Effect of Potting Technique on the Measurement of Six Degree-of-Freedom Viscoelastic Properties of Human Lumbar Spine Segments

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Dhara B. Amin ◽  
Isaac M. Lawless ◽  
Dana Sommerfeld ◽  
Richard M. Stanley ◽  
Boyin Ding ◽  
...  
Keyword(s):  
Phase Angle ◽  
Viscoelastic Properties ◽  
Biomechanical Testing ◽  
Axial Rotation ◽  
Intervertebral Discs ◽  
Degree Of Freedom ◽  
Potting Medium ◽  
Significant Difference ◽  
Flexion Extension ◽  
Six Degree Of Freedom

Polymethyl methacrylate (PMMA) and Wood's Metal are fixation media for biomechanical testing; however, the effect of each potting medium on the measured six degree-of-freedom (DOF) mechanical properties of human lumbar intervertebral discs is unknown. The first aim of this study was to compare the measured 6DOF elastic and viscoelastic properties of the disc when embedded in PMMA compared to repotting in Wood's Metal. The second aim was to compare the surface temperature of the disc when potted with PMMA and Wood's Metal. Six human lumbar functional spinal units (FSUs) were first potted in PMMA, and subjected to overnight preload in a saline bath at 37 °C followed by five haversine loading cycles at 0.1 Hz in each of 6DOF loading directions (compression, left/right lateral bending, flexion, extension, left/right axial rotation, anterior/posterior, and lateral shear). Each specimen was then repotted in Wood's Metal and subjected to a 2-h re-equilibrating preload followed by repeating the same 6DOF tests. Outcome measures of stiffness and phase angle were calculated from the final loading cycle in each DOF and were expressed as normalized percentages relative to PMMA (100%). Disc surface temperatures (anterior, left/right lateral) were measured during potting. Paired t-tests (with alpha adjusted for multiple DOF) were conducted to compare the differences in each outcome parameter between PMMA and Wood's Metal. No significant differences in stiffness or phase angle were found between PMMA and Wood's Metal. On average, the largest trending differences were found in the shear DOFs for both stiffness (approximately 35% greater for Wood's Metal compared to PMMA) and phase angle (approximately 15% greater for Wood's Metal). A significant difference in disc temperature was found at the anterior surface after potting with Wood's Metal compared to PMMA, which did not exceed 26 °C. Wood's Metal is linear elastic, stiffer than PMMA and may reduce measurement artifact of potting medium, particularly in the shear directions. Furthermore, it is easier to remove than PMMA, reuseable, and cost effective.

scholarly journals Range of Motion Testing of a Novel 3D-Printed Synthetic Spine Model

2019 ◽  
Vol 10 (4) ◽  
pp. 419-424
Author(s):  
Michael A. Bohl ◽  
Sarah McBryan ◽  
Anna G. U. S. Newcomb ◽  
Jennifer N. Lehrman ◽  
Brian P. Kelly ◽  
...  
Keyword(s):  
Range Of Motion ◽  
Axial Compression ◽  
Biomechanical Testing ◽  
Model Performance ◽  
Biomechanical Model ◽  
Axial Rotation ◽  
Intervertebral Discs ◽  
Model Parameters ◽  
Flexion Extension ◽  
Spine Model

Study Design: Biomechanical model study. Objective: The Barrow Biomimetic Spine (BBS) project is a resident-driven effort to manufacture a synthetic spine model with high biomechanical fidelity to human tissue. The purpose of this study was to investigate the performance of the current generation of BBS models on biomechanical testing of range of motion (ROM) and axial compression and to compare the performance of these models to historical cadaveric data acquired using the same testing protocol. Methods: Six synthetic spine models comprising L3-5 segments were manufactured with variable soft-tissue densities and print orientations. Models underwent torque loading to a maximum of 7.5 N m. Torques were applied to the models in flexion-extension, lateral bending, axial rotation, and axial compression. Results were compared with historic cadaveric control data. Results: Each model demonstrated steadily decreasing ROM on flexion-extension testing with increasing density of the intervertebral discs and surrounding ligamentous structures. Vertically printed models demonstrated markedly less ROM than equivalent models printed horizontally at both L3-4 (5.0° vs 14.0°) and L4-5 (3.9° vs 15.2°). Models D and E demonstrated ROM values that bracketed the cadaveric controls at equivalent torque loads (7.5 N m). Conclusions: This study identified relevant variables that affect synthetic spine model ROM and compressibility, confirmed that the models perform predictably with changes in these print variables, and identified a set of model parameters that result in a synthetic model with overall ROM that approximates that of a cadaveric model. Future studies can be undertaken to refine model performance and determine intermodel variability.

A biomechanical comparison of three anterior thoracolumbar implants after corpectomy: are two screws better than one?

2006 ◽  
Vol 4 (3) ◽  
pp. 213-218 ◽  
Author(s):  
Dean Chou ◽  
Adolfo Espinoza Larios ◽  
Robert H. Chamberlain ◽  
Mary S. Fifield ◽  
Roger Hartl ◽  
...  
Keyword(s):  
Biomechanical Testing ◽  
Three Dimensional ◽  
Axial Rotation ◽  
Single Screw ◽  
Flexion Extension ◽  
Rod System ◽  
Mesh Cage ◽  
Left And Right ◽  
Plate System ◽  
Better Than

Object A flexibility experiment using human cadaveric thoracic spine specimens was performed to determine biomechanical differences among thoracolumbar two-screw plate, single-screw plate, and dual-rod systems. A secondary goal was to investigate differences in the ability of the systems to stabilize the spine after a one- or two-level corpectomy. Methods The authors evaluated 21 cadaveric spines implanted with a titanium mesh cage and three types of anterior thoracolumbar supplementary instrumentation after one-level thoracic corpectomies. Pure moments were applied quasistatically while three-dimensional motion was measured optoelectronically. The lax zone, stiff zone, and range of motion (ROM) were measured during flexion, extension, left and right lateral bending, and left and right axial rotation. Corpectomies were expanded to two levels, and testing was repeated with longer hardware. Biomechanical testing showed that the single-bolt plate system was no different from the dual-rod system with two screws in limiting ROM. The single-bolt plate system performed slightly better than the two-screw plate system. Across the same two levels, there was an average of 19% more motion after a two-level corpectomy than after a one-level corpectomy. In general, however, the difference across the different loading modes was insignificant. Conclusions Biomechanically, the single-screw plate system is equivalent to a two-screw dual-rod and a two-screw plate system. All three systems performed similarly in stabilizing the spine after one- or two-level corpectomies.

Biomechanical Assessment of a PEEK Rod System for Semi-Rigid Fixation of Lumbar Fusion Constructs

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Matthew F. Gornet ◽  
Frank W. Chan ◽  
John C. Coleman ◽  
Brian Murrell ◽  
Russ P. Nockels ◽  
...  
Keyword(s):  
Lumbar Fusion ◽  
Dynamic Performance ◽  
Load Sharing ◽  
Axial Rotation ◽  
Rigid Fixation ◽  
Peek Rods ◽  
Significant Difference ◽  
Flexion Extension ◽  
Rod System

The concept of semi-rigid fixation (SRF) has driven the development of spinal implants that utilize nonmetallic materials and novel rod geometries in an effort to promote fusion via a balance of stability, intra- and inter-level load sharing, and durability. The purpose of this study was to characterize the mechanical and biomechanical properties of a pedicle screw-based polyetheretherketone (PEEK) SRF system for the lumbar spine to compare its kinematic, structural, and durability performance profile against that of traditional lumbar fusion systems. Performance of the SRF system was characterized using a validated spectrum of experimental, computational, and in vitro testing. Finite element models were first used to optimize the size and shape of the polymeric rods and bound their performance parameters. Subsequently, benchtop tests determined the static and dynamic performance threshold of PEEK rods in relevant loading modes (flexion-extension (F/E), axial rotation (AR), and lateral bending (LB)). Numerical analyses evaluated the amount of anteroposterior column load sharing provided by both metallic and PEEK rods. Finally, a cadaveric spine simulator was used to determine the level of stability that PEEK rods provide. Under physiological loading conditions, a 6.35 mm nominal diameter oval PEEK rod construct unloads the bone-screw interface and increases anterior column load (approx. 75% anterior, 25% posterior) when compared to titanium (Ti) rod constructs. The PEEK construct’s stiffness demonstrated a value lower than that of all the metallic rod systems, regardless of diameter or metallic composition (78% < 5.5 mm Ti; 66% < 4.5 mm Ti; 38% < 3.6 mm Ti). The endurance limit of the PEEK construct was comparable to that of clinically successful metallic rod systems (135N at 5 × 106 cycles). Compared to the intact state, cadaveric spines implanted with PEEK constructs demonstrated a significant reduction of range of motion in all three loading directions (> 80% reduction in F/E, p < 0.001; > 70% reduction in LB, p < 0.001; > 54% reduction in AR, p < 0.001). There was no statistically significant difference in the stability provided by the PEEK rods and titanium rods in any mode (p = 0.769 for F/E; p = 0.085 for LB; p = 0.633 for AR). The CD HORIZON® LEGACY™ PEEK Rod System provided intervertebral stability comparable to currently marketed titanium lumbar fusion constructs. PEEK rods also more closely approximated the physiologic anteroposterior column load sharing compared to results with titanium rods. The durability, stability, strength, and biomechanical profile of PEEK rods were demonstrated and the potential advantages of SRF were highlighted.

In vitro evaluation of a lateral expandable cage and its comparison with a static device for lumbar interbody fusion: a biomechanical investigation

2014 ◽  
Vol 20 (4) ◽  
pp. 387-395 ◽  
Author(s):  
Sabrina A. Gonzalez-Blohm ◽  
James J. Doulgeris ◽  
Kamran Aghayev ◽  
William E. Lee ◽  
Jake Laun ◽  
...  
Keyword(s):  
Pedicle Screw ◽  
Haptic Feedback ◽  
Biomechanical Testing ◽  
Axial Rotation ◽  
Pedicle Screw Fixation ◽  
Interbody Cage ◽  
Disc Space ◽  
Significance Level ◽  
Flexion Extension

Object Through in vitro biomechanical testing, the authors compared the performance of a vertically expandable lateral lumbar interbody cage (EC) under two different torque-controlled expansions (1.5 and 3.0 Nm) and with respect to an equivalent lateral lumbar static cage (SC) with and without pedicle screw fixation. Methods Eleven cadaveric human L2–3 segments were evaluated under the following conditions: 1) intact; 2) discectomy; 3) EC under 1.50 Nm of torque expansion (EC-1.5Nm); 4) EC under 3.00 Nm of torque expansion (EC-3.0Nm); 5) SC; and 6) SC with a bilateral pedicle screw system (SC+BPSS). Load-displacement behavior was evaluated for each condition using a combination of 100 N of axial preload and 7.5 Nm of torque in flexion and extension (FE), lateral bending (LB), and axial rotation (AR). Range of motion (ROM), neutral zone stiffness (NZS), and elastic zone stiffness (EZS) were statistically compared among conditions using post hoc Wilcoxon signed-rank comparisons after Friedman tests, with a significance level of 0.05. Additionally, any cage height difference between interbody devices was evaluated. When radiographic subsidence was observed, the specimen's data were not considered for the analysis. Results The final cage height in the EC-1.5Nm condition (12.1 ± 0.9 mm) was smaller (p < 0.001) than that in the EC-3.0Nm (13.9 ± 1.1 mm) and SC (13.4 ± 0.8 mm) conditions. All instrumentation reduced (p < 0.01) ROM with respect to the injury and increased (p ≤ 0.01) NZS in flexion, extension, and LB as well as EZS in flexion, LB, and AR. When comparing the torque expansions, the EC-3.0Nm condition had smaller (p < 0.01) FE and AR ROM and greater (p ≤ 0.04) flexion NZS, extension EZS, and AR EZS. The SC condition performed equivalently (p ≥ 0.10) to both EC conditions in terms of ROM, NZS, and EZS, except for EZS in AR, in which a marginal (p = 0.05) difference was observed with respect to the EC-3.0Nm condition. The SC+BPSS was the most rigid construct in terms of ROM and stiffness, except for 1) LB ROM, in which it was comparable (p = 0.08) with that of the EC-1.5Nm condition; 2) AR NZS, in which it was comparable (p > 0.66, Friedman test) with that of all other constructs; and 3) AR EZS, in which it was comparable with that of the EC-1.5Nm (p = 0.56) and SC (p = 0.08) conditions. Conclusions A 3.0-Nm torque expansion of a lateral interbody cage provides greater immediate stability in FE and AR than a 1.5-Nm torque expansion. Moreover, the expandable device provides stability comparable with that of an equivalent (in size, shape, and bone-interface material) SC. Specifically, the SC+BPSS construct was the most stable in FE motion. Even though an EC may seem a better option given the minimal tissue disruption during its implantation, there may be a greater chance of endplate collapse by over-distracting the disc space because of the minimal haptic feedback from the expansion.

scholarly journals Biomechanical Analysis of Cortical Bone Trajectory Screw Versus Bone Cement Screw For Fixation In Porcine Spinal Low Bone Mass Model

2021 ◽  
Author(s):  
Yifan Li ◽  
Wei Xu ◽  
Silian Wang ◽  
Liwei Chen ◽  
Zhangpeng Shi ◽  
...  
Keyword(s):  
Bone Mass ◽  
Bone Cement ◽  
Cortical Bone ◽  
Axial Rotation ◽  
Low Bone Mass ◽  
Mass Model ◽  
Pull Out ◽  
Significant Difference ◽  
Flexion Extension ◽  
Insertional Torque

Abstract Purpose: To compare the biomechanics of cortical bone trajectory screw(CBT) and bone cement screw(BC) in isolated porcine spinal low bone mass model.Method: Ten porcine spines with 3 segments were treated with EDTA decalcification. After 8 weeks, all the models met the criteria of low bone mass. Ten specimens were randomly divided into two groups, one group was implanted with CBT screw(CBT group) and the other group was implanted with bone cement screw(BC group).The biomechanical material testing machine was used to compare the porcine spine activities of the two groups in flexion, extension, bending and axial rotation, and then insertional torque, pull-out force and anti-compression force of two groups were compared. Independent-sample t test was used for comparison between groups.Result: Ten 3 segments porcine spine models with low bone mass were established, the bone mineral density of all models was lower than 0.75g/cm2. The flexion, extension, bending and axial rotation angle of CBT group and BC group respectively were 7.1±1.3°,4.3±0.8°,3.4±0.8°,6.8±0.7°and 6.4±0.8°, 4.5±0.5°, 3.5±0.5°, 6.8±0.8°, there was no significant difference between the two groups,P＞0.05.However, there were significant differences between the two groups and the control group,P＜0.01.The insertional torque of the CBT group and BC group respectively were 0.43±0.09N-m and 0.30±0.07N-m (P=0.03), and the screw pull-out force were 462.67±72.51N and 325.60±77.27N (P=0.021), respectively. There were significant differences between the two groups. The anti-compression forces between the two groups were 3561.81±522.7N and 3586.80±607.42N, respectively, and there was no significant difference between the two groups (P =0.946).Conclusion: The insertional torque and pull-out force of the CBT were higher than those of the BC in the isolated low bone porcine spine model, and the range of motion and anti-compression ability of model were similar between the two fixation methods.

In Vitro Biomechanical Comparison of Four Different Ventral Surgical Procedures on the Canine Fourth-Fifth Cervical Vertebral Motion Unit

2018 ◽  
Vol 31 (06) ◽  
pp. 413-421
Author(s):  
Benjamin Voumard ◽  
Maja Waschk ◽  
Bianca Hettlich ◽  
Franck Forterre ◽  
Andreas Hermann
Keyword(s):  
Surgical Procedures ◽  
Vertebral Column ◽  
Axial Rotation ◽  
Biomechanical Properties ◽  
Inverted Cone ◽  
Ct Examination ◽  
Significant Difference ◽  
Flexion Extension ◽  
Motion Unit

Introduction Biomechanical properties of four different ventral surgical procedures at the canine fourth-fifth cervical (C4–C5) vertebral motion unit (VMU) were assessed and compared with the intact C4–C5 VMU. Materials and Methods The third-sixth cervical vertebral column from 24 skeletally mature Beagle cadavers were randomly allocated to four groups (standard ventral slot, slanted slot, inverted cone slot and intervertebral disc fenestration). Standardized tests were performed for each specimen in flexion/extension, lateral bending and axial rotation. The specimens were tested intact and after completion of one of the three slots techniques or fenestration. Pre-testing, cadaver specimens were confirmed to be free of disease by computed tomography (CT) examination. Post-testing, dimensions of slots and fenestration were determined based on a second CT examination. Results All ventral surgical procedures increased range of motion (ROM) at the C4–C5 VMU compared with intact specimens. The only significant difference in the increase in ROM was observed between slanted slot and fenestration in flexion/extension. The standard ventral slot had a significant higher increase in ROM in extension compared with the other three techniques. The slanted slot had a significant lower increase in ROM in flexion. Discussion/Conclusion The described ventral slot techniques have similar biomechanical effects on the canine cervical vertebral column. In contrast to the findings of a previous study, the slanted slot and inverted cone slot do not appear to provide a biomechanical benefit compared with standard ventral slot.

scholarly journals Biomechanical Comparison of Vertebroplasty, Kyphoplasty, Vertebrae Stent for Osteoporotic Vertebral Compression Fractures—A Finite Element Analysis

2021 ◽  
Vol 11 (13) ◽  
pp. 5764
Author(s):  
Jen-Chung Liao ◽  
Michael Jian-Wen Chen ◽  
Tung-Yi Lin ◽  
Weng-Pin Chen
Keyword(s):  
Finite Element ◽  
Axial Rotation ◽  
Vertebral Compression Fractures ◽  
Lateral Bending ◽  
Compression Fractures ◽  
Significant Difference ◽  
Flexion Extension ◽  
Von Mises ◽  
Von Mises Stresses ◽  
Osteoporotic Compression Fractures

Vertebroplasty (VP), balloon kyphoplasty (BKP), and vertebral stent (VS) are usually used for treating osteoporotic compression fractures. However, these procedures may pose risks of secondary adjacent level fractures. This study simulates finite element models of osteoporotic compression fractures treated with VP, BKP, and VS Vertebral resection method was used to simulate vertebra fracture with Young’s modulus set at 70 MPa to replicate osteoporosis. A follower load of (1175 N for flexion, and 500 N for all others) was applied in between vertebral bodies to simulate the muscle force. Moment loadings of 7.5 N-m in flexion, extension, lateral bending, axial rotation were applied respectively. The VS model had the highest von Mises stresses on the bone cement under all different loading conditions (flexion/5.91 MPa; extension/3.74 MPa; lateral bending/3.12 MPa; axial rotation/3.54 MPa). The stress distribution and maximum von Mises stresses of the adjacent segments, T11 inferior endplate and L1 superior endplate, showed no significant difference among three surgical models. The postoperative T12 stiffness for VP, BKP, and VS are 2898.48 N/mm, 4123.18 N/mm, and 4690.34 N/mm, respectively. The VS model led to superior surgical vertebra stiffness without significantly increasing the risks of adjacent fracture.

Restabilization of the Occipitocervical Junction After a Complete Unilateral Condylectomy: A Biomechanical Comparison of Unilateral and Bilateral Fixation Techniques

2019 ◽  
Vol 19 (2) ◽  
pp. 157-164 ◽  
Author(s):  
Ilyas M Eli ◽  
Michael Karsy ◽  
Darrel S Brodke ◽  
Kent N Bachus ◽  
William T Couldwell ◽  
...  
Keyword(s):  
Biomechanical Testing ◽  
Axial Rotation ◽  
Neurological Injury ◽  
Occipital Condyle ◽  
Posterior Fixation ◽  
Lateral Bending ◽  
Flexion Extension ◽  
Fixation Techniques ◽  
The Difference ◽  
Biomechanical Comparison

Abstract BACKGROUND Occipitocervical instability may result from transcondylar resection of the occipital condyle. Initially, patients may be able to maintain a neutral alignment but severe occipitoatlantal subluxation may subsequently occur, with cranial settling, spinal cord kinking, and neurological injury. OBJECTIVE To evaluate the ability of posterior fixation constructs to prevent progression to severe deformity after radical unilateral condylectomy. METHODS Eight human cadaveric specimens (Oc-C2) underwent biomechanical testing to compare stiffness under physiological loads (1.5 N m). A complete unilateral condylectomy was performed to destabilize one Oc-C1 joint, and the contralateral joint was left intact. Unilateral Oc-C1 or Oc-C2 constructs on the resected side and bilateral Oc-C1 or Oc-C2 constructs were tested. RESULTS The bilateral Oc-C2 construct provided the greatest stiffness, but the difference was only statistically significant in certain planes of motion. The unilateral constructs had similar stiffness in lateral bending, but the unilateral Oc-C1 construct was less stiff in axial rotation and flexion-extension than the unilateral Oc-C2 construct. The bilateral Oc-C2 construct was stiffer than the unilateral Oc-C2 construct in axial rotation and lateral bending, but there was no difference between these constructs in flexion-extension. CONCLUSION Patients who undergo a complete unilateral condylectomy require close surveillance for occipitocervical instability. A bilateral Oc-C2 construct provides suitable biomechanical strength, which is superior to other constructs. A unilateral construct decreases abnormal motion but lacks the stiffness of a bilateral construct. However, given that most patients undergo a partial condylectomy and only a small proportion of patients develop instability, there may be scenarios in which a unilateral construct may be appropriate, such as for temporary internal stabilization.

scholarly journals Unilateral C-1 posterior arch screws and C-2 laminar screws combined with a 1-side C1–2 pedicle screw system as salvage fixation for atlantoaxial instability

2016 ◽  
Vol 24 (2) ◽  
pp. 315-320 ◽  
Author(s):  
Jin Guo-Xin ◽  
Wang Huan
Keyword(s):  
Biomechanical Testing ◽  
Pedicle Screws ◽  
Atlantoaxial Instability ◽  
Posterior Arch ◽  
Lateral Bending ◽  
Significant Difference ◽  
Flexion Extension ◽  
Intact Condition ◽  
Atlantoaxial Fixation ◽  
Group B

OBJECT Atlantoaxial instability often requires surgery, and the current methods for fixation pose some risk to vascular and neurological tissues. Thus, new effective and safer methods are needed for salvage operations. This study sought to assess unilateral C-1 posterior arch screws (PASs) and C-2 laminar screws (LSs) combined with 1-side C1–2 pedicle screws (PSs) for posterior C1–2 fixation using biomechanical testing with bilateral C1–2 PSs in a cadaveric model. METHODS Six fresh ligamentous human cervical spines were evaluated for their biomechanics. The cadaveric specimens were tested in their intact condition, stabilization after injury, and after injury at 1.5 Nm of pure moment in 6 directions. The 3 groups tested were bilateral C1–2 PSs (Group A); left side C1–2 PSs with an ipsilateral C-1 PAS + C-2 laminar screw (Group B); and left side C1–2 PSs with a contralateral C-1 PAS + C-2 LS (Group C). During the testing, angular motion was measured using a motion capture platform. Data were recorded, and statistical analyses were performed. RESULTS Biomechanical testing showed that there was no significant difference among the stabilities of these fixation systems in flexion-extension and rotation control. In left lateral bending, the bilateral C1–2 PS group decreased flexibility by 71.9% compared with the intact condition, the unilateral C1–2 PS and ipsilateral PAS+LS group decreased flexibility by 77.6%, and the unilateral C1–2 PS and contralateral PAS+LS group by 70.0%. Each method significantly decreased C1–2 movements in right lateral bending compared with the intact condition, and the bilateral C1–2 PS system was more stable than the C1–2 PS and contralateral PAS+LS system (p = 0.036). CONCLUSIONS A unilateral C-1 PAS + C-2 LS combined with 1-side C-1 PSs provided the same acute stability as the PS, and no statistically significant difference in acute stability was found between the 2 screw techniques. These methods may constitute an alternative method for posterior atlantoaxial fixation.

Validation of a six degree-of-freedom robotic system for hip in vitro biomechanical testing

2015 ◽  
Vol 48 (15) ◽  
pp. 4093-4100 ◽  
Author(s):  
Mary T. Goldsmith ◽  
Matthew T. Rasmussen ◽  
Travis Lee Turnbull ◽  
Christiano A.C. Trindade ◽  
Robert F. LaPrade ◽  
...  
Keyword(s):  
Biomechanical Testing ◽  
Robotic System ◽  
Degree Of Freedom ◽  
Six Degree Of Freedom
Sign in / Sign up

Export Citation Format

Share Document