Shoulder joint explosion (AC joint explosion)

First of all, let’s examine what the diastasis of the acromioclavicular joint is and how to recognize it, and let’s try to understand whether surgical intervention is necessary.

The separation of collarbone and acromion is also known as shoulder joint explosion.

In contact athletes, half of shoulder injuries affect this joint (Kaplan – 2005).

As a rule, this injury arises from a fall on the shoulder, but differs significantly from a shoulder dislocation.

The trauma injures the ligaments that surround and stabilize the joint between the collarbone and the shoulder blade.

Shoulder joint explosion is an injury at the point where the collarbone and shoulder meet.

Usually this is an injury to the connective tissue or ligaments, but can also occur with a fracture.

In more severe cases, the coracoclavicular ligament (between the collarbone and the raven’s beak process of the shoulder blade) is also torn.


Classification by severity

Severity Type of injury I

  • ribbons stretched,
  • Joint well aligned.


  • Complete rupture of the AC band*
  • Stretching of the CC band**
  • Slight displacement of the collarbone
  • (less than the depth of the joint).


  • Complete tear of the AC and CC band
  • Displacement of the collarbone
  • (more than the depth of the joint).


  • Same as Severity III
  • The collarbone recedes relative to the trapezius.


  • Significant displacement of the collarbone
  • Replacement of Deltoid and Trapezius.


  • Collarbone enters under the raven’s beak process.

Source: Pubmed (Michele Boffano – 2017)

* AC = Acromioclavicular

** CC = Coracoclavicular

Causes of shoulder joint explosion

The most common causes are:

  1. sports accidents,
  2. car accidents,
  3. Fall on one side of the body.

Symptoms of shoulder joint explosion

  1. Shoulder pain
  2. Arm weakness
  3. Shoulder swelling
  4. Movement restriction
  5. A bone protrusion on the shoulder
  6. Asymmetry of the AC joint compared to the normal side (Babhulkar – 2014)
  7. Annoying feeling of pressure at the AC joint.

Complications of shoulder joint explosion

  1. Chronic instability of the shoulder,
  2. Development of arthrosis.

These complications occur in 50% of cases with diastase I and II degree.

Diagnosis of shoulder joint explosion

These lesions can be easily diagnosed by inspection and palpation.

It is also important to examine the nerves and blood vessels, especially the arm plexus and the subclavian artery, which is located below the middle of the collarbone.

It must also be excluded:

  • joint injuries,
  • Lung injuries such as pneumothorax (Ebraheim et al. – 1988).

As a rule, the patient supports the arm with the other hand when he gets to the hospital.

Tests for shoulder joint explosion

Physical tests must be performed to detect if it is a shoulder joint explosion.

For diagnosis and treatment in this case, it is necessary to consult the doctor.

Horizontal adduction of the arm

  1. Sit down
  2. Stretch out the aching arm,
  3. Shift the elbow to the other (healthy) shoulder,
  4. In case of pain in the AC joint, the test is positive.


  • Place the hand of the affected arm on the opposite shoulder,
  • Position the hand of the healthy arm under the elbows,
  • Push the elbow upwards.
  • The test is positive if the patient feels pain in the AC joint.

Tensile test

  • Raise the elbows to shoulder height,
  • Unite both hands,
  • Each arm pulls outwards,
  • The test is positive if there is pain in the AC joint.

If all tests are positive, it is almost certainly diastasis.

If only one or both are positive, there is probably a diastase.

Treatment of shoulder joint explosion

Conservative treatment involves immobilization of the shoulder through a bandage, ice packs and medications that can help relieve the pain.

Most patients regain almost complete shoulder functionality after this injury, even if a significant deformity remains.

Some people still feel pain in the acromioclavicular joint, even if there is only a slight deformity.

The symptoms can have the following causes:

  • irregular bone contact when the joint moves,
  • Arthritis
  • Injury to a cartilage disc located between the articular bones (Iannotti – 1999).

When to operate?

In many cases, it is worthwhile to wait with the operation first.

Surgery may be considered if the pain persists or is a serious deformity.

Conservative treatment is recommended for lesions of the first and second degree.

According to Mouhsine et al., 27% of patients treated conservatively continue to show symptoms after 26 months.

If the symptoms persist, the doctor may proceed as follows:

  1. cortisone injections,
  2. A resection operation (removal) of the outer collarbone part.

With high-grade diastasis (IV, V and VI), the patient suffers from constant pain and loses the functionality of the hand. Here, surgical intervention is required.

The orthopedist may advise removing the end of the collarbone so that it no longer rubs against the acromion.

If there is a significant deformity, the ligaments attached under the collarbone should be reconstructed (Scheibel – 2011).

This type of procedure is very successful, even if healing takes a few months.

Regardless of whether the shoulder is treated conservatively or surgically, physiotherapy aftercare is important for the recovery of:

  • Range of motion
  • Brawn
  • Mobility.


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