MRI findings of acromioclavicular joint osteoarthritis are the norm after age 40

Abstract

Background: Acromioclavicular joint (AC) arthritis (A) is a common incidental finding on shoulder imaging. An improved knowledge of the age- and sex-specific prevalence (or base rate) of incidental ACA can inform diagnosis and treatment strategies for shoulder pain.

Hypothesis: There is no relationship between age or gender and the presence or severity of MRI findings consistent with osteoarthritis of the acromioclavicular joint.

Methods: We rated ACA on 475 MRIs from a database of patients who had MRIs for non-AC indications. The cohort consisted of 51% men, 49% women and had an average age of 55. Bivariate analyses were used for analysis of age and sex-specific prevalence.

Results: The prevalence of findings consistent with ACA on MRI for non-AC indications was 83%. The prevalence increased from 75% between ages 40 and 50 to 100% after age 70. Logistic regression demonstrated an association between age and ACA (Odds Ratio 2.89; 95% confidence interval [CI]=2.30 to 3.63; p=0.001). No difference was seen by sex (Chi-Square, 0.16; p=0.67). There was a positive correlation between age and ACA severity (Spearman's rho=0.43; p=0.000010).

Discussion: The observation that MRI evidence of ACA is the norm (75%) after age 40 and is universal with human aging (100% after age 70), makes it very difficult to discern ACA as a cause of shoulder symptoms. Given the near universal prevalence of radiological ACA, imaging cannot be used as a reference standard for diagnosis of symptomatic ACA based on symptoms and signs.

Level of evidence: Not applicable.

Keywords: Acromioclavicular joint; Arthritis; Diagnostics; MRI; Osteoarthritis; Prevalence; Shoulder pain.