clavicle dislocates from the acromion. Depending on the severity of injury, different grades of injury can occur ranging from Grade I through to Grade VI. The greater the Grade of injury, the more prominent the dislocated the clavicle becomes. Grades I – II generally don’t need surgical intervention whereas Grades IV – VI do. Grade III injuries may require intervention however the decision to proceed with surgery is usually dependant on the patients symptoms as well as the individuals’ needs and potentially the types of sport and activities undertaken.
The clinical symptoms vary depending on the grade of the injury with usually the more severe symptoms being present with the higher grades of injury. Pain and tenderness over the AC joint are the most common symptoms, with the pain particularly noticeable when the affected arm is taken across ones chest of if one attempts to lie on their affected shoulder. Swelling over the AC joint is also common, with a more prominent clavicle being noted with the higher grades of injury. Injuries classified as a Grade III or above often resort in the injured person cradling their affected arm in an attempt to reduce the pain.
Causes & Risk factors
An acromioclavicular joint dislocation is commonly caused by a fall directly on to the point of the shoulder or on to an outstretched arm. Individuals who participate in contact sports are therefore most commonly affected however a simple fall on to a hard surface can result in the injury.
The grade of AC joint dislocation is dependent on the extent of the injury to the acromioclavicular and coroclavicular ligaments:
Grade I - The acromioclavicular capsular ligaments are stretched or only partially torn. This is the most common type of injury and results in minimal, if any, clavicle displacement.
Grade II - The acromioclavicular capsular ligaments are completely torn however the coroclavicular ligaments remain intact. This results in a partial dislocation of the joint however this may not necessarily be noticeable during clinical examination. However the ACJ is usually tender to touch.
Grade III - In this injury there is a complete dislocation of the joint. There is a rupture of the acromioclavicular and coroclavicular ligaments as well as the surrounding joint capsule such that the clavicle is displaced upwards. This degree of injury is usually clinically obvious because when the shoulder loses its support from the clavicle, the shoulder drops thereby making the end of the clavicle more prominent.
Grade IV – This is similar to a Grade III injury, however the force of the injury displaces the clavicle backwards into and through, the trapezius muscle. However, unlike in a Grade III injury, the direction of the displacement of the clavicle is such that it is not very prominent when examined clinically.
Grade V – This is similar to a Grade III injury with a complete disruption of the acromioclavicular and coroclavicular ligaments however it is further complicated by the loss of the attachments of the trapezius and deltoid muscles that overly the AC joint. This results in the complete dislocation of the clavicle with significant displacement upwards.
Grade VI – This is a rare injury where the clavicle is displaced in a downwards direction and is usually associated with extensive injuries to the shoulder and arm.
The diagnosis is largely based on a clinical examination supported by radiographs. A prominent clavicle, ACJ tenderness and clavicle instability may all be present at the time of a clinical examination. Sometimes shoulder movement can also result in an audible and painful ‘clunk’ as the clavicle is further displaced from its dislocated position. The radiographs help in determining the degree of displacement of the clavicle, especially in acute injuries when the degree of swelling can mask the extent of the injury. They can also help in determining if there are any other associated fractures. MRI scan can also be used to clarify the extent of the injury.
The treatment of an AC joint dislocation is dependant on the grade of the injury. Grade I – II injuries can be treated non-operatively. After an initial period of discomfort the pain settles leaving a fully functional shoulder even if there remains a prominence to the distal clavicle. However, in some instances, continued pain can develop in the long term and if this is the case it is usually die to some inherent damage to the cartilage meniscus that is present within the acromioclavicular joint. In such instances an arthroscopic ACJ excision may be warranted.
Grade III dislocations may be managed conservatively, however surgery may also be indicated. The indications for stabilisation surgery in a Grade III dislocation are based on the severity of the symptoms and in particular, the expectations of the individual. Overhead workers and athletes often require surgery. Grade IV – VI injuries usually require surgical intervention to restore shoulder function, especially when the arm is taken to, or above, shoulder height.
Treatment options include;
- Non-operative treatment; initially rest, ice and a sling to support the shoulder are all that is necessary. After approximately two weeks the sling can be discarded and a physiotherapy programme started to restore the range of shoulder motion and gently strengthen the shoulder. Heavy lifting should be avoided for at least 8 weeks but a longer period may be needed in Grade III injuries. One can return to sport once a full range of shoulder movement is achievable and when there are no symptoms from the AC joint. In Grade III injuries that have persistent pain, a stabilisation operation may be required.
- Surgical treatment; the aim of surgery is to stabilise the AC joint. This can be done in a variety of ways and is dependant on the nature of the injury as well as the time elapsed following the injury.
In acute injuries, stabilising the clavicle using a synthetic ligature or tape can be undertaken. This is called an Acromioclavicular (AC) joint stabilisation and is aimed at reconstructing the Coracoclavicular (CC) ligaments. If, however, there is a more significant injury or if there has been a delay in presentation, then for greater security, the acromioclavicular capsular ligaments may also need to be reinforced. This is termed a Weaver Dunn procedure and entails the excision of a small amount of the outer end of the clavicle and the transfer of the Coracoacromial (CA) ligament to the excision site. Once it has healed this transfer will act as a "new" or additional coracoclavicular ligament and will work in association with a synthetic ligature/tape, to stabilise the joint.
In any grade of injury, the cartilage that separates the clavicle from the acromion, the meniscus, can be injured at the time of the initial accident. This can give rise to long-term symptoms of pain such that an arthroscopic AC joint excision is needed to address any ACJ related pain.