How proximal ulnar shaft fracture could easily result in radial head dislocation? A critical value analysis for proximal ulnar fracture in Monteggia fracture

Abstract

Abstract Background Monteggia fracture is defined as a combination of proximal ulnar fracture with radial head dislocation. Radial head dislocation may be misdiagnosed under elbow X-ray, leading to further complications. This study aimed to analyze the fracture pattern between extra-articular Monteggia fracture and an isolated proximal ulnar fracture to determine the difference 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 is a single-center, retrospective study. In 2014/01-2022/06, adult patients with fractures in the proximal to midshaft ulna were collected. Nonacute trauma, revision surgeries, and intra-articular ulnar fractures were excluded. All patients received elbow X-rays in AP and lateral views, and forearm X-rays. The fracture pattern and injury mechanism were recorded. Results We included 51 patients in this study. The mean patient age was 38.5 ± 16.1 years. 70.1% were men (n = 36). Extra-articular 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). 63% were traffic accidents (n = 32). 45% were oblique type ulnar fractures(n = 23). Monteggia fracture and proximal ulnar fracture presented with mean ulnar fragment lengths of 6.12 ± 2.32 cm and 9.00 ± 3.00 cm (p < 0.01). As per the ROC, a proximal ulnar fragment length of 7.325 cm had the highest value for the AUC (0.807). Angulations of Monteggia fracture and 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. Conclusions Fractures of the proximal ulna within 7.325 cm from the coronoid are more likely to cause an extra-articular Monteggia fracture than a pure proximal ulnar fracture. Otherwise, a Montelggia fracture is prone to more severe angulation.