Acromio-clavicular (AC) joint injury is a common pathology of the shoulder consisting in the sprain or tear of one or more ligaments that hold the acromion and clavicle together. It is also referred to as shoulder separation.
The AC joint is located at the junction between the acromion on the upper scapula and the clavicle or collarbone and is supported by multiple ligaments. The distal end of the clavicle is fixed at the AC joint by the capsule and its ligaments. The clavicle has an attachment, the coraco-clavicular ligament, which consists of two components, the conoid and the trapezoid ligaments that provide horizontal stability to the AC joint. Depending on the severity of the AC injury, one
or more ligaments can be damaged or ruptured. This causes sprains or separations of the AC joint. In addition to ligament injury, a fracture of the distal clavicle and/or acromion can be associated with this pathology.
The injuries to the AC joint are graded according to the severity of damage caused to the ligaments, as well as the presence of joint displacement and deformity.
Type 1: mild sprain of the AC capsule and coraco-clavicular ligament.
Type 2: tear of the AC joint capsule and a sprain of the coraco-clavicular ligaments. In some cases one of these ligaments, either the conoid or the trapezoid ligament is torn.
Type 3: complete tear of the AC joint capsule and two components of the
coraco-clavicular ligament. The latter results in the evident bump on the
Type 4, 5 and 6: less common severe injuries with high degree displacement of the distal clavicula in different directions (not shown).
According to the Habermeyer Classification the fractures to the proximal humerus are divided into:
Type 0 one fractured part without dislocation
Type A two-part fracture of the great tuberosity and lesser tuberosity avulsion
Type B involves the humerus “surgical” neck below the femoral head as two-part, three-part and four-part with one or both tuberosities
Type C involves the humerus anatomical neck (between the head and greater tuberosity) as two-part, three-part and four-part with one or both the greater and lesser tuberosities.
These are defined further as:
One-part fractures are non-displaced fractures or fractures with minimal displacement
Two-part fractures only involve a single segment
Three-part fractures involve two segments
Four-part fractures occur when all humeral segments are involved (see image in pathology section)
The injury severity is proportional to the increasing number of fractures.
The most common mechanisms for an AC joint injury are a fall or a blow directly onto the upper shoulder (acromion). This includes a fall onto an outstretched hand and a downward force applied to the shoulder, pushing down the scapula.
In athletes, injuries to the AC joint are the most frequent type of shoulder injury followed by shoulder dislocation. Usually men between 20 and 40 years are affected by this pathology almost exclusively with an incomplete ligament tear. Sports exposing to the risk for his pathology include:
The most common symptoms of an AC joint injury are:
Shoulder tenderness and swelling
Increasing pain particularly over the AC joint
Appearance of a bruise and/or protrusion of the distal clavicle (Type 3)
Pain while exercising (weight lift)
Pain when sleeping onto the injured shoulder
Popping or catching noises with movement
Limited shoulder range of movement when raising the arm (“cross body adduction test”).
A detailed medical history is discussed including past and present injuries of the shoulder, and description of ongoing symptoms. Medical examination is usually sufficient to diagnose an AC joint injury. This involves palpation of the shoulder, measurement of movement restrictions and evaluation of pain intensity.
X-rays are performed when AC joint injury is suspected and to exclude a clavicle or other bone fractures. Different types of imaging planes are used for this diagnosis: Panorama X-rays of both shoulders: The patient is asked to hold a weight keeping the arms straight while doing X-rays. Lateral view of the shoulders with the arms resting along the body to detect any anatomical differences. MRI is only employed with recurrent discomfort in older patients to establish the possibility of a rotator cuff tear or presence of arthritic changes of the AC joint.
Conservative treatment is recommended for uncomplicated Type 1, 2 and possibly Type 3 AC injuries beginning with a period of rest using a sling, administration of NSAIDs, if necessary intra-articular steroid injection, and application of ice pads to control pain and swelling. Fractures in the AC area are usually treated with a sling unless bone misplacement is present. Physical therapy is critical for those patients with restricted range of movement caused by a mild AC injury/sprain.
Surgery is usually advised in Type 3 and more severe types of AC injuries, especially if accompanied by bone fractures. Different forms of materials are available to fix the clavicle (soft wires, screws, non-resolvable sutures) to immobilise the AC joint and allow the ligaments to heal. The screws are usually removed after 6-8 weeks. Reconstruction of ruptured AC ligaments is achieved using local tissue or exogenous material (tendon graft).
Approximately four weeks post-surgery when the ligaments have healed, physiotherapy can begin with passive exercises performed by a therapist. Strenuous exercises are recommended 6 to 8 weeks post-surgery to restore the range of movement and strength of shoulder muscles.
Healing of AC joint injury may require a long time and it is essential to keep the muscles toned and the joint flexible at all times to prevent secondary injuries. Although most patients heal well after an AC injury, some complications may arise. Pain may remain a recurrent problem. If the alignment of the bones is altered there is a high risk of permanent deformity, impaired function and development of AC joint arthritis.
The main preventative strategy for an AC joint injury and its associated complications is to avoid falls in the elderly and high-energy impacts in the younger population. The following measures are recommended:
Use of a walker if balance is poor
Use of handrails when walking on stairs
Injury prevention in automobile (airbags)
Shoulder taping and padding when returning to sport practice
Prevention of recurrent AC joint injuries relies on the early diagnosis of an initial injury. Following such pathology, returning to sport activities is only recommended when swelling and pain have subsided, and when normal range of movement has been achieved. This can take a few weeks to months. An educational program with a trained physiotherapist informs patients on how to approach specific movements to avoid future AC joint injuries.