Pullout strength of adjusting pedicle screw with or without self-bone grafting in the previous trajectory using an osteoporotic human vertebral body

Abstract

Objectives The aim of this study is to explore the pullout strength of adjusting pedicle screw with or without self-bone grafting in the previous trajectory using an osteoporotic human vertebral body. Methods Thirty vertebrae from six cadavers were collected and all of the vertebrae were divided into two groups according to bone mineral density: control group with normal bone mineral density; osteoporosis group with osteoporosis. The osteoporosis group was randomly and evenly divided into five subsamples according to direction of reinsert pedicle screw: the normal angle, sagittal angle, sagittal bone grafting, horizontal angle, horizontal bone grafting. Axial pullout strength testing of the pedicle screw was performed and the maximum axial pullout force (Fmax) was applied to analyse. Result The bone mineral density of the control group was 1.115±0.065 g/cm3, and the bone mineral density of the osteoporosis group was 0.678±0.055 g/cm3, presenting significantly different between the two group (P<0.001). Compared with the control group, the Fmax of the normal angle group was smaller (600.64±43.10 vs 1100.74±49.08 N, P<0.001). Compared with the normal angle group, the Fmax of the sagittal angle group (339.13±38.90 vs 600.64±43.10 N, P<0.001) and the horizontal angle group (342.06±33.01 vs 600.64±43.10 N, P<0.001) were smaller. The Fmax in sagittal bone grafting group was higher than that with non-implanted bone in primary screw canal (492.30±42.06 vs 342.06±33.01 N, P<0.001), and the Fmax of the horizontal bone grafting group was higher than that with non-implanted bone in primary screw canal (502.02± 50.26 vs 342.06±33.01 N, P<0.001). Conclusion The pullout strength of adjusting pedicle screw is seriously decreased in osteoporotic human vertebral body and self-bone grafting in the previous trajectory is an effective remedial measure.