Atypical presentation of an intra-articular osteoid osteoma in the proximal humerus excised with arthroscopy: a case report.

An adult man presented with a 5-month history of anterior right shoulder pain. He denied previous trauma or night pain. On the otherwise normal physical examination, pain was elicited in maximum abduction and external rotation. Radiographs were negative. The primary imaging findings were bone marrow oedema of the inferomedial proximal metaphysis of the humerus on MRI and cortical demineralisation on CT located posteromedially. A superficial elevation was also observed around the lesion. A provisional diagnosis of an osteoid osteoma was made based on these imaging findings. Arthroscopic excision of the lesion was performed, and histopathological examination confirmed the diagnosis of an osteoid osteoma. Diagnosis of intra-articular osteoid osteomas may be challenging due to atypical symptomatology and lack of pathognomonic imaging findings. Arthroscopic excision of such lesions in the shoulder is a safe and reliable option and should be considered as the treatment of choice.