Intra-articular fracture patterns associated with tibial shaft fractures: more than just the posterior malleolus

Background The association of tibial shaft fractures (TSFs) with posterior malleolar fractures is well described. The purpose of this study was to identify specific radiographic parameters that are predictive of any pattern of associated distal intra-articular fractures in TSFs. Methods All TSFs presenting over a 6-year period were identified. A radiographic review of plain radiographs and CT scans included: identification of any associated ankle fracture, classification using the OTA System, measurements of the TSF obliquity angle (FOA), relative distance from distal extent of the TSF to plafond (DFP%), and presence and level of any associated fibular fractures. Patients with and without associated ankle fractures were statistically compared. Multivariate logistic regression determined independent predictors of associated ankle fractures. Results 405 TSFs in 397 patients were identified, with 145 TSFs with associated distal intra-articular fractures. There were 94 (23.2%) posterior malleolar fractures, 19 (13.1%) medial malleolar fractures, 42 (29.0%) lateral malleolar fractures involving the syndesmosis and 14 (9.7%) Chaput fragments. Multivariate regression demonstrated AO/OTA classification type 42-A1, 42-B1 or 42-C1 (OR 2.3 [95% CI 1.3-4.0]; p = 0.003), FOA greater than 45 degrees (OR 2.7 [95% CI 1.5-4.8]; p = 0.001) and DFP% less than 33% (OR 4.1 [95% CI 2.0-9.0]; p = 0.005) were independent correlates of associated ankle fractures regardless of mechanism of injury. Conclusions Different patterns of intra-articular fractures beyond posterior malleolar fractures can occur in TSFs. Fracture angles greater than 45 degrees and extent into the distal 33% of the tibial shaft are independent predictors of distal intra-articular fractures in TSFs regardless of mechanism of injury.