The effect of insertion time on the axial pullout strength of anterior vertebral body screws

Saunders, Nicole M. & Adam, Clayton J. (2009) The effect of insertion time on the axial pullout strength of anterior vertebral body screws. In Adelaide Centre for Spinal Research (ACSR) - Spinal Research Symposium VII , 25-27 August, Barossa Valley, Adelaide, Australia. (Unpublished)


Top screw pullout occurs when the screw is under too much axial force to remain secure in the vertebral body. In vitro biomechanical pullout tests are commonly done to find the maximum fixation strength of anterior vertebral body screws. Typically, pullout tests are done instantaneously where the screw is inserted and then pulled out immediately after insertion. However, bone is a viscoelastic material so it shows a time dependent stress and strain response. Because of this property, it was hypothesised that creep occurs in the vertebral trabecular bone due to the stress caused by the screw. The objective of this study was therefore to determine whether the axial pullout strength of anterior vertebral body screws used for scoliosis correction surgery changes with time after insertion. This study found that there is a possible relationship between pullout strength and time; however more testing is required as the sample numbers were quite small. The design of the screw is made with the knowledge of the strength it must obtain. This is important to prevent such occurrences as top screw pullout. If the pullout strength is indeed decreased due to creep, the design of the screw may need to be changed to withstand greater forces.

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ID Code: 27412
Item Type: Conference Paper
Refereed: No
Keywords: anterior scoliosis surgery, adolescent idiopathic scoliosis, top screw pullout, vertebral body screws, axial pullout strength
Subjects: Australian and New Zealand Standard Research Classification > ENGINEERING (090000) > BIOMEDICAL ENGINEERING (090300) > Biomechanical Engineering (090302)
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 2009 [contact the authors]
Deposited On: 21 Sep 2009 02:06
Last Modified: 09 Jun 2010 14:00

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