AC JOINT ARTHRITIS

The acromioclavicular joint is a joint between the clavicle and the acromion. This joint is significantly involved in raising the arm above shoulder level. Although it is a so-called ‘synovial joint’, its tight ligamentous apparatus makes it a kind of ‘unit’ with the scapula. 

An acromioclavicular joint dislocation is an injury/damage to the ligamentous apparatus that can subsequently cause malpositions/disorders in the joint. There are different degrees of severity of AC dislocation, which require various forms of treatment depending on the severity (see picture). 

Type I

clavicle not elevated with respect to the acromion

AC ligament: mild sprain

CC ligament: intact

joint capsule: intact

deltoid muscle: intact

trapezius muscle: intact

Type II

clavicle elevated but not above the superior border of the acromion

AC ligament: ruptured

CC ligament: sprain

joint capsule: ruptured

deltoid muscle: minimally detached

trapezius muscle: minimally detached

Type III

clavicle elevated above the superior border of the acromion but the coracoclavicular distance is less than twice normal (i.e. <25 mm)

AC ligament: ruptured

CC ligament: ruptured

joint capsule: ruptured

deltoid muscle: detached

trapezius muscle: detached

Type IV

clavicle displaced posterior into the trapezius

AC ligament: ruptured

CC ligament: ruptured

joint capsule: ruptured

deltoid muscle: detached

trapezius muscle: detached

Type V

clavicle is markedly elevated and coracoclavicular distance is more than double normal (i.e. >25 mm) – bilateral weight-bearing projections are able to distinguish type V injuries

AC ligament: ruptured

CC ligament: ruptured

joint capsule: ruptured

deltoid muscle: detached

trapezius muscle: detached

Type VI

clavicle inferiorly displaced behind coracobrachialis and biceps tendons, which is rare

AC ligament: ruptured

CC ligament: ruptured

joint capsule: ruptured

deltoid muscle: detached

trapezius muscle: detached

Affected persons usually have severe pain. Starting with type III, a deformity is visible from the outside. Typically, swelling, bruising, and skin abrasions occur after/with trauma. At the same time, depending on the extent of the injury, there may be a loss of function and limited range of motion due to pain.

A panoramic X-ray is used to assess both sides of the shoulder. The position of the clavicle in the acromioclavicular joint is visible here. In addition, a side-by-side comparison can provide information on the extent of the dislocation or bony injury. The extent of dislocation can be determined by measuring the distances between the clavicles and coracoid processes on both sides. If the clavicle is elevated, there is likely a torn ligament, making an additional MRI unnecessary.

To gain more insight regarding soft tissue and accompanying injuries (rotator cuff, ligaments, etc.) in the joint, MRI can be used to take conclusive images. An MRI is critical when you want to rule out other injuries. If surgery is necessary, an arthroscope (camera) can also evaluate the affected area. Injuries that may not be clearly visible in other diagnostic procedures can also be made visible here.

In the case of type I and II, relief can often be achieved with conservative interventions. The initial focus is on pain relief through medication and functional follow-up treatment, such as protection and immobilization, of the affected area. A sling can be used here for greater comfort.

Movements should be made according to the level of discomfort and should not exceed the pain tolerance. The duration of immobilization and protection varies from individual to individual, depending on the extent of the injury, and can last from a few days to several weeks.

Type III and above may require surgery or no surgery. If no surgery is performed, a protrusion or clavicle elevation will remain. People who do not want to take time off work due to their job, such as rugby players, may choose this option. Under certain circumstances, if the muscles are strong enough, surgical intervention is not necessary. However, this option may subsequently promote instability in the acromioclavicular joint and may also be rejected for cosmetic reasons. Difficulties may occur, especially during movements under load. If surgery is performed, the timing is critical as to what type of surgery is performed.

A solid fixation is often inserted in the acute phase (the first 2 weeks) (see picture). The clavicle is permanently attached to the coracoid process with the help of an artificial ligament and the so-called ‘buttons’ (titanium plates). Once stabilization has been achieved, the torn ligaments can be secured with synthetic sutures and enabled to heal or scar. The scarred ligaments can also contribute to stabilization again. The titanium plates are applied in cases where there is upward instability, and the clavicle needs to be brought down.

In the case of anterior or posterior instability, the so-called suture cerclage (tape connecting two bones) is applied. This is a method in which the bone is wrapped with tape for stabilization. If surgery is performed later (from 2 to 3 weeks), it may be necessary to fix the clavicle to the coracoid process using the tendon. The joint is reinforced with a tendon donated by the patient’s body or a foreign tendon donor. In technical jargon, this is also referred to as ‘augmentation with the aid of an allograft’.