Accompanying injuries in tibial shaft fractures: how often is there an additional violation of the posterior malleolus and which factors are predictive? A retrospective cohort study

INTRODUCTION: An undislocated fracture of the posterior malleolus is a common concomitant injury in tibial shaft spiral fractures. Nevertheless, these accompanying injuries cannot always be reliably assessed using conventional X-rays. Thus, the aim of the study is to evaluate how often a fracture of the posterior malleolus occurs with tibial shaft fractures (AO:42A/B/C and AO:43A) and which factors—identifiable in conventional X-rays—are predictive. METHODS: Retrospective evaluation of X-ray and CT images revealed a total of 103 patients with low-energy tibial shaft fractures without direct joint involvement. Proximal fractures and fractures involving the knee were excluded. Basic data on injury, the trauma mechanism, the path of the fracture, bony avulsions of the posterior syndesmosis and the procedures performed were evaluated. RESULTS: Thirty-nine fractures were located in the middle third of the tibia, 64 in the distal third. In 65 cases, a spiral fracture (simple or wedge fracture) was found. In 31/103 fractures, an additional osseous avulsion of the posterior syndesmosis could be detected, 5 (16.1%) of them were not recognized preoperatively due to an absence of CT imaging. In three of these patients, a fracture of the posterior malleolus was only recognized postoperatively, and an additional surgery was necessary. The spiral fractures were classified in the a.p. X-ray according to their path from lateral proximal to medial distal (Type A) or from medial proximal to lateral distal (Type B). A Pearson chi-square test and Fisher’s exact test showed a highly significant accumulation of accompanying posterior malleolus fractures for type A fractures (p = 0.001), regardless of the location of the fracture. In addition, the fractures with involvement of the posterior malleolus had a significantly higher proportion in the fractures of the distal third (p = 0.003). There was no statistically significant relationship between the height of the fracture and the path of the fracture (type A or B). These two factors seem to be independent factors for participation of the posterior malleolus. CONCLUSION: In 40.6% of the tibial shaft fractures in the distal third, in 56.9% of the type A spiral fractures and in 67.6% of the type A fractures in the distal third, the ankle joint is involved with bony avulsion of the posterior syndesmosis, which is not always recognized in conventional X-rays. To avoid complications such as additional operations, instability and post-traumatic arthrosis, we recommend preoperative imaging of the ankle using CT for these fractures. LEVEL OF EVIDENCE: III, retrospective cohort study. TRAIL REGISTRATION NUMBER: DRKS00024536.