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Orthopaedic Proceedings
Vol. 102-B, Issue SUPP_6 | Pages 102 - 102
1 Jul 2020
Mosley G Nasser P Lai A Charen D Evashwick-Rogler T Iatridis J
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Low back pain is more common in women than men, yet most studies of intervertebral disc (IVD) degeneration do not address sex differences. In humans, there are sex differences in spinal anatomy and degenerative changes in biomechanics, and animal models of chronic pain have demonstrated sex differences in pain transduction. However, there are few studies investigating sex differences in annular puncture IVD degeneration models. IVD puncture is known to result in progressive biomechanical alterations, but whether these IVD changes correlate with pain is unknown. This study used a rat IVD injury model to determine if sex differences exist in mechanical allodynia, biomechanics, and the relationship between them, six weeks after IVD injury.

Procedures were IACUC approved. 24 male & 24 female four-month-old Sprague-Dawley rats underwent a sham or annular puncture injury surgery (n=12 male, 12 female). In injury groups, three lumbar IVDs were each punctured three times with a needle, and injected with tumor necrosis factor-alpha. Mechanical allodynia was tested biweekly using von Frey filaments. Six weeks after IVD injury, rats were euthanized and motion segments were dissected for non-destructive axial tension-compression and torsional rotation biomechanical testing. Two-way ANOVA with Bonferroni corrections identified statistically significant differences (p < 0 .05) and correlations used Pearson's coefficient.

Annular puncture injury induced a significant increase in mechanical allodynia compared to sham in male but not female rats up to six weeks after injury. There was a significant sex effect on both torque range and torsional stiffness, with males exhibiting greater stiffness and torque range than females. Tensile stiffness, compressive stiffness, and axial range of motion showed no sex difference. Males and females showed similar patterns of correlation between variables when sham and injury groups were analyzed together, but correlations were stronger in males. Most correlations were clustered within testing approach: axial biomechanics negatively correlated, torsional biomechanics positively correlated, and von Frey thresholds positively correlated. Surprisingly, mechanical allodynia did not correlate with any biomechanics after injury, and the axial and torsional biomechanics showed little correlation.

This study demonstrates that males and females respond to IVD injury differently. Given the absence of correlation between pain and biomechanics, pain cannot be attributed completely to biomechanical changes. This may explain why spinal fusion surgery, an intervention limited to the spine, has produced inconsistent results and is controversial for patients with low back pain. Thus, in addressing low back pain, we must consider both spinal tissues and the nervous system. Further, the limited correlation between axial and torsional biomechanics indicates that IVD injury may have distinct effects on nucleus pulposus and annulus fibrosus. Biomechanics did not differ between sham and injury at week six, suggesting healing after injury. It remains possible that acute biomechanical changes may initiate chronic pain pathogenesis. We conclude that the observed sex differences demonstrate the need for inclusion of both males and females in IVD injury and pain studies, and suggest that males and females may require different treatments for conditions that appear similar.


Orthopaedic Proceedings
Vol. 91-B, Issue SUPP_II | Pages 350 - 350
1 May 2009
Costi J Stokes I Gardner-Morse M Laible J Scoffone H Iatridis J
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During certain motions, the disc is at risk of annular injury. Axial compression coupled with various combinations of excessive flexion, lateral bending or axial rotation has been shown to lead to disc injury. However, similar injuries have also been caused by repetitive activity at lower, more physiological ranges of motion. The primary objectives of this study were to determine the regions of largest shear strain experienced by disc tissues in six degrees of freedom (DOF), since shear is considered a likely tissue failure criterion, and to identify the physiological motions that may place the disc at greatest risk of injury.

A grid of wires was inserted into the mid-transverse plane of nine human lumbar discs that were subjected to each of six principal displacements and rotations. Stereo-radiographs were taken in each position and digitised for reconstruction of the 3D position of each grid intersection. Maximum shear strains (MSS) were calculated from relative grid-intersection displacements and normalised by the input displacement or rotation. Physiological MSS were calculated using the maximum reported physiological lumbar segmental motion for each DOF.

The largest MSS were found in the posterior, posterolateral and lateral regions of the disc. For the translation motions, lateral shear and compression produced the largest MSS (approx. 9%/mm). For the rotation motions, lateral bending had significantly larger MSS than all other tests (5.8±1.6 %/°, P< 0.001).

The physiological MSS was greatest for lateral bending, being significantly larger than all other motions (57.8±16.2%, P< 0.001). In addition, physiological MSS for flexion was also significantly larger than for all remaining motions (38.3±3.3%, P< 0.001).

This study has identified lateral bending and flexion as the lumbar segmental motions that may place the disc at greatest risk of injury. The exact failure criterion for intervertebral disc tissue is not known, and MSS was used because it is related to maximum and minimum principal strains, and it was shown that disc tears may be initiated by large interlamellar shear strains that dominate over radial and circumferential annular fibre strains. These results provide improved understanding of disc behaviours under loading and may also be of value validating finite element models.


Orthopaedic Proceedings
Vol. 91-B, Issue SUPP_II | Pages 351 - 351
1 May 2009
Costi J Korecki C Iatridis J
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Defects in annulus fibrosus induced by needle puncture can compromise mechanical integrity of the disc and lead to degeneration in animal models. This study examined the immediate and short-term mechanical and biological response to annulus injury through needle puncture using small and large gauge needles in a bovine organ culture system.

Bovine caudal intervertebral discs were harvested, assigned to one of two needle puncture groups (small = 25G, N=11; large = 14G, N=12) or an unpunctured control group (N=10), and cultured in organ culture for 6 days. After measuring initial heights, diameters, and wet weights, discs were placed in an organ culture chamber and incubated with constantly circulating media in standard culture conditions under a 0.2 MPa static load. Discs underwent a daily dynamic compression loading protocol for five days from 0.2 – 1 MPa at 1 Hz for one hour. Disc structure and function were assessed with measurements of dynamic modulus, creep, height loss, water content, proteoglycan loss to the culture medium, cell viability and histology.

Needle insertion caused a rapid decrease in dynamic modulus and increase in creep during one hour of loading, although no changes were detected in water content, disc height, or proteoglycan lost to the media. Cell viability was maintained except for localised cell death at the needle insertion site. An increase in cell number and possible remodelling response was seen in the insertion site in the nucleus pulposus.

Relatively minor disruption in the disc from needle puncture had immediate and progressive mechanical and biological consequences with important implications for the use of needle puncture in discography, and repair/regeneration techniques. Results also suggest diagnostic techniques sensitive to mechanical changes in the disc may be important for early detection of degenerative changes in response to annulus injury.


Orthopaedic Proceedings
Vol. 91-B, Issue SUPP_II | Pages 351 - 351
1 May 2009
Costi J Stokes I Gardner-Morse M Lubinski J Iatridis J
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Biomechanical properties of the disc provide both flexibility and shock absorption. We hypothesised that frequency-dependent effects in shear and torsion deformations in which intrinsic viscoelasticity (solid phase) predominates would differ from compression and bending, in which fluid flow-mediated poroelasticity is also present.

Disc-vertebra-disc preparations (N=8) from human lumbar spines were subjected to each of three displacements and three rotations (6 degrees of freedom - DOF) at each of four frequencies (0.001, 0.01, 0.1, and 1 Hz) after equilibration overnight under a 0.4 MPa preload in a bath of PBS at 37C with protease inhibitors. The forces and torques were recorded along with the applied translation or rotation. The stiffness (force/displacement or torque/rotation) and the phase angle (between each force and displacement) were calculated for each degree of freedom from recorded data.

The stiffness significantly increased linearly with the log-frequency in most DOF (P< 0.001) apart for lateral bending and flexion/extension (P> 0.055). The increases over the four decades of frequency were 28%, 23% and 25% for antero-posterior (AP) shear, lateral shear and torsion respectively, and were 53%, 33% and 36% for compression, lateral bending and flexion.

The phase angle (a measure of energy absorption) significantly decreased overall with increasing frequency in all DOF (P< 0.005) apart for lateral bending. During AP and lateral shear, significant decreases in phase angle of 10% were found between 0.001 Hz compared to 0.01 Hz and 0.1 Hz (P< 0.026) with no differences found at 1 Hz. For torsion, the phase angle at 1 Hz was significantly lower by 40% compared to all slower frequencies (P< 0.001). During compression, a large significant drop in phase angle of 25%–35% occurred between 0.001 Hz and all other frequencies (P< 0.016). No significant post-hoc differences were found for flexion-extension (P> 0.057).

The dynamic effects (stiffness increase, and phase angle decrease with frequency) were consistently greater for deformation modes in which fluid flow effects are thought to be greater. Both the solid phase viscoelasticity and the fluid phase poroelasticity of the tissue appear to contribute to the disc stiffness and energy absorption, although these differences become more apparent at 1 Hz compared to the slower frequencies.


Orthopaedic Proceedings
Vol. 90-B, Issue SUPP_I | Pages 128 - 128
1 Mar 2008
Antoniou J Demers C Michalek A Iatridis J Goswami T Beaudoin G Beckman L Alini M Mwale F
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Purpose: Quantitative MRI is currently being tested as an early and non-invasive diagnostic tool of disc problems prior to the appearance of symptoms. The aim of the present study was to determine the effects of cyclic loading and enzymatic digestion on quantitative MRI, biochemical composition, and mechanical properties of intervertebral disc tissue.

Methods: Bovine tail segments consisting of three discs were subjected to 16h of cyclic compression loading (50N–300N–50N at 1Hz) or left unloaded for 16h while in saline solution at 37°C. Prior to loading, the nucleus pulposus were injected with either a trypsin or buffer solution. MR examinations were carried out in a 1.5T Siemens` Avanto system to measure T1 and T2 relaxation times, magnetization transfer ratio (MTR), and trace of the apparent diffusion coefficient (TrD). The nucleus pulposus and annulus fibrosus were dissected and analyzed for contents of water, glycosaminoglycan, total collagen, and denatured collagen. Cylindrical nucleus pulposus and annulus fibrosus tissue plugs were harvested, prepared, and tested under confined compression to measure compressive modulus (HA) and hydraulic permeability (k). ANOVA and linear regression analyses were performed (p< 0.05).

Results: Loading decreased the T1, T2, and TrD of NP while it increased MTR. Only water content in the nucleus pulposus was significantly influenced by loading. T1, water content, and k of the annulus fibrosus tissue were significantly reduced with loading.|Enzymatic treatment of the nucleus pulposus had no effect on its MR properties, but increased the percent of denatured collagen and thus decreased HA. None of the biochemical, mechanical, and MR parameters of the annulus fibrosus changed with trypsin treatment.

Conclusions: Dynamic loading of the disc segments for 16h decreased the permeability of both disc tissues. This was consistent with the measured drop in tissue hydration and was observed as a decrease in T1. Targeted trypsin digestion of the nucleus pulposus was confirmed with no detectable changes in the biochemical, biomechanical, or MR properties of the annulus fibrosus. Future studies will address additional quantitative MR parameters such as T1-rho, a higher strength magnet, and different enzymatic treatments. Funding: Other Education Grant Funding Parties: Canadian Institutes of Health Research, McGill William Dawson Scholar Award, and Whitaker Foundation