Anteroposterior radiograph of a 40-year-old man with left shoulder pain aggravated by overhead activities and lifting objects.
Outlet view radiograph of the patient.
A 40-year-old man presents with left shoulder pain of several months’ duration. Overhead activities and lifting objects with the left arm seem to aggravate the pain. The man denies any known injury or precipitating event. Anteroposterior and outlet view radiographs are ordered. On examination, the patient has positive impingement signs, pain to palpation over the anterior acromion, and no weakness with rotator cuff testing.
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Os acromiale can be seen on this patient’s initial radiographs. Axillary lateral radiograph is the best image to view the size and shape of os acromiale and should be ordered next. Os acromiale occurs when the anterior acromial apophysis fails to fuse. Complete union of the acromial ossification centers typically occurs by age 15 to 18 years but can take up to 25 years.
Os acromiale is prevalent in up to 8% of the population and occurs bilaterally in as many as 60% of patients. Os acromiale is often an incidental finding on radiographs and is rarely a source of shoulder pain. More often, people complaining of shoulder pain who have os acromiale have other underlying shoulder pathology, including bursitis, rotator cuff tendinitis, and rotator cuff tear.1
Physical examination findings in those with os acromiale usually include direct tenderness to palpation over the nonunion site and impingement-type pain with deltoid contraction. Contraction of the deltoid can flex the unstable os acromiale forward, creating dynamic impingement on the rotator cuff. Those with symptomatic os acromiale often complain of pain and weakness with overhead activities, pain at night, and localized pain over the anterior acromion.
Grashey, outlet, and axillary view radiographs should be ordered initially. Magnetic resonance imaging is often used along with radiographs to help make the diagnosis and rule out other sources of shoulder pathology and pain. Initial treatment is nonsurgical and may include rest, nonsteroidal anti-inflammatory drugs, physical therapy, subacromial injections, and steroid injections into the nonunion site. A period of conservative treatment is recommended for at least 6 months. Surgical options for symptomatic os acromiale include arthroscopic decompression, excision of the fragment, and open reduction and internal fixation with bone grafting.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
- Kurtz CA, Humble BJ, Rodosky MW, Sekiya JK. Symptomatic os acromiale. J Am Acad Orthop Surg. 2006;14:12-19.
- Warner JJ, Beim GM, Higgins L. The treatment of symptomatic os acromiale. J Bone Joint Surg Am. 1998;80:1320-1326.