BackgroundMultiple authors have highlighted the increased incidence of occult posterior malleolar fractures (PMFs) with spiral tibial shaft fractures, although other reported associated risks of intra-articular extension have been limited. The aim of our study is to investigate both PMFs and non-PMFs intra-articular extensions associated with tibial diaphyseal fractures to try to determine any predictive factors.MethodsWe undertook a retrospective review of a prospectively collected database. The inclusion criteria for this study were any patient who had sustained a diaphyseal tibial fracture, who had undergone surgery during the study period and who had also undergone a CT scan in addition to plain radiographs. The study time period for this study was between 01/01/2013 and 9/11/2021.ResultsOut of 764 diaphyseal fractures identified, 442 met the inclusion criteria. A total of 107 patients had PMF extensions (24.21%), and a further 128 patients (28.96%) had intra-articular extensions that were not PMF’s. On multivariate analysis, spiral tibial fracture subtypes of the AO/OTA classification (OR 4.18,p< 0.001) and medial direction of tibial spiral from proximal to distal (OR 4.38,p< 0.001) were both significantly associated with PMF. Regarding intra-articular fractures, multivariate analysis showed significant associations with non-spiral (OR 4.83,p< 0.001) and distal (OR 15.32,p< 0.001) tibial fractures and fibular fractures that were oblique (OR 2.01,p= 0.019) and at the same level as tibia fracture (OR 1.83,p= 0.045) or no fracture of the fibular (OR 7.02,p< 0.001).ConclusionIn our study, distal tibial articular extension occurs in almost half of tibial shaft fractures. There are very few fracture patterns that are not associated with some type of intra-articular extension, and therefore, a low threshold for preoperative CT should be maintained.Level of evidence4.