The acromion is a continuation of the scapular spine which has four ossification centers. Four separate parts of the acromion appear by fourteen years of age and fuse by the age of twenty-five. These four ossification centers are called the basi-acromion, meta-acromion, meso-acromion, and the pre acromion. Failure of the ossification centers to fuse to the acromion process is called Os Acromiale. A fusion failure between MTA and MSA is the most common scenario. The unfused segment is connected to the AC joint and to the coracoid—this may cause movement of the unfused segment.
Failure of the anterior ossification center to fuse to the acromion process occurs in less than 10% of people. X-rays are usually to diagnose os acromiale but, it is sometimes hard to see in an AP view x-ray. The axillary view is the best for viewing the unfused segment.
Symptoms of os acromiale include: localized tenderness and pain due to the motion of the fragment. Impingement of the rotator cuff due to the unfused fragment tiling forward or due to the contraction of the deltoid muscle and movement of the shoulder is common. The impingement does not cause a rotator cuff tear, however a tear may be associated.
Treatment of os acromiale include: Physiotherapy, NSAIDs, Injections, and Surgery. Surgery will consist of a decompression with minimal removal of the bone or an excision of the small unfused segment. An open fixation with bone graft may be necessary for larger fragments.
You will not perform an acromionectomy as this will weaken the deltoid muscle and leave the patient with a very bad functional outcome.
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