The acromioclavicular joint connects the clavicle to the acromion and plays a crucial role in raising the arm above shoulder level. Although it is a “true” joint, its strong ligamentous structures allow it to function as a kind of “unit” with the shoulder blade.

An acromioclavicular joint separation is an injury or damage to the ligament complex that can subsequently lead to deformity and functional impairment of the joint. Acromioclavicular joint separations are classified into different grades of severity, each requiring different treatment approaches (see illustration).

Type I: These injuries involve sprains or partial tears of the ligament complex without a complete rupture. The bony structures, particularly the clavicle, remain in their normal position.

Type II: Only some of the ligaments are torn, while the others remain intact. This typically affects the ligaments between the clavicle and the acromion. The clavicle often remains in its original position.

Type III: This type involves a complete tear of the ligament complex of the acromioclavicular joint. Both the ligaments between the clavicle and the acromion and those between the clavicle and the coracoid process are affected. In addition, the clavicle may become displaced upward.

Type IV: The entire ligament complex is torn, and the clavicle is displaced posteriorly.

Type V: In this case, not only are the ligaments torn, but the clavicle is also displaced. In addition, the muscle fascia, a layer of connective tissue that covers the muscles, is torn. The displaced clavicle is clearly visible and palpable beneath the skin.

Type VI: In Type VI injuries, varying degrees of deformity and functional impairment of the joint may occur.

People with an acromioclavicular joint separation typically experience significant pain. From Grade III (Type III) onward, a visible deformity may become apparent. The injury is commonly accompanied by swelling, bruising, and abrasions. Depending on the severity of the injury, loss of function and pain-related restriction of movement may also occur.

A panoramic X-ray allows both shoulders to be assessed simultaneously. It shows the position of the clavicle in relation to the acromioclavicular joint. Comparing both sides provides information about the extent of the dislocation or any associated bony injuries. The degree of displacement can be determined by measuring the distances between the clavicles and the coracoid processes on both sides.

An elevated position of the clavicle generally indicates a ligament tear, making additional MRI scans unnecessary.

To assess soft-tissue and associated injuries, such as those affecting the rotator cuff or ligaments within the joint, detailed images can be obtained using an MRI scan. An MRI is particularly important when other injuries need to be ruled out.

If surgery is required, the affected area can be assessed using an arthroscope (a small camera). This can also reveal injuries that may not be clearly visible with other diagnostic methods.

For Type I and II injuries, symptoms can often be relieved with conservative treatment. In the initial stages, the focus is on pain relief with medication and functional aftercare, including rest and immobilization of the affected area. A sling may be used to improve comfort.

Movements should be guided by individual pain levels and should not exceed the pain threshold. The duration of immobilization varies depending on the severity of the injury and may range from a few days to several weeks.

From Type III onward, surgery may or may not be necessary. If no surgical intervention is performed, the prominence or elevated position of the clavicle will remain. This option is sometimes chosen by people who cannot afford prolonged downtime for professional reasons, such as rugby players. Under certain circumstances, and if the surrounding musculature is sufficiently strong, surgery may be avoided. However, this decision may subsequently lead to instability of the acromioclavicular joint and may be undesirable for cosmetic reasons. Difficulties may occur particularly during strenuous, high-impact activities. If surgery is required, the timing of the procedure is crucial in determining the appropriate surgical technique.

In the acute phase, within the first two weeks, a highly stable fixation is often performed (see illustration). The clavicle is securely connected to the coracoid process using an artificial ligament and so-called “buttons” (titanium plates). Once stability has been restored through the procedure, the torn ligaments can be repaired using surgical sutures, allowing them to heal and form scar tissue.

The scarred ligaments can also contribute to stabilization. Titanium plates are used in cases of superior instability, when the clavicle needs to be repositioned downward.

In cases of anterior or posterior instability, a so-called suture cerclage may be used, in which the bone is stabilized by wrapping it with a strong suture. If surgery is performed at a later stage (after 2 to 3 weeks), it may be necessary to stabilize the clavicle by fixing it to the coracoid process using a tendon. The joint is additionally reinforced with an autologous or donor tendon graft. In medical terminology, this is also referred to as “augmentation with an allograft.”