Fracture of the Anteromedial Facet of the Coronoid is More Common Than Previously Thought in Combined Fractures of the Coronoid and Radial Head

Abstract

Background: The terrible triad injury involves an ulnohumeral dislocation, radial head fracture, and coronoid process fracture. According to traditional teaching, these injuries are strongly associated with anterolateral coronoid tip fractures and can be addressed via a lateral approach to the elbow. However, recent small clinical series suggest that some terrible triad injuries have larger coronoid fractures involving the anteromedial facet. It is important to understand how often these larger coronoid fractures occur because anteromedial facet fractures may need a different approach and different implants for fixation. An improved understanding of coronoid fracture morphology in terrible triad injuries may help surgeons construct a surgical plan.

Questions/purposes: To better define coronoid fracture morphology in combined coronoid and radial head fractures, we therefore asked: What is the distribution of anterolateral facet versus anteromedial facet coronoid fragments in combined coronoid and radial head fractures without an ulnar shaft fracture?

Methods: This retrospective, multicenter descriptive study evaluated preoperative CT scans from adult patients (18 years or older) diagnosed with combined coronoid and radial head fractures. Between February 2014 and March 2023, we identified 10,016 adult patients with elbow or forearm injuries who underwent CT scans. Among these patients, we considered those diagnosed with combined coronoid and radial head fractures without an ulnar shaft fracture based on elbow CT scans performed within 4 weeks of the injury as potentially eligible. During that time, elbow CT scans were generally ordered to assess complex fractures, confirm diagnoses when radiographs were inconclusive, evaluate joint involvement, or plan for surgical interventions. Based on that, 2% (175 of 10,016) were eligible; a further 0.001% (8 of 10,016) were excluded because of preexisting elbow pathology, prior surgery, or low-quality CT images (including slice thickness greater than 2 mm, motion artifacts, and incomplete visualization of the osseous structure of the elbow and all its articulations), leaving 2% (167 of 10,016) for analysis. The mean age was 50 ± 15 years, and more than half of the patients were female (54% [90 of 167]). Coronoid fractures in patients with combined coronoid and radial head fractures were classified using the O'Driscoll classification into three types: Type 1 (anterolateral tip fractures), Type 2 (anteromedial facet fractures), and Type 3 (base fractures). Each type was further subcategorized based on specific fracture characteristics. Two of three trained researchers independently classified the coronoid fracture type of each patient using radiographs, two-dimensional (2D) CT scans, three-dimensional (3D) CT scans, and intraoperative findings, with interrater reliability assessed by the Cohen kappa, yielding a substantial agreement value of 0.658. Disagreements were resolved through discussions with a fellowship-trained orthopaedic trauma surgeon.

Results: Sixty-five percent (109 of 167) of patients had a Type 1 anterolateral coronoid tip fracture, 30% (50 of 167) had a Type 2 anteromedial facet fracture, and 5% (8 of 167) had a Type 3 basal fracture.

Conclusion: Surgeons should recognize that anteromedial facet involvement in coronoid fractures is more prevalent in combined coronoid and radial head fractures than previously appreciated. Future research should investigate whether these anteromedial fractures are more likely to need an additional medial approach to improve patient outcomes.

Clinical relevance: This study suggests that anteromedial facet involvement is more common than traditionally recognized in terrible triad injuries, and surgeons should be prepared to address a larger fragment when treating these injuries.