Could Junctional Problems at the End of a Long Construct be Addressed by Providing a Graduated Reduction in Stiffness?

Durrani, Atiq; Jain, Viral V.; Desai, Rasesh; Bucklen, Brandon; Ingalhalikar, Aditya; Muzumdar, Aditya; Moldavsky, Mark; Khalil, Saif

doi:10.1097/brs.0b013e31821eb295

Cited by 18 publications

(3 citation statements)

References 19 publications

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“…10 In contrast to the results of Mageswaran et al, Durani et al reported that a dynamic stabilization system could reduce the hypermobility caused by extended arthrodesis. 11 In addition, other study assessed the intradiscal pressure (IDP) in monosegmental fusion at L5-S1 and hybrid surgery (Dynesys at L4-5 and rigid fixation at L5-S1). 12 The IDP at the segment adjacent to the fusion was reduced when a dynamic stabilization system was added above the segment that underwent fusion.…”

Section: Discussionmentioning

confidence: 99%

Hybrid Surgery Combined with Dynamic Stabilization System and Fusion for the Multilevel Degenerative Disease of the Lumbosacral Spine

2015

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Section: Discussionmentioning

confidence: 99%

Hybrid Surgery Combined with Dynamic Stabilization System and Fusion for the Multilevel Degenerative Disease of the Lumbosacral Spine

2015

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“… 16 Similarly, Durrani et al reported that the use of posterior dynamic stabilization at the caudal-most level reduces the adjacent-level hypermobility and the potential for distal junctional kyphosis. 17 Less-restrictive hook instrumentation has also been shown to reduce the risk of PJK clinically 3 10 15 18 ; however, in vitro studies demonstrating their mechanical advantage in the thoracic spine is limited.…”

Section: Introductionmentioning

confidence: 99%

Biomechanical Analysis of the Proximal Adjacent Segment after Multilevel Instrumentation of the Thoracic Spine: Do Hooks Ease the Transition?

Metzger

Robinson

Svet

et al. 2015

Global Spine Journal

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Study Design Biomechanical cadaveric study. Objective Clinical studies indicate that using less-rigid fixation techniques in place of the standard all-pedicle screw construct when correcting for scoliosis may reduce the incidence of proximal junctional kyphosis and improve patient outcomes. The purpose of this study is to investigate whether there is a biomechanical advantage to using supralaminar hooks in place of pedicle screws at the upper-instrumented vertebrae in a multilevel thoracic construct. Methods T7–T12 spines were biomechanically tested: (1) intact; (2) following a two-level pedicles screw fusion from T9 to T11; and after proximal extension of the fusion to T8–T9 with (3) bilateral supra-laminar hooks, (4) a unilateral hook + unilateral screw hybrid, or (5) bilateral pedicle screws. Specimens were nondestructively loaded while three-dimensional kinematics and intradiscal pressure at the supra-adjacent level were recorded. Results Supra-adjacent hypermobility was reduced when bilateral hooks were used in place of pedicle screws at the upper-instrumented level, with statistically significant differences in lateral bending and torsion (p < 0.05 and p < 0.001, respectively). Disk pressures in the supra-adjacent segment were not statistically different among top-off techniques. Conclusions The use of supralaminar hooks at the top of a multilevel posterior fusion construct reduces the stress at the proximal uninstrumented motion segment. Although further data is needed to provide a definitive link to the clinical occurrence of PJK, this in vitro study demonstrates the potential benefit of “easing” the transition between the stiff instrumented spine and the flexible native spine and is the first to demonstrate these results with laminar hooks.

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“…In a retrospective review of a multicenter database, rod fracture occurred in 15 % of patients [ 31 ]. The high stiffness of conventional metal rods creates compliance mismatches between spine and instrumentation, stress concentrations, and motion redistribution, factors which likely contribute to rod breakage, screw pull-out, auto-fusion, and junctional kyphosis [ 15 , 32 , 33 ]. Using a computational model, a more flexible non-fusion correction system for AIS which used non-locking polyaxial pedicle screws and mobile connectors was reported to reduce intervertebral rotation less than more rigid implants [ 34 ].…”

Section: Introductionmentioning

confidence: 99%

Flexible growing rods: a biomechanical pilot study of polymer rod constructs in the stability of skeletally immature spines

et al. 2016

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BackgroundSurgical treatments for early onset scoliosis (EOS) correct curvatures and improve respiratory function but involve many complications. A distractible, or ‘growing rod,’ implant construct that is more flexible than current metal rod systems may sufficiently correct curves in small children and reduce complications due to biomechanical factors. The purpose of this pilot study was to determine ranges of motion (ROM) after implantation of simulated growing rod constructs with a range of clinically relevant structural properties. The hypothesis was that ROM of spines instrumented with polymer rods would be greater than conventional metal rods and lower than non-instrumented controls.MethodsBiomechanical tests were conducted on six thoracic spines from skeletally immature domestic swines (35–40 kg). Paired pedicle screws were used as anchors at proximal and distal levels. Specimens were tested under the following conditions: control, then dual rods of polyetheretherketone (PEEK) (diameter 6.25 mm), titanium (4 mm), and cobalt-chrome alloy (CoCr) (5 mm). Lateral bending (LB) and flexion-extension (FE) moments were applied, and vertebral rotations were measured. Differences were determined by two-tailed t-tests and Bonferroni for four primary comparisons: PEEK vs control and PEEK vs CoCr, in LB and FE (α = 0.05/4).ResultsIn LB, ROM of spine segments after instrumenting with PEEK rods was lower than the non-instrumented control condition at each instrumented level. ROM was greater with PEEK rods than with Ti and CoCr rods at every instrumented level. Combining treated levels, in LB, ROM for PEEK rods was 35 % of control (p < 0.0001) and 270 % of CoCr rods (p < 0.01). In FE, ROM with PEEK was 27 % of control (p < 0.001) and 180 % of CoCr (p < 0.01). At proximal and distal adjacent non-instrumented levels in FE, mean ROM was lower for PEEK than for either metal.ConclusionsPEEK rods increased flexibility versus metal rods, and decreased flexibility versus non-instrumented controls, both over the entire instrumented segment and at each individual level. Smaller mean increases in ROM at proximal and distal adjacent motion segments occurred with PEEK compared to metal rods, which may help decrease complications, such as junctional kyphosis. Flexible growing rods may eventually help improve treatment options for young patients with severe deformity.

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Could Junctional Problems at the End of a Long Construct be Addressed by Providing a Graduated Reduction in Stiffness?

Abstract: Reduction of hypermobility caused by extended arthrodesis may represent a new and ideally suited function for PDS devices. Mechanically, the devices were seen to kinematically restore abnormal distal motion, especially with placement of the PDS at the thoracolumbar junction.

Cited by 18 publications

References 19 publications

Hybrid Surgery Combined with Dynamic Stabilization System and Fusion for the Multilevel Degenerative Disease of the Lumbosacral Spine

Hybrid Surgery Combined with Dynamic Stabilization System and Fusion for the Multilevel Degenerative Disease of the Lumbosacral Spine

Biomechanical Analysis of the Proximal Adjacent Segment after Multilevel Instrumentation of the Thoracic Spine: Do Hooks Ease the Transition?

Flexible growing rods: a biomechanical pilot study of polymer rod constructs in the stability of skeletally immature spines

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