Three-Dimensional Computed Tomographic Scan of the External Third of the Clavicle

Purpose: The aims of this radiologic study were to explore the anatomic aspect of the external third of the clavicle and to determine anatomic elements that can be useful for surgeons who perform surgery that involves this area. Methods: Twenty patients with healthy acromioclavicular (AC) joints underwent computed tomographic (CT) scan for assessment of the lateral clavicle. Three-dimensional reconstruction of the AC joint and of the external third of the clavicle was performed. The axis of the external third was determined by CT scan reconstruction. Two-dimensional reconstructions were performed perpendicular to this axis; each involved 5 mm for exploration of the size of the 4 cortical bones and of the inner diameter of the clavicle. Results: The average size of the external third before the anterior curve of the clavicle was 40 mm. The average inner diameter of the clavicle ranged from 8.24 to 4.7 mm when measured medially, but many differences were noted between patients. The upper cortical bone was thicker than 2 mm at an average of 17 mm from the AC joint. Three forms of the external third of the clavicle were identified: truncated (n = 6), conical (n = 4), and cylindrical (n = 10). The projection of the axis of the external third of the clavicle at the external side of the acromial bone ranged from 4.8 to 21 mm (average, 12.42 mm) at the backward anterior side of the acromial bone. Conclusions: Our study shows the great variability of the anatomy of the external third of the clavicle. Clinical Relevance: Anatomic data should be useful for surgeons who perform fixation or resection of the distal part of the clavicle.