Os acromiale is a failure of fusion of the acromial process. It is usually asymptomatic and discovered by chance. When it is painful a differential diagnosis must be made in relation to the subacromial impingement syndrome.

Unstable os acromiale is the cause of atypical scapulalgias. Stabilization by tension band wiring and an embedded slot shaped graft achieves union and relieves pain.

This series includes 10 patients mean age 43 years old presenting with shoulder pain resistant to a mean 15 months of conservative treatment. Pain followed trauma in three cases. Three patients had a history of acromioplasty, which had not relieved pain. All had pain during palpation of the superior aspect of the acromion. The diagnosis was confirmed in eight patients by positive results to local injection of the os acromiale. The mean preoperative Constant score was 53.4. The procedure included open reduction and fixation of the acromion by tension band wiring and pinning associated with an embedded iliac crest graft without acromioplasty.

The mean follow-up was 48 months. Pain was relieved in seven cases and all patients had improved and were satisfied. Union of os acromiale was confirmed on CT scan in all patients. The mean Constant score was 82.2.

The role of os acromiale in the origination of pain is confirmed by the efficacy of preoperative injection of the os acromiale and pain relief after achieving union. Moreover, our technique is reliable and always resulted in union of the os acromiale. Internal fixation by tension banding favors minimal upward migration of the os acromiale and union. In case of subacromial impingement syndrome an os acromiale should be looked for, as this condition could deteriorate with simple acromioplasty.

Level IV retrospective observational study.