MR observations of posttraumatic osteolysis of the distal clavicle after traumatic separation of the acromioclavicular joint

Purpose: The purpose of this work was to characterize the MR features of po sttraumatic osteolysis of the distal clavicle in patients who have sustaine d a previous separation of the ipsilateral acromioclavicular (AC) joint. Method: We studied eight male patients (mean age 25 years) with intractable pain in the AC joint after sustaining a traumatic joint separation. With u se of the Rockwood classification, the separations were classified as Type 1 in one patient, Type 2 in two patients, and Type 3 in five patients. The MR studies were evaluated for periarticular soft tissue swelling, cortical irregularity defined as thinning or absence of portions of the cortex in th e acromial and clavicular articular surfaces, hypertrophic osseous changes, periostitis, bone marrow edema, periarticular cyst-like changes, and joint space widening exceeding 6 mm. Radiographs were evaluated independently of the MR studies. Osteolysis of the distal clavicle was confirmed pathologic ally in seven patients and with surgery in one patient. Results: The incidence of osteolysis in patients who have had a previous AC joint separation was estimated to be similar to 6%. Observations on MRI in cluded soft tissue swelling, bone marrow edema in the distal clavicle, and cortical irregularity associated with periarticular cyst-like erosions in e ight patients, joint space widening in six patients, clavicular periostitis in three patients, and marrow edema in the cromion in five patients. Only one patient had osteophyte formation. Radiographic observations of periarti cular soft tissue swelling, osteopenia of the distal clavicle, articular er osions, and joint space widening allowed diagnosis in only four patients pr ospectively. Conclusion: The MR features of posttraumatic osteolysis are characteristic of this process. We advocate the use of MRI in patients with chronic AC joi nt pain who have had a prior AC joint dislocation, particularly if follow-u p radiographs are nonspecific, equivocal, or do not indicate the presence o f secondary osteoarthritis.