In vivo study of extracellular matrix coating enhancing fixation of the pedicle screw-bone's interface / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Based on in vivo research on the effect of the coating of the extracellular matrix composition of pedicle screws on the conduction and induction of bone formation in young sheep, the aim of this study was to investigate the application of coated pedicle screws in sheep with scoliosis whose spines are under constant development.</p><p><b>METHODS</b>Four groups of pedicle screws were randomly implanted into bilateral L2-L5 pedicles of 2.5- to 3-month-old sheep. A static experiment was performed on one side and a loading test was performed on the other side by implanting connecting rods at the L2-L3 and L4-L5 segments. The changes in the force on the coated screws and the combination of the surface of the coated screws with the surrounding bone in the growth process of young sheep's spines with aging were observed. After 3 months, the lumbar vertebrae with the screws were removed and examined by micro-CT, histological, and biomechanical analyses.</p><p><b>RESULTS</b>Under nonloading conditions, there is bone formation around the surfaces of coated screws. The bone forming on the surface of collagen/chondroitin sulfate/hydroxyapatite coating of pedicle screws is the most, the one of the collagen/chondroitin sulfate coating and hydroxyapatite coating is followed, and no significant difference between the two groups. In terms of the trabecular bone morphology parameters of the region of interest around the surface of the pedicle screws, such as bone mineral content, bone mineral density, tissue mineral content, tissue bone mineral density, bone volume fraction, and connection density, those associated with collagen/chondroitin sulfate/hydroxyapatite coatings are largest and those unassociated with coatings are smallest. Under nonloading conditions, the pullout strength of the collagen/chondroitin sulfate/hydroxyapatite-coated screws was largest, and that of the uncoated screws was minimal (P < 0.01). Under loading conditions, the maximum pullout strength of each group of pedicle screws was less than that of the pedicle screws in the nonloading state (P < 0.01) with no significant difference between the groups (P > 0.05).</p><p><b>CONCLUSIONS</b>Under nonloading conditions, the coatings of both organic and inorganic components of the extracellular matrix of titanium pedicle screws can conduct or induce bone formation around the surface of the screws. The ability of collagen/chondroitin sulfate/hydroxyapatite coatings to induce bone formation is stronger; under loading conditions, a large amount of connective tissue formed around the surfaces of the screws in each group. No significant differences were found between the groups.</p>

Feasibility of vertebral internal fixation using deer and sheep as animal models / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Studies on new vertebral internal fixations of animals are very important prior to clinical application. This study aimed to determine the feasibility of vertebral internal fixation on morphologic and biomechanical properties using deer and sheep as animal models and comparing to human data.</p><p><b>METHODS</b>Thirty sets of fresh Sika deer lumbar, 30 sets of fresh sheep lumbar, and 20 sets of fresh lumbar from male cadavers were used. We examined the morphology of the centra and pedicles of the three groups, and determined the cancellous bone density and biomechanical properties in all groups.</p><p><b>RESULTS</b>There were marked differences in all parameters measured between the different species. The sizes of the upper, middle, and lower transverse diameter were largest in the human, followed by the deer, then the sheep. The index of centrum transverse diameters and sagittal diameters were less than 0.8 (a triangle), and the deer was more similar to the human. The heights of the right vertebral pedicles and the anterior disc heights (IDH) were largest in the human, followed by the deer, then the sheep. The apparent density, elastic modulus, and ultimate load were largest in the sheep, followed by the deer, then the human. The range of motion (ROM) of functional lumbar units (FLUs) with a combined flexion-extension moment was largest in the human, followed by the deer then the sheep.</p><p><b>CONCLUSIONS</b>The deer lumbar is more similar to that of human in anatomical form and biomechanics than the sheep lumbar. As such, deer is more appropriate as an animal model for use in vertebral internal fixation studies.</p>