Acromioclavicular dislocation

Acromioclavicular dislocation is caused by a fall onto the point of the shoulder. The lesion is usually a simple dislocation but a fracture of the clavicle may leave a fragment of bone attached to the acromion.

The fall causes sufficient stress to tear the acromioclavicular ligaments and the stronger coracoclavicular ligaments.

• acute dislocation of the acromioclavicular (AC) joint typically occurs in young, athletic adults and is one of the most common injuries of the shoulder girdle (1)
  • absolute incidence is approximately 3-4/100 000 population
  • native stabilizers of the AC joint are frequently damaged during high-risk/high-energy contact sports, such as ice hockey, rugby or handball

The patient can generally point to the site of injury. There is tenderness with deformity in the form of a prominent 'step' that can be seen and felt.

X-ray of the joint shows considerable separation of the shoulder and the clavicle.

Classification of AC injury

• in 1989, Rockwood et al. presented a radiographic classification system for AC joint injury which is still in use today (1,2)
  • Type I represents a sprain of the acromioclavicular ligament complex
  • Type II a rupture of the AC ligaments, while the coracoclavicular (CC) ligaments are still intact
  • Type III injuries are characterized by a complete rupture of both the AC ligaments and the CC ligaments
    • the deltotrapezial fascia is not injured; thus, the clavicle is only displaced by the width of the shaft (25% to 100% increased CC distance)
  • Type IV describes an injury where the lateral clavicle is displaced posteriorly
    • injury is caused by a complete rupture of the AC ligaments and a partial rupture of the CC ligaments
    • relative elevation of the lateral clavicle varies with the severity of the injury to the CC ligaments
  • Type V injury involves a complete rupture of the AC ligaments and the CC ligaments as well as a rupture of the deltotrapezial fascia

Persistent instability can lead to chronic, painful limitation of shoulder function, particularly with respect to working above the head. Surgical stabilization is therefore recommended for high-grade instability of Rockwood types IV and V

For Rockwood type III injuries, the currently available data is not sufficient to support surgical or conservative treatment (3).

In frail, elderly patients then a shared decision might be made that no treatment is administered except the use of a sling until the pain subsides. This form of treatment results in the persistence of a 'bump' and some mild disability.

Reference:

• Martetschlager F et al. The Diagnosis and Treatment of Acute Dislocation of the Acromioclavicular Joint.Dtsch Arztebl Int. 2019 Feb; 116(6): 89-95.
• Williams GR, Nguyen VD, A. RC. Classification and radiographic analysis of acromioclavicular dislocations. Appl Radiol. 1989;18:29-34
• Longo UG, Ciuffreda M, Rizzello G, Mannering N, Maffulli N, Denaro V. Surgical versus conservative management of Type III acromioclavicular dislocation: a systematic review. Br Med Bull. 2017;122:31-49