Objective: The purpose of this study was to describe the MRI appearance in atraumatic osteolysis of the distal clavicle (AODC).
Materials and methods: We retrospectively evaluated MRI, medical records, ancillary diagnostic imaging studies and clinical course in five men and two women (mean age, 39 years) in whom the final clinical diagnosis of AODC was established. None of the patients had significant shoulder injury, but all participated in activities involving repetitive strain of the acromioclavicular (AC) joint. In three of these patients, we performed follow-up MRI (ranging from 5 1/2 to 15 months after the initial MRI).
Results: In all seven patients, signal intensity changes within the intramedullary portion of the distal clavicle on MRI were consistent with diffuse bone marrow edema. Marrow edema was most conspicuous on STIR imaging and occasionally could be misinterpreted as normal marrow signal patterns on spin-echo imaging. Cortical thinning or irregularity of the distal clavicle was seen in six cases and tiny subchondral cysts were seen in three, corresponding to subtle cystic changes on shoulder radiography. Limited bone scans obtained in two patients showed markedly increased uptake of radiotracer at the distal clavicle and AC joint. Histologic examination in one case showed disruption of articular cartilage, subchondral cysts, and metaplastic bone formation with increased osteoclastic activity. Follow-up MRI in three patients who were asymptomatic following conservative therapy showed normalization of marrow signal intensity.
Conclusion: Atraumatic osteolysis of the distal clavicle is a relatively uncommon but important cause of shoulder pain. Particularly when the clinical history is suggestive of repetitive AC joint stress, MRI of the distal clavicle should be examined closely for marrow edema, cortical irregularity, and cystic changes. Such abnormalities may be especially conspicuous when STIR imaging techniques are used.