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

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

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