Radial Head Fractures Cluster in the Anterolateral and Anteromedial Quadrants and Do Not Correlate With Coronoid Fracture Types.

BACKGROUND: Combined radial head and coronoid fractures, including terrible triad injuries, are challenging patterns associated with elbow instability, poor clinical outcomes, and other complications. While both radial head and coronoid fractures contribute to joint stability, the relationship between their fracture morphologies remains poorly understood. Clarifying these associations may aid in preoperative planning and guide surgical decision-making for restoring elbow stability.

QUESTIONS/PURPOSES: (1) In patients with combined coronoid and radial head fractures, what radial head fracture patterns are most common? (2) Are radial head fracture patterns associated with coronoid fracture types?

METHODS: This study was a secondary data analysis of a retrospective, multicenter descriptive study of patients with combined coronoid and radial head fractures identified on elbow CT scans. The cohort was derived from two urban tertiary level 1 trauma centers with specialized upper extremity and orthopaedic trauma services. Of 10,016 patients with elbow or forearm injuries who underwent CT imaging, 2% (175) met eligibility criteria for combined coronoid and radial head fractures; eight patients were excluded because of prior pathophysiologic conditions of the elbow, previous surgery, or inadequate imaging quality, leaving 167 patients for analysis, 54% (90) of whom were female, with a mean ± SD age of 50 ± 15 years. The radial head was divided into four quadrants (anterolateral, anteromedial, posterolateral, and posteromedial) using the radial tuberosity as a reference landmark on axial CT images. The anterolateral quadrant corresponds approximately to the surgical "safe zone," the region opposite the radial tuberosity and in line with the radial styloid. Coronoid fractures were classified according to the O'Driscoll classification, which categorizes fractures into Type 1 (tip fractures involving the coronoid apex), Type 2 (anteromedial facet), and Type 3 (basal fractures involving the coronoid base) patterns. Interrater reliability was determined using the Cohen kappa, yielding substantial agreement for the radial head quadrant involvement (κ = 0.715) and O'Driscoll classification (κ = 0.658) and reflecting typical reliability for CT-based fracture classification, with disagreements resolved through consensus.

RESULTS: The most common radial head fracture pattern was a single fragment involving both the anterolateral and anteromedial quadrants (31% [51 of 167]), followed by two separate fragments involving the anterolateral and anteromedial quadrants (15% [25 of 167]). Most fractures consisted of one fragment (49% [82 of 167]). Radial head fracture patterns were not associated with coronoid fracture type.

CONCLUSION: Radial head fractures in combined coronoid and radial head fractures most commonly involved the anterolateral and anteromedial quadrants, often as a single fragment. We found no association between coronoid fracture types and radial head fracture patterns, suggesting that these injury components occur independently. These findings may help surgeons anticipate fragment location in relation to surgical exposure, while emphasizing the importance of evaluating the radial head and coronoid as separate elements during preoperative planning and intraoperative assessment.

LEVEL OF EVIDENCE: Level IV, prognostic study.