A biomechanical study of top screw pullout in anterior scoliosis correction constructs

Mayo, Andrew E., Labrom, Robert D., Askin, Geoffrey N. and Adam, Clayton J. (2010) A biomechanical study of top screw pullout in anterior scoliosis correction constructs. Spine, 35 13: E587-E595.


Author Mayo, Andrew E.
Labrom, Robert D.
Askin, Geoffrey N.
Adam, Clayton J.
Title A biomechanical study of top screw pullout in anterior scoliosis correction constructs
Journal name Spine   Check publisher's open access policy
ISSN 0362-2436
1528-1159
Publication date 2010-06
Sub-type Article (original research)
DOI 10.1097/BRS.0b013e3181cd389d
Volume 35
Issue 13
Start page E587
End page E595
Total pages 9
Place of publication Philadelphia, PA, United States
Publisher Lippincott Williams & Wilkins
Language eng
Formatted abstract Study Design. Biomechanical testing of vertebral body screw pullout resistance with relevance to top screw pullout in thoracoscopic anterior scoliosis constructs.
Objective. To analyze 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 thoracoscopic anterior scoliosis surgery, with rates of up to18% 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 radiuses 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 2 screws (maximum pullout radius) increased the pullout resistance by 88% compared with “standard” screw positioning (screws inserted perpendicular to rod at midbody height).
Conclusion. The positioning of the top screw in anterior scoliosis constructs can significantly alter its pullout resistance.
Keyword Anterior scoliosis correction
Thoracoscopic
Scoliosis instrumentation
Top screw pullout
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Medicine Publications
 
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