Publication:

The radiological prevalence and co-pathology associations of acromioclavicular joint arthritis in symptomatic shoulders: preliminary observations from an MRI-based study

Background Acromioclavicular joint (ACJ) arthritis is a frequent but often overlooked cause of shoulder pain in older adults. Differentiating symptomatic ACJ degeneration from incidental, age-related changes is challenging, particularly when other conditions such as rotator cuff (RC) tears are present.

Methods Forty-eight patients (mean age 61.6 years) with shoulder pain underwent standardized shoulder MRI. Three independent, blinded radiologists graded ACJ arthritis severity using the Shubin-Stein system. Inter-rater reliability was assessed with Fleiss’ kappa. Associations with RC tears, glenohumeral (GH) arthritis, labral pathology, and biceps tendon pathology were analyzed.

Results ACJ arthritis (grade ≥2) was found in 93.8% of patients, with 54.2% showing moderate-to-severe changes. The prevalence observed was higher than that reported in several asymptomatic cohorts. Inter-rater agreement for the Shubin-Stein classification was almost perfect (κ=0.821). Increasing age was significantly associated with greater arthritis severity (p=0.003). Severe ACJ arthritis was strongly correlated with full-thickness or massive RC tears (p=0.001), but not with GH arthritis, labral pathology, or biceps pathology.

Conclusions MRI-detectable ACJ arthritis is highly prevalent in symptomatic shoulders over age 50 and often coexists with significant RC pathology. The Shubin-Stein classification system shows high inter-rater reliability, supporting its clinical utility. These findings demonstrate the need for comprehensive shoulder evaluation, as concurrent ACJ pathology can affect diagnosis and intervention.