gms | German Medical Science

Objectives/Interrogation: To clarify whether the preoperative MRI for pediatric Monteggia fracture predicts the cases of irreducible or easily re-dislocated radial head dislocations.

Methods: We retrospectively evaluated 6 patients (3 male, 3 female) below the age of 15 years who underwent preoperative MRI and surgical treatment for Monteggia fractures from 2012 to 2018. The average patient age at the operation was 8.7 years (range, 4-14 y). We initially treated the ulnar fractures including acute plastic bowing deformities by closed or open reduction followed by tried to reduce radial head dislocations by closed means. When the radial head dislocations were irreducible or easily re-dislocated, we performed open reduction. On MRI, we obtained the T2-weighted fat-saturated sagittal images of the injured elbow, and checked whether the annular ligament was entrapped between the radial head and the capitellum. Further, to evaluate an extent of interposed annular ligament quantitatively, we measured the length of entrapped anterior band of annular ligament (d mm) below the posterior side of radial head, and the diameter of radial head (D mm) in both open and closed reduction groups. We calculated and evaluated the d/D ratio in each group.

Results and Conclusions: Out of 6 cases, 3 cases (1 irreducible and 2 easily re-dislocated cases) were underwent open reduction of the radial head. On the basis of preoperative MRI, the annular ligament entrapment was detected in 2 cases (67%) with open reduction of radial head and 2 cases (67%) with closed reduction. Furthermore, in the 4 cases which detected annular ligament entrapment, the value of d/D ratio in open reduction group (0.50 and 0.75) was higher than the ratio in the closed reduction group (0.23 and 0.25). On the other hand, in only one case, open reduction of radial head was needed even though the annular ligament was not interposed in the radiocapitellar joint on the preoperative MRI. In this case, we confirmed intra-operatively subluxation of radial head because of partially injured and slightly elongated annular ligament. These results indicated the possibility of the relevance between the extent of interposed annular ligament and the necessity of radial head open reduction. Meanwhile, in case the annular ligament was partially or fully ruptured, we might not be able to detect interposition on MRI. In the present study, we conclude that preoperative MRI may help predict irreducible or easily re-dislocated patients of pediatric Monteggia fracture.