Effect of Graded Facetectomy on Biomechanics of Dynesys Dynamic Stabilization System
ABSTRACT Finite element (FE) method was used to compare the biomechanics of L3-S1 lumbar spine with graded facetectomy before and after placement of Dynesys.
To evaluate the biomechanics of Dynesys as a function of graded bilateral facetectomies.
Spinal fusion or posterior dynamic stabilization systems are used to restore stability after facetectomies.
The intact FE spine was modified to simulate decompression at L4-L5 with 50% and 75% and total facetectomy with/without dynamic stabilization with Dynesys. Biomechanics of the implanted level was investigated under different physiological loadings.
Total facetectomy increased the motion in extension (8.7° vs. 2.7° for intact) and axial rotation (8.4° vs. 2.4° for intact). However the decrease in motion in the Dynesys model ranged from 65% in axial rotation to 80% in flexion for all facetectomies, except in the total facetectomy axial rotation case (motion higher than intact). The center of rotation of dynamic stabilized segment moved inferior/posterior in partial facetectomy and superior/posterior in total facetectomy with respect to the intact and destabilized cases. The Dynesys screws observed peak stresses up to 28% higher than those of a rigid fixation system in certain loadings, such as lateral bending and extension. The critical loosening torque applied to the screws in total facetectomy case was 6 times the partial facetectomy case in axial rotation.
Partial facetectomy had a minimal effect on range of motion on the Dynesys-implanted segment. However, in the case of total facetectomy the motion increased by almost 40% in flexion and by 200% in axial rotation. The higher stresses applied to the screws in Dynesys in specific loadings may lead to higher risk of screw failure in Dynesys than in a generic rigid fixation construct.
SourceAvailable from: Chaudhry Raza Hassan[Show abstract] [Hide abstract]
ABSTRACT: Lumbar spine degeneration diseases require precise prediction of biomechanical parameters. These parameters include stress in ligaments, intradiscal pressure and facet loads. For this purpose, several symmetrical FE models of lumbar spine have been proposed previously with inherent simplifications in design. Such models may not give realistic results for biomechanical analysis because of the assumptions in their design. An asymmetrical 3D finite element L1-L5 lumbar spine was developed using computed tomographic scans of a healthy individual. All lumbar spinal elements were added to the model, including vertebra, intervertebral discs, ligaments and facet joints. 400N pre-compression load was applied and model was simulated at 10Nm pure moment in all six planes of motion. L4-L5 motion segment was used for prediction of biomechanical parameters. Facet loads reached the maximum value of 200N in extension and axial rotation. Intradiscal pressure had highest value in lateral bending where it was predicted as 2.3MPa. Flexion showed significantly higher pressure of 1.67MPa in disc. Stress in interspinous ligament had maximum value of 3.27MPa in flexion motion whereas capsular ligament had maximum stress value of 29MPa in extension motion. Based on these predictions and literature values, it is concluded that facet joints and capsular ligaments are effective in load sharing during extension motion. Interspinous ligaments are utilized during flexion while intervertebral discs performed load sharing in lateral bending, axial rotation and flexion.International Conference on Biomedical Engineering and Systems, Prague, Czech Republic; 08/2014
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ABSTRACT: Lumbar disc replacement and motion preservation is a popular concept to treat degenerative disc disease in the lumbar spine. These surgical interventions are thought to maintain mobility at the operated level and subsequently aid in the prevention of adjacent level degeneration. This article reviews the current status of lumbar disc replacement and motion preservation devices. A literature search was performed via PubMed with an emphasis on reviewing articles published within the last 2 years to discuss recent developments and trends on lumbar disc replacement and motion preservation devices. Based on this criterion, we reviewed over 40 articles in detail recently published on lumbar disc replacement and motion preservation devices. More than 20 of these articles discussed lumbar disc replacement specifically. These articles ranged from outcome studies to the biomechanics of the prosthesis to discussion of adjacent segment degeneration. Ten articles discussed various posterior motion preservation devices ranging from pedicle-based systems to one article that discussed facet joint resurfacing. The remaining articles discussed various other modalities of treatment for the lumbar spine from biologics to manipulative therapy. After this thorough review of the literature, approximately 30 articles are highlighted, as they are particularly relevant to the topic of discussion. Compared with some spine topics, there is little recent literature available for review on this important topic. There are motion preservation devices available for use in the US with proven clinical success, but there is no evidence of definitive prevention or dissipation of adjacent level degeneration with the use of these devices. Further clinical research and product development is imperative to allow for the evolution of this intriguing treatment modality to prosper.Current Orthopaedic Practice 01/2014; 25(1):4-8. DOI:10.1097/BCO.0000000000000068
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ABSTRACT: OBJECT The authors evaluated the biomechanical effects of an interspinous process (ISP) device on kinematics and load sharing at the implanted and adjacent segments. METHODS A 3D finite-element (FE) model of the lumbar spine (L1-5) was developed and validated through comparison with published in vitro study data. Specifically, validation was achieved by a flexible (load-control) approach in 3 main planes under a pure moment of 10 Nm and a compressive follower load of 400 N. The ISP device was inserted between the L-3 and L-4 processes. Intact and implanted cases were simulated using the hybrid protocol in all motion directions. The resultant motion, facet load, and intradiscal pressure after implantation were investigated at the index and adjacent levels. In addition, stress at the bone-implant interface was predicted. RESULTS The hybrid approach, shown to be appropriate for adjacent-level investigations, predicted that the ISP device would decrease the range of motion, facet load, and intradiscal pressure at the index level relative to the corresponding values for the intact spine in extension. Specifically, the intradiscal pressure induced after implantation at adjacent segments increased by 39.7% and by 6.6% at L2-3 and L4-5, respectively. Similarly, facet loads at adjacent segments after implantation increased up to 60% relative to the loads in the intact case. Further, the stress at the bone-implant interface increased significantly. The influence of the ISP device on load sharing parameters in motion directions other than extension was negligible. CONCLUSIONS Although ISP devices apply a distraction force on the processes and prevent further extension of the index segment, their implantation may cause changes in biomechanical parameters such as facet load, intradiscal pressure, and range of motion at adjacent levels in extension.Journal of neurosurgery. Spine 05/2015; DOI:10.3171/2014.12.SPINE14419 · 2.36 Impact Factor