DCO, often referred to as “weightlifter’s shoulder,” predominantly affects individuals engaged in repetitive upper extremity activities involving heavy loading or stress across the ACJ, particularly athletes and manual laborers [11]. It is most commonly reported in weightlifters, with a higher prevalence among those who regularly perform bench press exercises, overhead presses, or similar exercises that stress the ACJ [3, 12]. Higher frequency and intensity of bench pressing, as well as longer duration of bench pressing, are known risk factors for developing DCO [12].

DCO has been classically reported in young- to middle-aged males due to the demographic distribution of weight training and physically demanding occupations, and in other populations subjected to chronic stress or trauma to the ACJ [3, 9]. With increasing recognition of the importance of muscle mass on overall health and emphasis on strength training, there has been a gradual rise in the popularity of weightlifting across all ages and in women [13]. There has been a concomitant rise in weightlifting-associated injuries, which is likely to continue as individuals become increasingly more health-conscious [12, 13].

MRI is the study of choice for demonstrating findings of DCO, including bone marrow edema, osseous resorption/erosion, and pericapsular edema. While reciprocal edema in the anterior acromion has been documented in patients with DCO [8], our study demonstrates a distinct variant in which resorptive changes are seen at the anterior acromion in addition to the distal clavicle. On analysis of demographic data and activity patterns, this was more commonly seen in males and in patients with greater bench press loads. We suspect this represents a more advanced stage in the natural history of the disease, associated with a higher intensity of weightlifting causing increased stress upon the joint. This hypothesis aligns with the widely recognized association between weightlifting and the development of DCO and helps explain the trend of longer symptom duration in patients with anterior acromial involvement. Previous research studies have identified weightlifting as a significant risk factor for DCO, particularly when the activity involves greater intensity, higher frequency, or longer durations of bench pressing [12, 14]. These observations underscore the mechanical burden that such exercises impose upon the ACJ, potentially accelerating the onset or progression of DCO in susceptible individuals. It is interesting that the two cases in which there was an os acromiale and three cases in which there was a history of prior shoulder surgery were all in the group with anterior acromial involvement. It is possible that destabilization or alteration of the normal biomechanics at the ACJ may predispose to more extensive osteolysis.

Our study, although small in size, has implications for diagnosis, treatment, and management of these patients. Bone marrow and resorptive changes spanning the ACJ in an otherwise healthy, active individual may be mistaken for septic arthritis or an inflammatory arthropathy, leading to unnecessary medical workup and inappropriate treatment. Inflammatory and crystalline arthropathies such as rheumatoid arthritis and gout, septic arthritis, or hyperparathyroidism can cause erosion, bone marrow edema, and periarticular inflammation about the ACJ with a similar imaging appearance [15]. The treatment for these pathologies is varied, making accurate diagnosis critical. The diagnosis of DCO, and our proposed variant, can be confidently made with the appropriate clinical history and characteristic imaging findings on MRI. DCO is usually a self-limited disease when identified early and treated with conservative measures. Activity modification plays a pivotal role in alleviating symptoms and preventing disease progression. During its early stages, DCO does not contribute to joint instability, making timely intervention particularly beneficial. However, if diagnosis and treatment are delayed or the provoking insult is not removed, this may result in foreshortening of the distal clavicle with ACJ widening, instability, and eventual osteoarthritis [3, 6].

Our study has several limitations, the most significant being that it was performed as a retrospective analysis at a single institution, lacking a normal control group and reference standard. Follow-up imaging and clinical notes were not reliably available in our study population, and therefore, we could not assess if patients responded appropriately to conservative treatment. However, none of the included patients returned to our institution for image-guided ACJ aspiration or biopsy. Our study is also dependent upon patient-reported data and thus limited by missing data points. Although our findings suggest that maximum bench press weight may influence involvement of the anterior acromion, other associations could be further elucidated in a larger, more diverse patient population data set. This could help confirm if anterior acromial involvement represents a more severe or advanced form of DCO. Likewise, imaging and clinical follow-up after appropriate treatment would help confirm a biomechanical etiology and determine if this variant has a higher predilection for development of ACJ instability and/or osteoarthritis.

While we did exclude cases in which there was significant (i.e., more than mild) pre-existing ACJ osteoarthritis, cases in which there were other concomitant shoulder findings, such as rotator cuff tendinopathy or labral tears, may have confounded our results. However, in routine clinical practice, DCO often coexists with other shoulder pathology, particularly in older individuals. Although images were reviewed by consensus of a musculoskeletal radiology fellow and attending, which may introduce consensus bias, it is important to note that all included cases had already been initially reported by a radiologist within our musculoskeletal division. In other words, patients had already been independently diagnosed with DCO on MRI by a subspecialty-trained musculoskeletal radiologist (nine interpreting radiologists with 5–30 years experience). Many of the issued reports acknowledged involvement of the acromion, though the verbiage and descriptions were variable. We hope that introducing this variant into the literature will help improve reporting in such cases.

In cases of DCO caused by mechanical overuse or repetitive microtrauma, bone marrow edema in the distal clavicle may precede findings of bone resorption and cystic change. In such cases, we advise reporting this as osseous stress reaction, which may be a precursor lesion to true osteolysis. Thus, when looking at this specific variant of DCO with involvement of the acromion, we chose to focus on cases in which there was true osteolysis of the anterior acromion, not simply reciprocal bone marrow edema. In a previously published study examining shoulder MRIs with DCO, 22/36 patients (61%) had additional mild bone marrow edema in the acromion, which was subjectively less intense than the distal clavicle [8]. Another study examining DCO excluded cases in which there was any edema in the acromion entirely [3]. Thus, while it has been reported that disproportionate acromial bone marrow edema may co-occur with DCO, the finding of acromial osteolysis has not yet been presented. Comparison can be drawn to osteitis pubis in the pelvis, in which excessive mechanical load at the pubic symphysis results in osseous stress reaction and clinical symptoms of athletic pubalgia. In more advanced cases, osteitis pubis may also show findings of bone resorption/erosion with osteolysis and cyst-like changes spanning the symphysis, which may be symmetric or asymmetric [16, 17]. Certainly, intrinsic biomechanical differences between the ACJ and pubic symphysis exist, which likely helps explain the variabilities in imaging appearance and patterns of involvement.

Despite these limitations, our data strongly suggest that DCO can have a varied imaging appearance with involvement of the anterior acromion. This variant of DCO should be suggested when characteristic imaging findings are seen in the appropriate clinical context. Patients with DCO typically respond well to conservative treatment, and delayed clinical diagnosis can lead to potential complications such as ACJ osteoarthritis or instability. If clinical history is insufficient or unavailable, or if there is significant underlying osteoarthritis, one may consider other differential diagnoses such as degenerative, inflammatory, and crystalline arthropathies, septic arthritis, or hyperparathyroidism. Further studies may benefit from a more stringent clinical arm and quantifying involvement of the acromion.