Introduction Understanding how annular failure might occur following increased nuclear pressurisation requires an experimental approach that avoids artefactual injury to the annulus but reveals structural disruption resulting directly from the pressurisation event. The aim of this study was to investigate the fundamental mechanisms by which both intra and inter-lamellar relationships are disrupted by nuclear pressurisation, with the development of a model that might accurately reproduce mechanisms of intervertebral disc injury secondary to events causing raised intradiscal pressure. Methods Bovine motion segments were subjected to internal pressurisation using a novel “through vertebra” method. Intra and inter-lamellar sections were deliberately chosen so as to expose systematic patterns of structural disruption resulting from the pressurisation event. This micro-disruption was investigated using a novel method which combined microtensile manipulation and simultaneous differential contrast imaging of the fully hydrated unstained sections. Results The inner annulus was most severely disrupted. The middle regions developed a series of regular clefts along axes of weakness within the in-plane arrays of fibres in each lamella with a slight oblique passage radially away from the centre. These annular clefts separated the pre-existing transverse or side-to-side interconnections within the longitudinal fibre arrays. Progression to the peripheral lamellae occurred when the clefts crossed lamellae with associated inter-lamellar junction separation, with progressively lesser degrees of disruption further from the central area of pressurisation. Discussion This study demonstrates that raised intradiscal pressure creates a consistent pattern of annular failure, which may preceed clinically relevant disc lesions, and specifically annular lesions. These findings offer a possible explanation for (a) annular weakening that alters the ability of the nucleus to maintain hydration after load, (b) the initiation of paths for annular tear development, (c) pathways that may expand to allow disc prolapse and (d) pathways for ingrowth of inflammatory and neural tissue mediating disc pain

Aims. The presence of facet tropism has been correlated with an elevated susceptibility to lumbar disc pathology. Our objective was to evaluate the impact of facet tropism on chronic lumbosacral discogenic pain through the analysis of clinical data and finite element modelling (FEM). Methods. Retrospective analysis was conducted on clinical data, with a specific focus on the spinal units displaying facet tropism, utilizing FEM analysis for motion simulation. We studied 318 intervertebral levels in 156 patients who had undergone provocation discography. Significant predictors of clinical findings were identified by univariate and multivariate analyses. Loading conditions were applied in FEM simulations to mimic biomechanical effects on intervertebral discs, focusing on maximal displacement and intradiscal pressures, gauged through alterations in disc morphology and physical stress. Results. A total of 144 discs were categorized as ‘positive’ and 174 discs as ‘negative’ by the results of provocation discography. The presence of defined facet tropism (OR 3.451, 95% CI 1.944 to 6.126) and higher Adams classification (OR 2.172, 95% CI 1.523 to 3.097) were important predictive parameters for discography-‘positive’ discs. FEM simulations showcased uneven stress distribution and significant disc displacement in tropism-affected discs, where loading exacerbated stress on facets with greater angles. During varied positions, notably increased stress and displacement were observed in discs with tropism compared to those with normal facet structure. Conclusion. Our findings indicate that facet tropism can contribute to disc herniation and changes in intradiscal pressure, potentially exacerbating disc degeneration due to altered force distribution and increased mechanical stress. Cite this article: Bone Joint Res 2024;13(9):452–461

PEEK rods construct has been proposed to allow better load sharing among spinal components when compared to the more traditional Titanium rods constructs. However, such proposal has largely derived from single-load in-vitro testing and the biomechanical differences between the two constructs when subjected to fatigue loading remain unknown. Current study comparatively analyzed the in-vitro biomechanical performance of PEEK and Titanium rod constructs as spinal implants through a 5 hour fatigue loading test. The disc height and intradiscal pressure of the instrumented and adjacent levels pre- and post-loading were recorded for analysis. The stress levels on the rods and bone stress near the screw-bone interface were also collected to investigate the likely failure rates of the two constructs. The results showed that the Titanium rods construct demonstrated a minimum amount of loss of disc height and intradiscal pressure at the instrumented level, however, a significant loss of the disc height and intradiscal pressure at adjacent levels compared to the intact spine were identified. In contrast, the disc height and intradiscal pressure of the PEEK rods were found to be comparable to those of the intact spine for all levels. The PEEK rods group also showed significantly less bone stress near the screw-bone interface compared to the Titanium rods group. Current study has demonstrated the potential benefits of the PEEK rods construct in reducing the risks of adjacent segment disease and implant failure rates when compared to the more traditional Titanium rods construct

As the intervertebral disc is largely avascular, needle injection is the most practical method for delivery of therapeutic agents used in treatments for degenerative disc disease. Intradiscal pressure increases during injection, and insufficient recovery time prior to needle retraction may result in injectate leakage. In order to determine the maximum pressure and post-injection recovery time for a given injection volume and rate, an analytical model of intradiscal injection was developed and calibrated experimentally. A governing equation was derived defining intradiscal pressure as a function of effective permeability, initial elastic stiffness, nonlinear stiffness term, and injection rate. The equation was solved using a fourth order Runge-Kutta routine with a 0.05s time step and a ramp-dwell injection. The model was calibrated by performing controlled intradiscal injections on five bovine caudal intervertebral discs. Three had adjacent vertebrae intact, while two were separated from vertebrae and constrained between porous stainless steel platens. A syringe driven by a linear actuator was used to inject phosphate buffered saline through a 21g hypodermic needle inserted radially into the disc to a depth of one half of the disc diameter. Injection was performed at a rate of 75μL/s to a volume of 250μL followed by a 240s dwell. Fluid pressure was recorded during both the injection phase and subsequent recovery phase. For each experimental pressure vs time trace, model parameters were varied in order to obtain an optimal fit. The model was run with the average parameter values across a grid of possible injection protocols, with injection volume ranging from 30 to 300μL and injection time ranging from 0.1 to 5s. For each case, peak pressure and time required to reach a 1kPa threshold were recorded. Experimentally measured peak pressure ranged from 68 to 88kPa. Pressure at the end of the 240s dwell ranged from 49 to 69kPa. There was no apparent difference between discs with and without endplates. Leakage of fluid following needle retraction was observed in all specimens. Experimental data were well fit by the analytical model, which predicted higher peak pressure and longer recovery time with increasing volume, from approximately 1500s at 30μL to nearly 3000s at 300μL. The model was nearly insensitive to injection rate. The experimental data confirm pressurization of the disc during injection and injectate leakage resulting from insufficient recovery time. The model predicts that the time required to recover to below threshold leakage pressure is impractically long for both laboratory and clinical injection protocols. Similar behavior with and without endplates confirms that fluid flow is limited by permeability of the tissue itself, not the boundary conditions. Slow recovery is likely attributable to the fact that peak injection pressures were lower than the hydraulic swelling pressure of the nucleus pulposus, which has been reported to be approximately 140kPa. Due to the high swelling pressure of the nucleus pulposus, it is unlikely that intradiscal injection procedures can be performed without substantial injectate leakage following needle retraction

Spinal deformations are posture dependent. Official data from the Netherlands show that youth are encountering increasing problems with the musculoskeletal system (>40% back pain, and sport injury proneness). Prolonged sloth and slumped sitting postures are causative factors. Dutch youth are “champion sitting” in Europe. The effects of sitting on the development of posture and function of locomotion (stiffness) during growth have only been reported clearly in classic textbooks (in German) of practical anatomy and orthopaedics. Research with relevant clinical examinations is being done to understand epidemiological data on the increasing posture-dependent problems. A cohort of adolescents (15–18 years) in secondary school was assessed for sagittal postural deviations while bending. 248 children completed a questionnaire, and tests were done on neuromuscular tightness. The femorotibial angle was used to measure hamstring tightness. Measurement of the dorsiflexion of the foot was used to assess the tightness of calf muscles and Achilles tendons. All adolescents were photographed laterally while performing the finger–floor test (used to test flexibility), assessed as a knockout test: “Can you reach the floor or not?” The spinal profiles while bending were classified as abnormal arcuate or angular kyphosis. Hamstring tightness was present in 62.1% of the cohort in both legs, and in 18.2% unilaterally. Achilles tendon tightness was present bilaterally in 59.3%, and unilaterally in 19.4%. Activities with presence of stiffness (finger–floor distance), in descending order, were football, running, no sports, field hockey, tennis, dance, and gymnastics. 93.5% of the soccer players had tight hamstrings in both legs compared with none of those performing gymnastics. The correlation of the finger–floor test with tight hamstrings was 73.2%. For sagittal bending deformities, the correlation between form and function deficits cannot be made yet. 80 of 248 spines were rated by the examiners as having deformed flexion. Since Andry (1741) and at the zenith of continental orthopaedics and anatomy around 1900, the prolonged flexed positions of a young spine were indicated as being the main cause of deformity by overload and shear loads on immature discs and cartilage, preventing normal development of the discs. Nachemson proved that the intradiscal pressure in sitting adults was extremely high, so it follows that children must also be at risk. Evidence suggests that youth, generally because of their sedentary and “screenful lifestyle”, will encounter serious problems in growth, manifesting as incongruent neuro-osseous growth (Roth), serious neuromuscular tightness (being prone to injury), and spinal deformations, leading to pain

Objective: To measure intradiscal pressures in scoliotic spines to further understand the role of mechanical forces in the development of scoliosis. Design: Pressure readings were obtained in consented patients with ethical approval. A needle mounted pressure transducer was introduced into the disc during routine anterior scoliosis surgery. Subjects: Ten human scoliotic discs from three patients. Outcome measures: Intradiscal pressure profiles. Results: Nuclear hydrostatic pressures varied from 0.2 to 0.6 MPa. The mean nuclear pressures for the three spines were 0.27+0.12, 0.35+0.06 and 0.47+0.12 MPa. High stress, non- hydrostatic regions were consistently recorded in the concave annulus. Conclusions: Nuclear pressures in these scoliotic patients were significantly higher than the 0.12 and 0.15 MPa recorded previously in non-scoliotic recumbent individuals. 1;. 2. suggesting that spinal loading is abnormal in scoliosis

Scoliosis is a disease characterised by vertebral rotation, lateral curvature and changes in sagittal profile. The role of mechanical forces in producing this deformity is not clear. It is thought that abnormal loading deforms the disc, which becomes permanently wedged. Modelling and in vitro studies suggest that such deformations should increase intradiscal pressure. Intradiscal pressure has been measured previously in a variety of clinical environments. The aim of this study is to measure pressure profiles across scoliotic discs to provide further information on the role of mechanical forces in scoliosis. Pressure readings were obtained in consented patients with ethical approval using a needle-mounted sterilised pressure transducer (Gaeltec, Dunvegan, Isle of Skye) calibrated as described previously. The transducer needle was introduced into the disc of an anaesthetised patient during routine anterior scoliosis surgery and pressure profiles measured. Signals were collected, amplified and analysed using Power-lab and a laptop computer. Pressure profiles across 10 human scoliotic discs from 3 patients have been measured to date. Pressures varied from 0.1 to 1.2 MPa. Annular pressures showed high pressure, non-isotropic regions on the concave but not convex side of these discs. Nuclear pressures recorded from the discs of these scoliotic patients were higher than those recorded previously in non-scoliotic recumbent individuals

INTRODUCTION. The elimination of motion and disc stress produced by spinal fusion may have potential consequences beyond the index level overloading the spinal motion segments and leading to the appearance of degenerative changes. So the “topping-off” technique is a new concept instructing dynamic fixation such as interspinous process device (IPD) for the purpose of avoiding adjacent segment disease (ASD) proximal to the fusion construct. MATERIALS AND METHODS. The study simulated spinal fusion in L4-L5, fusion combined DIAM in L3-L4. The ROM and maximum von Miss stresses were analyzed in flexion, extension, lateral bending, and torsion in response to hybrid method, compared to intact modeland fusion model. RESULTS. The investigation revealed that decreased ROM, intradiscal stress in implanted level but a considerable increase in stresses at more upper level (L2-L3) during flexion and extension in hybrid model, comparing with the fusion model. CONCLUSIONS. The raise of intradiscal pressure at the adjacent segment to a rigid fusion segment can be reduced when the rigid construct is augmented with an interspinous process device. However, the burden of stress over total spinal segments was still the same, the stress and ROM were just shift to supraadjacent levels

Low back pain (LBP) is the leading cause of disability worldwide, interfering with an individual's quality of life and work performance. Understanding the degeneration mechanism of the intervertebral disc (IVD), one of the key triggers of LBP, is hence of great interest. Disc degeneration can be mimicked in animal studies using the injection of enzymatic digestion, needle puncture, stab injury, or mechanical over-loading [1]. However, the detailed response of the artificial degenerated disc using needle puncture under physiological dynamic loading in diurnal activities has not yet been analyzed using FE-models. To fill the gap in literature, this study investigates the role of needle puncture injury on the biomechanical response of IVD using a combination of Finite Element (FE) simulations and in-vitro lumbar spine sheep experiments. 16 lumbar motion segments (LMS) were dissected from juvenile sheep lumbar spines. The harvested LMSs were assigned equally to two groups (control group with no incision and an injured group punctured with a 16-gauge needle). All specimens were mounted in a homemade chamber filled with saline solution and underwent a stress-relaxation test using a mechanical testing apparatus (Zwick/Roell, Ulm-Germany). A validated inverse poroelastic FE methodology [2] in conjunction with in-vitro experiments were used to find the elastic modulus and permeability. Subsequently, specimen-specific FE models for the 16 discs were simulated based on daily dynamic physiological activity (i.e., 8h rest followed by a 16h loading phase under compressive loads of 350 N and 1000 N, respectively). The results of the individual FE models were well fitted with the in-vitro stress-relaxation experiments, with an average error of 7.48 (±2.24)%. The results of the simulations demonstrated that the variation of axial displacement in the control discs was significantly higher than the injured ones (P=0.037). At the end of day, the intradiscal pressure (IDP) was slightly higher in the control group (P=0.061) although the maximum axial stress in the annulus fibrosus (AF) was significantly higher in the injured group (P=0.028). The total fluid loss after 24h was significantly higher in the control group (p<0.001). We found that needle puncture can decrease the strain range, IDP, and fluid loss in an IVD, although it increases the axial stress. We therefore hypothesize that the fissures, clefts or tears produced by needle puncture alter the saturation time for disc deformation and pore pressure. The collapsed disc structure hinders the fluid flow capability; hence, the total fluid loss decreases for the injured discs, inhibiting the transportation of nutrients. Higher stresses in the AF were observed for the injured group in alignment with previous studies [3]. It is therefore concluded that the needle puncture injury methodology can be effectively used to mimic the degeneration mechanism in animal models. It is a convenient, reproducible, and cost-effective technique. Future work includes exploring degenerated disks induced by needle puncture to investigate potential regenerative therapeutics

The purpose of this retrospective study, is to demonstrate the survivorship and clinical effectiveness of the Wallis implant, against low back pain and functional disability in patients with degenerative lumbar spine disease. The Wallis Interspinous implant, was developed as a minimally invasive and anatomically conserving procedure, without recourse to rigid fusion procedures. The initial finite element analysis and cadaver biomechanical studies showed that the Wallis ligament improves stability in the degenerate lumbar motion segment. Unloading the disc and facet joints reduces intradiscal pressures at same and adjacent levels allowing for the potential of the disc to repair itself. A total of 157 patients who had wallis ligament insertion between 2003 and 2009 were reviewed, with a mean age of 54 and were followed for 48 months on average. Patients were assessed pre-operatively and post-operatively every 6 months by VAS pain score, Oswestry Disability Index and SF-36. 90% of patients improved, to show a minimal clinical difference, compared to the pre-operative evaluation. There is overall 75-80% good clinical outcome. Low infection rate of 1.1%. Two cases of prolapsed discs at the same level requiring further discectomy, 7 required fusion. No fractures or expulsions. The Wallis implant represents a safe non-fusion stabilisation device in the treatment of degenerative lumbar spine disease with canal stenosis. There is less soft tissue damage, quick rehabilitation, less morbidity and associated low complication rate

Purpose of study. This RCT is to determine whether or not there is a clinical benefit from inserting a dynamic stabilising implant such as the Wallis ligament on the functional recovery of patients who have undergone lumbar decompression surgery. This Interspinous implant was developed as an anatomically conserving procedure without recourse to lumbar spinal fusion surgery. The biomechanical studies have shown that unloading the disc and facet joints reduces intradiscal pressures at same and adjacent levels. The aim of this study was to identify a patential Wallis affect. Methods. Ethicallly approved. Patients were randomized into 2 groups, decompression alone or decompression with wallis interspinous ligament stabilisation. Patients were assessed pre operatively and post operatively every 6 months by VAS pain score and Oswestry Disability Index. Summary of findings. A total of 60 patients were recriuted the study from October 2005. Equal number had been randomized into two groups. The mean age of 54 (24–85) and the average follow is 36 months (6–48). The results were significantly better in decompression plus Wallis group compared to decompression alone, showing a minimal clinical difference compared to the control group. Relationship between findings and existing knowledge: Our results deomonstrate that clincial outcomes are significantly better when a Wallis implant was used in lumbar deompression. Patients experienced less back pain. Overall significance of findings: The Wallis implant represents a successful non fusion stabilisation device in the treatment of degenerative lumbar spine disease with canal stenosis. Minimal soft tissue dissection, quick rehabilitation, low morbidity. The Wallis ligament sucessfully treats spinal stenosis by reducing pain score, preserving mobility, and function

Background and Objective. In industrialized societies, the prevalence of radicular low back pain has exploded in recent years. Lumbar disc prolaps, protrusion, or extrusion account for less than 5% of all low back problems, but are the most common causes of nerve root pain and surgical interventions. The primary rationale for any form of surgery for disc prolaps is to relieve nerve root irritation or compression due to herniated disc material. The primary modality of surgical treatment continues to be either open or microdiscectomy, but several alternative techniques including. Nucleoplasty. It provokes ablation of the nucleus of the disk by a controlled thermal effect produced by radiofrequency. Nucleoplasty is minimally invasive treatment aimed at removing nuclear material and lowering intradiscal pressure and decompressing through coblation needle inserted percutaneously into the nucleus of intervertebral discs. This paper will show a 3 years experience with 110 cases with lumbar radicular pain secondary to a disc protrusion that underwent Nucleoplasty as their secondary therapy. Methods. Included in this series were 110 patients with significant lumbar radicular pain, resistant to interventional therapy done before hand like fluoroscopically guided spinal transforaminal epidural injections or sacral injections with steroids. These cases were done under local anaesthesia with short analgesia and stand by monitoring. Results. In the overall cohort, the average Visual Analogue Scale (VAS) pain score decreased. Conclusions. We conclude that with use of the present selection criteria, Nucleoplasty is very effective long-term treatment for lumbar radicular pain. We recommend modifying the criteria to include only those cases with lumbar radicular pain due to protrusion whose annular integrity is confirmed via MRI and by either selective nerve root blocks and to exclude cases with axial pain

To investigate whether restoration of mechanical function and spinal load-sharing following vertebroplasty depends upon cement distribution. Fifteen pairs of cadaver motion segments (51-91 yr) were loaded to induce fracture. One from each pair underwent vertebroplasty with PMMA, the other with a resin (Cortoss). Various mechanical parameters were measured before and after vertebroplasty. Micro-CT was used to determine volumetric cement fill, and plane radiographs (sagittal, frontal, and axial) to determine areal fill, for the whole vertebral body and for several specific regions. Correlations between volumetric fill and areal fill for the whole vertebral body, and between regional volumetric fill and changes in mechanical parameters following vertebroplasty, were assessed using linear regression. For Cortoss, areal and volumetric fills were significantly correlated (R=0.58-0.84) but cement distribution had no significant effect on any mechanical parameters following vertebroplasty. For PMMA, areal fills showed no correlation with volumetric fill, suggesting a non-uniform distribution of cement that influenced mechanical outcome. Increased filling of the vertebral body adjacent to the disc was associated with increased intradiscal pressure (R=0.56, p<0.05) in flexed posture, and reduced neural arch load bearing (F. N. ) in extended posture (R=0.76, p<0.01). Increased filling of the anterior vertebral body was associated with increased bending stiffness (R=0.55, p<0.05). Cortoss tends to spread evenly within the vertebral body, and its distribution has little influence on the mechanical outcome of vertebroplasty. PMMA spreads less evenly, and its mechanical benefits are increased when cement is concentrated in the anterior vertebral body and adjacent to the intervertebral disc

Introduction. Disc degeneration is often scored using macroscopic and microscopic scoring systems. Although reproducible, these scores may not accurately reflect declining function in a degenerated disc. Accordingly, we compared macroscopic and microscopic degeneration scores with measurements of disc function. Methods. Thirteen cadaveric motion segments (62–93 yrs) were compressed to 1kN while a pressure-transducer was pulled across the mid-sagittal diameter of the disc. Resulting stress profiles indicated intradiscal pressure (IDP), and maximum stress in the anterior (MaxStress_Ant) and posterior (MaxStress_Post) annulus. Macroscopic grade (1–4) of disc degeneration was based on visual examination of mid-sagittal sections, using subscales that yielded a maximum score of 48. Microscopic grade (1–4) was based on histological sections of the disc + vertebral body taken from anterior annulus, nucleus pulposus and posterior annulus, using subscale scores that totalled 108. Cartilage endplate thickness (CEP_thickness) was measured histologically, and porosity of the bony endplates was measured using micro-CT. ANOVA was used to compare between grades, and regression was used to establish dependence on scores. Results. IDP and CEP_thickness both decreased with increasing macroscopic grade (1–4) of degeneration (P= 0.021 & 0.022 respectively). Also, IDP, CEP_thickness and MaxStress_Ant decreased with increasing macroscopic score (1–48) (R. 2. = 0.39, P = 0.022; R. 2. = 0.36, P = 0.03; R. 2. = 0.30, P = 0.04 respectively). IDP and MaxStress_Ant decreased with increasing microscopic grade (1–4) of degeneration (P=0.05 & 0.005 respectively) and increasing microscopic score (1–108) (R. 2. = 0.36, P = 0.02; R. 2. = 0.47, P = 0.009 respectively) whereas inferior endplate porosity increased with increasing microscopic grade (P = 0.05) and score (R. 2. = 0.36, P = 0.03). Conclusion. Macroscopic and microscopic ‘degeneration’ scores both reflect changes in disc function and endplate integrity

We attempted to correlate the findings of MRI and discography in patients with low back pain, examining 108 lumbar intervertebral discs in 33 consecutive patients. MRI results were assessed from the intensity and shape of the signal obtained from the central part of the disc. Discography was classified according to the pattern of contrast material, the pressure accepted and the pain reproduced. All discs which were abnormal on MRI had altered patterns on discography, but 18 of the 60 discs with normal MRI had abnormal discograms. Of 39 asymptomatic discs, 33 had normal MRI signals and 24 had normal discograms. None of the 15 discs showing severe degeneration on MRI sustained high levels of intradiscal pressure, but only six of the 60 discs giving normal MRI had low pressure. With current techniques, discography is more accurate than MRI for the detection of annular pathology: a normal MRI does not exclude significant changes in the peripheral structure of the intervertebral disc which can produce low back pain

Introduction. Osteoporotic fracture reduces vertebral stiffness, and alters spinal load-sharing. Vertebroplasty partially reverses these changes at the fractured level, but is suspected to increase deformations and stress at adjacent levels. We examined this possibility. Methods. Twelve pairs of three-vertebra cadaver spine specimens (67-92 yr) were loaded to induce fracture. One of each pair underwent vertebroplasty with PMMA, the other with a resin (Cortoss). Specimens were then creep-loaded at 1.0kN for 1hr. In 15 specimens, either the uppermost or lowest vertebra was fractured, so that compressive stress distributions could be determined in the disc between adjacent non-fractured vertebrae. Stress was measured in flexion and extension, at each stage of the experiment, by pulling a pressure-transducer through the disc whilst under 1.0kN load. Stress profiles quantified intradiscal pressure (IDP), stress concentrations in the posterior annulus (SP. P. ), and compressive load-bearing by the neural arch (F. N. ). Elastic deformations in adjacent vertebrae were measured using a MacReflex tracking system during 1.0kN compressive ramp loading. Results. No differences were found between Cortoss and PMMA so data was pooled. Following fracture, IDP fell by 27% in extension (P=0.009), and SP. P. increased by 277% in flexion (P=0.016). F. N. increased from 17% to 30% of the applied load in flexion, and from 23% to 37% in extension (P<0.05). Vertebroplasty partially reversed these changes without inducing any increase in elastic deformation of the adjacent vertebrae. Conclusion. Vertebral fracture increases stress concentrations acting on the vertebral bodies and neural arches of adjacent (non-fractured) vertebrae, and these increases can be partially reversed by vertebroplasty

Introduction. Vertebroplasty helps to restore mechanical function to a fractured vertebra. We investigated how the distribution of injected cement benefits both fractured and neighbouring vertebrae. Methods. Nine pairs of three-vertebra cadaver spine specimens (aged 67–90 yr) were compressed to induce fracture. One of each pair underwent vertebroplasty with PMMA, the other with a resin (Cortoss). Specimens were then creep-loaded at 1.0kN for 1hr. Before and after vertebroplasty, compressive stiffness was determined, and stress profilometry was performed by pulling a pressure-transducer through each disc whilst under 1.0kN load. Profiles indicated intradiscal pressure (IDP) and compressive load-bearing by the neural arch (F. N. ) at both disc levels. Micro-CT was used to quantify cement fill in the anterior and posterior halves of each augmented vertebral body, and also in the region immediately adjacent to the fractured endplate. Results. Fracture reduced stiffness and IDP, and increased F. N. Following vertebroplasty, anterior fill was greater for Cortoss (30%) than PMMA (17%) (P<0.01). With Cortoss, increased posterior fill was associated with a greater restoration of IDP in the adjacent disc (P<0.05). Furthermore, specimen stiffness increased in proportion to cement fill adjacent to the fractured end-plate. With PMMA, increased anterior fill caused a greater reduction in F. N. in the non-adjacent disc (P<0.05), whereas increased posterior fill and increased fill adjacent to the fracture caused a greater restoration of IDP in the adjacent disc (P<0.05). Conclusion. Cement distribution varied between the two cements. However, increased filling immediately adjacent to the fractured endplate was linked most consistently to improved mechanical function. Conflicts of Interest. None. Source of Funding. This work was funded by Action Medical Research. Vertebroplasty materials were provided by Stryker and by Orthovita. We can confirm that this abstract has not been published previously in whole or substantial part, and the findings have not been presented previously at a national meeting

Background: Intervertebral discs and vertebrae deform under load, narrowing the intervertebral foramen and increasing the risk of nerve entrapment. Little is known about these deformations in elderly spines. Purpose: To test the hypothesis that, in ageing spines, vertebrae deform more than discs, and contribute to time-dependent creep. Methods: 117 thoracolumbar motion segments, mean age 69 yr, were compressed at 1 kN for 0.5, 1 or 2 hr. Immediate “elastic” deformations were followed by “creep”. A three-parameter model was fitted to experimental data to characterise their viscous modulus E1, elastic modulus E2 (initial stiffness), and viscosity η (resistance to fluid flow). Intradiscal pressure (IDP) was measured using a miniature needle-mounted transducer. In 17 specimens loaded for 0.5 hr, an optical MacReflex system measured compressive deformations separately in the disc and each vertebral body. Results: On average, the disc contributed 28% of the spine’s elastic deformation, and 51% of the creep. Elastic, creep, and total deformations of 84 motion segments over 2 hrs averaged 0.87mm, 1.37mm and 2.24mm respectively. Measured deformations were predicted accurately by the model, but E1, E2 and η depended on loading duration. E1 and η decreased with advancing age and degeneration, in proportion to falling IDP (p< 0.001). Total compressive deformation increased with age, but rarely exceeded 3mm. Conclusions: In ageing spines, vertebral bodies show greater elastic deformations than intervertebral discs, and a similar amount of creep. Deformations depend largely on IDP, but appear to be limited by impaction of adjacent neural arches. Total deformations are sufficient to cause foraminal stenosis in some individuals. Conflicts of Interest: none. Source of Funding: Action Medical Research

Purpose: To determine how cement volume during vertebroplasty influences:. stress distributions on fractured and adjacent vertebral bodies,. load-sharing between the vertebral bodies and neural arch, and. cement leakage. Methods: Nineteen thoracolumbar motion segments from 13 cadavers (42–91 yrs) were loaded to induce fracture. Fractured vertebrae received two sequential injections (VP1 and VP2) of 3.5cm3 of polymethylmethacrylate cement. Before and after each injection, motion segment stiffness was measured in compression and in bending, and the distribution of compressive “stress” in the intervertebral disc was measured in flexed and extended postures. Stress profiles yielded the intradiscal pressure (IDP), stress peaks in the posterior (SPP) annulus, and the % of the applied compressive force resisted by the neural arch (FN). Cement leakage and vertebral body volume were quantified by water-immersion, and % cement fill was estimated. Results: Bending and compressive stiffness fell by 37% and 50% respectively following fracture, and were restored only after VP2. Depending on posture, IDP fell by 59%–85% after fracture whereas SPP increased by 107%–362%. VP1 restored IDP and SPP to prefracture values, and VP2 produced no further changes. Fracture increased FN from 11% to 39% in flexion, and from 33% to 59% in extension. FN was restored towards pre-fracture values only after VP2. Cement leakage, IDP and compressive stiffness all increased with %fill. Conclusions: 3.5cm3 of cement largely restored normal stress distributions to fractured and adjacent vertebral bodies, but 7cm3 were required to restore load-sharing between the vertebral bodies and neural arch. Risks of cement leakage increased with %fill. Conflicts of Interest: None. Source of Funding: This work was funded by Action Medical Research and The Hospital Saving Association Charitable Trust. Vertebroplasty materials were provided by Stryker