The capsular attachment of the ulnar coronoid process: an MRI arthrography study

Background: Ulnar coronoid fractures are relatively rare injuries usually occurring in association with elbow dislocations and contributing to elbow instability. Recent evidence supports a role for coronoid tip fractures in elbow instability. The purpose of this study was to determine where the capsule inserts onto the ulnar coronoid process. Methods: Twenty MRI arthrograms from patients with no evidence of osteoarthrosis or posttraumatic changes were evaluated. The distance from the tip of the coronoid process to the proximal edge of the anterior elbow joint was recorded as was the coronoid height. Results: The average distance from the tip of the coronoid process to the proximal edge of the anterior elbow joint capsular insertion was 1.7 +/- 1.1mm. The average coronoid height measured 17.6 +/- 1.9mm. Conclusions: Elbow instability after posterior elbow dislocations is a difficult and well-described entity. There is recent evidence regarding the role of small coronoid fractures in posttraumatic instability. These data support the assertion that most coronoid tip fractures involve disruption of the anterior capsule, which potentially explains why instability can be associated with these fractures.