A Hybrid Flexible-Rigid Body Approach for the Simulation of Cross-Link in Short-Segment Fixations after Spinal Posterior Decompression
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The use of less-invasive short-segment fixation for spinal stabilization after epidural spinal cord decompression (SCD) is still limited due to lower mechanical stiffness and the risk severity of pedicle screws failure [1]. Through a hybrid flexible-rigid body modelling, this study explores whether radiotransparent cross-link (CL) augmentation might address these drawbacks. From a validated physiological non-linear rigid body T12-S1 model (MSC Adams), the SCD was simulated assuming L3 as the lesioned vertebra. Short-segment fixations involving one level above and below the lesioned vertebra were then created, without (Sf) and with a transverse rod-rod CL (SfCL). A severe mobilisation of the right L2 pedicle screw impeding any load transmission was also simulated (Sfm, SfCLm). Rods and CL were modelled as flexible bodies with modal theory, while pedicle screws with cantilever beam theory. The fixations were validated from a previous in vitro work [2] (Fig.1A), and then subjected to pure moments along the three anatomical planes within spinal stability-related range of motions (Fig.1B). CL augmentation proves effective in enhancing the stiffness in lateral bending (+5%) and in axial rotation (+13%). Observing Fig.1C, the intervertebral discs (IVD) at fixed levels experience reduced shear forces upon the addition of CL, both under intact fixation (-80%) and during mobilisation (-42%). This is crucial as these loads contribute to anterior instability and unfavourable kinematics. In conclusion, this study highlights CL augmentation as a viable solution to promote short-segment fixation employment following SCD oncologic procedures.
