Biomechanical analysis of the effect of postero-latero-central tibial plateau fractures in the knee joint: Can posterior soft tissues prevent instability? A finite element study.

Background: Almost 86 % of all tibial plateau fractures involves the failure of the postero-latero-central region of the tibial plateau. Surgical treatment of this region is technically demanding and in case of limited depression, it's occasionally chosen to leave them untreated. The aim of the study is to numerically check to what extent this choice can be accepted avoiding inferior outcomes (i.e. joint instability), and to analyze posterior soft tissues role in presence of this fractures. Methods: Starting from a previous validated finite element model with baseline structures, several configurations were developed by inserting posterior soft tissues and postero-latero-central fracture, with different articular depressions. Squat motion was numerically simulated and tibio-femoral kinematics were compared among configurations. Findings: An increasing step-off led to a progressive joint instability, especially in the first 35 degrees-40 degrees of flexion. Posterior soft tissues showed to be beneficial in initial stabilization and early flexion. Tibial Axial Rotation didn't show any restorative effect of posterior soft tissues on knee kinematics. Tibial Antero-Posterior Translation is the most significant biomechanical parameter, showing posterior soft tissues restoring native antero-posterior translation, completely for 1-mm step-off fracture, only partially for 2-mm step-off fracture, and not sufficiently for 3-mm step-off fracture, at least in the first 30 degrees of flexion. Interpretation: The results suggest that postero-latero-central fractures with step-off >= 2 mm should be treated to restore articular kinematic, whereas fractures with step-off <2 mm need a broad evaluation to assess the effective need of surgery. These information can be valuable for surgeons, to aid their decision to surgically operate or not.