What Injury Mechanism and Patterns of Ligament Status Are Associated With Isolated Coronoid, Isolated Radial Head, and Combined Fractures?

BACKGROUND: Isolated coronoid, isolated radial head, and combined coronoid and radial head fractures are common elbow fractures, and specific ligamentous injury of each fracture configuration has been reported. However, the osseous injury mechanism related to ligament status remains unclear. QUESTIONS/PURPOSES: The objectives of this study were: (1) to determine what ligamentous injury patterns (medial or lateral collateral) and bone contusion patterns (medial or lateral) are associated with isolated coronoid, isolated radial head, and combined coronoid and radial head fractures; (2) to correlate the osseous injury mechanism based on these findings with isolated coronoid, isolated radial head, and combined coronoid and radial head fractures; and (3) to determine whether isolated and combined coronoid fractures have different fracture lines through the coronoid (tip or anteromedial facet), speculated to be caused by different injury mechanisms.
METHODS: Between June 2007 and June 2012, 100 patients with elbow fractures were included in the cohort, with 46 of these patients being excluded owing to incongruity for our surgical indication. Finally, 54 patients with surgically treated elbow fractures who had MRI preoperatively were assessed retrospectively. There were 17 elbows with isolated coronoid fractures, 22 with isolated radial head fractures, and 15 with combined coronoid and radial head fractures. Collateral ligament injury pattern and existence of distal humerus bone contusion were reviewed on MR images.
RESULTS: Patients with isolated radial head fractures were at greater risk of medial collateral ligament rupture compared with patients with isolated coronoid fractures (radial head only: 15 of 22 [68%]; coronoid only: three of 17 [18%]; odds ratio [OR], 10.0; 95% CI, 2.2-46.5; p = 0.002). Patients with isolated coronoid fractures had greater risk of lateral ulnar collateral ligament ruptures (coronoid: 16 of 17 [94%]; radial head: seven of 22 [32%]; OR, 3.5; 95% CI, 3.8-333.3; p < 0.001). The presence of radial head fractures was associated with the risk of lateral bone bruising (isolated radial head fracture: 32 of 37 [86%], isolated coronoid fracture: four of 17 [24%]; OR, 29.6; 95% CI, 5.2-168.9; p < 0.001). Medial bone bruising was only detected in isolated coronoid fractures (isolated coronoid fracture: 12 of 17 [71%], others: zero of 37 [0%]). All isolated coronoid fractures involved the anteromedial facet of the coronoid (17 of 17; 100%). However, combined coronoid and radial head fractures often involved the tip (13 of 15; 87%).
CONCLUSIONS: Isolated coronoid fractures mostly involved the anteromedial facet of the coronoid process associated with lateral ulnar collateral ligament rupture and medial bone bruising. However, isolated radial head fractures were associated with medial collateral ligament rupture and lateral bone bruising. Combined coronoid and radial head fractures mostly involved a tip fracture of the coronoid with lateral ulnar collateral ligament rupture and lateral bone bruising. Thus surgeons may predict which ligament they should be aware of in the surgical field. LEVEL OF EVIDENCE: Level III, prognostic study.