O3269: Proximal UCL Bony Avulsion and Cortical Sleeve Avulsion Subtypes in Pediatric Humeral Medial Epicondyle Injuries

Background: The anterior oblique bundle of the medial ulnar collateral ligament (UCL) originates from the anteroinferior aspect of the medial epicondyle apophysis while the flexor pronator mass (FPM) originates broadly above the upper border of the anterior oblique bundle. Based on the different footprints of the UCL and FPM, it is possible that valgus stress on the elbow may result in partial avulsion fractures involving only focal areas of the medial epicondyle. The goal of this study is to investigate the morphology of medial epicondyle fractures to determine patterns of partial avulsions. Our hypothesis is that the UCL and FPM can either independently or jointly act on the medial epicondyle to form partial avulsion subtypes of medial epicondyle fractures in the pediatric population

Methods: A review of patient records from 2012 to 2022 was performed using the electronic medical record database from a single pediatric institution. 709 patients were diagnosed with medial epicondyle fracture. Radiographs and MR imaging were screened for evidence of fragmentation or partial avulsion patterns and confirmed by a fellowship trained pediatric sports orthopedic surgeon.

Results: 16% (113/709) of medial epicondyle fractures had radiographic evidence of a partial avulsion pattern with the main medial epicondyle still in anatomic position. Thirty-two of these patients had radiographs and MR imaging available at time of injury. Twenty-four proximal UCL avulsion patients had a well-corticated fragment off the inferior pole of the medial epicondyle on AP radiographs with MR imaging demonstrating the anterior oblique bundle of the UCL attached to the avulsed fragment. The FPM origin remained preserved on the main medial epicondyle in these patients. These findings were confirmed by two operative reports. Eight cortical sleeve avulsion patients had either a well-defined cortical shell or an ill-defined radio-opaque body off the inferomedial aspect of the medial epicondyle on AP radiographs with MR imaging demonstrating the anterior oblique bundle of the UCL in addition to the FPM origin attached to the avulsed cortical sleeve. These findings were also confirmed by two operative reports.

Conclusion: The present study is the first to report definitive evidence that a distinct cortical fragment inferior to the medial epicondyle sometimes seen in radiographs of medial elbow injuries represents a proximal UCL avulsion. Two injury patterns were seen, comprising a total of 16% of our medial epicondyle fracture population. An isolated proximal UCL avulsion was more common than a cortical sleeve avulsion involving both UCL and FPM origins. Identification of these injury patterns is crucial to understanding the degree of involvement and displacement of stabilizing soft tissue structures in the medial elbow. Further studies are required to assess the clinical outcomes of operative and nonoperative management of these subtypes.