title: Effect of various factors on pull out strength of pedicle screw in normal and osteoporotic cancellous bone models.
abstract: Pedicle screws are widely used for the treatment of spinal instability by spine fusion. Screw loosening is a major problem of spine fusion, contributing to delayed patient recovery. The present study aimed to understand the factor and interaction effects of density, insertion depth and insertion angle on pedicle screw pull out strength and insertion torque. A pull out study was carried out on rigid polyurethane foam blocks representing osteoporotic to normal bone densities according to the ASTM-1839 standard. It was found that density contributes most to pullout strength and insertion torque. The interaction effect is significant (p < 0.05) and contributes 8% to pull out strength. Axial pullout strength was 34% lower than angled pull out strength in the osteoporotic bone model. Insertion angle had no significant effect (p > 0.05) on insertion torque. Pullout strength and insertion torque had no significant correlation (p > 0.05) in the case of the extremely osteoporotic bone model.
authors.affiliation: Biomedical Devices and Technology, Department of Biotechnology, IIT Madras, Chennai 600036, India. Electronic address: vicky.varghese@gmail.com.
authors.forename: Vicky
authors.initials: V
authors.lastname: Varghese
authors.affiliation: Department of Engineering Design, IIT Madras, Chennai 600036, India. Electronic address: gsaravana@iitm.ac.in.
authors.forename: Gurunathan
authors.initials: G
authors.lastname: Saravana Kumar
authors.affiliation: Spinal Disorder Surgery Unit, Department of orthopedics, Christian Medical College, Vellore 632004, Tamil Nadu, India. Electronic address: venkateshortho1@cmcvellore.ac.in.
authors.forename: Venkatesh
authors.initials: V
authors.lastname: Krishnan
mesh_terms: D000071556:Cancellous Bone; D055595:Mechanical Phenomena; D008954:Models, Biological; D010024:Osteoporosis; D065289:Pedicle Screws; D013314:Stress, Mechanical; D019415:Torque
keywords: Insertion torque; Osteoporosis; Pedicle screw; Polyurethane foam; Pull out strength