Os acromiale is a rare anatomical abnormality and treatment is controversial. Our retrospective study analyses the outcome of excision, acromioplasty and bony fusion of the os acromiale when it is associated with a tear of the rotator cuff.

After a mean follow-up of 41 months, 33 patients were radiologically and clinically assessed using the Constant score. The surgical procedure was to repair the rotator cuff together with excision of the os acromiale in six patients, acromioplasty in five, and fusion in 22.

Of the 22 attempted fusions seven failed radiologically. The Constant scores were 82%, 81%, 81% and 84% for patients who had excision, acromioplasty, successful fusion and unsuccessful fusion respectively. There were no statistically significant differences.

We conclude that a small mobile os acromiale can be resected, a large stable os acromiale treated by acromioplasty and a large unstable os acromiale by fusion to the acromion. Even without radiological fusion the clinical outcome can be good.