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. © 2016 IPEM

G. Saravana Kumar

Department of Engineering Design

PATIENT REHABILITATION

Polyurethanes

Rigid foamed plastics

Screws

Torque

INSERTION TORQUE

Osteoporosis

PEDICLE SCREWS

Polyurethane foam

PULL-OUT STRENGTH

Bone

POLYURETHAN FOAM

article

biological model

biomechanics

BONE DENSITY

controlled study

CORRELATIONAL STUDY

MUSCULOSKELETAL SYSTEM PARAMETERS

PEDICLE SCREW

physical chemistry

Statistical significance

Strength

trabecular bone

mechanical stress

mechanics

CANCELLOUS BONE

Mechanical Phenomena

Models, Biological

Stress, Mechanical

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Medical Engineering and Physics

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. © 2018 by Korean Society of Spine Surgery.

Fulltext

Asian Spine Journal

Testing pullout strength of pedicle screw using synthetic bone models: Is a bilayer foam model a better representation of vertebra?

Effect of various factors on pull out strength of pedicle screw in normal and osteoporotic cancellous bone models

Pullout strength of pedicle screw is an important index used by surgeon and engineers for design and development of the implant. Increasing pullout strength is difficult since it is dependent on several factors such as density of bone, insertion technique etc. Current study uses a validated 2 D FE model of pullout strength experiment to study the effect of number of threads, inner and outer diameter and thread geometry on holding power of pedicle screw in a synthetic osteoporotic bone model. It was found that outer diameter has highest effect on pullout strength of pedicle screw. Coarser thread provides better holding power in an osteoporotic bone. This study can be used for developing screws with improved holding power in osteoporotic bone. © 2016 IEEE.

IECBES 2016 - IEEE-EMBS Conference on Biomedical Engineering and Sciences

A finite element analysis based sensitivity studies on pull out strength of pedicle screw in synthetic osteoporotic bone models

Medical Engineering & Physics

Editorial Board

Archives of Orthopaedic and Trauma Surgery

Predictive validity of preoperative CT scans and the risk of pedicle screw loosening in spinal surgery

World Neurosurgery

Adjustment of Suboptimally Placed Lumbar Pedicle Screws Decreases Pullout Strength and Alters Biomechanics of the Construct: A Pilot Cadaveric Study

Applied Bionics and Biomechanics

Evaluation of the Effect of Fixation Angle between Polyaxial Pedicle Screw Head and Rod on the Failure of Screw-Rod Connection

Journal	Data powered by TypesetMedical Engineering and Physics
Publisher	Data powered by TypesetElsevier Ltd
ISSN	13504533
Open Access	No