Pedicle-based Dynamic Stabilization Research Articles

Comparison of Cortical Bone Trajectory to Pedicle-Based Dynamic Stabilization: An Analysis of 291 Patients.

Pedicle-based dynamic stabilization (DS) has gained popularity outside of America. Although pedicle screw (PS) loosening has always been a concern, it is reportedly innocuous. Cortical bone trajectory (CBT) screw is an emerging option with less invasiveness and similar effectiveness to PS in short-segment lumbar fusion. This study aimed to verify the use of CBT for DS by comparing the outcomes between pedicle- and CBT-based DS. Consecutive patients with lumbar spondylosis or low-grade spondylolisthesis who underwent 1- or 2-level DS between L3-5 with a minimum follow-up of 24 months were reviewed. Screw loosening was determined by computed tomography and the incidences were compared. A total of 291 patients who underwent Dynesys DS (235 pedicle- and 56 CBT-based, respectively) were compared. The demographics and preoperative conditions were similar. All the clinical outcomes improved at 24-month postoperation, while the CBT-based group had less operation time and blood loss than the pedicle-based group. The rates of screw loosening were lower in the CBT-based (5.4% per screw and 12.5% per patient) than the pedicle-based group (9% per screw and 26.4% per patient). Furthermore, there were no differences in the clinical outcomes and complication profiles. The CBT-based DS for 1- or 2-level lumbar degeneration demonstrated equivalent clinical improvement as the pedicle-based DS. The adaption of CBT-based screws for DS could be a less invasive approach (shorter operation time and less blood loss), with lower chances of screw loosening than the conventional PS-based DS.

Lumbar dynamic pedicle-based stabilization versus fusion in degenerative disease: a multicenter, double-blind, prospective, randomized controlled trial.

Fusion is the standard of treatment for degenerative lumbar symptomatic instabilities. Dynamic stabilization is a potential alternative, with the aim of reducing pathological motion. Potential advantages are a reduction of surgical complexity and morbidity. The aim of this study was to assess whether dynamic stabilization is associated with a higher degree of functional improvement while reducing surgical complexity and thereby surgical duration and perioperative complications in comparison with lumbar fusion. This was a multicenter, double-blind, prospective, randomized, 2-arm superiority trial. Patients with symptomatic mono- or bisegmental lumbar degenerative disease with or without stenosis and instability were randomized 1:1 to instrumented fusion or pedicle-based dynamic stabilization. Patients underwent either rigid internal fixation and interbody fusion or pedicle-based dynamic stabilization. The primary endpoint was the Oswestry Disability Index (ODI) score, and secondary endpoints were pain, health-related quality of life, and patient satisfaction at 24 months. Of 293 patients randomized to fusion or dynamic stabilization, 269 were available for analysis. The duration of surgery was significantly shorter for dynamic stabilization versus fusion, and the blood loss was significantly less for dynamic stabilization (380 ml vs 506 ml). Assessment of primary and secondary outcome parameters revealed no significant differences between groups. There were no differences in the incidence of adverse events. Dynamic pedicle-based stabilization can achieve similar clinical outcome as fusion in the treatment of lumbar degenerative instabilities. Secondary failures are not different between groups. However, dynamic stabilization is less complex than fusion and is a feasible alternative.

Biomechanical Investigation of Lumbar Interbody Fusion Supplemented with Topping-off Instrumentation Using Different Dynamic Stabilization Devices.

A biomechanical comparison study using finite element method. The aim of this study was to investigate effects of different dynamic stabilization devices, including pedicle-based dynamic stabilization system (PBDSS) and interspinous process spacer (ISP), used for topping-off implants on biomechanical responses of human spine after lumbar interbody fusion. Topping-off stabilization technique has been proposed to prevent adjacent segment degeneration following lumbar spine fusion. PBDSS and ISP are the most used dynamic stabilizers for topping-off instrumentation. However, biomechanical differences between them still remain unclear. A validated, normal FE model of human lumbosacral spine was employed. Based on this model, rigid fusion at L4-L5 and moderately disc degeneration at L3-L4 were simulated and used as a comparison baseline. Subsequently, Bioflex and DIAM systems were instrumented at L3-L4 segment to construct PBDSS-based and ISP-based topping-off models. Biomechanical responses of the models to bending moments and vertical vibrational excitation were computed using FE static and random response analyses, respectively. Results from static analysis showed that at L3-L4, the response parameters including annulus stress and range of motion were decreased by 41.6% to 85.2% for PBDSS-based model and by 6.3% to 67% for ISP-based model compared with rigid fusion model. At L2-L3, these parameters were lower in ISP-based model than in PBDSS-based model. Results from random response analysis showed that topping-off instrumentation increased resonant frequency of spine system but decreased dynamic response of annulus stress at L3-L4. PBDSS-based model generated lower dynamic stress than ISP-based model at L3-L4, but the dynamic stress was higher at L2-L3 for PBDSSbased model. Under static and vibration loadings, the PBDSSbased topping-off device (Bioflex) provided a better protection for transition segment, and likelihood of degeneration of supraadjacent segment might be relatively lower when using the ISPbased topping-off device (DIAM).Level of Evidence: 5.

Implant failure following pedicle based dynamic stabilization of the lumbar spine

Pedicle-based dynamic stabilization (PBDS) devices such as Dynesys are promoted as an alternative and less invasive option for rigid stabilization of one and even more levels of the lumbar spine. Promising features of the Dynesys system, as well as shortcomings, became obvious in several clinical studies. Since 2012, we started using a new PBDS device as an alternative for the Dynesys, to avoid the screw loosening and the kyphosing effect. The objective is to compare failure rates between the Dynesys and Balan-C type PBDS implant and factors affecting outcome. In a retrospective study we investigated a total of 90 patients with lumbar pedicle screw dynamic stabilization (a group of 64 patiënts with Dynesys stabilization is compared to a group of 26 patients with Balan-C stabilization). Mean follow-up was 48 and 38 months, respectively. Using logistic regression analysis the impact of baseline characteristics such as gender, age, body mass index (BMI), indication for surgery, primary or revision surgery, single versus more level surgery, surgeon's experience and type of the implant on implant failure was analyzed. We found a statistically significant difference in failure rates between the two systems (13% in the Dynesys group versus 62% in the Balan-C group). In multivariate analysis, type of implant was associated with implant failure (odds ratio : 13). Our current results call for an optimization of the pre-and post-marketing surveillance of pedicle-based dynamic stabilization.

Comparison of Clinical and Radiographic Results Between Posterior Pedicle-Based Dynamic Stabilization and Posterior Lumbar Intervertebral Fusion for Lumbar Degenerative Disease: A 2-Year Retrospective Study.

To compare outcomes between K-rod dynamic stabilization system (KDSS) and posterior lumbar intervertebral fusion (PLIF) for lumbar degenerative disease. This study retrospectively reviewed 98 patients who underwent lumbar surgery from March 2012 to June 2014, including 48 in the KDSS group and 50 in the PLIF group. All patients were followed up for at least 2 years. Duration of operation, blood loss, hospital stay, complications, and patient satisfaction were recorded and analyzed. Clinical outcomes were evaluated by visual analog scale and Oswestry Disability Index. Radiographic results including disk height index, foraminal height, and range of motion (ROM) were compared between groups. Compared with PLIF group, KDSS group had shorter duration of operation and less blood loss (P<0.001). There were no differences in hospital stay, complications, and patient satisfaction. Both groups demonstrated significant improvement in visual analog scale back and leg pain and Oswestry Disability Index. No significant difference was found between groups at any time point (P > 0.05). Postoperative disk height index and foraminal height increased significantly compared with preoperatively (P < 0.05). Although disk height index and foraminal height in KDSS group were smaller than PLIF group values, there were no significant differences between groups. ROM of total lumbar and implanted segment was decreased compared with preoperative ROM in both groups (P < 0.05), but the 2 values were higher in KDSS group (P < 0.05). Both KDSS and PLIF can improve clinical and radiographic outcomes for early-stage lumbar degenerative disease. Compared with PLIF, KDSS has better operative time, less blood loss, and better preservation of ROM, but prospective, randomized, controlled trials with larger sample size and longer follow-up are required.

Does stabilization of the degenerative lumbar spine itself produce multifidus atrophy?

The effect of stabilization of the degenerative segment on changes in the pattern of paraspinal muscle activity was investigated using a previously developed musculoskeletal model. Muscle activity change depending on L4-L5 segment stabilization with and without taking into account the presence of multifidus atrophy according to direct invasion of the back muscle during surgery (MADIBM) was analysed in erect standing and 20° flexed postures. For the stabilization of the degenerative segment, a fusion or non-fusion stabilization with a pedicle-based dynamic stabilization system (PBDS) was applied. During erect standing, fusion generated a 12% reduction in the total multifidus muscle force, while its reduction was 6.6% with PBDS application. The presence of MADIBM produced 23.0% and 22.5% reductions in fusion and with PBDS application, respectively. During 20° flexion, 10.5% and 9.3% reductions were produced for fusion and PBDS application, respectively, and the corresponding values were 23.4% and 23.0%, respectively, in the presence of MADIBM. Increased facet joint contact forces were produced at the non-stabilized levels after stabilization while in erect standing posture. Alterations in muscle activity, which could be regarded as adaptions to altered spinal stability, may generate unexpected secondary problems in the spine.

Effects of the level of mono-segmental dynamic stabilization on the whole lumbar spine

Little biomechanical data has been gathered for the biomechanical effects of pedicle-based dynamic stabilization system (PBDS) and fusion (a conventional titanium rod and cage) to the whole lumbar spine according to the instrumentation level. A previously validated three-dimensional, intact osteoligamentous L1-S1 finite element model was modified to incorporate three different PBDS (Dynesys, Nflex, or PEEK) and fusion at three different levels (L3-L4, L4-L5, and L5-S1). A new loading method that can create the segmental motion similar to an in-vivo measurement was applied to the model. The biomechanical changes in the stabilized models were compared with those of the intact model during sagittal plane motion. The simulation results demonstrated that Dynesys generated relatively larger motion when it was instrumented at the L3-L4 segment, whereas the Nflex was the most appropriate device for L4-L5 stabilization. Depending on the stabilization device and instrumented level, whole-lumbar segmental motion also varied. During flexion, stabilization at the L3-L4 level or L4-L5 level produced a relatively higher increase in the motion at all cranial levels. Stabilization at the L5-S1 level generated a slight decrease in the motion at the adjacent cranial level without respect to the type of fixation. In cases of fusion, the change in the motion was higher relative to that with PBDS. Given the biomechanical change at each level after stabilization, adjacent segment degeneration was expected cranially rather caudally, and the probability of this degeneration differed depending on the stabilization level and device.

Non-fusion procedure using PEEK rod systems for lumbar degenerative diseases: clinical experience with a 2-year follow-up.

BackgroundPolyetheretherketone (PEEK) rod system is a novel pedicle-based dynamic stabilization system. This study evaluated clinical and radiographic outcomes of non-fusion surgery by PEEK rod systems for treatment of degenerative lumbar diseases with a 2-year follow-up.MethodsFrom February 2012 to October 2012, 38 patients who underwent non-fusion surgery using PEEK rod systems were included in the study. Data on Oswestry Disability Index (ODI) score and Japanese Orthopaedics Association (JOA) score were collected and radiographs were obtained to evaluate disc height index (DHI) and range of motion (ROM) at each interval.ResultsBoth JOA and ODI scores significantly improved postoperatively. DHI showed a slight increase immediately after the surgery but gradually dropped below preoperative levels. Mean ROM values changed from 8.8° preoperatively to 1.8° at the 2-year follow-up point. Screw loosening occurred in one case at the 2-year follow-up.ConclusionsThe preliminary results indicated a significant improvement in clinical outcomes and advantageous implant safety. The non-fusion procedure using PEEK rod systems might be a viable alternative for treatment of lumbar degenerative diseases. The distraction technique needs to be improved for better postoperative DHI.

Clinical Outcomes and Complications After Pedicle-anchored Dynamic or Hybrid Lumbar Spine Stabilization: A Systematic Literature Review.

A systematic medline review. An overview of pedicle-based dynamic stabilization devices clinical outcomes. Fusion is the standard instrumentation for many pathologies of the lumbar spine. Worrying rates of failure, including adjacent segment degeneration (ASD), have consistently been reported. The interest for dynamic stabilization came from the need of minimizing the long-term complications related to the restriction of the lumbar motion. However, pedicle-based dynamic stabilization advantages and drawbacks remain controversial. Articles about the clinical outcomes were identified by a comprehensive Medline search. The inclusion criteria were a minimum follow-up of 12 months, indications for lumbar dynamic stabilization, and assessment of clinical outcomes and adverse events. The studied parameters included self-reported outcomes (pain, disability, and satisfaction) and complications. A total of 46 articles fulfilling the inclusion criteria were reviewed providing results for 2026 patients with a mean follow-up of 33 months. The postoperative improvements in terms of pain and disability were significant. Subjective assessment showed an overall patient satisfaction of 83.4%. Radiographic ASD occurred in 0%-34% of patients. Device breakage occurred in 0%-30%, and device loosening in 0%-72% of patients. The global amount of revision surgeries reached 9.4% mainly for breakage, ASD, or persistent pain, not always associated with screw loosening. Dynamic stabilization seems as safe and effective but benefits might partly come from decompressive gestures. Reported clinical outcomes seems to be comparable with outcomes published for fusion and no clear evidence of protection of the adjacent segments emerge from this mid-term review. Technical failures are design related but also linked with patient specificities. Relationships between sagittal balance and surgery outcomes are still rarely reported. Dynamic stabilization might display advantages in selected indications, such as moderate degeneration and beginning instability associated with clinical symptoms, but further clinical studies are needed.

Clinical Study of a New Transpedicular Nonfusion Posterior Dynamic Stabilization System for Treating Herniated Lumbar Intervertebral Disks

Nonfusion posterior dynamic stabilization systems, in which semirigid rods are used to restore spinal stability and to provide flexibility, aim to reduce or eliminate drawbacks associated with rigid fusion. In this study, we evaluated the 12-month clinical outcomes of patients treated with the K-Rod, a pedicle-based dynamic stabilization system. Patient participation was based on the presence of a herniated lumbar intervertebral disk complicated with endplate osteochondritis at L4-L5 or L5-S1. The clinical outcome at each assessment was assessed by Visual Analogue Scale to measure back pain, and the Oswestry Disability Index and range of motion to measure functional status preoperatively and postoperatively. Thirty-three patients (20 men and 13 women) with a mean age of 45.5 years were included. The mean Visual Analogue Scale score improved by 77% and the mean Oswestry Disability Index score improved by 77% from preoperative to postoperative. The range of motion results were statistically significant in the disease segment, but were not significant in adjacent segments. Nonfusion posterior dynamic stabilization using the K-Rod system is effective in improving clinical outcome, with sustained medium-term clinical improvements. Further observation is needed to evaluate its long-term effects.

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.

Back Muscle Changes after Pedicle Based Dynamic Stabilization

ObjectiveMany studies have investigated paraspinal muscle changes after posterior lumbar surgery, including lumbar fusion. However, no study has been performed to investigate back muscle changes after pedicle based dynamic stabilization in patients with degenerative lumbar spinal diseases. In this study, the authors compared back muscle cross sectional area (MCSA) changes after non-fusion pedicle based dynamic stabilization.MethodsThirty-two consecutive patients who underwent non-fusion pedicle based dynamic stabilization (PDS) at the L4-L5 level between February 2005 and January 2008 were included in this retrospective study. In addition, 11 patients who underwent traditional lumbar fusion (LF) during the same period were enrolled for comparative purposes. Preoperative and postoperative MCSAs of the paraspinal (multifidus+longissimus), psoas, and multifidus muscles were measured using computed tomographic axial sections taken at the L4 lower vertebral body level, which best visualize the paraspinal and psoas muscles. Measurements were made preoperatively and at more than 6 months after surgery.ResultsOverall, back muscles showed decreases in MCSAs in the PDS and LF groups, and the multifidus was most affected in both groups, but more so in the LF group. The PDS group showed better back muscle preservation than the LF group for all measured muscles. The multifidus MCSA was significantly more preserved when the PDS-paraspinal-Wiltse approach was used.ConclusionPedicle based dynamic stabilization shows better preservation of paraspinal muscles than posterior lumbar fusion. Furthermore, the minimally invasive paraspinal Wiltse approach was found to preserve multifidus muscles better than the conventional posterior midline approach in PDS group.

Comparison of the biomechanical effect of pedicle-based dynamic stabilization: a study using finite element analysis

Recently, nonfusion pedicle-based dynamic stabilization systems (PBDSs) have been developed and used in the management of degenerative lumbar spinal diseases. Still effects on spinal kinematics and clinical effects are controversial. Little biomechanical information exists for providing biomechanical characteristics of pedicle-based dynamic stabilization according to the PBDS design before clinical implementation. To investigate the effects of implanting PBDSs into the spinal functional unit and elucidate the differences in biomechanical characteristics according to different materials and design. The biomechanical effects of implantation of PBDS were investigated using the nonlinear three-dimensional finite element model of L4-L5. An already validated three-dimensional, intact osteoligamentous L4-L5 finite element model was modified to incorporate the insertion of pedicle screws. The implanted models were constructed after modifying the intact model to simulate postoperative changes using four different fixation systems. Four models instrumented with PBDS (Dynesys, NFlex, and polyetheretherketone [PEEK]) and rigid fixation systems (conventional titanium rod) were developed for comparison. The instrumented models were compared with those of the intact and rigid fixation model. Range of motion (ROM) in three motion planes, center of rotation (COR), force on the facet joint, and von Mises stress distribution on the vertebral body and implants with flexion-extension were compared among the models. Simulated results demonstrated that implanted segments with PBDSs have limited ROM when compared with the intact spine. Flexion motion was the most limited, and axial rotation was the least limited, after device implantation. Among the PBDS selected in this analysis, the NFlex system had the closest instantaneous COR compared with the intact model and a higher ROM compared with other PBDS. Contact force on the facet joint in extension increased with an increase of moment in Dynesys and NFlex; however, the rigid or PEEK rod fixation revealed no facet contact force. Implanted segments with PBDSs have limited ROM when compared with the intact spine. Center of rotation and stress distribution differed according to the design and materials used. These biomechanical effects produced a nonphysiological stress on the functional spinal unit when they were implanted. The biomechanical effects of current PBDSs should be carefully considered before clinical implementation.

NFlex Dynamic Stabilization System : Two-Year Clinical Outcomes of Multi-Center Study

ObjectivePedicle-based dynamic stabilization systems, in which semi-rigid rods or cords are used to restrict or control spinal segmental motion, aim to reduce or eliminate the drawbacks associated with rigid fusion. In this study, we analyzed the two-year clinical outcomes of patients treated with the NFlex (Synthes Spine, Inc.), a pedicle-based dynamic stabilization system.MethodsFive sites participated in a retrospective study of 72 consecutive patients who underwent NFlex stabilization. Of these 72 patients, 65 were available for 2-year follow-up. Patients were included based on the presence of degenerative disc disease (29 patients), degenerative spondylolisthesis (16 patients), lumbar stenosis (9 patients), adjacent segment degeneration (6 patients), and degenerative lumbar scoliosis (5 patients). The clinical outcome measures at each assessment were Visual Analogue Scale (VAS) to measure back pain, and Oswestry Disability Index (ODI) to measure functional status. Radiographic assessments included evidence of instrumentation failure or screw loosening.ResultsSixty-five patients (26 men and 39 women) with a mean age of 54.5 years were included. Mean follow-up was 25.6 months. The mean VAS score improved from 8.1 preoperatively to 3.8 postoperatively, representing a 53% improvement, and the ODI score from 44.5 to 21.8, representing a 51% improvement. Improvements in pain and disability scores were statistically significant. Three implant-related complications were observed.ConclusionPosterior pedicle-based dynamic stabilization using the NFlex system seems effective in improving pain and functional scores, with sustained clinical improvement after two years. With appropriate patient selection, it may be considered an effective alternative to rigid fusion.

Screw loosening in the Dynesys stabilization system: radiographic evidence and effect on outcomes

Dynamic stabilization systems are used to stabilize degenerative lumbar spondylosis. Loosening of the pedicle screws in such nonfusion implants is predictable. This retrospective study evaluated the incidence of screw loosening and its effect on clinical outcomes. Charts, radiographic films, and medical records of 71 consecutive patients who underwent decompression using Dynesys dynamic stabilization for 1- or 2-level lumbar spondylosis were reviewed. Radiographic films were evaluated and compared to detect screw loosening. A visual analog scale (VAS) for back pain and the Oswestry Disability Index (ODI) were used for measuring clinical outcome. Statistical analysis was conducted using the chi-square test and Student t-test. The 71 patients in the study sample had a mean age of 59.2 +/- 11.65 years (range 23-80 years), with slight female predominance (39 women, 32 men). The mean follow-up duration was 16.6 months (range 8-29 months). There were loose screws in 14 of 71 patients (19.7%), for a rate of 4.6% per screw (17 of 368 screws). Most screw loosening occurred in patients >/= 55 years old (13 of 14 patients) although age and sex had no effect on screw loosening (p = 0.233 and 0.109, respectively). Both the loose screw and solid screw groups experienced significant improvement after the surgery in VAS and ODI scores. On the VAS, scores improved from 5.9 +/- 2.99 to 2.1 +/- 2.14 in the loose screw group (p = 0.003), and from 5.7 +/- 3.45 to 2.9 +/- 2.68 in the solid screw group (p < 0.001). For the ODI scale, scores improved from 43.5 +/- 16.78% to 28.0 +/- 18.18% (p = 0.006) in the loose screw group, and from 52.1 +/- 20.92% to 24.6 +/- 19.78% (p < 0.001) in the solid screw group. There were no significant differences between the 2 groups (p = 0.334 for VAS, p = 0.567 for ODI). The preliminary study of this pedicle-based dynamic stabilization device for 1- and 2-level lumbar spondylosis shows radiographic evidence of screw loosening in 19.7% of patients and 4.6% of screws. Nonetheless, the loosening of screws has no adverse effect on clinical improvement.