Os peroneum fragment separation of 6 mm or more suggests os peroneum fracture and associated full-thickness peroneus longus tendon tear. Separation of 2 mm or less may be seen with nondisplaced os peroneum fractures and bipartite os peroneum.

Primary diagnosis of longitudinal stress fracture is made by finding a vertical cleft on one or more axial images. Secondary signs of position of the nutrient foramen and patterns of edema may be useful.

Infection in the acromioclavicular joint is uncommon, but is seen in increased frequency in immune-compromised patients and intravenous drug users. A normal glenohumeral joint on ultrasound in a patient suspected of having a septic shoulder should prompt careful review of the acromioclavicular joint. Aspiration of the acromioclavicular joint is easily performed under ultrasound guidance.