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The acromioclavicular (AC) distance or joint space is an important measurement in the evaluation of acromioclavicular joint injury.
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The AC distance is assessed on the frontal radiograph of the shoulder as the distance between the medial cortex of the acromion and the lateral cortex of the clavicle.
Alternatively, the measurement can be taken as the average of the distances between the superior and inferior borders of the acromioclavicular joint, which has the advantage of smoothing irregularities of the joint space and can be used for a more precise measurement 2.
The acromioclavicular joint space normally measures 1-6 mm (females) and 1-7 mm (males) 4, decreasing with age - a joint space of <0.5 mm can be considered normal in patients >60 years old 2.
When the AC distance is >7 mm (males) and >6 mm (females) is abnormal and can be from:
- acromioclavicular injury 4
- effusion 4
- distal clavicular erosion
- prior surgery
- 1. Väätäinen U, Pirinen A, Mäkelä A. Radiological Evaluation of the Acromioclavicular Joint. Skeletal Radiol. 1991;20(2):115-6. doi:10.1007/BF00193822 - Pubmed
- 2. Petersson C & Redlund-Johnell I. Radiographic Joint Space in Normal Acromioclavicular Joints. Acta Orthop Scand. 1983;54(3):431-3. doi:10.3109/17453678308996596 - Pubmed
- 3. Charles M. Court-Brown, James D. Heckman, Margaret M. McQueen et al. Rockwood and Green's Fractures in Adults. (2015) ISBN: 9781451175318 - Google Books
- 4. Flores D, Goes P, Gómez C, Umpire D, Pathria M. Imaging of the Acromioclavicular Joint: Anatomy, Function, Pathologic Features, and Treatment. Radiographics. 2020;40(5):1355-82. doi:10.1148/rg.2020200039 - Pubmed