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Os acromiale

What is os acromiale?

The roof of the shoulder (the acromion) has three growth centers made of cartilage. During development, these growth centers become bone and the roof of the shoulder transforms from four separate bones into one bigger bone. Occasionally, one or more of these growth centers does not undergo bony change. This persistent growth center of the roof of the shoulder is called the os acromiale. This cartilage growth plate allows for some motion of the acromion, which may pinch the rotator cuff tendon or bursa, causing symptoms of rotator cuff inflammation. Alternatively, this entity may not cause any pain or problems.

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How does os acromiale occur?

The growth center of the acromion fails to undergo bony change. This allows for motion of the acromion, which may pinch the rotator cuff and bursa, causing inflammation, degeneration, and, eventually, tearing of the cuff.

What increases the risk?

  • Growth plate not fusing
  • Overhead activity, including sports such as tennis, volleyball, swimming and baseball
  • Heavy lifting or hard labor
  • Poor physical conditioning (strength and flexibility)

What are the symptoms of os acromiale?

Sometimes there is no pain with this problem, and it is found when X-rays are taken for other reasons. Other times, symptoms can include the following:

  • Tenderness and, occasionally, redness and warmth on the top of the shoulder
  • Shoulder pain, especially when moving the shoulder against resistance or with lifting, and particularly when reaching overhead
  • Pain  at night
  • Limitation of shoulder motion
  • Crepitation (a crackling sound) when the shoulder is moved

How is it diagnosed?

Conventional X-rays are usually sufficient to demonstrate the os acromiale. A CT scan, a 3-D reconstruction of the shoulder bones, can better delineate the size and shape of the os, and, if surgery is necessary, is particularly helpful for pre-operative planning.

Are there any special tests?

  • CT scan shows the os, and for most patients is the definitive test
  • An MRI will also show the os, but is not as good at showing bone as soft tissue. Because some patients with rotator cuff problems have an os acromiale, in this population an MRI is the preferred imaging study of choice.

How is it treated?

Non-operative treatment: Initial treatment consists of medications and ice to relieve pain, stretching and strengthening exercises (particularly of the rotator cuff and scapular [shoulder blade] stabilizing muscles), and modification of activities. Specifically, avoiding overhead activities and heavy lifting will help reduce the inflammation. The exercises for the shoulder can all be carried out at home. Referral to a physical therapist or athletic trainer for further evaluation or treatment may also be recommended. Uncommonly, injection of cortisone into the subacromial bursa may be attempted.

Operative treatment: Surgery to fuse the growth plate or to remove part of the bone, if it is particularly small, is recommended if symptoms persist despite 3 to 6 months of conservative treatment. Surgery to fuse the growth plate usually involves pins, screws or wires to hold the bone, often with bone grafting. If the rotator cuff is torn, this should be fixed at the same time.

Treatment Complications:

Possible complications of non-operative treatment include persistent pain and activity impairment.

Possible complications of operative treatment include:

  • Surgical complications not specifically associated with os acromiale repair, such as pain, bleeding (uncommon), infection (<1percent), nerve injury (uncommon), stiffness, problems with anesthesia, and inability to return to previous level of pre-injury activity.
  • Complications specific to surgical treatment of this condition: Failure to achieve fusion, pain related to hardware (screws), pain due to associated pathology such as rotator cuff tear or AC (acomioclavicular) arthritis.

When can you return to your sport or activity?

Mild cases can be resolved with slight reduction of activity level, whereas moderate to severe cases may require significantly reduced activity for 3 to 4 months. Occasionally surgery is necessary.

How can os acromiale be prevented?

  • Symptoms related to os acromiale may be minimized with appropriate warm-up and stretching before practice or competition.
  • Maintain appropriate conditioning:
    • Shoulder muscle strength
    • Flexibility and endurance
  • Os acromiale cannot be prevented as it is a developmental condition.
  • Most cases are not symptomatic and do not require treatment; it is often an incidental finding when taking shoulder X-rays for patients with shoulder pain.
 

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