Circles measurement is a simple, but reliable parameter for assessing acromioclavicular joint (ACJ) displacement, a new study finds.
Circles Measurement Reliable for Acromioclavicular Joint Injuries
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The researchers of “Evaluation of the Circles Measurement and the ABC Classification of Acromioclavicular Joint Injuries,” published online on April 15, 2021 in The American Journal of Sports Medicine wrote, “Acromioclavicular joint injuries are common. Despite this, it remains unclear how best to assess, classify, and manage these cases. A simple, reliable, valid, and accurate radiographic parameter to measure ACJ displacement would allow improved consistency of diagnosis and subsequent treatment pathways.”
The researchers propose that circles measurement be used in conjunction with ABC classification to define acromioclavicular joint injuries more accurately.
Taken from a lateral Alexander radiograph of the shoulder, circles measurement is the center-to-center distance between two circles drawn to define the lateral extent of the clavicle and the anteromedial extent of the acromion.
It is a single measurement calculated as the difference between values recorded for the injured and uninjured sides, the researchers said. Validation was performed using lateral Alexander radiographs (including ±20˚projection error in all planes) and computed tomography of standardized acromioclavicular joint (ACJ) injury simulations.
According to the data collected, the circles measurement was both reliable and valid. Interrater reliability (ICC [intraclass correlation coefficient] [2,1]. 95% CI; n = 78; 4 observers) was 0.976 (0.964-0.985). Intrarater reliability (ICC [2,1], 95% CI; n = 78; 2 measures) was 0.996-0.998).
In addition, convergent validity (Pearson correlation coefficient, r) was 0.970 for ideal radiographs and 0.889 with ±20˚projection error in all planes.
Discriminant validity with 1-way analysis of variance, showed a p value of < .0001 and effect size (n2) of 0.960. It is able to tell the difference between previously defined stable (Rockwood IIIA) and unstable (Rockwood IIIB) injuries.
The researchers wrote, “The results permitted objective statistically sound parameters for the proposed ABC classification system.”
They added, “This novel parameter has the potential to standardize the initial assessment and possibly the subsequent clinical management of ACJ injuries, in addition to providing a standardized measure for future research.”
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This is a fascinating development. In my practice we've seen similar outcomes with the revised protocol. The key differentiator seems to be patient selection criteria. Has anyone else noticed the correlation with BMI thresholds?
Great point. I'd push back slightly on the conclusion, the sample size in the cited study is too small to draw population-level inferences. That said, the directional signal is compelling and worth a larger RCT.
We implemented a similar approach last year. Early results are promising but we're still gathering 12-month follow-up data. Happy to share our protocol if anyone is interested.
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