Article Figures & Data
Figures
- Figure 1
Image of the FFX device (Courtesy of SC MEDICA).
- Figure 2
X-ray image showing bilateral placement of the FFX device in the L4-L5 facet joint, lateral view.
- Figure 3
Finite element model of the lumbar spine (L1-S1) used for the present study. (A) Lateral view. (B) Disc alone. (C) Posterior view.
- Figure 4
Comparison of current model vs model reported by Guan et al.19
- Figure 6
Comparison of current model vs ex vivo (cadaveric) and finite element (FE) models reported by Renner et al.21
- Figure 5
Comparison of current model vs model reported by Dreischarf et al.20
- Figure 7
Location of assessments used for comparative studies using finite element model of lumbar spine. (A) Range of motion (ROM; overall and segmental). (B) Facet joint stress. (C) Disc stress.
- Figure 8
Stress pattern before laminectomy in (A) frontal and (B) sagittal views and after laminectomy in (C) frontal and (D) sagittal views. The force direction (arrows) is perpendicular to the stress gradient. The force applied on the facet joints changes following laminectomy from anteroposterior (A) in the healthy spine to mediolateral (D) in the laminectomized spine with a net result of an inward movement of the facets.
- Figure 9
Stress mapping comparing (A) a healthy spine, (B) laminectomy (LAM), and (C) LAM plus bilateral placement of FFX devices prior to fusion.
Tables
Anatomical Structure Young’s Modulus (MPa)20,21 Lateral Young’s Modulus (MPa)21 Poisson’s Ratio20,21 Axial Spring Stiffness Nm/° Disc 3–15 1–3 0.3 10–30 Cortical bone endplate 11,000 - 0.3 - Cancellous bone 110 - 0.3 - Model Description Load for iso-Range of Motiona (Nm) Healthy Healthy intact spine 4 LAM Laminectomy only 4 LAM + FFX (U) Laminectomy plus bilateral FFX devices (unfused) 5.5 LAM + FFX (F) Laminectomy plus bilateral FFX devices (fused) 6.1 LAM + PS (U) Laminectomy plus pedicle screws and rods (unfused) 6.1 LAM + PS (F) Laminectomy plus pedicle screws and rods (fused) 6.3 Abbreviations: F, fused; FFX, FFX device;LAM, laminectomy; PS, pedicle screw system; U, unfused.
↵a Loads modeled for sagittal extension only.
Spine Segments AP Coordinate No Load AP Coordinate at 4 Nm Load Load to No Load Distance Displacement Variation vs Healthy Displacement Variation vs LAM Healthy 15.99 15.84 0.15 - - LAM 15.99 15.79 0.20 33.3% - LAM + FFX (U) 15.99 15.94 0.05 −66.7% −75% LAM + FFX (F) 15.99 15.95 0.04 −73.3% −80% LAM + PS (U) 15.99 15.99 0 −100% −100% LAM + PS (F) 15.99 15.99 0 −100% −100% Abbreviations: AP, anteroposterior; F, fused; LAM, laminectomy; PS, pedicle screw system; U, unfused.
Note: Significance threshold = 4.4%.
↵a Loads modeled for sagittal extension only.
Spine Segments Healthy LAM LAM + FFX (Unfused) LAM + Pedicle Screw System (Unfused) L1-L2 1.76 1.75 1.81 1.90 L2-L3 1.70 1.70 1.77 1.84 L3-L4 1.71 1.70 1.78 1.85 L4-L5 1.40 1.38 0.90 0.4 L5-S1 3.84 3.80 4.14 4.46 Total all segments 10.41 10.33 10.40 10.45 Difference vs healthy spinea 0.00% −0.77% −0.10% 0.38% Abbreviations: LAM, laminectomy; ROM, range of motion.
↵a Overall ROM was controlled to be ±0.8% for all scenarios prior to assessing the other endpoints.
Spine Segments Healthy LAM LAM + FFX (Unfused) LAM + FFX (Fused) LAM + PS (Unfused) LAM + PS (Fused) L2-L3 3.40 3.40 5.81 6.75 6.00 6.93 L3-L4 3.30 3.20 6.52 7.63 7.40 7.83 L4-L5 3.40 3.60 6.28 11.07 0.00 0.00 L5-S1 1.52 1.70 2.68 3.07 3.10 3.16 Abbreviations: LAM, laminectomy; PS, pedicle screw system.
Spine Segments Healthy LAM LAM + FFX (Unfused) LAM + FFX (Fused) LAM + PS (Unfused) LAM + PS (Fused) L2-L3 0.45 0.45 0.53 0.55 0.55 0.56 L3-L4 0.35 0.35 0.40 0.42 0.41 0.42 L4-L5 0.16 0.15 0.14 0.03 0.08 0.04 L5-S1 0.32 0.32 0.39 0.41 0.42 0.42
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