Impact of ulnar fracture level on radial head dislocation: A Monteggia fracture study.

Background: Monteggia fracture is defined as a combination of a proximal ulnar fracture with radial head dislocation. Radial head dislocation may be misdiagnosed under an elbow radiograph, leading to further complications. This study aimed to compare the ulnar fracture pattern characteristics between Monteggia fracture and an isolated proximal ulnar fracture in terms of how close the fracture site is to the coronoid and what type of fracture pattern is more likely to result in radial head dislocation.

Methods: This single-center retrospective study, conducted from January 2014 to June 2022, included adult patients with proximal to midshaft ulnar fractures, excluding nonacute trauma, revision surgeries, and intra-articular fractures. All patients underwent anteroposterior (AP) and lateral elbow radiographs and forearm radiograph. Fracture patterns and injury mechanisms were recorded for analysis.

Results: We included 51 patients in this study. The mean age was 38.5 ± 16.1 years, and 70.1% were men (n = 36). Monteggia fractures were classified according to the Bado classification into type I (n = 5), type II (n = 7), type III (n = 8), and type IV (n = 0). Traffic accidents comprised 63% of the injuries (n = 32), and 45% were oblique type ulnar fractures (n = 23). Monteggia fracture and proximal ulnar fracture presented with mean distance from coronoid tip to fracture of 6.12 ± 2.32 cm and 9.00 ± 3.00 cm ( p < 0.01). As per the receiver operating characteristic curve (ROC), the distance from coronoid tip to fracture of 7.33 cm had the highest area under the curve (AUC) value (0.807). Angulations of Monteggia fracture and isolated ulnar fracture were 24.02° ± 12.10° and 10.77° ± 8.10° ( p < 0.01). However, there were no differences in the length of the fracture line between two groups.

Conclusion: The distance from coronoid tip to fracture within 7.3 cm is more likely to cause a Monteggia fracture than an isolated proximal ulnar fracture. Otherwise, a Monteggia fracture is prone to more severe angulation.