Introduction. Lumbar spondylolysis is a fatigue fracture of the pars interarticularis and correlates with Spina Bifida Oculta (SBO) in 67%. Hpothesis. Load is normally transferred across the arch in axial rotation. Bifid arch results in increased strain across the isthmus of the loaded inferior articular process. Aim of investigation. Finite element (FE) analysis of altered load transfer in combined axial rotation and anteroposterior shear in SBO potentially predisposing to fatigue fracture of the pars interarticularis. Methods. FE models of natural and SBO (L5-S1) including ligaments were axially load to 1kN and an axial rotation of 3° applied. Bilateral stresses and strains on intact and SBO lateral inferior lines of the L5 isthmus were assessed and compared. Results. Under 1000N axial load: Maximum
Anchorage of pedicle screw rod instrumentation in the elderly spine with poor bone quality remains challenging. Our study aims to evaluate how the screw bone anchorage is affected by screw design, bone quality, loading conditions, and cementing techniques. Micro-finite element (µFE) models were created from micro-CT (μCT) scans of vertebrae implanted with two types of pedicle screws (L: Ennovate and R: S4). Simulations were conducted for a 10 mm radius region of interest (ROI) around each screw and for a full vertebra (FV) where different cementing scenarios were simulated around the screw tips. Stiffness was calculated in pull-out and anterior bending loads.Aims
Methods