Morphological Analysis of Intraarticular Fragments in AO/OTA 44 Category Posterior Malleolar Fractures

Abstract

Category: Ankle; Trauma Introduction/Purpose: Intraarticular fragments (IAFs) associated with posterior malleolar fractures are a major obstacle in the treatment of ankle fractures. However, their frequency, location, and morphology, as well as their relationship with the classification of ankle posterior malleolar fractures, are poorly understood and unresolved. The Purpose of this study is to clarify the frequency and morphology of IAFs in posterior malleolar ankle fractures. Methods: This study was conducted at a single institution and included 104 consecutive patients with trimalleolar ankle fractures treated between 2015 and 2022. The inclusion criteria were 1) acute fracture within 2 weeks after injury and 2) cases with computed tomography (CT) images at the time of injury. The exclusion criteria were 1) previous ipsilateral ankle fracture, 2) pathological fracture, and 3) younger age with open physis. CT images at the time of injury were reviewed and each posterior malleolar fracture was classified using the Mason classification. Frequency of occurrence, size (long diameter × short diameter), and angle (the angle between the long diameter and fracture surface of the posterior malleolar fracture) of the IAF. The location of the IAF was described from CT axial images The dislocated distance of the IAF from the articular surface was measured on the sagittal CT view. Results: The patient’s mean age was 54.6 years. 46 cases were Type 1, 32 cases were Type 2A, 9 cases were Type 2B, and 17 cases were Type 3 according to the Mason’s classification. In Mason Type 2 and 3 cases, the IAF was present in 32 (78.0%) and 12 (70.6%) cases, respectively. The IAF was more frequently observed laterally in type 2 (22 cases) and medially in type 3 (7 cases). The long × short diameter of the IAF averaged 11.2 × 4.9 mm and 9.0 × 3.7 mm for Types 2 and 3, respectively. The angle of IAF was 10.5 ± 13.4° and 8.5 ± 7.8°, the distance of displacement was 3.0 ± 2.6 mm and 2.4 ± 1.2 mm, respectively. Conclusion: This study revealed a high incidence of IAFs in posterior malleolar ankle fractures. The IAF has a long medial to lateral shape, as well as the direction of the posterior malleolus fracture, occurs more often laterally in Mason Type 2 and medially in type 3. These findings suggest a pathophysiology in which the axial force causes secondary intraarticular impingement after the main fracture of the posterior malleolus. resulting in the development of an IAF. Handling IAFs is one of the keys in the treatment of posterior malleolar fractures and the surgical approach should be also selected based on the IAF.