Osteoid osteoma of the acromion simulating acromioclavicular pain.

The osteoid osteoma is a benign bone tumour that usually presents with nocturnal pain in young adults, relieved by rest and anti-inflammatories. It can affect any bone; however, their occurrence is rare in the acromion. The authors describe a case of osteoid osteoma located in the acromion, with symptoms that simulated acromion claviculararthrosis. The diagnosis was made by CT scan and treatment was excision of the nidus through arthroscopy. The diagnosis was confirmed by histopathology. In the outpatient segment, the patient remained asymptomatic, with complete recovery of function of the affected limb.