Needle puncture in rabbit functional spinal units alters rotational biomechanics

Immuno-stimulatory capacity of decorin in the rat tail intervertebral disc and the mechanical consequence of resultant inflammation

PURPOSE

Determine whether decorin is immuno-stimulatory to rat tail IVD cells and to characterize the mechanical consequence of inflammation at the whole rat tail IVD level.

METHODS

Cultured rat tail annulus fibrosus (AF) cells were exposed to decorin, a resident IVD small leucine-rich proteoglycan (SLRP), with and without the presence of a toll-like receptor (TLR) 4 inhibitor, TAK-242. Resultant expression of pro-inflammatory cytokine and chemokines (MCP-1; MIP-2; RANTES; IL-6; TNFα) were quantified over 24 h. Whole rat tail IVD cultures (n = 50) were also treated with decorin (two concentrations: 0.5 and 5.0 μg/mL) with and without TAK-242 (via nucleus pulpous injection with a 33-gauge needle), and resultant mechanical properties were measured.

RESULTS

AF cells exposed to decorin showed significant increases in pro-inflammatory cytokine and chemokine production; this was significantly blunted with the presence of TAK-242. Whole IVDs injected with decorin showed a dose-dependent decrease in neutral zone and tensile stiffness and an increase in neutral zone size. When TAK-242 was injected into the IVD with the decorin, mechanical stiffness was preserved and not different from sham controls (injected with PBS).

CONCLUSION

AF cells are capable of detecting decorin and inducing inflammation. Decorin further resulted in a functional deterioration in IVD mechanical integrity. TAK- 242, a TLR4 inhibitor, blunted chemokine production at the cellular level and preserved mechanical stiffness in the whole IVD.

Biomechanical test protocols to detect minor injury effects in intervertebral discs

Intervertebral discs (IVDs) maintain flexibility of the spine and bear mechanical load. Annulus fibrosus (AF) defects are associated with IVD degeneration and herniation which disrupt biomechanical function and can cause pain. AF puncture injuries can induce IVD degeneration but are needed to inject therapies. Identifying small AF defects with biomechanical testing can be difficult because IVDs have a complex, composite structure and nonlinear biomechanical properties that are dependent on AF fiber tension. It remains unclear how choice of biomechanical testing protocols affect the sensitivity of biomechanical properties to AF injuries. This study determined whether axial preload or magnitude of cyclic axial or torsional testing affected the ability to detect minor AF defects in rat caudal motion segments using ex vivo biomechanical testing. Intact and injured motion segments were subjected to a repeated measures study design with multiple biomechanical testing protocols that varied axial tension-compression force amplitude (±1.6 N, ±8.0 N, ±16.0 N), axial preload (-1.6 N, -8.0 N, -16.0 N, corresponding to -0.1 MPa, -0.5 MPa, and -1.0 MPa, respectively), and torsional rotation angle (±10°, ±15°, and ±20°). Biomechanical properties obtained from the lowest force testing conditions for axial tension-compression (±1.6 N), axial preload (-1.6 N), and angular rotation (±10°) exhibited the largest differences in biomechanical properties between intact and injured conditions. Biomechanical properties determined under low axial force or torsion amplitudes involve less AF fiber tension and were most sensitive to injury. Low force testing protocols are recommended for detecting minor structural AF defects and may enable more precise assessments of IVD injuries, healing or repair.

Novel use of telescoping growth rods in treatment of early onset scoliosis: An in vivo and in vitro study in a porcine model

INTRODUCTION

Treatment of early-onset scoliosis (EOS) can be difficult. Various forms of growing rods exist to correct deformity while delaying definitive spinal fusion. The disadvantage of traditional growing rods is need for repeated surgical lengthening procedures. Telescoping growth rods (TelGR) are a prototype new, guided growth technology with a rod mechanism that allows spontaneous longitudinal growth over time without manual lengthening. We hypothesized that the TelGR system will permit unrestricted growth with limited complications through 12 weeks in vivo, and that the range of motion (RoM) in each of three directions and stiffness of the TelGR system would not be significantly different than the rigid rod system in vitro.

MATERIALS AND METHODS

In vivo: Six immature pigs were surgically implanted with TelGR with cephalad fixation at T6-7 and caudal fixation at T14-L1. Radiographs of the involved vertebral segments were measured postoperatively and after 12 weeks. In vitro: A robotic testing system was utilized for flexibility tests in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) of eight immature porcine specimens (T3-T15). Testing was performed on both dual rigid rods and bilateral TelGR with instrumentation at T4-5 and T13-14.

RESULTS

In vivo: Over the 12-week period, the rod length of the TelGR increased an average of 65 mm. In vitro: TelGR demonstrated significantly increased motion in LB and AR RoM compared with rigid rods. No difference was noted in FE RoM.

DISCUSSION

The in vivo results in this study showed expected skeletal growth with spines instrumented with TelGR. In vitro findings of increased RoM in AR and LB suggest that the TelGR system may be less rigid than traditional growing rods. Treatment with TelGR might, if proven efficacious in the clinical setting, decrease the need for repeated surgical intervention compared with traditional growing rods. This study adds to the limited body of biomechanical evidence examining guided growth technology.

Biomechanical Evaluation of Transpedicular Nucleotomy With Intact Annulus Fibrosus

STUDY DESIGN

Biomechanical testing of partially nucleotomized ovine cadaveric spines.

OBJECTIVE

To explore how the nucleus pulposus (NP) affects the biomechanical behavior of the intervertebral disc (IVD) by performing a partial nucleotomy via the transpedicular approach.

SUMMARY OF BACKGROUND DATA

Mechanical loading represents a crucial part of IVD homeostasis. However, traditional regenerative strategies require violation of the annulus fibrosus (AF) resulting in significant alteration of joint mechanics. The transpedicular nucleotomy represents a suitable method to create a cavity into the NP, as a model to study IVD regeneration with intact AF.

METHODS

A total of 30 ovine-lumbar- functional spinal units (FSUs) (L1-L6) randomly assigned to 5 groups: control; transpedicular tunnel (TT); TT + polymethylmethacrylate (PMMA) to repair the bone tunnel; nucleotomy; nucleotomy + PMMA. Flexion/extension, lateral-bending, and axial-rotation were evaluated under adaptive displacement control. Axial compression was applied for 15 cycles of preconditioning followed by 1 hour of constant compression. Viscoelastic behavior was modeled and parameterized.

RESULTS

TT has minimal effects on rotational biomechanics. The nucleotomy increases ROM and neutral zone (NZ) displacement width whereas decreasing NZ stiffness. TT + PMMA has small effects in terms of ROM. Nucleotomy + PMMA brings ROM back to the control, increases NZ stiffness, and decreases NZ displacement width. The nucleotomy tends to increase the rate of early creep. TT reduces early and late damping. The use of PMMA increased late elastic stiffness (S2) and reduced viscous damping (η2) culminating in faster resolution of creep.

CONCLUSION

Biomechanical properties of NP are crucial for IVD repair. This study demonstrated that TT does not affect rotational stability whereas partial nucleotomy with intact AF induce rotational instability, highlighting the central role of NP in early stages of IDD. Therefore, this model represents a successful platform to validate and optimize disc regeneration strategies.

LEVEL OF EVIDENCE

N/A.

Biological responses to flexion/extension in spinal segments ex-vivo

Mechanical loading is a salient factor in the progression of spinal disorders that contribute to back pain. Biological responses to loading modes like flexion/extension (F/E) in relevant spinal tissues remain unstudied. A novel, multi-axial experimental system was developed to subject viable functional spinal units (FSUs) to complex, in-situ loading. The objective was to determine biological effects of F/E in multiple spinal tissues-annulus fibrosus, nucleus pulposus, facet cartilage, and ligamentum flavum. Rabbit lumbar FSUs were mounted in a bioreactor within a robotic testing system. FSUs underwent small (0.17/0.05 Nm) and large (0.5/0.15 Nm) range-of-motion F/E for 1 or 2 h of cycling. Outcomes in each tissue, compared to unloaded FSUs, included (i) relative mRNA expression of catabolic (MMP-1, 3 and ADAMTS-5), pro-inflammatory (COX-2), and anabolic (ACAN) genes and (ii) immunoblotting of aggrecan degradation. Total energy applied to FSUs increased in groups subject to large range-of-motion and 2-h cycling, and moment relaxation was higher with large range-of-motion. F/E significantly modulated MMP1,-3 and COX-2 in facet cartilage and MMP-3 and ACAN in annulus fibrosus. Large range-of-motion loading increased MMP-mediated aggrecan fragmentation in annulus fibrosus. Biological responses to complex loading ex vivo showed variation among spinal tissues that reflect tissue structure and mechanical loading in F/E.