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Acromioclavicular joint injury is usually caused by direct injury to the acromion during a fall on an adducted arm. It is classified according to the Rockwood classification, which considers the extent of injury to the acromioclavicular (AC) ligament and the coracoclavicular (CC) ligament, as well as the displacement of the clavicle and type of dislocation in the AC joint. Patients present with local tenderness, swelling, limited range of motion, and/or deformity of the joint. X-ray is used to diagnose joint subluxation and clavicular displacement. Treatment is usually conservative and may include rest and analgesia for a few weeks. Surgery is recommended for more severe injuries when ligament repair is required.

Most common: direct force injury to the superior aspect of the acromion while the arm is adducted (e.g., a fall while cycling or riding a horse)
Less common: indirect injury via falling on an outstretched hand, which transmits force up the arm through the humerus to the acromion, causing displacement that distresses the AC ligaments

Local tenderness, swelling, and/or bruising
Pain is elicited by the cross-body adduction test, in which the patient elevates their arm to 90° and actively adducts it across their body.
Limited range of motion of the shoulder joint
Visible deformity of the lateral aspect of the clavicle may be seen in types III and above

Piano key sign (1/2) Piano key sign (2/2)

References:[1]

Approach: AC joint injury is a clinical diagnosis that can be classified according to the Rockwood classification via x-ray. If x-ray findings are questionable, an MRI, CT, or possibly ultrasound may be considered.
Classification

Rockwood classification of AC joint injury
Injury type	AC ligament	Joint capsule	CC ligament	Distal clavicle	Deltoid and trapezius muscles
Type I	Sprained	Intact	Intact	Intact	Intact
Type II	Ruptured		Sprained	AC joint widening and minimal elevation	Possibly partial detachment from clavicle
Type III	Ruptured			Moderately elevated and unstable to stress Reducible (“piano key” sign)	Likely detached from distal clavicle
Type IV	Ruptured			Posteriorly displaced through the trapezius Not reducible	Likely detached from distal clavicle Deltotrapezial fascia displaced
Type V	Ruptured			Severely elevated Not reducible	Detached from distal clavicle Deltotrapezial fascia ruptured
Type VI (rare)	Ruptured			Inferiorly displaced in subcoracoid position	Usually detached from clavicle

Rockwood classification of acromioclavicular injury (types I-VI) Piano key sign (spring test)

X-ray (anterior-posterior view, oblique view, axillary view) of the shoulder joint, acromion, and scapula:
- Subluxation of the AC joint space
- Widening of the CC space
- Displacement of the clavicle
- Accompanying injuries (e.g., clavicle fracture)
- Chronic cases: features of AC arthritis, distal clavicle osteolysis

Y view (lateral scapula view) of the shoulder Type III acromioclavicular joint injury

References:[2][3][4][5]

Acute management

Conservative treatment

Indications: types I and II
Methods
- Sling for comfort: 1–3 weeks (e.g., Desault or Gilchrist bandage)
- Avoid heavy lifting
- Analgesia (e.g., NSAIDs)

Surgical treatment

Indications
- Types III and above
  - Management of type III is controversial and determined on an individual basis
  - All patients with type III and above should be referred to an orthopedist
- Open fractures
- Neurovascular injury
- Failed conservative treatment
Objective: ligament repair and reconstruction
Methods
- Arthroscopic (all or assisted): preferred as less invasive
- Open surgery

Long-term management

Indications
- Persistent pain after healing of initial ligamentous injury
- Repeated minor injury without instability but persistent AC joint arthralgia
Methods
- Avoiding painful movement and analgesia
- Intraarticular glucocorticoid injections

References: [1][2]

See complications of fractures.
Brachial plexus injury (rare)
Chronic pain

We list the most important complications. The selection is not exhaustive.