Os acromiale is a condition that occurs when the acromion, which is part of the shoulder blade, fails to fuse properly, leaving a gap. Usually, this gap in the bone doesn’t cause problems. However, this condition can sometimes cause shoulder pain. So, what exactly is an Os acromiale, how can it cause pain, and what can doctors do about it?  

What is Os acromiale?

The acromion is the outer part of the shoulder blade that connects with the collarbone (clavicle) through the AC joint. It lies above the shoulder joint. 

During normal development, the acromion ossifies in distinct segments, known as ossification centres. Gradually, these segments join during adolescence to form one single bone. Generally, by the age of 18, all the centres have fused. However, in about 8% of people, one of these centres does not fuse, leading to a gap between the bones. This gap consists of cartilage. We refer to this unfused bone as an os acromiale. 

What causes pain is Os acromiale? 

In some people, the cartilage gap in the bone can cause problems due to movement. This movement can occur from a fall onto the shoulder, causing a crack in the cartilage. At other times, the movement of the bones can happen for no particular reason. However, we see more problems in males, throwing athletes, swimmers, weightlifters, or individuals involved in repetitive or heavy lifting. In rare cases, surgery for another shoulder problem can lead to bone movement and cause post-surgery pain. 

This movement of bones can lead to the following problems:

  • Chronic pain in the gap secondary to excessive movement 
  • Rotator cuff tendonitis causes rubbing of the acromion on the tendons 

Os acromiale assessment 

Individuals with a painful Os Acromiale present with the following features: 

  • Pain in the shoulder, especially with overhead activities 
  • Clicking or grinding sensation as the arm is moved overhead 
  • Pinpoint tenderness at the acromion.
  • If the rotator cuff tendons are affected, pain can move to the front of the shoulder and down the arm. Also, weakness can occur if the tendons are torn. 

It is essential to consult your doctor for a thorough assessment of your shoulder. If your doctor suspects you have this condition, they will order imaging tests to confirm the diagnosis. Standard X-ray views detect the gap in the bones in the acromion. The key feature is a black line between the ossification centres. MRI helps detect swelling around the gap, indicating pain from the Os acromiale. Additionally, MRI can detect associated rotator tendon pathology, such as tendinosis or tears. Sometimes, we use a CT scan to visualise the bone more clearly. 

CT scan showing Os acromiale

Treatment

Treatment for os acromiale depends on the severity of symptoms, the patient’s age, and their activity level. It ranges from conservative management to surgical intervention, although we typically start with conservative measures.  

Conservative measures include the following:

  • Rest from aggravating activities and modify your sport. For weightlifters, we suggest reducing the weight of overhead lifts and avoiding particularly provocative exercises, such as the incline bench press and military press. 
  • Anti-inflammatory treatments, such as regular ice after sports and NSAIDS (ibuprofen), reduce inflammation in the bone and the rotator cuff tendons.
  • Physiotherapy helps by strengthening the muscles around the shoulder. If the rotator cuff tendons are swollen, focusing on scapular strengthening can reduce tendon impingement. 
  • Sometimes, a cortisone injection into the gap between the bones or the rotator cuff bursa can help reduce pain and facilitate rehabilitation. 
  • One study found that shockwave therapy to the acromion and rotator cuff tendons can be beneficial in chronic cases. 

Surgery

Surgery is only indicated in severe cases that limit activity and fail conservative measures. Generally, we wait 6-12 months before considering surgery. The options for surgery include:

  • Excision of the Os Acromiale Fragment: The unfused segment is removed to alleviate symptoms. This is generally preferred for smaller fragments that don’t significantly impact shoulder mechanics.
  • Acromioplasty and Fragment Fixation: For larger fragments or those causing significant instability, the surgeon may reattach the fragment to the rest of the acromion using screws or other fixation devices. Bone grafting is sometimes performed to help the fragment fuse.

Final word from Sportdoctorlondon about Os acromiale

Os acromiale is a rare condition due to unfused ossification centres in the acromion. In severe cases, a thorough assessment is crucial to inform treatment decisions. Whether managed conservatively or surgically, treatment focuses on reducing pain, restoring mobility, and allowing individuals to return to their preferred activities safely.

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