Peak Pullout Force Research Articles

Nondestructive acoustic modal analysis for assessing bone screw stability: An ex vivo animal study.

Conventional insertion torque and pull-out tests are destructive and unsuitable for clinical bone screw fixation. This study evaluates screw stability using acoustic modal analysis (AMA) and Periotest compared to traditional methods in an ex vivo animal model. Titanium self-tapping screws (STS) and nonself-tapping screws (N-STS) were implanted in the proximal tibia of 12 rabbits. Four testing methods were used to assess screw stability: peak insertion torque (PIT) during implantation, AMA for natural frequency (NF), Periotest for Periotest value (PTV), and pull-out test for peak pullout force (PPF). Euthanization was performed at 0 (primary stability), 4, and 8 weeks (secondary stability). No significant difference in primary stability was found between STS and N-STS except for AMA (STS: NF 2434 ± 67 Hz, N-STS: NF 2572 ± 43 Hz; p = 0.62). Secondary stability increased significantly over time for both screw types (4-week: NF 3687 ± 36 vs. 3408 ± 45 Hz, PTV 1.4 ± 1.6 vs. -1.5 ± 1.8, PPF 236 ± 29 vs. 220 ± 34 N; 8-week: NF 3890 ± 39 vs. 3613 ± 31 Hz, PTV -3.2 ± 2.5 vs. -2 ± 4.3, PPF 248 ± 25 vs. 289 ± 28 N). Higher NF values for given PTV/PPF indicate potential clinical advantages. Significant differences between primary and secondary stabilities suggest osteointegration was mainly achieved in the 4-week group.

Anchorage performance of a new rebar bolt under different surrounding rock strength and borehole depth

The theory and technology of rock bolting are fundamental research topics for strata control in civil and mining engineering. Rebar bolts are commonly used for roadway primary support in underground coal mine. To adapt to deep resource mining, a new left threaded rebar bolt has been developed. Compared to conventional rebar bolts, the result of installation test showed that the new bolt reduced of 41.5% and 57.9% in stirring resistance force and torque, respectively. In laboratory pullout tests, PVC and aluminum sleeves were used to simulate weak and medium strength surrounding rocks. The average peak pullout force, displacement at the peak load and energy absorption increased by 27%, 107% and 108%, respectively, using PVC sleeve; and increased by 113%, 109% and 212%, respectively, using aluminum sleeve. Field tests were conducted under soft coal, hard coal and medium strength rock geo-conditions. Different borehole depths were selected to precisely calculate the average anchorage performance of the new bolt. Results showed that the average peak pullout force of the new bolt increased by 37%, 38% and 28%, respectively, under different surrounding rock conditions. Moreover, based on on-site test results, the pullout curves in field-testing were summarised and classified into 6 different patterns, which were discussed from a viewpoint of causality mechanism. The research findings validate that the newly developed bolt has better anchorage performance compared to conventional rebar bolts, making it a new anchorage material for deep resource mining.

Experiments and simulations for dynamic yarn pull-out response of Kevlar® fabrics

This work presents a novel experimental method for performing dynamic yarn pull-out using a modified tensile split Hopkinson pressure bar. The pull yarn is fixed to a piezoelectric load cell, while the woven fabric specimen is displaced at pull-out velocities ranging from 22 to 32 m/s. Pull-out force, displacement, and energy absorption over time are quantified for commercially available Kevlar® KM2+ woven fabric with pull lengths L = 5 mm and 27 mm in both quasi-static (QS) and dynamic loading. Dynamic peak pull-out force increases over QS by as much as 290–460% and 170–220% for L = 5 mm and L = 27 mm, respectively, and overall energy absorption increases by 140–420% and 40–140% for L = 5 mm and L = 27 mm, respectively. In QS loading, stick–slip interactions result in forces dropping by approximately 70–80% between oscillating peaks for L = 5 mm and 30–40% between peaks for L = 27 mm, and displacements between peaks are typically 1.5 mm, corresponding to two yarn crossings or two spans. However, at dynamic rates, stick–slip stage force drops by 100% after the first and all subsequent peaks due to the dynamic release of the pull yarn from the fabric, resulting in the pull yarn passing through multiple yarn crossings. To better understand the underlying mechanisms for these observations, finite element simulations of the experiments are performed. Strain rate dependent longitudinal shear stiffness of the yarn is found to significantly affect the dynamic yarn pull-out response and explain the enhanced dynamic yarn pull-out peak force and energy absorption. While the shorter yarn of L = 5 mm experiences a more uniform loading along the entire length, non-uniform loading via progressive uncrimping is observed in the longer yarn of L = 27 mm along the length.

Effect of curing stress on the interface property of cement-treated dredged mud and geogrid

The cement-treated dredged mud mixture is suitable for backfill in earthwork projects because of its high water content and flowability. Incorporating geogrid can enhance the mixture’s tensile strength. Constructing with cement-treated mud at greater heights generates curing stress, affecting the interface with geogrid. Pullout tests were performed to analyze the impact of curing stress, water content, and cement content on the interface performance. Results showed similar pullout force-displacement curves regardless of curing stress, indicating strain-softening behavior. Higher water content resulted in decreased pullout forces, while higher cement content led to increased pullout forces. Samples under curing stress exhibited increased peak pullout forces ranging from 2% to 70% compared to samples without curing stress. The rate of increase in pullout force because of curing stress decreased with higher water or cement contents. Curing stress influenced the interface friction angle in specimens with water contents 1.5 and 2 times the liquid limit. It significantly affected the interface cohesion in samples with water contents 2.5 times the liquid limit. Samples subjected to curing stress demonstrated a higher apparent friction coefficient, with an average increase ranging from 4% to 43%, which decreased with higher water content and lower cement content, regardless of curing stress.

Multimodal Locomotion in a Soft Robot Through Hierarchical Actuation.

Soft and continuum robots present the opportunity for extremely large ranges of motion, which can enable dexterous, adaptive, and multimodal locomotion behaviors. However, as the number of degrees of freedom (DOF) of a robot increases, the number of actuators should also increase to achieve the full actuation potential. This presents a dilemma in mobile soft robot design: physical space and power requirements restrict the number and type of actuators available and may ultimately limit the movement capabilities of soft robots with high-DOF appendages. Restrictions on actuation of continuum appendages ultimately may limit the various movement capabilities of soft robots. In this work, we demonstrate multimodal behaviors in an underwater robot called "Hexapus." A hierarchical actuation design for multiappendage soft robots is presented in which a single high-power motor actuates all appendages for locomotion, while smaller low-power motors augment the shape of each appendage. The flexible appendages are designed to be capable of hyperextension for thrust, and flexion for grasping with a peak pullout force of 32 N. For propulsion, we incorporate an elastic membrane connected across the base of each tentacle, which is stretched slowly by the high-power motor and released rapidly through a slip-gear mechanism. Through this actuation arrangement, Hexapus is capable of underwater locomotion with low cost of transport (COT = 1.44 at 16.5 mm/s) while swimming and a variety of multimodal locomotion behaviors, including swimming, turning, grasping, and crawling, which we demonstrate in experiment.

INFLUENCE OF CEMENT CONTENT AND MOISTURE CONTENT ON THE PULLOUT-INTERFACE PROPERTIES OF GEOGRID-SOLIDIFIED WASTE MUD

In engineering, waste mud is often used as a filling material after a solidification treatment. Geogrids, being excellent geotechnical engineering materials, are often used for soil reinforcement. In this work, a pullout test that considered the influence of different waste-mud moisture contents and cement contents was conducted to investigate the interface characteristics of geogrid-solidified waste-mud-reinforced soil. Then, the relationship between the pullout force and displacement, and the variations in the cohesion, friction angle and quasifriction coefficient were analysed. The results showed that the pullout force-displacement curve represented a strain-softening pattern. With the increasing moisture content, the peak pullout force, interfacial cohesion and quasifriction coefficient decreased gradually, but the internal friction angle did not change substantially. With the increasing cement content, the peak pullout force, interfacial cohesion, internal friction angle and quasifriction coefficient increased gradually. The peak pullout force was linearly correlated with the change in the moisture content and logarithmically correlated with the change in the cement content. Compared with the moisture content, the reinforcement-soil interface was more affected by the cement content. This study provides guidelines for the mixture design of reinforced solidified waste mud.

Experimental investigation of the behaviour of injection anchors in rubble stone masonry

The seismic response of historical masonry buildings is largely controlled by the effectiveness of wall-to-diaphragm connections, which can be improved using injection anchors. Despite their use, there is a need for a better understanding of the performance of such anchoring system in stone masonry walls. This paper presents quasi-static pull-out tests performed on twelve specimens to investigate the behaviour of injection anchors in rubble stone masonry walls when breakout failure occurs. For each specimen, the experimental results are presented in terms of force–displacement curves, propagation of damage and crack pattern. It is shown that the anchoring details adopted in this study had a negligible influence on the pull-out force capacity of the anchoring system, while an increase in peak pull-out force was observed with increasing overburden stress applied. Because stone masonry specific capacity formulations have not yet been presented in the literature, the capacity is predicted using state-of-the art formulations for the pull-out load capacity of anchors installed in brick masonry. The limits of their applicability are discussed using the obtained experimental results.

A Novel Pedicle Screw Design with Variable Thread Geometry: Biomechanical Cadaveric Study with Finite Element Analysis.

Pedicle screw fixation provides one of the most stable spinal constructs. Their designs together with osseous characteristics have been known to influence the screw-bone interplay during surgical maneuvers and thereafter the fusion process. Various technical modifications to enhance screw performance have been suggested. This study evaluated the pull-out strength and axial stiffness of a novel pedicle screw design with variable thread geometry and pitch. The newly designed triple threaded pedicle screw is tapered, and has unique out-turned flanges to hold the cancellous bone and a finer pitch at its distal and proximal end to engage the cortical bone. Five lumbar and 4 lower thoracic cadaveric vertebrae were divided into hemivertebrae. A standard cancellous pedicle screw and the newly designed pedicle screw were inserted into each hemivertebra. Axial stiffness and peak pull-out force between the screw types were compared; a finite element analysis was also performed to additionally compare the pull out under toggle forces. In cadaveric study, the axial stiffness of the new screw was significantly better than that of the standard screw. However, the peak load between the screws was not statistically different. Finite element analyses suggested lesser stress at bone-implant interface for the new screw along with better axial stiffness under both co-axial and toggle forces. Our novel pedicle screw design with variable thread geometry demonstrates greater axial stiffness compared with the standard screws, and therefore is likely to withstand a greater surgical manipulation.

How Does Embedding Angle Affect Root–Soil Mechanical Interactions?

Root–soil mechanical interactions are of vital importance in soil reinforcement by plant roots. However, it is unclear how the angles of the roots in the soil affect the root–soil mechanical interactions. To better understand the effect of this factor on root–soil mechanical interactions, pullout tests were conducted on alfalfa (Medicago sativa L.) roots with five root diameter groups (0.10–0.30 mm, 0.31–0.50 mm, 0.51–0.70 mm, 0.71–0.90 mm and 0.91–1.10 mm) and four embedding angles (30°, 45°, 60° and 90°) in sandy loam soil. Root tensile tests were also carried out to understand the process of root failure in the pullout tests. The results showed that the roots had two failure modes, slippage failure and breakage failure. The critical diameter of the two failure modes was 0.35 mm. Peak pullout force and pullout energy were positively related to the root diameter in power functions. Displacement was negatively related to the root diameter and embedding angle in exponential functions. Peak pullout force, root–soil friction coefficient and pullout energy all increased and then decreased with increasing embedding angles. The peak pullout force and root–soil friction coefficient reached their maximum values under an embedding angle of 60°, and pullout energy reached the maximum value under an embedding angle of 45°. Pullout energy was suggested as a preferred index of root–soil mechanical interactions for both thick/fine roots and inclined/upright roots.

Experimental Study on Bond Behavior of Glass Textile Mesh in Earth-Based Matrix.

The bond behavior between the textile and the earth-based matrix determined the reinforcement effectiveness of the composite systems. This paper presented a pull-out experimental study on the glass textile mesh reinforced earth-based matrix. The bond behavior was studied using different development length, mesh spacing size and matrix thickness, with a total of 32 experimental specimens. The test results showed that the peak pull-out force had increased by 31.7% and 40.5% with 200 mm and 300 mm versus 100 mm development length, respectively. The 16 mm compared to 10 mm matrix thickness specimens had a high strength improvement (9.73%) because the elevated thickness had increased the matrix strength. However, the 20 mm versus 10 mm mesh spacing size specimens had achieved a slight reduction (5.72%) due to the reduction in the number of textiles along the weft direction. The failure mode shifted from pulling out, compound modes (both pulling out and textile rupture) to textile rupture mainly accompanied by elevated development length. In addition, we discussed the applicability of the trilinear bond-slip model on the earth-based matrix and proposed a method based on the fracture energy concept for estimating the effective development length, which could provide a reference for future research.

Experimental Investigation of the Influence of Metallic Coatings on Yarn Pull-Out Behavior in Kevlar® Fabrics

This work reports yarn pull-out studies of commercially available Kevlar® KM2+ individual yarns coated with metallic layers (copper, aluminum, aluminum nitride and silver) via a directed vapor deposition process. The uncoated control and metal-coated Kevlar® yarns are hand-woven into fabric swatches for quasi-static pull-out experiments. To perform these experiments, a yarn pull-out fixture is custom-designed and fabricated to apply transverse pre-tension to the fabric. Three levels of transverse pre-tensions are studied at 100 N, 200 N, and 400 N. The results showed that both peak pull-out force and energy absorption during the pull-out process increase with increase in transverse pre-tension. All the metal-coated groups showed an approximately 200% increase in peak pull-out force and a 20% reduction in tenacity compared to uncoated control. Furthermore, all the metal-coated groups showed an increase in energy absorption, with aluminum-coated yarns showing the highest increase of 230% compared to control. These results suggest enhanced frictional interactions during yarn pull-out in metal-coated yarns compared to uncoated control as evidenced by the surface roughness profile of individual fibers and inter-yarn frictional calculations.

Impact resistance and yarn pull-out behaviour of polymer spray-coated UHMWPE fabrics

The impact response of polymer spray-coated Ultra-high Molecular Weight Polyethylene (UHMWPE) plain woven fabrics has been studied. Several commercial spray coatings comprising various polymers and adhesives were used on the UHMWPE fabrics. Yarn pull-out tests revealed that the pull-out force significantly increased upon coating the fabric samples, and for rubber-coated samples the peak pull-out force increased by approximately 95 times that of the neat counterpart. Subsequently, two samples that exhibited the highest pull-out load per unit of areal density were selected for ballistic testing using a 12-mm (7.05 g) spherical steel projectile. Impact velocities of the projectiles were in the range of between 140 m/s and 230 m/s. Each sample consisted of four plies of either coated or neat fabrics. It was observed that rubber-coated samples showed the highest specific energy absorption when subjected to ballistic impact and perforation. The neat fabric targets were perforated purely by a wedge-through mechanism, whereas the coated samples were perforated by a combination of wedge-through and yarn failure mechanisms, with a considerable membrane effect. The enhanced pull-out force promoted the cohesive behaviour of the fabric by diminishing the windowing effect. A novel, highly computationally efficient numerical modelling approach was proposed which predicted the residual velocity, pull-out behaviour and the transverse deformation behaviour with high accuracy.

Pullout properties of Hippophae rhamnoides L. roots in the loess area

ABSTRACT Root pullout properties are significant for strengthening soil and improving slope stability. In order to understand the influence of root morphology and soil properties on pullout properties of plant roots, pullout tests were conducted on Hippophae rhamnoides L. roots. The results showed that with root diameter increasing, displacement at the peak pullout force decreased, peak pullout force and pullout energy increased in power function. With root burial depth increasing, duration of the peak pullout force decreased, displacement at the peak pullout force increased, peak pullout force and pullout energy increased in power function. The displacement at the peak pullout force first decreased and then increased with root burial angle increasing. The peak pullout force first increased and then decreased with soil moisture content increasing. Peak pullout force and pullout energy increased in power function with soil bulk density increasing. Grey correlation analysis showed that root burial depth had the greatest influence on pullout properties, root burial angle had the least influence. The study could improve the understanding of root pullout properties of shrub plants, and serve as a basis for mechanical properties of soil reinforcement by plant roots.

Fabric-to-cementitious matrix bond behavior in carbon fabric reinforced cementitious matrix (FRCM) composites with added short fibers

Fabric reinforced cementitious matrix (FRCM) composites are promising composite materials with useful properties, such as non-toxicity, fire resistance, corrosion resistance, and vapor permeability. However, the brittle failure mode, fabric efficiency, and tensile strength of FRCM composites require further improvement. Accordingly, the addition of short fibers to the matrix is proposed to improve the mechanical properties of FRCM composites, which are highly influenced by the fabric-to-cementitious matrix bond behavior. The objective of this study is to investigate the fabric-to-cementitious matrix bond behavior in carbon FRCM composites with added short fibers and to propose a method to evaluate the bond parameters. In total, 75 pullout specimens were designed to investigate the effects of short fiber type, short fiber volume content, and embedded length on the fabric-to-cementitious matrix bond behavior using double-sided pullout tests. The experimental results were evaluated in terms of the peak pullout force, displacement at peak pullout force, toughness, average bond strength, and initial stiffness. A closed-form solution was presented for the pullout force-displacement relationship based on a trilinear bond-slip model that accounted for the contribution of weft yarn. Furthermore, a method for the analytical extraction of bond parameters was proposed using the main characteristics of the experimental pullout force-displacement responses.

DEM investigation of shear mobilisation during tyre strip pull-out test

This paper presents an evaluation of the pull-out behaviour of tyre strip-reinforced granular soil. The three-dimensional discrete element method (3D DEM) and laboratory testing were used to systematically calibrate the soil particles and the tyre strip based on their stress-strain relationship, tensile stiffness, and interface shear strength. Particle shapes were considered during sand calibration. The scaled pull-out resistance was found to match that of the experimental data. Contributions of the sectional interface shear force to the total pull-out resistance were calculated to explain the progressive failure mechanism mobilised at the tyre-sand interface. The shear force along the tyre strip was not uniformly distributed but higher in the middle portion of the tyre strip. It gradually extended towards the front end of the tyre strip before global interface slipping failure occurred. Comparing the pull-out behaviour of extensible and inextensible tyre strips, the elastic deformation of the tyre strip delayed the occurrence but not the magnitude of peak pull-out force. Micro-mechanical interactions between tyre strip and sand during shear mobilisation were discussed, and induced anisotropy was revealed. The experimental and DEM investigation results in this study provide researchers with an improved understanding of tyre-soil interaction under pull-out loads.

Analytical solution for calculation of pull out force-deformation of geosynthetics reinforcing unsaturated soils

Performing tests on geosynthetic-reinforced soils under pullout conditions gives a comprehensive understanding of soil-geosynthetic interaction. However, they may be expensive and time-consuming. Therefore, the development of theoretical solutions may be beneficial to recognize characteristics of geosynthetic-reinforced soils under pullout conditions. This paper proposes an analytical solution for the determination of pullout force-deformation variation of planar geosynthetics reinforcing unsaturated cohesive-frictional soils. The solution predictions were validated with experimental results, demonstrating the capability of the presented solution. The solution can extend limited results obtained from experiments to a wider range of conditions. It has been demonstrated that under 20 kPa overburden stress, with decreasing the soil suction from 1153 to 312 kPa, corresponding to increasing the moisture content from 16% to 20%, the peak pullout force decreases by about 28%. The results also illustrate that by increasing the value of matric suction, the amount of U* (relative soil-reinforcement displacement corresponding to the total mobilization of friction) decreases.

Effect of Collagen Nerve Wrapping in a Rabbit Peripheral Neuropathy Model.

Background:Collagen nerve wraps (CNWs) theoretically allow for improved nerve gliding and decreased perineural scarring, and create a secluded environment to allow for nerve myelination and axonal healing. The goal of this study was to investigate the effect of CNWs on nerve gliding as assessed by pull-out strength and nerve changes in a rabbit model of peripheral neuropathy.Methods:Ten New Zealand rabbits were included. Sham surgery (control) was performed on left hindlimbs. To simulate compressive neuropathy, right sciatic nerves were freed of the mesoneurium, and the epineurium was sutured to the wound bed. Five rabbits were euthanized at 6 weeks [scarred nerve (SN); n = 5]. Neurolysis with CNW was performed in the remaining rabbits at 6 weeks (CNW; n = 5), which were euthanized at 22 weeks. Outcomes included peak pull-out force and histopathological markers of nerve recovery (axonal and Schwann cell counts).Results:The CNW group demonstrated significantly higher pull-out forces compared with the CNW sham control group (median: 4.40N versus 0.37N, P = 0.043) and a trend toward greater peak pull-out forces compared with the SN group (median: 4.40N versus 2.01N, P = 0.076). The CNW group had a significantly higher median Schwann cell density compared with the CNW control group (CNW: 1.30 × 10−3 cells/μm2 versus CNW control: 7.781 × 10−4 cells/μm2, P = 0.0431) and SN group (CNW: 1.30 × 10−3 cells/μm2 versus SN: 7.31 × 10−4 cells/μm2, P = 0.009). No significant difference in axonal density was observed between groups.Conclusion:Our findings suggest using a CNW does not improve nerve gliding, but may instead play a role in recruiting and/or supporting Schwann cells and their proliferation.

Gluing Living Bone Using a Biomimetic Bioadhesive: From Initial Cut to Final Healing.

Osteoporotic fractures are a growing issue due to the increasing incidence of osteoporosis worldwide. High reoperation rates in osteoporotic fractures call for investigation into new methods in improving fixation of osteoporotic bones. In the present study, the strength of a recently developed bone bioadhesive, OsStictm, was evaluated in vivo using a novel bone core assay in a murine animal model at 0, 3, 7, 14, 28, and 42 days. Histology and micro-CT were obtained at all time points, and the mean peak pull-out force was assessed on days 0–28. The adhesive provided immediate fixation to the bone core. The mean peak bone core pull-out force gradually decreased from 6.09 N (σ 1.77 N) at day 0 to a minimum of 3.09 N (σ 1.08 N) at day 7, recovering to 6.37 N (σ 4.18 N) by day 28. The corresponding fibrin (Tisseel) control mean peak bone core pull-out characteristic was 0.27 N (σ 0.27 N) at day 0, with an abrupt increase from 0.37 N (σ 0.28) at day 3, 6.39 N (σ 5.09 N) at day 7, and continuing to increase to 11.34 N (σ 6.5 N) by day 28. The bone cores failed either through core pull-out or by the cancellous part of the core fracturing. Overall, the adhesive does not interrupt healing with pathological changes or rapid resorption. Initially, the adhesive bonded the bone core to the femur, and over time, the adhesive was replaced by a vascularised bone of equivalent quality and quantity to the original bone. At the 42 day time point, 70% of the adhesive in the cancellous compartment and 50% in the cortical compartment had been replaced. The adhesive outwith the bone shell was metabolized by cells that are only removing the material excess with no ectopic bone formation. It is concluded that the adhesive is not a physical and biochemical barrier as the bone heals through the adhesive and is replaced by a normal bone tissue. This adhesive composition meets many of the clinical unmet needs expressed in the literature, and may, after further preclinical assessments, have potential in the repair of bone and osteochondral fragments.

15. Supplemental fixation of lateral mass screws: a strategy to improve fixation strength

<h3>BACKGROUND CONTEXT</h3> Elderly patients are increasingly meeting the indications for spinal fusion and are more likely to have suboptimal bone quality. Patients with suboptimal bone quality who have undergone posterior cervical fusion have increased risk of fixation failure of up to 5.4% and may require stronger forms of fixation. Adding supplemental fixation to lateral mass screws (LMS) can increase fixation as measured by pullout strength. <h3>PURPOSE</h3> This work addresses the question: can supplemental screw fixation of lateral mass screws improve pullout strength? <h3>STUDY DESIGN/SETTING</h3> Biomechanical cadaveric study. <h3>PATIENT SAMPLE</h3> Fifteen C3-C6 vertebral bodies and 15 additional motion segments (C3-C4 or C5-C6) (age: 49-67). <h3>OUTCOME MEASURES</h3> Lateral mass screw construct peak pullout strength. <h3>METHODS</h3> All specimens were CT scanned with a phantom to obtain bone mineral density (BMD). The individual vertebral bodies and the cranial body of the motion segments were implanted with bilateral lateral mass screws. Supplemental fixation was added on one side of the vertebral body using two 2.4mm diameter unicortical screws (length 8-12mm). One side of the cranial vertebral body of the motion segments was supplemented with a single 2.4mm diameter transfacet tricortical screw (length 12-16mm). Screw constructs were subjected to posterior pullout coincident with the axis of the lateral mass screw at a rate of 5mm/min until failure. <h3>RESULTS</h3> A paired comparison was made of the peak pullout force of the LMS alone and LMS with supplemental fixation. Analysis was also made comparing BMD and pullout force.In the vertebral bodies with two supplemental unicortical screws, pullout force was significantly higher in the supplemented screw side. The average pullout force was 48.2% higher with supplemental screws (865±213N vs 637±206N; p=0.0038). There was moderate correlation between pullout force and bone mineral density for both the supplemented and LMS alone (correlation coefficients of 0.34 and 0.45 respectively). In the motion segments, peak pullout force was significantly higher in the side supplemented with a tricortical transfacet screw. The pullout force was 25.9% higher with supplemental transfacet screw fixation (1055±521N vs 912±508N; p=0.047). The pullout strength of the LMS with transfacet fixation was highly correlated with BMD (correlation coefficient of 0.71) while the LMS pullout strength was moderately correlated with BMD (correlation coefficient of 0.64). <h3>CONCLUSIONS</h3> Our data confirms the hypotheses that the pullout strength of C3-C6 LMS fixation using LMS supplemented with two unicortical screws or LMS supplemented with one-tricortical transfacet screw is superior to LMS fixation alone. <h3>FDA DEVICE/DRUG STATUS</h3> Cervical Fusion System (Approved for this indication)

Replacement of Destructive Pull-out Test with Modal Analysis in Primary Fixation Stability Assessment of Spinal Pedicle Screw.

Pedicle screw fixation devices are the predominant stabilization systems adopted for a wide variety of spinal defects. Accordingly, both pedicle screw design and bone quality are known as the main parameters affecting the fixation strength as measured by the pull-out force and insertion torque. The pull-out test method, which is recommended by the standards of the American Society for Testing and Materials (ASTM), is destructive. A non-destructive test method was proposed to evaluate the mechanical stability of the pedicle screw using modal analysis. Natural frequency (ωn) extracted from the modal analysis was then correlated with peak pull-out force (PPF) and peak insertion torque (PIT). Cylindrical pedicle screws with a conical core were inserted into two different polyurethane (PU) foams with densities of 0.16 and 0.32 g/cm3. The PIT and PPF were measured according to the well-established ASTM-F543 standard at three different insertion depths of 10, 20, and 30 mm. Modal analysis was carried out through recording time response of an accelerometer attached to the head of the screw impacted by a shock hammer. The effect of the insertion depth and foam density on the insertion torque, natural frequency, and pull-out force were quantified. The maximum values of ωn, PIT, and PPT were obtained at 2,186 Hz, 123.75 N.cm, and 981.50 N, respectively, when the screw was inserted into the high-density foam at the depth of 30 mm. The minimum values were estimated at 332 Hz, 16 N.cm, and 127 N, respectively, within the low-density PU at the depth of 10 mm. The higher value of ωn was originated from higher bone screw stability and thus more fixation strength. According to the regression analysis outcomes, the natural frequency (ωn) was linearly dependent on the PIT (ωn=14 PIT) and also on the PPF (ωn=1.7 PPF). Coefficients of variation as the results of the modal analysis were significantly less than those in conventional methods (i.e. pull-out and insertion torque). The modal analysis was found to be a reliable, repeatable, and non-destructive method, which could be considered a prospective alternative to the destructive pull-out test that is limited to the in-vitro application only. The modal analysis could be applied to assess the stability of implantable screws, such as orthopedic and spinal screws.