A biomechanical analysis of the self-retaining pedicle hook device in posterior spinal fixation |
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Authors: | Wilbert van Laar Rinse J Meester Theo H Smit Barend J van Royen |
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Institution: | (1) Department of Orthopaedic Surgery, VU University Medical Centre, P.O. Box 7057, 1007 MB Amsterdam, The Netherlands;(2) Department of Physics and Medical Technology, VU University Medical Centre, Amsterdam, The Netherlands |
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Abstract: | Regular hooks lack initial fixation to the spine during spinal deformity surgery. This runs the risk of posterior hook dislodgement
during manipulation and correction of the spinal deformity, that may lead to loss of correction, hook migration, and post-operative
junctional kyphosis. To prevent hook dislodgement during surgery, a self-retaining pedicle hook device (SPHD) is available
that is made up of two counter-positioned hooks forming a monoblock posterior claw device. The initial segmental posterior
fixation strength of a SPHD, however, is unknown. A biomechanical pull-out study of posterior segmental spinal fixation in
a cadaver vertebral model was designed to investigate the axial pull-out strength for a SPHD, and compared to the pull-out
strength of a pedicle screw. Ten porcine lumbar vertebral bodies were instrumented in pairs with two different instrumentation
constructs after measuring the bone mineral density of each individual vertebra. The instrumentation constructs were extracted
employing a material testing system using axial forces. The maximum pull-out forces were recorded at the time of the construct
failure. Failure of the SPHD appeared in rotation and lateral displacement, without fracturing of the posterior structures.
The average pull-out strength of the SPHD was 236 N versus 1,047 N in the pedicle screws (P < 0.001). The pull-out strength of the pedicle screws showed greater correlation with the BMC compared to the SPHD (P < 0.005). The SPHD showed to provide a significant inferior segmental fixation to the posterior spine in comparison to pedicle
screw fixation. Despite the beneficial characteristics of the monoblock claw construct in a SPHD, that decreases the risk
of posterior hook dislodgement during surgery compared to regular hooks, the SPHD does not improve the pull-out strength in
such a way that it may provide a biomechanically solid alternative to pedicle screw fixation in the posterior spine. |
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Keywords: | Spinal deformities Biomechanics Pedicle screw Self-retaining pedicle hook Pull-out strength |
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