Distal clavicular osteolysis (DCO) is a self-limiting pathology most caused by overuse injury. The pathogenesis is debated, but likely involves subchondral microfractures caused by repetitive activity with compression of the distal clavicle [1]. Stress-induced DCO is most often seen in weightlifters or athletes who are engaged in strenuous training of the upper extremity in which the AC-joint is subjected to forces as if it were a weight-bearing joint, sometimes leading to bilateral DCO [2]. DCO is also seen in overhead athletes and workers [3].
Clinical findings are non-specific and include tenderness to palpation of the AC-joint, elicited pain with cross-body adduction but a normal range of motion [4]. Patients complain of vague anterior shoulder girdle pain: increased at night following intense weightlifting during the day, relieved with decreased activity [5].
Digital radiographs are not sensitive to detect DCO in the early stage of the disease. Initial findings are subtle, such as periarticular osteopenia or loss of subchondral cortex. In the progressive lytic stage, cortical thinning, irregularity and erosions in the distal clavicula can be seen, while the acromial surface remains normal [5]. For early diagnosis, both MR-imaging and bone scintigraphy are far more sensitive. MR-imaging typically shows high signal intensity to muscle in the distal clavicle on T2- or PD-fat suppressed sequence, correlating with bone marrow oedema. This may also be present in the articular part of the acromion, but less pronounced [6]. Other MR findings include the same radiographic features, but also capsular thickening and joint effusion of the AC joint [6]. In the early stage, bone scintigraphy will demonstrate increased uptake in the distal clavicle, consistent with the theorized pathogenesis, visualizing increased osteoblast activity [5].
Initial treatment is mostly conservative, including activity modification and nonsteroidal anti-inflammatory drugs (NSAIDs), often successful after 3-6 months. Long-term sequelae on MRI include widening of the AC joint and AC joint osteoarthritis. In severe cases, resection of the distal clavicle has demonstrated acceptable clinical outcome [5, 6].
The radiologist should be aware that DCO affects a certain population such as weightlifters and should be included in the differential diagnosis in case of atraumatic shoulder pain. Key for the diagnosis are subtle changes on digital radiograph, which can be magnified by comparative incidences, followed by MRI or bone scintigraphy to confirm the diagnosis. Comparative MRI will be helpful to exclude bilateral DCO.
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