Acromioclavicular joint separation !
An acromioclavicular separation is an injury to the joint at the top of the shoulder where the collarbone meets the shoulder blade; severe ones lift the bone.
Updated 2026-10-29
Structures involved
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- AC ligament
- AC capsule
- Conoid ligament
- Trapezoid ligament
- Clavicle
- Scapula
- AC disc
- Coracoacromial ligament
- Front deltoid
- Upper trapezius
What it is
Injury of the joint between the acromion and the outer end of the clavicle, from a sprain of its capsule and ligaments to complete tearing of the coracoclavicular (conoid and trapezoid) ligaments with the clavicle displaced. Severity is graded with the Rockwood classification.
Who gets it
Common in young adults, mostly men, in contact sports (football, rugby), cycling, motorcycling and falls. It is among the commonest shoulder injuries in athletes.
Causes
- Fall or direct blow on the point of the shoulder with the arm adducted, driving the acromion downward
- Less often, a fall on the outstretched hand or the elbow transmitting force upward
Risk factors
- Contact sports, cycling and motorcycling
- Young male sex
- Falls from height or road traffic collisions
Pathophysiology
The acromioclavicular ligaments and capsule give horizontal stability; the conoid and trapezoid (coracoclavicular) ligaments give vertical stability. A downward force on the acromion tears the acromioclavicular ligaments first and then the coracoclavicular ligaments; with more energy the deltoid and trapezius are stripped and the arm sags, so the clavicle seems to rise.
Classification
- Rockwood I: acromioclavicular ligament sprain, no displacement
- Rockwood II: acromioclavicular ligaments torn, coracoclavicular ligaments intact, slight displacement
- Rockwood III: both ligament groups torn, clavicle displaced by about the width of the clavicle
- Rockwood IV: clavicle displaced backward into or through the trapezius
- Rockwood V: marked upward displacement with deltoid and trapezius fascia stripped
- Rockwood VI: rare, clavicle displaced below the acromion or coracoid
Symptoms and signs
- Pain and tenderness over the top of the shoulder after a fall
- Step or bump at the end of the clavicle in higher grades
- Pain on reaching across the body or overhead
- Swelling and bruising over the acromioclavicular joint
Diagnosis
- Clinical
- Tenderness over the acromioclavicular joint, a visible step and pain on cross-body adduction. Examination with the patient sitting or standing lets the arm's weight show the deformity.
- Tests
- Generally not needed.
- Imaging
- X-rays including a Zanca view (beam tilted upward) and comparison with the other side; an axillary view shows posterior displacement. Ultrasound or MRI help in unclear cases and associated injuries.
Differential diagnosis
- Distal clavicle fracture
- Shoulder dislocation
- Rotator cuff tear
- Coracoid or acromion fracture
- Acromioclavicular osteoarthritis
Goal of treatment
Relieve pain, restore pain-free shoulder function and strength, and restore stable alignment when displacement is severe.
Treatment
- Conservative
- Types I and II: sling for comfort, cold and analgesics (including nonsteroidal anti-inflammatory drugs), with early range of motion as pain allows.
- Rehabilitation
- Physiotherapy for range of motion, then scapular and rotator cuff strengthening before return to sport.
- Conservative
- Type III: most patients are first treated without surgery; operative repair is considered for some overhead athletes or manual workers, and criteria vary between texts.
- Surgical
- Types IV to VI, and type III cases that fail non-operative care: reduction and stabilisation, such as coracoclavicular ligament reconstruction or fixation with a plate or suture device.
Complications
- Persistent prominence of the clavicle (cosmetic bump)
- Acromioclavicular osteoarthritis or osteolysis of the distal clavicle
- Chronic pain and scapular dyskinesis
- After surgery: loss of reduction, hardware problems, infection or coracoid or clavicle fracture
Prognosis
Low-grade injuries usually recover fully within weeks. Many type III injuries do well without surgery, although some patients keep pain or weakness with overhead work. High-grade injuries generally do well after stabilisation.
Prevention
- Protective technique and equipment in contact sports
- Safe cycling and motorcycling
Test yourself
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Which ligaments are torn in a Rockwood type III acromioclavicular separation?
Both the acromioclavicular ligaments and the coracoclavicular (conoid and trapezoid) ligaments.
What is the typical mechanism of an acromioclavicular joint separation?
A fall or direct blow on the point of the shoulder with the arm adducted, driving the acromion downward.
Which X-ray view best shows the acromioclavicular joint?
The Zanca view, an anteroposterior view with the beam tilted upward; an axillary view shows posterior displacement.
In which Rockwood type is the clavicle displaced backward through the trapezius?
Type IV.
How are Rockwood types I and II usually treated?
Without surgery: sling for comfort, analgesia and early range of motion followed by rehabilitation.
Related conditions
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Acromioclavicular Joint Injury (StatPearls (NCBI Bookshelf), 2022).
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