Pathoanatomy and incidence of the posterolateral fractures in bicondylar tibial plateau fractures: a clinical computed tomography-based measurement and the associated biomechanical model simulation

The aim of our study is to evaluate the incidence and pathoanatomy of posterolateral fragments and analyze the associated fracture mechanism in bicondylar tibial plateau fractures. From 1.1.2008 to 3.15.2012, all patients suffering bicondylar tibial plateau fractures were identified, scanned and analyzed at the Shanghai Clinical Trauma Center. Furthermore cadaver knees were selected into three groups of 30/60/90 knee flexion to simulate the posterolateral tibial plateau fracture by an impact device. One hundred and sixty-four (44.32 %) bicondylar tibial plateau fractures finally satisfied our requirements. Fifty-three and ninety-four cases were measured eventually in the groups of posterolateral split and depression. The posterolateral articular fragment proportion was 15.43 %. The posterolateral articular fragment angle showed an average of 12.94A degrees. The posterolateral fragment cortical height was on average 2.96 cm. The posterolateral sagittal fragment angle averaged at 72.06A degrees. Ninety-four cases were measured in the posterolateral depression group. The average posterolateral articular depression proportion was 16.74 %. The average posterolateral articular depression height was 2.47 cm. In the biomechanical modeling of such kinds of fracture patterns, posterolateral split fractures in 30A degrees and 60A degrees flexion are significantly more than those in 90A degrees flexion. Posterolateral splits combined with anterolateral depression fractures in 30A degrees flexion are significantly more than those in 90A degrees flexion. The incidence of posterolateral fractures is 44.32 % in bicondylar tibial plateau fractures. The morphology of posterolateral area can be referenced for the surgeon in the future clinical work. The information is also helpful for the design of locking plate and fracture modeling in biomechanical test. In addition, that posterolateral split and posterolateral depression might be caused by different injury mechanisms. Different angles of knee flexion under the axial impact loading are possibly the interpretations for these two fracture patterns.