Purpose: While performing CT examinations of the elbow, we frequently observed a previously undescribed fracture fragment of the supinator crest of the ulna. According to the anatomy of the lateral collateral ligament complex, this fracture might be an avulsion fracture of the annular ligament and/or the lateral ulnar collateral ligament. The aim of this study was to further characterize these fragments and document their associated injuries. Methods: Retrospective evaluation of CT scans of the elbow was performed. Conventional X-ray and CT diagnoses were used to systematically document any associated injuries. Results: A total of 152 CT scans were evaluated. The fragment in question was discovered in 17 patients (11.2 %). The average age of the patients was 40 years (±14.9; 9-71 years). The fragment size varied between a few millimetres and 2.4 cm. Multifragmented fractures were observed. In 82.3 % of the cases, associated radial head fractures were diagnosed. In 29.4 %, a coronoid process fracture was present. Distal humerus fractures were found in 23.5 %. Instability in the medial collateral ligament and an Osborne-Cotterill lesion were found in 11.8 % of the patients, respectively. Conclusions: In a significant percentage of the population, a previously undescribed fracture fragment of the supinator crest of the ulna could be detected. The most frequently occurring associated injuries were fractures of the radial head, the coronoid process, and the distal humerus. The aetiology of these lesions is unknown; however, bony avulsion of the annular or the lateral ulnar collateral ligament seems to be the most likely cause. If this fragment is to be diagnosed by CT, the possibility of lateral or posterolateral instability should be considered.
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