Testing Pullout Strength of Pedicle Screw Using Synthetic Bone Models: Is a Bilayer Foam Model a Better Representation of Vertebra?

Asian Spine Journal

Gurunathan Saravana Kumar¹  Vicky Varghese²  Venkatesh Krishnan³ 

[1] Department of Engineering Design, Indian Institute of Technology Madras, Chennai, India;Division of Biomedical Devices and Technology, Department of Biotechnology, Indian Institute of Technology Madras, Chennai, India;Spinal Disorder Surgery Unit, Department of Orthopedics, Christian Medical College, Vellore, India;

关键词: Pedicle screws;    Pullout strength;    Bone density;    Osteoporosis;    Rigid polyurethane foam;   

DOI  :  10.4184/asj.2018.12.3.398

来源: DOAJ

【 摘 要 】

Study Design A biomechanical study. Purpose A new biomechanical model of the vertebra has been developed that accounts for the inhomogeneity of bone and the contribution of the pedicle toward the holding strength of a pedicle screw. Overview of Literature Pullout strength studies are typically carried out on rigid polyurethane foams that represent the homogeneous vertebral framework of the spine. However, the contribution of the pedicle region, which contributes to the inhomogeneity in this framework, has not been considered in previous investigations. Therefore, we propose a new biomechanical model that can account for the vertebral inhomogeneity, especially the contribution of the pedicles toward the pullout strength of the pedicle screw. Methods A bilayer foam model was developed by joining two foams representing the pedicle and the vertebra. The results of the pullout strength tests performed on the foam models were compared with those from the tests performed on the cadaver lumbar vertebra. Results Significant differences (p <0.05) were observed between the pullout strength of the pedicle screw in extremely osteoporotic (0.18±0.11 kN), osteoporotic (0.37±0.14 kN), and normal (0.97±0.4 kN) cadaver vertebra. In the monolayer model, significant differences (p <0.05) were observed in pullout strength between extremely osteoporotic (0.3±0.02 kN), osteoporotic (0.65±0.12 kN), and normal (0.99±0.04 kN) bone model. However, the bilayer foam model exhibited no significant differences (p >0.05) in the pullout strength of pedicle screws between osteoporotic (0.85±0.08 kN) and extremely osteoporotic bone models (0.94±0.08 kN), but there was a significant difference (p <0.05) between osteoporotic (0.94±0.08 kN) and normal bone models (1.19±0.05 kN). There were no significant differences (p >0.05) in pullout strength between cadaver and bilayer foam model in normal bones. Conclusions The new synthetic bone model that reflects the contribution of the pedicles to the pullout strength of the pedicle screws could provide a more efficacious means of testing pedicle-screw pullout strength. The bilayer model can match the pullout strength value of normal lumbar vertebra bone whereas the monolayer foam model was able to match that of the extremely osteoporotic lumbar vertebra.

【 授权许可】

Unknown