Posterior Dynamic Stabilization Research Articles

“Dynamic Fusion” in Degenerative Lumbar Spine Disorders

Introduction Dynamic stabilization in lumbar degenerative disorders has become very popular in the last few years. The basic concept of pedicle-screw-based systems is to reduce stiffness of the implants to allow load sharing between instrumentation system and functional spine (movement) unit to prevent adjacent segment syndrome. Basic biomechanical requirements for this philosophy are as follows: (a) a predicable load distribution to the intervertebral disk, (b) the limitation (control) of range of motion, and (c) to maintain and/or to restore the sagittal (sacral) balance. Disk degeneration results in loss of disk height and increase of axial compression loading in the posterior spine elements, probably accompanied with accelerated facet degeneration (arthrosis). Challenged by G. Perrinás reports in the late 1990s we started in 2002 with dynamic (semirigid) transpedicular stabilization systems in degenerative lumbar spine disorders using Isolock device, later using Isobar and AladynR device also. Materials and Methods This paper presents an inhomogene case presentation of 26 patients with different perception of degenerative lumbar disorders. Patients underwent a so called “Dynamic Fusion” between 2003 and 2007 using PLIF or TLIF added by posterior transpedicular dynamic (semirigid) stabilization. The case presentation presents preoperative, postoperative radiographs, and maximally follow-up radiographs to show a perfect bony healing in anterior elements. Definition of Dynamic Fusion Semirigid pedicle screw systems allow an increased anterior column load-sharing leading to favor osteogenesis with enhanced interbody fusion. This physical phenomenon is related to Wolffás Law. Lavaste and Perrin validated in 1993 in a finite element model of the lumbar spine that semirigid posterior instrumentation increases compared to rigid instrumentation of the load transmission through the anterior column. This observation and the publication by Goel et al confirmed that dynamic stabilization systems enable more load through the anterior column and the interbody graft compared to rigid systems without compromising stability, led to changing philosophy. We started to combine PLIF/TLIF with posterior transpedicular semirigid stabilization over the instrumented segment. Results No loosening signs of the PLIF/TLIF implants have been followed-up in this patient cohort. The evaluated pain relief is depended on many factors but all patients had a pain level degree in the VAS (25%). Conclusion The PLIF/TLIF in degenerative lumbar spine disorders showed in combination with posterior semirigid stabilization good clinical and radiographical results. No implant loosening has been followed up. I confirm having declared any potential conflict of interest for all authors listed on this abstract Yes Disclosure of Interest None declared Perrin G: Treatment of lumbar spondylolisthesis and related unstable spinal lesions: the usefulness of PLIF with cages and dynamic interpedicular posterior fixation for circumferential arthrodesis and prevention of adjacent level degeneration. presented at the 3rd World Spine Meeting, Rio de Janeiro, 2005 Goel VK, Lim Th, Gwon J, et al. Effects of rigidity of an internal fixation device. A comprehensive biomechanical investigation. Spine 1991;16:155–161

Unusual cause of acute low-back pain: sudden annulus fibrosus rupture.

Low-back pain is a common problem in neu-rosurgery practice, and an algorithm has been developed for assessing these cases. However, one subgroup of these patients shares several clinical features and these individuals are not easy to categorize and diagnose. We present our observations for 8 of these patients, individuals with low-back pain caused by atypical annulus fibrosus rupture (AAR). The aim of this study is to show the consequences of overlooked annular tears on acute onset of low back pain. Eight patients with acute-onset severe low-back pain were admitted. Physical examinations were normal and each individual was examined neurologically and assessed with neuroradiologic studies [plain x-rays, magnetic resonance imaging (MRI), discography and computed tomography (CT) discography]. AAR was ultimately diagnosed with provocative discography. In all cases, MRI showed a healthy disc or mild degeneration, whereas discography and CT discography demonstrated disc disease. Anterior interbody cage implantation was performed in 3 of the 8 cases and posterior dynamic stabilization was carried out in 3 cases. The other 2 individuals refused surgery, and we were informed that one of them developed disc herniation at the affected level 1 year after our diagnosis. Clinical and radiological outcomes were evaluated. In cases where AAR is suspected, MRI, discography, and CT discography should be performed in addition to routine neuroradiologic studies.

Interpedicular Travel in the Evaluation of Spinal Implants

In vitro flexibility testing of the lumbar spine. The goal of this study was to evaluate a motion-preserving posterior dynamic stabilization (PDS) implant based on newly defined parameters describing interpedicular kinematics. PDS implants have been designed as either motion-preserving or adjunct-to-fusion devices to treat various degenerative spinal pathologies. The ambiguity of design and evaluation goals and the inability of traditional biomechanical parameters to appropriately describe the behavior of PDS devices in vitro have served as the impetus to develop kinematic parameters more specific to this class of device. Flexibility testing of 6 fresh-frozen human lumbar spines was conducted before and after destabilization of the index level (L4-L5). Testing under the same protocol was repeated after treatment at the index level with a 1-level PDS device, extension of the device to the adjacent inferior level (L5-S1), and treatment with a hybrid construct consisting of the PDS implant at L4-L5 and rigid fixation at L5-S1. The kinematic response was recorded using an optoelectric tracking system and reported in terms of intervertebral range of motion (ROM) and newly developed parameters describing interpedicular motion. Based on ROM and interpedicular kinematics, the devices implanted at L4-L5 provide significant but not differing stabilization in flexion-extension with implantation after a significant destabilization procedure. Interpedicular kinematic results indicate that the 2-level construct contributes to significantly more motion at L5-S1 compared with rigid fixation. This result was not detected when evaluated by the ROM metric. Those involved in the design and evaluation of PDS devices may benefit from evaluation of interpedicular kinematics. Evaluating intervertebral motion from the perspective of the pedicle screw allows for a direct and intuitive translation between in vitro test results and design parameters. Furthermore, these parameters may provide additional clinical insight into the biomechanics of the healthy and pathological spine. The study presented indicates that this approach may be more sensitive in detecting differences in implant motion between PDS devices.

Prospective evaluation of a dorsal decompression and posterior dynamic flexion-limiting stabilization in patients with spinal stenosis and degenerative disk disease: Twelve-month follow-up

Prospective evaluation of a dorsal decompression and posterior dynamic flexion-limiting stabilization in patients with spinal stenosis and degenerative disk disease: Twelve-month follow-up

Effect of Graded Facetectomy on Biomechanics of Dynesys Dynamic Stabilization System

Finite element (FE) method was used to compare the biomechanics of L3-S1 lumbar spine with graded facetectomy before and after placement of Dynesys. To evaluate the biomechanics of Dynesys as a function of graded bilateral facetectomies. Spinal fusion or posterior dynamic stabilization systems are used to restore stability after facetectomies. The intact FE spine was modified to simulate decompression at L4-L5 with 50% and 75% and total facetectomy with/without dynamic stabilization with Dynesys. Biomechanics of the implanted level was investigated under different physiological loadings. Total facetectomy increased the motion in extension (8.7° vs. 2.7° for intact) and axial rotation (8.4° vs. 2.4° for intact). However the decrease in motion in the Dynesys model ranged from 65% in axial rotation to 80% in flexion for all facetectomies, except in the total facetectomy axial rotation case (motion higher than intact). The center of rotation of dynamic stabilized segment moved inferior/posterior in partial facetectomy and superior/posterior in total facetectomy with respect to the intact and destabilized cases. The Dynesys screws observed peak stresses up to 28% higher than those of a rigid fixation system in certain loadings, such as lateral bending and extension. The critical loosening torque applied to the screws in total facetectomy case was 6 times the partial facetectomy case in axial rotation. Partial facetectomy had a minimal effect on range of motion on the Dynesys-implanted segment. However, in the case of total facetectomy the motion increased by almost 40% in flexion and by 200% in axial rotation. The higher stresses applied to the screws in Dynesys in specific loadings may lead to higher risk of screw failure in Dynesys than in a generic rigid fixation construct.

Rationale of a Test Setup with a Defined COR for Extra-Discal Motion-Preserving Implants with a Low Implant Stiffness

Abstract In the current version of ASTM F2624, the center of rotation (COR) is not specified. Potentially, each device can be tested using a different COR, which subsequently makes a direct design comparison of results difficult. Four posterior dynamic stabilization (PDS) devices (Dynesys, DYN, Zimmer; DSS, Paradigm Spine; and two Aesculap implant concepts) were tested in comparison to a rigid-fixation device and to the native situation of the lumbar spine on fresh-frozen human lumbar spines (L3–L5). The instrumented level was L4–L5. The PDS systems have axial compressive stiffness values ranging from 10 N/mm to 230 N/mm and were all made compatible to connect with the pedicle-screw system. The specimens were loaded in a spinal simulator, applying pure moments for flexion/extension, lateral bending and axial rotation (+/−7.5 Nm) with a defined velocity. The COR was analyzed based on the data measured with a 3-dimensional (3D) motion-analysis system. The effect of the PDS on the location of the COR is most pronounced in the sagittal plane. In general, the higher the implant stiffness, the more the COR shifted in a posterior direction. The DYN had a similar COR to the rigid fixator. However, the PDS systems with low axial compressive stiffness values (range: 10–70 N/mm) showed very similar results on CORs, which are located in the region of the posterior border of the intervertebral disc. In the frontal and transversal plane, the COR was found to be close to the native situation for each system. Therefore, for PDS devices with low implant stiffness, the location of the COR varies only marginally and can be specified for a test setup. An initial proposal that will allow side-by-side comparison for these kinds of PDS systems is given and the feasibility of the new test setup could be proven for all three loading conditions.

Radiographic and clinical results of posterior dynamic stabilization for the treatment of multisegment degenerative disc disease with a minimum follow-up of 3 years

This study aims to compare radiographic and clinical outcomes of Dynesys and posterior lumbar interbody fusion (PLIF) for the treatment of multisegment disease. Thirty-five consecutive patients who received Dynesys implantation at three levels from L1 to S1 from November 2006 to July 2007 were studied. A retrospective analysis of the medical records of 25 patients with the same indications who received 3-level PLIF (L1-S1) was also conducted. Radiographic and clinical outcomes between the groups were compared. All patients included in the analysis completed 3-year follow-up. Dynesys stabilization resulted in higher preservation of motion at the operative levels, as well as total range of motion from L1 to S1. A decrease of anterior disc height was seen in the Dynesys group and an increase was seen in the PLIF group. An increase in posterior disc height was noted in both groups; however, was greater in the PLIF group at 3 years. The Dynesys group showed a greater improvement in Oswestry Disability Index and visual analogue scale back pain scores at 3 years postoperatively. There were no differences in complications between the two groups. In conclusion, Dynesys is an acceptable alternative to PLIF for the treatment of multisegment lumbar disease.

Could Junctional Problems at the End of a Long Construct be Addressed by Providing a Graduated Reduction in Stiffness?

The effect of long, rigid fixation on adjacent level hypermobility was investigated in a human cadaver model with and without a transitional posterior dynamic stabilization (PDS) device placed at the last caudal level. To evaluate if PDS devices are useful in the setting of spinal deformities to restore increased adjacent level motions, which occur in long constructs. The hypothesis is that load-sharing benefits of these devices will be most suitable in long constructs and may reduce thoracolumbar junctional effects. The PDS device evaluated has a compressive spacer and flexion-dampening bumper. Mechanical factors such as excessive mobility, increased disc height due to instrumentation, and abnormal loading are thought to accentuate distal level problems, which occur in extended instrumentation. Specifically adjacent level degeneration and distal junctional kyphosis are known to occur in these cases. Seven cadaver spines were tested from T7 to L3. Long instrumentation was applied in 2 rigid groups, R1: Rigid (T8-L2) and R2: Rigid (T8-L1), and PDS to the last caudal level of each, RP1: Rigid (T8-L1) + PDS (L1-L2), and RP2: Rigid (T8-T12) + PDS (T12-L1). Range of motion was evaluated at surgical and distal adjacent levels after displacement controlled loading in a spine tester. Distal adjacent level motion was increased after 5- and 6-level rigid fixation in flexion-extension, lateral bending, and axial rotation. Most of the increases were seen in axial rotation and lateral bending. Replacing the last caudal instrumented level with the PDS test device was able to alleviate hypermobile conditions of the adjacent noninstrumented level, closer to intact (24%, 12% reduction in RP2, RP1, respectively). Reduction of hypermobility caused by extended arthrodesis may represent a new and ideally suited function for PDS devices. Mechanically, the devices were seen to kinematically restore abnormal distal motion, especially with placement of the PDS at the thoracolumbar junction.

Can posterior dynamic stabilization reduce the risk of adjacent segment deterioration?

The aim of this study was to systematically review the relevant literature to develop a benchmark for the incidence of adjacent segment degeneration (ASDeg) and adjacent segment disease (ASDis) following the posterior dynamic stabilization (PDS) procedure and to investigate whether conclusions can be made with regard to the isolated PDS procedure in reducing the risk of ASDeg and ASDis compared with fusion, and with regard to the role of additional PDS devices implanted adjacent to fusion in protecting from ASDeg and ASDis caused by the neighboring fusion. We retrieved electronic databases of Medline, Ovid and Cochrane Central Registry of Controlled Trials, combined with a supplemental hand search. Thirty-one articles met our inclusion criteria. The pooled incidence of ASDeg and ASDis following PDS procedure was 16.4% and 5.5% respectively. Data from comparative studies showed a significantly lower incidence of ASDeg and nonsignificantly lower incidence of ASDis following PDS than following fusion surgery. Further, the additional PDS devices implanted adjacent to fusion could significantly reduce the risk of ASDeg and nonsignificantly decrease that of ASDis caused by fusion. These results suggested relative success of the PDS procedure in protecting against ASDeg and ASDis.

Posterior dynamic stabilization for the treatment of patients with lumbar degenerative disc disease: long-term clinical and radiological results

Comparison of long-term preoperative and postoperative clinical and radiological results for patients diagnosed with degenerative disc disease that underwent posterior dynamic stabilization. Lumbar disc degeneration is caused by a variety of factors. Disruptions in the vertebral endplate result in defects in disc nutrition and, thus, disc degeneration. The aims of dynamic stabilization are to unload the disc/facet joints, preserve motion under mechanical load, and restrict abnormal motion in the spinal segment. Twenty-five patients diagnosed with lumbar degenerative disc disease were enrolled. Totally, 25 vertebral segments were subjected to posterior dynamic stabilization. Patients were clinically evaluated in the preoperative and postoperative periods using the Oswestry Disability Index (ODI) and Visual Analog Scale (VAS). Segmental movement was evaluated radiologically in the late postoperative period by measuring the segmental angles during flexion and extension. Significant postoperative improvements were observed in the ODI and VAS measurements (P < 0.01). During the long postoperative period (averaging 5 years and 2 months), lumbar lordosis angles, intervertebral space ratio and segmental ratio were measured and compared statistically. Adjacent segment disease developed in two patients. Both patients received L5-S1 discectomy. Good clinical outcomes were observed in the treatment of lumbar degenerative disc disease with a posterior dynamic system.

Skipping Posterior Dynamic Transpedicular Stabilization for Distant Segment Degenerative Disease

Objective. To date, there is still no consensus on the treatment of spinal degenerative disease. Current surgical techniques to manage painful spinal disorders are imperfect. In this paper, we aimed to evaluate the prospective results of posterior transpedicular dynamic stabilization, a novel surgical approach that skips the segments that do not produce pain. This technique has been proven biomechanically and radiologically in spinal degenerative diseases. Methods. A prospective study of 18 patients averaging 54.94 years of age with distant spinal segment degenerative disease. Indications consisted of degenerative disc disease (57%), herniated nucleus pulposus (50%), spinal stenosis (14.28%), degenerative spondylolisthesis (14.28%), and foraminal stenosis (7.1%). The Oswestry Low-Back Pain Disability Questionnaire and visual analog scale (VAS) for pain were recorded preoperatively and at the third and twelfth postoperative months. Results. Both the Oswestry and VAS scores showed significant improvement postoperatively (P < 0.05). We observed complications in one patient who had spinal epidural hematoma. Conclusion. We recommend skipping posterior transpedicular dynamic stabilization for surgical treatment of distant segment spinal degenerative disease.

Long-term Follow-up (Minimum 5 Years) Study of Single-level Posterior Dynamic Stabilization in Lumbar Degenerative Disease; 'Interspinous U' & 'DIAM'.

ObjectivesRecently posterior dynamic stabilizations (PDS) are increased in degenerative lumbar disease. But, some previous studies had doubts its long term prognosis. Long term clinical and radiological results of PDS using interspinous device (Interspinous U, DIAM) were analyzed.MethodsWe have used the 'interspinous U' and 'DIAM' for patients with lumbar spinal stenosis. We included single level lumbar spinal stenosis patients who completed minimum 60 months follow-up evaluation. All patients checked plain lateral and flexion-extension views at immediately after the surgery and each follow-up. The clinical outcome was measured by Odom's criteria. Complications including post operative infection, bony erosion, device fracture, device malformations, and instabilities were surveyed.ResultsWe included 18 for 'Interspinous U' and 7 patients 'DIAM' groups. Mean follow-up durations for 'Interspinous U' and 'DIAM' were 74.6 and 62.6 months, respectively. Satisfactory groups were 50.0% and 42.9 % for 'Interspinous U' and 'DIAM' groups. In 'Interspinous U' group disc height ratio increased transiently in immediate postoperative period (from 0.18 to 0.21) and then, decreased significantly in last follow-up (0.18). In 'DIAM' group, disc height ratio increased transiently in immediate postoperative period (from 0.18 to 0.19), and then decreased significantly in the last follow-up (0.16). Three (16.7%) and two (28.6%) patients undergo on a re-operation due to severe back pain in 'Interspinous U' and 'DIAM' groups.ConclusionLong term follow up 'Interspinous U' and 'DIAM' group showed low patient satisfaction and poor radiological outcomes. To ascertain the benefit of PDS compare with posterior screw fixation, prospective analysis with larger population and multi-center study will be needed.

Pedicle Screw-Based Posterior Dynamic Stabilization: Literature Review

Posterior dynamic stabilization (PDS) indicates motion preservation devices that are aimed for surgical treatment of activity related mechanical low back pain. A large number of such devices have been introduced during the last 2 decades, without biomechanical design rationale, or clinical evidence of efficacy to address back pain. Implant failure is the commonest complication, which has resulted in withdrawal of some of the PDS devices from the market. In this paper the authors presented the current understanding of clinical instability of lumbar motions segment, proposed a classification, and described the clinical experience of the pedicle screw-based posterior dynamic stabilization devices.

A Short History of Posterior Dynamic Stabilization

Interspinous spacers were developed to treat local deformities such as degenerative spondylolisthesis. To treat patients with chronic instability, posterior pedicle fixation and rod-based dynamic stabilization systems were developed as alternatives to fusion surgeries. Dynamic stabilization is the future of spinal surgery, and in the near future, we will be able to see the development of new devices and surgical techniques to stabilize the spine. It is important to follow the development of these technologies and to gain experience using them. In this paper, we review the literature and discuss the dynamic systems, both past and present, used in the market to treat lumbar degeneration.

Biomechanics of Disc Degeneration

Disc degeneration and associated disorders are among the most debated topics in the orthopedic literature over the past few decades. These may be attributed to interrelated mechanical, biochemical, and environmental factors. The treatment options vary from conservative approaches to surgery, depending on the severity of degeneration and response to conservative therapies. Spinal fusion is considered to be the “gold standard” in surgical methods till date. However, the association of adjacent level degeneration has led to the evolution of motion preservation technologies like spinal arthroplasty and posterior dynamic stabilization systems. These new technologies are aimed to address pain and preserve motion while maintaining a proper load sharing among various spinal elements. This paper provides an elaborative biomechanical review of the technologies aimed to address the disc degeneration and reiterates the point that biomechanical efficacy followed by long-term clinical success will allow these nonfusion technologies as alternatives to fusion, at least in certain patient population.

Which Radiographic Parameters Are Linked to Failure of a Dynamic Spinal Implant?

Knowledge about factors leading to failure of posterior dynamic stabilization implants is essential to design future implants and establish surgical indications. Therefore, we analyzed an implant for single-level or hybrid configuration (adjacent to spondylodesis), which was recalled due to high failure rates. We asked: (1) Were postoperative radiographic changes linked to implant failure? (2) Were radiographic parameters different between the two configurations? And (3) was implant failure related to inferior clinical scores? The implant was used in 18 patients with lumbar single-level spinal stenosis or with (recurrent) disc herniation and concurrent degenerative disc disease and in 22 patients with an initially degenerated segment adjacent and superior to a fusion site. We prospectively obtained preoperative and postoperative (immediate, 6-, 12- and 24-month) clinical and radiographic evaluations; 37 of the 40 patients completed the 24-month followup. Using plain and extension-flexion radiographs, we compared implant failure rates and their association with postoperative implant translation, anterior and posterior disc height, and ROM for each configuration and between configurations. We assessed associations between clinical scores (VAS pain scores for back and leg, Oswestry Disability Index) and implant failure. Implant failure occurred in 10 of the 37 implants and corresponded to greater posterior disc height (single-level only) and implant translation. Adjacent-segment ROM increases and posterior disc height decreases over time were greater with the hybrid configuration. Implant failure rate related to higher Oswestry Disability Index (single-level only) and higher back pain scores. Implant translation is associated with failure likely due to insufficient resistance to shear forces. Load transfer may cause progressive degeneration in the dynamic and adjacent segments, especially in the hybrid configuration.

The Pedicle-to-Pedicle Distance Translation in Normal Lumbar Spine during Flexion-Extension and its Importance in Dynamic Stabilization

Kinematic effects of pedicle-screw based posterior dynamic stabilization (PDS) devices are closely related to devices’ fatigue failure risk and pain relief function. Conventionally, such effects are assessed mainly by Range of angular Motion (ROM). However, angular ROM was found to be inadequate to explain fatigue failure of some recent PDS devices. The reason behind is normal segmental angular motion may involve changes in the Inter-Pedicular Distance (IPD), whereas PDS device may permit angular motion without permitting changes in the IPD distances.

Comparison of Three Posterior Dynamic Stabilization Devices

A biomechanical study using human cadaveric lumbar spinal motion segments and three different posterior stabilization devices. To compare the range of motion, disc height, and foraminal area of a spinal motion segment intact, injured, and fixed with each of three posterior lumbar motion preservation devices. Motion-sparing lumbar posterior dynamic stabilization devices are gaining increasing popularity, particularly for the treatment of degenerative disc disease. The PercuDyn, the X-Stop, and the Isobar posterior stabilization devices were compared using an in vitro cadaveric model. First, pure moments of ±8 Nm were applied in all three planes, then a follower load of 700 N was applied, and finally, sagittal bending tests were repeated. All tests were conducted using an 8-df servohydraulic load frame. Experiments were performed intact, with a simulated injury, and then with each of the three devices for a total of four specimens per device. Foraminal area and disc height (posterolateral and anterior surface) were measured under neutral and peak torques in all three planes and range of motion was recorded for all experimental conditions. Overall, the injury model successfully increased range of motion and decreased disc height and foraminal area. Once treated with one of the three implants, the PercuDyn was most effective at preventing hyperextension, decreasing extension with a follower load by a mean of 52% compared to injured conditions (P = 0.07). The X-Stop stabilized the posterior column, increasing foraminal area under all conditions, particularly extension with a follower load, by 27% compared to injured conditions (P = 0.01). The Isobar, the only device to stabilize the anterior column, increased anterior disc height under flexion with a follower load by 22% (P = 0.03). All three devices functioned as intended by their respective manufacturers, but each appeared to excel in different areas; therefore, each should be used for unique clinical applications.

Motion-preserving technologies for degenerative lumbar spine: The past, present, and future horizons

Over the past few decades, remarkable advancements in the understanding of the origin of low-back pain and lumbar spinal disorders have been achieved. Spinal fusion is generally considered the “gold standard” in the treatment of low-back pain; however, fusion is also associated with accelerated degeneration of adjacent levels. Spinal arthroplasty and dynamic stabilization technologies, as well as the continuous improvement in diagnosis and surgical interventions, have opened a new era of treatment options. Recent advancements in nonfusion technologies such as motion-preservation devices and posterior dynamic stabilization may change the gold standard. These devices are designed with the intent to provide stabilization and eliminate pain while preserving motion of the functional spinal unit. The adaption of nonfusion technologies by the surgical community and payers for the treatment of degenerative spinal conditions will depend on the long-term clinical outcome of controlled randomized clinical studies. Although the development of nonfusion technology has just started and the adoption is very slow, it may be considered a viable option for motion preservation in coming years. This review article provides technical and surgical views from the past and from the present, as well as a glance at the future endeavors and challenges in instrumentation development for lumbar spinal disorders.

Intervertebral disc properties: challenges for biodevices

Intervertebral disc biodevices that employ motion-preservation strategies (e.g., nucleus replacement, total disc replacement and posterior stabilization devices) are currently in use or in development. However, their long-term performance is unknown and only a small number of randomized controlled trials have been conducted. In this article, we discuss the following biodevices: interbody cages, nuclear pulposus replacements, total disc replacements and posterior dynamic stabilization devices, as well as future biological treatments. These biodevices restore some function to the motion segment; however, contrary to expectations, the risk of adjacent-level degeneration does not appear to have been reduced. The short-term challenge is to replicate the complex biomechanical function of the motion segment (e.g., biphasic, viscoelastic behavior and nonlinearity) to improve the quality of motion and minimize adjacent level problems, while ensuring biodevice longevity for the younger, more active patient. Biological strategies for regeneration and repair of disc tissue are being developed and these offer exciting opportunities (and challenges) for the longer term. Responsible introduction and rigorous assessment of these new technologies are required. In this article, we will describe the properties of the disc, explore biodevices currently in use for the surgical treatment of low back pain (with an emphasis on lumbar total disc replacement) and discuss future directions for biological treatments. Finally, we will assess the challenges ahead for the next generation of biodevices designed to replace the disc.