Dynamic Stabilization Of Lumbar Spine Research Articles

Clinical outcome of posterior dynamic stabilization of lumbar spine: Experience in Indian and African population

Context: There is an increased interest in stabilization of lumbar spine without fusion as an alternative to traditional fusion for treatment of degenerative lumbar spine disease. Aim: To analyze short term outcomes of pedicle-based dynamic stabilization system (DSS). Setting and Design: Retrospective study of a consecutive series of 42 patients. Materials and Methods: Between 2009 to 2012, 42 patients underwent DSS with or without decompression on total 214 pedicles for various indications and were followed up for 12 months. Clinical improvement was evaluated with the Visual Analogue Scale (VAS) and Oswestry Disability Index (ODI). Post operative complications were noted and radiographic evaluation for screw positioning and loosening was done. Statistical Analysis: SPSS Version 21.0. Levene's Test for Equality of Variances, Chi square test and students T test. Results: Out of 66 stabilized segments in 42 patients accounting for 214 pedicles instrumented, 23(54.8%), 14(33.3%) and 5(11.9%) had 1, 2 and 3 segments stabilized respectively {L4-5 in 18, 42.86%, L4-5-S1 in 10, 23.81%, L5-S1 in 5, 11.90%, L2-3-4-5 and L3-4-5 in 3, 7.14% and L3-4 in 1, 2.38%}. Dynamic stabilization or an additional decompression procedure was done in 29 and 13 patients respectively. The VAS {7.40 ± 0.79 to 1.64 ± 0.93 (P < 0.05)} and ODI {65.92% ± 8.70% to 12.83% ± 6.73% (P < 0.05)} improved. One patient had wound infection, 2 had aseptic skin necrosis, 1 had DVT, 1 required screw repositioning and 1 required unilateral removal of implant for post-op radicular pain. Two patients had persistent sagittal imbalance. Conclusion: DSS is effective and safe in patients with various degenerative lumbar spine diseases.

Molecular MR imaging for the evaluation of the effect of dynamic stabilization on lumbar intervertebral discs

The dynamic stabilization of lumbar spine is a non-fusion stabilization system that unloads the disc without the complete loss of motion at the treated motion segment. Clinical outcomes are promising but still not definitive, and the long-term effect on instrumented and adjacent levels is still a matter of discussion. Several experiments have been devised in order to gain a better understanding of the effect of the device on the intervertebral disc. One of the hypotheses was that while instrumented levels are partially relieved from loading, adjacent levels suffer from the increased stress. But this has not been proved yet. The aim of this study was to investigate the long-term effect of dynamic stabilization in vivo, through the quantification of glycosaminoglycans (GAG) concentration within instrumented and adjacent levels by means of the delayed Gadolinium-Enhanced Magnetic Resonance Imaging of Cartilage (dGEMRIC) protocol. Ten patients with low back pain, unresponsive to conservative treatment and scheduled for Dynesys implantation at one to three lumbar spine levels, underwent the dGEMRIC protocol to quantify GAG concentration before and 6 months after surgery. Each patient was also evaluated with visual analog scale (VAS), Oswestry, Prolo, Modic and Pfirrmann scales, both at pre-surgery and at follow-up. Six months after implantation, VAS, Prolo and Oswestry scales had improved in all patients. Pfirrmann scale could not detect any change, while dGEMRIC data already showed a general improvement in the instrumented levels: GAG was increased in 61% of the instrumented levels, while 68% of the non-instrumented levels showed a decrease in GAG, mainly in the posterior disc portion. In particular, seriously GAG-depleted discs seemed to have the greatest benefit from the Dynesys implantation, whereas less degenerated discs underwent a GAG depletion. dGEMRIC was able to visualize changes in both instrumented and non-instrumented levels. Our results suggest that the dynamic stabilization of lumbar spine is able to stop and partially reverse the disc degeneration, especially in seriously degenerated discs, while incrementing the stress on the adjacent levels, where it induces a matrix suffering and an early degeneration.

Fulcrum Assisted Soft Stabilization System

An experimental study on cadaver spine and spine model for biomechanical evaluation of a novel dynamic stabilization device. First, to test the hypothesis that in dynamic stabilization of a lumbar spine using pedicle screws and ligament, addition of a fulcrum in front of the ligament can unload the disc. Second, to determine the relationship between the length and stiffness of the fulcrum and the ligament on disc unloading, lordosis and motion preservation. Activity related low back pain may be attributable to abnormal disc loading or abnormal movement. Spinal fusion addresses both the mechanisms, but it has limitations. Soft stabilization with Graf ligament restricts abnormal movement but increases the disc pressure. The Dynesys system uses a plastic cylinder around the ligament to prevent overloading the disc, but it restricts extension and loses lordosis. A novel dynamic stabilization system (fulcrum assisted soft stabilization or FASS) was developed in which a flexible fulcrum was placed in front of a ligament between the pedicle screws. It was hypothesized that the fulcrum should transform the compressive force of a ligament behind into a distraction force in front and unload the disc. Three spine models were developed using wooden blocks for vertebral bodies and neoprene rubber of different hardness for disc. Their load-deformation character was tested and compared with that of the cadaver spine in a spine tester. The spine model with the closest load-deformation property to cadaver spine was then tested for the effect of a FASS system, consisting of high density polythene rod as fulcrums and rubber "O" rings as ligaments. The disc pressure in the spine models were recorded with strain gauge in the center. Application of ligaments alone across the pedicle screws increased the disc pressure, produced a lordosis, and reduced the range of motion. Application of fulcrums reduced the disc pressure and maintained the lordosis. Increasing the fulcrum length resulted in progressive unloading of the disc but increased stiffness of the motion segment. As the fulcrum length approximated the height of the motion segment, the lordosis was lost, and the disc was completely unloaded. Decreasing the lateral bending stiffness of the fulcrum had minimal effect on disc unloading and motion-segment stiffness. The novel FASS system can unload the disc, control the range of motion, and maintain lordosis. These parameters may be controlled with a suitable combination of ligament and fulcrum system. The study provides an indication toward the desirable biomechanical properties of the fulcrum and ligament for future development of a clinically applicable prototype.