Intra-articular exostosis on the glenoid neck in a patient with hereditary multiple exostoses: a case report

Hereditary multiple exostoses (HME) is an autosomal dominant hereditary condition characterized by the presence of multiple benign bony outgrowths, termed exostoses or osteochondromas. The knee is the most common site for osteochondromas (40%). The most common complaints are pain and functional impairment. Shoulder exostoses are associated with more severe disease. We present the case of a HME patient with shoulder pain due to an isolated intra-articular exostosis on the anterior edge of the glenoid cavity.A 50-year-old male patient with HME diagnosed since adolescence had undergone surgery previously to remove a cervical intracanal exostosis and painful exostoses around the knees. Previously, he had been treated on several occasions for a left painful shoulder. The patient returned in 2023 because the left shoulder pain had become constant, leading to insomnia. Clinical examination showed full range of motion. Rotator cuff test results were normal but the belly-press test triggered pain. An exostosis in the anterosuperior part of the glenoid neck, facing the superior part of the subscapularis tendon, was observed on CT arthrography and MRI. There was no evidence of a subscapularis tendon lesion. Diagnostic shoulder arthroscopy was proposed to further investigate these atypical clinical findings. The exostosis was located in the anterosuperior part of the glenoid neck and was oriented perpendicular to the glenoid cavity in the direction of the subscapularis tendon, which had an atypical delamination tear of its articular layer leaving the humeral enthesis intact. The surgical procedure consisted in removing the entire exostosis with a burr and debriding the subscapularis tendon. The patient resumed daily activities without pain 3 months after surgery.To our knowledge, this is the first reported case of intra-articular exostosis on the glenoid side of the shoulder joint. Two previous cases of intra-articular exostosis have been described on the humeral side of the joint. Exostoses are also known to cause painful snapping scapula syndrome when located on the ventral side of the scapula. The unusual nature and cause of the injury explains the diagnostic delay. Subscapularis tendon tests showed no weakness but were painful, suggesting a possible anterior rotator cuff tear. However, imaging findings were inconclusive and showed an intact subscapularis tendon enthesis.The noteworthy features of this case are the previously unreported intraarticular location of the exostosis on the glenoid side of the shoulder joint and the unusual subscapularis tendon lesion it led to.