The unique aspect of our case report is the origin of the exostosis, from the spine of the scapula, which was not obvious on standard anterior-posterior and axial radiographs of the shoulder. Only after a year of symptoms did the radiographic findings, using a scapular Y-view, reveal the exostosis that had caused her persistent symptoms. Furthermore, to our knowledge arthroscopic excision of an exostosis for subacromial impingement is original to our report, offering a minimally invasive approach with relief of the patient’s symptoms.
Craig  is the only other author to have reported a patient with HME suffering from subacromial impingement syndrome secondary to osteochondromas of the acromion and distal clavicle. However, similar to our case, their patient had persistent shoulder symptoms for one year before the exostoses, arising from the under surface of the acromion and the clavicle, were evident on the plain radiographs and were subsequently excised through an open approach giving symptomatic relief. Reichmister et al.  reported a further two cases of isolated osteochondromas of the distal clavicle, describing persistent symptoms of subacromial impingement, before being eventually diagnosed. The exostosis reported in our patient was not originally observed on early radiographs, and only with persistence of their symptoms was further imaging performed. This illustrates the importance in acquiring early additional imaging, such as a MRI scan, for patients with mechanical symptoms who have apparently normal initial radiographs. This additional imaging would seem more important in patients with HME who are more prone to suffer with symptomatic exostosis. However, soft-tissue tumours within the subacromial space can also present with impingement type symptoms in patients without HME, who may also benefit from an early MRI scan [10, 11].
Artrhoscopic removal of the exostosis offers several advantages over open excision including less invasive surgery, an earlier recovery, and shorter hospital stay [12, 13]. Arthroscopic excision of osteochondromas for the treatment of snapping scapula has previously been described [14, 15]. The exostoses in patients with HME may be numerous, although many are asymptomatic and a cautious treatment approach is warranted with removal of symptomatic exostoses only [2, 16]. Arthroscopic surgery, however, offers advantages to patients with HME and should be considered as a management option for the excision of symptomatic osteochondromas.
The lifetime risk of sarcoma in HME is thought to be approximately 2% to 4% [17–20]. The commonest sites of malignant change are the ilium (40%), scapula (11%) and pubic rami (11%) . The scapula, clavicle and proximal humerus account for 18% of secondary chondrosarcomas in patients with HME . Exostoses of the scapula have an increased probability of malignant change relative to all other exostoses (odds ratio 12) . Prior to surgery, it is therefore important to ensure that the lesion is benign and if doubt exists the patient should undergo open biopsy and or excision.