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Background
Pathology of the clavicle can be challenging to interpret at imaging. The clavicle provides an important connection between the axial and appendicular skeleton and is affected by a wide range of different pathologies, including traumatic, degenerative, infectious, inflammatory, and neoplastic processes. In addition, various percutaneous ultrasound-guided treatments of the acromioclavicular (AC) and sternoclavicular (SC) joints can be offered, and awareness of different scanning techniques is important for treatment success. The purpose of this educational exhibit is to provide a comprehensive, multimodality review of clavicular anatomy, pathology, and ultrasound-guided treatments.

Educational Goals / Teaching Points
Essential anatomy of the clavicle will be reviewed, including normal anatomic variants such as the rhomboid fossa and supraclavicular foramen. Typical and atypical infectious and inflammatory causes of clavicular pathology will be presented, including osteoarthritis, CPPD, gout, septic arthritis, osteitis condensans, and SAPHO syndrome. Common and uncommon presentations of clavicular trauma will be reviewed, including different types of clavicular fractures, AC and SC joint separations, z-type fractures, muscle attachment tears, post-traumatic osteolysis, and pediatric distal clavicle apophyseal fractures. Rare cases of congenital and neoplastic clavicular abnormalities will be presented, including cleidocranial dysplasia and Ewing sarcoma. The rationale for AC and SC joint injections and aspirations will be presented with attention to the advantages and disadvantages of different ultrasound scanning techniques.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Clavicular anatomy and pathology will be presented using a multimodality approach, including important radiographic, CT, MRI, and ultrasound case examples. Knowledge of clavicular anatomy is essential to avoid pitfalls at the time of imaging interpretation. Normal anatomic variants, such as the rhomboid fossa and supraclavicular foramen, can mimic pathology. The clavicle is the most commonly fractured bone in the setting of trauma; a radiologist’s ability to properly diagnose clavicular fractures and assess joint integrity profoundly impacts patient care and surgical management. In addition, pitfalls exist when interpreting pediatric clavicular trauma where knowledge of clavicular anatomy and development is important. The clavicle is the first bone to ossify but its physes are often the last to close; subtle clavicle apophyseal fractures can mimic AC or SC joint separations, which are prone to misclassification at the time of imaging. When performing percutaneous ultrasound-guided treatments of the AC and SC joints, either an in-plane or out-of-plane approach can be used, each with their respective advantages and disadvantages.

Conclusion
Knowledge of clavicular anatomy, pathology, and imaging findings will allow for accurate and timely diagnosis, impacting patient care. Percutaneous ultrasound-guided injections and aspirations can be considered as a treatment for AC and SC joint pathology.