Biomechanical models of in vitro constructs for spinopelvic osteosynthesis

Spinopelvic lesions are the result of high-energy vertical trauma with axial skeletal overload where the spine impacts onto the sacrum, dissociating the lumbar spine from the pelvis. Therefore, lumbopelvic instrumentations are aimed to counteract these vertical forces, although various biomechanical aspects of the combinations of different constructs (with or without iliosacral screws) or the number of lumbar fixation levels (L5 or the combination of L5 with L4) are subject to controversy. The number of patients in each published series is too short, and the nature of the fixation is very different from one article to another, making comparison very difficult. In this paper the methodology for laboratory studies is discussed. The design of the test bench fixture, biomechanical testing protocol and data analysis are very important when inference to the clinical setting is desired.