Early stage disc degeneration does not have an appreciable affect on stiffness and load transfer following vertebroplasty and kyphoplasty |
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Authors: | Victor Kosmopoulos Tony S Keller Constantin Schizas |
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Institution: | (1) Department of Orthopaedic Surgery, Bone and Joint Research Center, University of North Texas Health Science Center, 3400 Camp Bowie Boulevard (CBH 407), Fort Worth, TX 76107, USA;(2) Department of Orthopaedic Surgery, John Peter Smith Hospital, Fort Worth, TX, USA;(3) Département de l’Appareil Locomoteur, Centre Hospitalier Universitaire Vaudois, The University of Lausanne, Lausanne, Switzerland |
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Abstract: | Vertebroplasty and kyphoplasty have been reported to alter the mechanical behavior of the treated and adjacent-level segments,
and have been suggested to increase the risk for adjacent-level fractures. The intervertebral disc (IVD) plays an important
role in the mechanical behavior of vertebral motion segments. Comparisons between normal and degenerative IVD motion segments
following cement augmentation have yet to be reported. A microstructural finite element model of a degenerative IVD motion
segment was constructed from micro-CT images. Microdamage within the vertebral body trabecular structure was used to simulate
a slightly (I = 83.5% of intact stiffness), moderately (II = 57.8% of intact stiffness), and severely (III = 16.0% of intact
stiffness) damaged motion segment. Six variable geometry single-segment cement repair strategies (models A–F) were studied
at each damage level (I–III). IVD and bone stresses, and motion segment stiffness, were compared with the intact and baseline
damage models (untreated), as well as, previous findings using normal IVD models with the same repair strategies. Overall,
small differences were observed in motion segment stiffness and average stresses between the degenerative and normal disc
repair models. We did however observe a reduction in endplate bulge and a redistribution in the microstructural tissue level
stresses across both endplates and in the treated segment following early stage IVD degeneration. The cement augmentation
strategy placing bone cement along the periphery of the vertebra (model E) proved to be the most advantageous in treating
the degenerative IVD models by showing larger reductions in the average bone stresses (vertebral and endplate) as compared
to the normal IVD models. Furthermore, only this repair strategy, and the complete cement fill strategy (model F), were able
to restore the slightly damaged (I) motion segment stiffness above pre-damaged (intact) levels. Early stage IVD degeneration
does not have an appreciable effect in motion segment stiffness and average stresses in the treated and adjacent-level segments
following vertebroplasty and kyphoplasty. Placing bone cement in the periphery of the damaged vertebra in a degenerative IVD
motion segment, minimizes load transfer, and may reduce the likelihood of adjacent-level fractures.
Dr. Tony S. Keller’s life was tragically taken on the 6th of December 2006. Tony was a bright and energetic researcher, an
outstanding teacher and mentor, and a beloved friend. He is greatly missed. |
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Keywords: | Load transfer Vertebroplasty Kyphoplasty Microstructural finite element analysis Vertebral motion segment |
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