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

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. Fracture of an osteoporotic vertebral body reduces vertebral stiffness and decompresses the nucleus in the adjacent intervertebral disc. This leads to high compressive stresses acting on the annulus and neural arch. Altered load-sharing at the fractured level may influence loading of neighbouring vertebrae, increasing the risk of a fracture ‘cascade’. Vertebroplasty has been shown to normalise load-bearing by fractured vertebrae but it may increase the risk of adjacent level fracture. The aim of this study was to determine the effects of fracture and subsequent vertebroplasty on the loading of neighbouring (non-augmented) vertebrae. Methods. Fourteen 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 17 specimens where the upper or lower vertebra fractured, compressive stress distributions were measured in the disc between adjacent non-fractured vertebrae by pulling a pressure transducer through the disc whilst under 1.0kN load. These ‘stress profiles’ were obtained at each stage of the experiment (in flexion and extension) in order to quantify intradiscal pressure (IDP), the size of stress concentrations in the posterior annulus (SP) and compressive load-bearing by anterior (FA) and posterior (FP) halves of the vertebral body and by the neural arch (FN). Results. No differences were found between Cortoss and PMMA so all data were pooled. Following fracture, IDP fell by 26% in extension (P=0.004) and SP increased by more than 200% in flexion (P=0.01). FA decreased from 55% to 36% of the applied load in flexion (P=0.002) and from 36% to 27% in extension (P=0.002). FN increased from 17% to 31% in flexion (P=0.006) and from 22% to 37% in extension (P=0.008). Vertebroplasty reduced stress concentrations in the disc and restored load-bearing towards pre-fracture values. Conclusion. Vertebral fracture transfers compressive load from the anterior vertebral body to the posterior vertebral body and neural arch of adjacent (non-fractured) vertebrae. Vertebroplasty largely restores normal load-sharing at both the augmented and adjacent levels and in doing so may help reduce the risk of a spinal fracture cascade

Although success has been achieved with implantation of bone marrow mesenchymal stem cells (bMSCs) in degenerative discs, its full potential may not be achieved if the harsh environment of the degenerative disc remains. Axial distraction has been shown to increase hydration and nutrition. Combining both therapies may have a synergistic effect in reversing degenerative disc disease. In order to evaluate the effect of bMSC implantation, axial distraction and combination therapy in stimulating regeneration and retarding degeneration in degenerative discs, we first induced disc degeneration by axial loading in a rabbit model.

The rabbits in the intervention groups performed better with respect to disc height, morphological grading, histological scoring and average dead cell count. The groups with distraction performed better than those without on all criteria except the average dead cell count.

Our findings suggest that bMSC implantation and distraction stimulate regenerative changes in degenerative discs in a rabbit model.