Bicondylar Tibial Plateau Fractures Involving the Posterior Fragment: Injury Mechanism and Fracture Characteristics

Background: Bicondylar tibial plateau fracture (BTPF) involving the posterior fragment is the most complex intra-articular fracture to treat. Although the fracture characteristics of BTPFs have been reported by many researchers, due to the sophisticated kinematics of the knee, reports focused on the injury mechanism are still scarce. The current injury mechanism is insufficient to explain the various fracture characteristics and to guide surgery. This study used a three-dimensional (3D) simulation method to investigate the injury mechanism and fracture characteristics of BTPFs involving the posterior fragment. Methods: Ninety-six BTPFs involving the posterior fragment were included. A computer-assisted 3D technique, which enabled us to move the femoral condyles to match the displaced fracture fragments of the tibial plateau, was applied to analysis the injury mechanism for all cases. The 3D and two-dimensional (2D) morphology of each fracture were reviewed thoroughly, and the main fracture lines were mapped and superimposed on a template. Results: After simulation and quantitatively analysis, three main types (extension, flexion-internal rotation, flexion-external rotation) and six sub-types (valgus and varus in each main type) of injury mechanism had been classified according to the degree of knee motion in three planes. In the extension type, femoral condyles compress the anterolateral tibial plateau and central medial plateau, resulting in an anterior-to-posterior fracture line. In the flexion-internal rotation type, the compressed areas are located on the posterolateral and anteromedial plateau, forming an oblique anteromedial-to-posterolateral fracture line. In the flexion-external rotation type, the compressed areas are located on the anterolateral and posteromedial plateau, exhibiting an anterolateral-to-posteromedial fracture line. Conclusions: Different injury mechanisms result in different fracture characteristics. A thorough understanding of the injury mechanisms underlying complex BTPFs involving the posterior fragment is meaningful not only for fracture characteristics reorganization but also for surgical decision making. The 3D simulation method employed in this study may be a useful supplemental method for investigating the mechanisms underlying fracture injuries.