Mechanical property of different cross-sectional area screws in middle and upper thoracic vertebral pedicle-rib complex / 中国组织工程研究

ABSTRACT

BACKGROUND:Due to the importance of pedicle adjacent structures, once the screw replacement appears a deviation, adjacent structures may be damaged, leading to extremely serious consequences. Although the security of screw placement in thoracic vertebral pedicle-rib complex is significantly greater than that of pedicle screws, the mechanics of the pedicle-rib complex at different cross-sectional areas of the screw are rarely reported. OBJECTIVE:To observe mechanical property of different cross-sectional area screws in the middle and upper thoracic vertebral pedicle-rib complex. METHODS:Five specimens of adult cadaveric thoracic spine (T 1-T 10 ) and adjacent rib segment (50-60 mm long) were used. The bone density of specimens was measured using difunctional bone density testing machine, and osteoporotic vertebral body was excluded. The position of the screws was detected with CT images. The maximal withdrawal force of the pedicle screw was measured with biomechanical force test machine. RESULTS AND CONCLUSION:Thirty-eight specimens at normal bone density were implanted with 25 screws (5.5 mm), 25 screws (6.0 mm) and 26 screws (6.5 mm). Because the pedicle screws destroyed the pedicle-rib complex and perforated the vertebral body, we final y obtained the withdrawal force of 68 screws. The axial withdrawal force of pedicle screws at different diameters was (812.36±147.22) N, (868.64±160.48) N and (946.48±157.58) N, respectively. There were significant differences between the 5.5 mm screws and the 6.5 mm screws (P5.5 mm) are suitable in the middle and upper thoracic vertebral pedicle-rib complex due to strong internal fixation and clinical requirement.