Preclinical evaluation of posterior spine stabilization devices: can the current standards represent basic everyday life activities?

Barbera, Luigi La; Galbusera, Fabio; Wilke, Hans–Joachim; Villa, Tomaso

doi:10.1007/s00586-016-4622-1

Cited by 24 publications

(46 citation statements)

References 35 publications

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“…This was expected since the screw, as an internal fixation system, does not undergo any relevant loadings typical of standard pedicle screw connected to stiff rigid posterior instrumentation. (La Barbera and Villa, 2016, 2017; La Barbera et al, 2016a,b, 2017).…”

Section: Discussionmentioning

confidence: 95%

“…Standing was simulated applying a 500N follower load (Rohlmann et al, 2009; La Barbera et al, 2016b, 2017). Flexion of the upper body, often associated to the event of VCF, was reproduced with a 1175N follower load and a 7.5 N/m moment on the L1 vertebra (Rohlmann et al, 2009; La Barbera et al, 2016b, 2017). In both cases the inferior portion of S1 was considered fully constrained.…”

Section: Methodsmentioning

confidence: 99%

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Stent-Screw Assisted Internal Fixation of Osteoporotic Vertebrae: A Comparative Finite Element Analysis on SAIF Technique

Barbera

Cianfoni

Ferrari

et al. 2019

Front. Bioeng. Biotechnol.

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Vertebral compression fractures are one of the most relevant clinical consequences caused by osteoporosis: one of the most common treatment for such fractures is vertebral augmentation through minimally invasive approaches (vertebroplasty or balloon-kyphoplasty). Unfortunately, these techniques still present drawbacks, such as re-fractures of the treated vertebral body with subsidence of the non-augmented portions or re-fracture of the non-augmented middle column at the junction with the augmented anterior column. A novel minimally-invasive augmentation technique, called Stent-Screw Assisted Internal Fixation, has been recently proposed for the treatment of severe osteoporotic and neoplastic fractures: this technique uses two vertebral body stents and percutaneous cannulated and fenestrated pedicular screws, through which cement is injected inside the expanded stents to achieve optimal stents' and vertebral body's filling. The role of the pedicle screws is to anchor the stents-cement complex to the posterior column, acting as a bridge across the middle column and preserving its integrity from possible collapse. In order to evaluate the potential of the new technique in restoring the load bearing capacity of the anterior and middle spinal columns and in reducing bone strains, a Finite Element model of an osteoporotic lumbar spine has been developed. Both standard vertebroplasty and Stent-Screw Assisted Internal Fixation have been simulated: simulations have been run taking into account everyday activities (standing and flexion) and comparison between the two techniques, in terms of strain distribution on vertebral endplates and posterior and anterior wall, was performed. Results show that Stent-Screw Assisted Internal Fixation significantly decrease the strain distribution on the superior EP and the cortical wall compared to vertebroplasty, possibly reducing the re-fracture risk of the middle-column at the treated level.

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Section: Discussionmentioning

confidence: 95%

Section: Methodsmentioning

confidence: 99%

Stent-Screw Assisted Internal Fixation of Osteoporotic Vertebrae: A Comparative Finite Element Analysis on SAIF Technique

Barbera

Cianfoni

Ferrari

et al. 2019

Front. Bioeng. Biotechnol.

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“…The complex loading conditions in the human spine have not been fully considered in ASTM F1717 and so the results of this study may not directly predict in vivo performance. ASTM F1717 is typically used to compare different component designs or surgical techniques in terms of the relative mechanical parameters [9,13,26,27]. This study also did not consider variations in screw design and size as the aim was to evaluate the overall effect of partial screw insertion.…”

Section: Discussionmentioning

confidence: 99%

Incomplete insertion of pedicle screws in a standard construct reduces the fatigue life: A biomechanical analysis

et al. 2019

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Pedicle screws are commonly used for posterior stabilization of the spine. When used in deformed or degenerated segments, the pedicle screws are often not fully inserted into the bone, but instead the threaded portion is exposed by 1 or 2 threads to accommodate rod placement and ensure alignment between the tulip of the screw and the rod. However, broken pedicle screws have been reported with the use of this method. The aim of this study was to determine how the fatigue life of the screw is affected by not fully inserting the screw into the bone. Spinal constructs were evaluated in accordance with ASTM F1717. The following three screw positions were subjected to compression bending fatigue loading; (i) pedicle screw fully inserted in the test block with no threads exposed (EXP-T0), (ii) pedicle screw inserted with one thread exposed outside the test block (EXP-T1), (iii) pedicle screw inserted with two threads exposed outside the test block (EXP-T2). Corresponding finite element models FEM-T0, FEM-T1 and FEM-T2 were also constructed and subjected to the same axial loading as the experimental groups to analyze the stress distribution in the pedicle screws and rods. The results showed that under a 190 N axial load, the EXP-T0 group survived the full 5 million cycles, the EXP-T1 group failed at 3.7 million cycles on average and the EXP-T2 groups failed at 1.0 million cycles on average, while the fatigue strength of both the EXP-T1 and EXP-T2 groups was 170 N. The constructs failed through fracture of the pedicle screw. In comparison to the FEM-T0 model, the maximum von Mises stress on the pedicle screw in the FEM-T1 and FEM-T2 models increased by 39% and 58%, respectively. In conclusion, this study demonstrated a drastic decrease in the fatigue life of pedicle screws when they are not full inserted into the plastic block.

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“…The protocols also need to be simple enough to provide a basic assessment of the implants' strength. The current standards (ie, ASTM‐F1717, 11 and ISO‐12189 12 ) have been modified to be a better representative of the real‐life performance of posterior spinal implants 2,13‐25 . However, these modifications still are not suitable for the evaluation of growing rods.…”

Section: Introductionmentioning

confidence: 99%

“…The ISO‐12189 was developed to evaluate posterior dynamic stabilization devices 12 and further modified over the years 17,18,22 . Due to the presence of the anterior support and its load sharing with spinal implants, authors claimed that ISO‐12189 simulated a more realistic scenario, compared with ASTM‐F1717 19,20,23,24 .…”

Section: Introductionmentioning

confidence: 99%

Clinically relevant finite element technique based protocol to evaluate growing rods for early onset scoliosis correction

et al. 2020

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Objective: The emergence of distraction-based growing rods has provided the means to reduce the progression of spinal deformity in early onset scoliosis (EOS). The current protocols for evaluating spinal implants (ie, ASTM-F1717 and ISO-12189) were developed for fusion/ dynamic devices. These protocols do not feature long unsupported rod lengths subjected to distraction. Due to the unsuitability of the existing guidelines for the evaluation of growing rods, a new distraction-based finite element protocol is presented herein for the first time. Method: A vertebrectomy (VO) model from current protocols was modified to accommodate multi-spinal segments (ie, MS model) in which springs with appropriate stiffness were simulated in between the plastic blocks. To assess the efficacy of the protocol, two different computational studies were conducted: (a) compression-bending (MS-CB) with no distraction, and (b) distraction followed by compression-bending (MS-D + CB). In each study, the model with no axial connector (rods-only) was modified to include a) 80-mm long tandem (LT) connectors, and b) side-by-side (SBS) connectors. Stiffness and yield loads were calculated as per ASTM-F1717 guidelines and compared with the corresponding VO models with no distraction. In the MS-D + CB models, distraction was applied at the top block, stretching the spring-block construct in a simulation of scoliosis surgery prior to locking the construct at the connector-rods' interface. Results: MS-CB models predicted higher stiffness and yield loads, compared to the VO models. The locking mechanism produced pre-existing stresses on the rod-connector interface, which caused a shift in the location of high-stress regions to the distraction site. Distraction led to a decrease in the construct's stiffness and yield load. Discussion: The proposed protocol enables the simulation of clinical parameters that are not feasible in the F1717 models and predicted stress patterns in the hardware consistent with observed clinical failures.

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Preclinical evaluation of posterior spine stabilization devices: can the current standards represent basic everyday life activities?

Abstract: The study increases our awareness on the use of the current standards to achieve meaningful results easy to compare and interpret.

Cited by 24 publications

References 35 publications

Stent-Screw Assisted Internal Fixation of Osteoporotic Vertebrae: A Comparative Finite Element Analysis on SAIF Technique

Stent-Screw Assisted Internal Fixation of Osteoporotic Vertebrae: A Comparative Finite Element Analysis on SAIF Technique

Incomplete insertion of pedicle screws in a standard construct reduces the fatigue life: A biomechanical analysis

Clinically relevant finite element technique based protocol to evaluate growing rods for early onset scoliosis correction

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