Biomechanical Evaluation of the Pedicle Screw Insertion Depth Effect on Screw Stability Under Cyclic Loading and Subsequent Pullout

Karami, Kristophe J.; Buckenmeyer, Laura E.; Kiapour, A. M.; Kelkar, Prashant; Goel, Vijay K.; Demetropoulos, Constantine K.; Soo, Teck M

doi:10.1097/bsd.0000000000000178

Cited by 63 publications

(60 citation statements)

References 44 publications

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“…Therefore, radial stress resistance may be more important than axial pullout strength in preventing the screw from loosening, which contradicts the standard axial pullout test established by the ASTM in publications F543 and F1717 . Furthermore, the effectiveness of the pullout test in predicting the pedicle screw loosening is controversial as it does not simulate physiological loading conditions; therefore, screws with a higher axial pullout strength do not necessarily possess a lower loosening rate. The study confirmed that standard axial pullout testing could not conclusively assess the screws’ stability when used in long bone fracture plate fixation.…”

Section: Discussionmentioning

confidence: 99%

“…However, studies on the pedicle screw found that pullout strength was an unsuitable predictor of pedicle screw loosening as it does not simulate physiological loading conditions . The toggling test, which can simulate physiological loading conditions, is a better predictor than the axial pullout test . Therefore, radial stress resistance may be more important than axial pullout strength in preventing screw loosening.…”

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confidence: 99%

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Bone resorption triggered by high radial stress: The mechanism of screw loosening in plate fixation of long bone fractures

Feng

Lin

Fang

et al. 2019

Journal Orthopaedic Research

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Screw loosening is a common complication in plate fixation. However, the underlying mechanism is unclear. This study investigated screw loosening mechanisms by finite element analysis (FEA) simulation and clinical X‐ray feature analysis. Two FEA models incorporated bone heterogeneity and orthotropy, representing fracture fixation using dynamic compression plate (DCP) and locking compression plate (LCP), were developed. These models were used to examine the volume of bone exceeding a certain stress value around each screw under physiologically‐relevant loading conditions. These damaged bone was then separated and compared by the axial stress and radial stress of each screw. In addition, features of patients’ X‐ray images showing screw loosening were analyzed to validate the loosening features simulated by the models. The FEA study showed that more damaged bone was found at the central two screws which gradually decreased toward the two end screws in all groups. More bone was damaged by the radial stress of each screw than by the axial stress. The radiological analysis of screw loosening showed that bone loss occurred at the screw closest to the fracture line first then subsequent bone loss at the screws further away from the fracture line occurred. This study found that the two screws nearest to the fracture line are more vulnerable to loosening. The radial stress of the screw plays a larger role in screw loosening than the axial stress. Bone resorption triggered by the high radial stress of screws is indicated as the mechanism of screw loosening in the diaphyseal plate fixation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1498–1507, 2019.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Bone resorption triggered by high radial stress: The mechanism of screw loosening in plate fixation of long bone fractures

Feng

Lin

Fang

et al. 2019

Journal Orthopaedic Research

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“…Another contributing factor to some cases of spinal hardware fixation failure is the implant site. In patients with osteoporosis, the low-density bone of the spine increases the risk for implant loosening or pullout (Karami et al, 2015). In response to implant loosening, screw augmentation with various fixatives such as hydroxyapatite, polymethylmethacrylate, or tricalcium phosphate have been employed as potential solutions.…”

Section: Discussionmentioning

confidence: 99%

Osseodensification for enhancement of spinal surgical hardware fixation

Lopez

Alifarag

Torroni

et al. 2017

Journal of the Mechanical Behavior of Biomedical Materials

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Integration between implant and bone is an essential concept for osseous healing requiring hardware placement. A novel approach to hardware implantation, termed osseodensification, is described here as an effective alternative. 12 sheep averaging 65 kg had fixation devices installed in their C2, C3, and C4 vertebral bodies; each device measured 4 mm diameter×10 mm length. The left-sided vertebral body devices were implanted using regular surgical drilling (R) while the right-sided devices were implanted using osseodensification drilling (OD). The C2 and C4 vertebra provided the t=0 in vivo time point, while the C3 vertebra provided the t=3 and t=6 week time points, in vivo. Structural competence of hardware was measured using biomechanical testing of pullout strength, while the quality and degree of new bone formation and remodeling was assessed via histomorphometry. Pullout strength demonstrated osseodensification drilling to provide superior anchoring when compared to the control group collapsed over time with statistical significance (p < 0.01). On Wilcoxon rank signed test, C2 and C4 specimens demonstrated significance when comparing device pullout (p=0.031) for both, and C3 pullout tests at 3 and 6 weeks collapsed over time had significance as well (p=0.027). Percent bone-to-implant contact (%BIC) analysis as a function of drilling technique demonstrated an OD group with significantly higher values relative to the R group (p < 0.01). Similarly, percent bone-area-fraction-occupancy (BAFO) analysis presented with significantly higher values for the OD group compared to the R group (p=0.024). As a function of time, between 0 and 3 weeks, a decrease in BAFO was observed, a trend that reversed between 3 and 6 weeks, resulting in a BAFO value roughly equivalent to the t=0 percentage, which was attributed to an initial loss of bone fraction due to remodeling, followed by regaining of bone fraction via production of woven bone. Histomorphological data demonstrated autologous bone chips in the OD group with greater frequency relative to the control, which acted as nucleating surfaces promoting new bone formation around the implants, providing superior stability and greater bone density. This alternative approach to a critical component of hardware implantation encourages assessment of current surgical approaches to hardware implantation.

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“…Caudo-cephalad loading in an in vitro setting (10) is well established and can be used as a preconditioning step prior to pullout or can itself be an endpoint for loosening (41)(42)(43)(44)(45)(46). Toggling generally decreases the stability of the screw/bone construct (11,32), however, this is not always the case. Lotz et al (47) reported pullout loads of 809±467 N without cyclic loading and 801±265 N following cyclic loading.…”

Section: Comparison To Existing Literaturementioning

confidence: 92%

“…Screw pull-out studies using human cadaveric tissues report a wide range of values from 102 to 1,741 N (15,26,28,(31)(32)(33)(34). Similarly, screw pull-out with the calf model reports values from 747 to 7,300 N, depending on treatment (30,35).…”

Section: Comparison To Existing Literaturementioning

confidence: 99%

The contribution of the cortical shell to pedicle screw fixation

Pelletier¹,

Bertollo²,

Al-Khawaja³

et al. 2017

J. Spine Surg.

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Background: A pedicle screw insertion technique known as "hubbing" involves the removal of cortical bone around the screw insertion with the aim of improving fixation and decreasing screw loosening.However, the efficacy of this procedure relative to bone density and early loading have not been fully explored. The purpose of this study is to establish the contribution of the cortical layer (hubbing), cancellous density, early loading (toggling) in an idealised model. This is an in vitro laboratory study.Methods: Synthetic bone blocks with cancellous bulk and a simulated cortical shell were implanted with 6.5 mm pedicle screws. Three key variables were evaluated in this study; density of the simulated bone (10-20 lb/ft 3 ), toggling (±0.5 mm for 10,000 cycles), and the presence or absence of the surrounding cortex (hubbing). Pullout testing after toggling was performed to determine maximum load, stiffness and energy.Results were analyzed to assess interaction and main effects.Results: Removal of the cortex decreased the pullout loads by approximately 1,100 N after toggling.Toggling in the presence of the cortical shell had no effect. However, once the cortical shell is removed damage to the weaker cancellous bone accumulates and further compromises the fixation.Conclusions: The addition of a cortical layer in the Sawbone model is significant and provides a more realistic model of load sharing. The cortex plays a considerable role in the protection of underlying cancellous bone as well as contributing to initial pullout strength. The results of this study demonstrate a negative synergistic effect when both toggling and hubbing are applied to the weaker bone.

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Biomechanical Evaluation of the Pedicle Screw Insertion Depth Effect on Screw Stability Under Cyclic Loading and Subsequent Pullout

Abstract: Although increased screw depth led to increased fixation and decreased loosening, additional purchase of the stiff anterior cortex is essential to reach superior screw-bone construct stability and stiffness.

Cited by 63 publications

References 44 publications

Bone resorption triggered by high radial stress: The mechanism of screw loosening in plate fixation of long bone fractures

Bone resorption triggered by high radial stress: The mechanism of screw loosening in plate fixation of long bone fractures

Osseodensification for enhancement of spinal surgical hardware fixation

The contribution of the cortical shell to pedicle screw fixation

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