A biomechanical study of top screw pullout in anterior scoliosis correction constructs
Study Design: Biomechanical testing of vertebral body screw pullout resistance with relevance to top screw pullout in endoscopic anterior scoliosis constructs.
Objectives: To analyse the effect of screw positioning and angulation on pullout resistance of vertebral body screws, where the pullout takes place along a curved path as occurs in anterior scoliosis constructs.
Summary of Background Data: Top screw pullout is a significant clinical problem in endoscopic anterior scoliosis surgery, with rates of up to 18% reported in the literature.
Methods: A custom designed biomechanical test rig was used to perform pullout tests of Medtronic anterior vertebral screws where the pullout occurred along an arc of known radius. Using synthetic bone blocks, a range of pullout radii and screw angulations were tested, in order to determine an ‘optimal’ configuration. The optimal configuration was then compared with standard screw positioning using a series of tests on ovine vertebrae (n=29).
Results: Screw angulation has a small but significant effect on pullout resistance, with maximum strength being achieved at 10 degree cephalad angulation. Combining 10 degree cephalad angulation with maximal spacing between the top two screws (maximum pullout radius) increased the pullout resistance by 88% compared to ‘standard’ screw positioning (screws inserted perpendicular to rod at mid-body height).
Conclusions: The positioning of the top screw in anterior scoliosis constructs can significantly alter its pullout resistance.
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|Item Type:||Journal Article|
|Keywords:||anterior scoliosis correction, endoscopic, thoracoscopic, scoliosis instrumentation, top screw pullout, biomechanics, vertebral body screw|
|Subjects:||Australian and New Zealand Standard Research Classification > ENGINEERING (090000) > BIOMEDICAL ENGINEERING (090300) > Biomedical Engineering not elsewhere classified (090399)|
Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > CLINICAL SCIENCES (110300) > Orthopaedics (110314)
|Divisions:||Past > QUT Faculties & Divisions > Faculty of Built Environment and Engineering|
Current > Institutes > Institute of Health and Biomedical Innovation
Past > Schools > School of Engineering Systems
|Copyright Owner:||Copyright 2010 Lippinciott Williams & Wilkins|
|Deposited On:||23 Jun 2010 08:22|
|Last Modified:||01 Mar 2012 00:23|
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