Effect of bone material properties on effective region in screw-bone model: an experimental and finite element study

Abstract

BackgroundThere have been numerous studies conducted to investigate the pullout force of pedicle screws in bone with different material properties. However, fewer studies have investigated the region of effect (RoE), stress distribution and contour pattern of the cancellous bone surrounding the pedicle screw.MethodsScrew pullout experiments were performed from two different foams and the corresponding reaction force was documented for the validation of a computational pedicle screw-foam model based on finite element (FE) methods. After validation, pullout simulations were performed on screw-bone models, with different bone material properties to model three different age groups (<50, 50–75 and >75 years old). At maximum pullout force, the stress distribution and average magnitude of Von Mises stress were documented in the cancellous bone along the distance beyond the outer perimeter pedicle screw. The radius and volume of the RoE were predicted based on the stress distribution.ResultsThe screw pullout strengths and the load–displacement curves were comparable between the numerical simulation and experimental tests. The stress distribution of the simulated screw-bone vertebral unit showed that the radius and volume of the RoE varied with the bone material properties. The radii were 4.73 mm, 5.06 mm and 5.4 mm for bone properties of ages >75, 75 > ages >50 and ages <50 years old, respectively, and the corresponding volumes of the RoE were 6.67 mm3, 7.35 mm3 and 8.07 mm3, respectively.ConclusionsThis study demonstrated that there existed a circular effective region surrounding the pedicle screw for stabilization and that this region was sensitive to the bone material characteristics of cancellous bone. The proper amount of injection cement for augmentation could be estimated based on the RoE in the treatment of osteoporosis patients to avoid leakage in spine surgery.

The stability of long-segment and short-segment fixation for treating severe burst fractures at the thoracolumbar junction in osteoporotic bone: A finite element analysis

“…In addition, the anterior body height of L1 was modeled with both normal bone and osteoporotic bone and was placed under flexion bending. The material properties of osteoporotic cancellous bone (age greater than 75 years old) were sourced from literature [28]. The range of motion of the segment was also recorded and found to be within the ranges reported from an in vitro study [29].…”

Design optimization of high tibial osteotomy plates using finite element analysis for improved biomechanical effect

“…The interfaces between the tibia-plate and the tibia-screw were modeled by using surface-surface contact elements, which allow for separation and slippage [22, 24]. Friction and hard-contact interfaces were modeled, and the friction coefficient was assumed to be 0.3 for tibia-plate and 0.2 for tibia-screw interfaces [21–24, 34]. The locking screws of the HTO plate were simulated to rigidly bond with the plate holes [21–24].…”

Multi‐objective design optimization of high tibial osteotomy for improvement of biomechanical effect by using finite element analysis

“…Friction and hard‐contact interfaces were modeled. The friction coefficient was assumed to be 0.3 for the tibia plate, and 0.2 for the tibia screw interfaces . The locking screws of the HTO plate were simulated to rigidly bond with the plate holes .…”