Spinal Stabilization System Research Articles

Bibliometric Patent Review of Minimally Invasive Spine Surgery.

This study analyzes patents associated with minimally invasive spine surgery (MISS) found on the Lens open online platform. The goal of this research was to provide an overview of the most referenced patents in the field of MISS and to uncover patterns in the evolution and categorization of these patents. MISS has rapidly progressed, with a core focus on minimizing surgical damage, preserving the natural anatomy, and enabling swift recovery, all while achieving outcomes that rival traditional open surgery. While prior studies have primarily concentrated on MISS outcomes, the analysis of MISS patents has been limited. To conduct this study, we used the Lens platform to search for patents that included the terms "minimally invasive" and "spine" in their titles, abstracts, or claims. We then categorized these patents and identified the top 100 with the most forward citations. We further classified these patents into 4 categories: Spinal Stabilization Systems, Joint Implants or Procedures, Screw Delivery System or Method, and Access and Surgical Pathway Formation. Five hundred two MISS patents were identified initially, and 276 were retained following a screening process. Among the top 100 patents, the majority had active legal status. The largest category within the top 100 patents was Access and Surgical Pathway Formation, closely followed by Spinal Stabilization Systems and Joint Implants or Procedures. The smallest category was Screw Delivery System or Method. Notably, the majority of the top 100 patents had priority years falling between 2000 and 2009, indicating a moderate positive correlation between patent rank and priority year. Thus far, patents related to Access and Surgical Pathway Formation have laid the foundation for subsequent innovations in Spinal Stabilization Systems and Screw Technology. This study serves as a valuable resource for guiding future innovations in this rapidly evolving field.

Role of Dynamic Neuromuscular Stabilization Exercises in Physical Rehabilitation: A Systematic Review

The objective of this study was to systematically review and evaluate the relevant literature on dynamic neuromuscular stabilization (DNS) exercises. A literature search was conducted from inception to February, 2023 within PubMed, Medline, Google Scholar, Science Direct and EBSCO to identify studies related to the role of DNS in the rehabilitation of musculoskeletal and neurological conditions. The databases were searched using the following key words: Dynamic neuromuscular stabilization, pain, physical function, stroke, hemiplegia. After the initial search full text studies related to the use of DNS exercises in the rehabilitation of musculoskeletal or neurological conditions were selected for further review irrespective of study design. A quantitative analysis of the selected studies was done by using the Joanna Briggs Institute Critical Appraisal tool. The systematic review identified a total of 16 studies (seven low risk, six medium risk and three high risk of bias) that met the inclusion criteria. These studies examined the effects of DNS exercises on a range of conditions, including low back pain, cerebral palsy, stroke, migraines, and posterior cortical atrophy. The findings consistently demonstrated significant improvements in core muscle activation, joint stability, functional movements, and pain reduction following DNS intervention. Additionally, improvements in specific condition-related outcomes were reported in several studies, indicating the potential effectiveness of DNS in addressing deficits related to musculoskeletal and neurological conditions. The findings of this systematic review suggest that DNS exercises have a beneficial impact on physical rehabilitation outcomes in individuals with musculoskeletal and neurological conditions. The activation of core muscles and the integrated spinal stabilization system (ISSS), facilitated through DNS, promote spinal stability, reduce pain, and enhance functional movements. This study is registered as PROSPERO No. CRD42021278224.

Comparing the Efficacy of Dynamic Neuromuscular Stabilization Exercises and Kegel Exercises on Stress Urinary Incontinence in Women: A Pilot Study.

Background and objective Stress urinary incontinence (SUI) is a prevalent condition affecting women of various age groups, significantly impacting their quality of life. To address this multifaceted issue, a comprehensive approach that goes beyond traditional pelvic floor exercises is needed. Dynamic neuromuscular stabilization (DNS) exercises, targeting the integrated spinal stabilization system, offera promising alternative. Thus, this study aimed to compare the effectiveness of DNS exercises and Kegel exercises in managing SUI among women. Methods This single-blinded, pilot study involved 24 women aged 18-40 years with mild to moderate SUI. Participants were divided into DNS and Kegel exercise groups. Outcome measures included perineometer readings, electromyography (EMG) data, and the Urogenital Distress Inventory-6 (UDI-6). Statistical analysis compared baseline and 12-week data within and between groups, and rank-biserial correlation coefficient (r) as a measure of effect size in our study wascalculated. Results At 12 weeks, the DNS group showed significant improvement in pelvic floor muscle strength compared to Kegel exercises (p = 0.005). Both groups had significantly enhanced pelvic floor muscle strength (p < 0.05). A significant change occurred for EMG average, EMG peak, and EMG maximum voluntary contraction (MVC) at 12 weeks (average p = 0.005; peak p = 0.001; MVC p = 0.009), with significant improvements in both groups (p < 0.05). For UDI-6, a significant difference emerged between the two groups at 12 weeks (p < 0.05), with significant improvements in both groups individually from baseline to 12 weeks (p < 0.05). The effect size "r" for all variables indicated a medium to large effect size, underscoring the substantial and significant impact of DNS exercises in managing SUI among women compared to Kegel exercises. Conclusion This study suggests that DNS exercises, emphasizing the coordinated activation of the diaphragm, abdominals, multifidus, and pelvic floor, may provide a more effective approach for managing SUI in women compared to traditional Kegel exercises.

Balance and muscle strength tests in patients with osteoporotic vertebral fractures to develop tailored rehabilitation programs.

Authors perform a cross-sectional study of functional abilities of the patients with osteoporotic vertebral fractures (VFs). Trunk muscle isometric strength and postural balance impairments were estimated. The development of osteoporotic VFs is associated with a significant decrease in strength of all the body muscles, especially the deep spinal stabilization system, i.e trunk extensor (TE), trunk flexsor (TF), where the VFs contribute to inappropriate distribution of back muscle strength with TE:TF ration of 1:1 instead of 3:2, observed both normally and in patients with uncomplicated osteoporosis. There is also a deterioration of stabilometry and functional coordination assessment tests in patients with pathological VFs, that indicate abnormalities of both static and dynamic postural balance. The obtained data should be taken into account when developing rehabilitation programmes for osteoporosis patients who have suffered compression VFs.

Balance and muscle strength tests in patients with osteoporotic vertebral fractures to develop tailored rehabilitation programs

Authors perform a cross-sectional study of functional abilities of the patients with osteoporotic VF. Trunk muscle isometric strength and balance impairments were estimated. The development of osteoporotic VFs is associated with a significant decrease in strength of all the body muscles, especially the deep spinal stabilization system (TE, TF), where the VFs contribute to inappropriate distribution of back muscle strength with TE:TF ration of 1:1 instead of 3:2, observed both normally and in patients with uncomplicated osteoporosis. There is also a deterioration of stabilometry and functional balance assessment tests in patients with pathological VFs, which indicates abnormalities of both static and dynamic balance. The obtained data should be taken into account when developing rehabilitation programmes for patients with osteoporosis who have suffered compression VFs.

Evaluation of DIAM™ Spinal Stabilization System for lower lumbar disc degenerative disease: A randomized, prospective, single-site study

ObjectiveTo determine the efficacy of DIAM Spinal Stabilization System compared with nonoperative treatment for patients with low back pain and lower lumbar disc degenerative disease. MethodsA single center collected prospective outcomes data on 38 patients randomized to an interspinous device or non-operative treatment for symptomatic lumbar degenerative disc disease with treatment crossover allowed at 6 months. ResultsAt all postoperative timepoints out to 2-years, statistically significant improvements in ODI and back pain scores were observed with the interspinous device. Clinically significant improvements (ODI >15-point improvement) were seen in 87.5% of DIAM patients at 2-years postoperatively. A high cross-over rate was noted from the non-operative cohort to the operative group (12 of 15) due to continued pain with nonoperative care. Additionally, 80% of patients receiving the DIAM implant reported a >15-point ODI reduction from pre-surgical scores at 2-year follow-up. ConclusionThe DIAM device demonstrates improvement in ODI and Back Pain scores maintained out to a 2-year follow-up timepoint and performed superior to conventional nonoperative treatment regimens commonly used in low back pain.

250. Interspinous process distraction compared to nonoperative care for moderate lumbar degenerative disc disease: results of the FDA IDE clinical trial

BACKGROUND CONTEXT Interspinous process distraction (IPD) devices aim to alleviate back and leg pain by limiting extension and unloading the 3-joint complex at the affected lumbar level. IPDs may offer a treatment option for painful degenerative disc disease (DDD) that is not yet indicated for fusion or disc replacement. PURPOSE To compare the safety and effectiveness of IPD and nonoperative treatment after 2 years for the treatment of moderate lumbar DDD. STUDY DESIGN/SETTING A prospective, randomized, controlled FDA IDE clinical trial at 23 US centers (ClinicalTrials.gov: NCT00456378). PATIENT SAMPLE A total of 278 patients with moderate low back pain for less than 1 year and radiographic evidence of single-level DDD between L2 and L5 who failed at least 6 weeks but less than 6 months of conservative management were randomized and treated with investigational IPD (n=181) or control nonoperative treatment (n=97). OUTCOME MEASURES The primary endpoint was Overall Success, a composite variable that included: 1) Oswestry Disability Index (ODI) score improvement of ≥ 15 points; and 2) no serious adverse event (AE) caused by the implant or by both the implant and surgical procedure (IPD) or caused by the nonoperative treatment (control); and 3) no secondary surgery (IPD) or treatment surgery (control) at the involved level. Additional safety and effectiveness endpoints included back and leg pain numerical (0-20) rating scales, SF-36 PCS/MCS, AEs and secondary surgeries. METHODS Investigational treatment consisted of the IPD implantation (without decompression) and nonoperative treatments, as necessary. Control treatment consisted of information/ education on low back pain, medication, physical therapy, and epidural and/or facet joint steroidal injections. Clinical and radiographic assessments were performed preoperatively, intra-operatively, and postoperatively up to 2 years. Statistical analyses used Bayesian methods with non-informative priors. Last observation was carried forward (LOCF) for patients lost to follow-up including patients receiving surgery (control crossovers) or additional surgery (IPD investigational) at the involved level. RESULTS Baseline demographic characteristics and outcomes scores were not statistically different between the two groups, except back pain (16.8 for investigational vs 16.1 for control, p=0.033). The IPD rate of Overall Success at 24-months was statistically superior to control (observed rate of 63.0% vs 13.4%, respectively; posterior probability of superiority (pps) > 99.9%). The improvement in outcomes for IPD was statistically superior to control (pps > 99.9%) for: ODI (26.4 vs 1.1), back pain (8.4 vs 1.2), leg pain (4.9 vs -1.1, PCS (12.6 vs.1.4), and MCS (4.4 vs -0.8). Spinous process bony erosion increased slowly to 33.7% (61/181) of patients but was not related to clinical outcomes. Treatment-related serious AEs in the control group were associated with increasing low back pain. Fifteen (8.3%) IPD and 34 (35.1%) control patients experienced a treatment-related serious AE. Twenty (11.0%) IPD patients had secondary surgery and 10 (10.3%) control patients had treatment surgery at the index level. After 6 months of nonoperative treatment, control patients had the option to crossover to IPD: 57 (58.8%) control patients had crossed over by 24 months. CONCLUSIONS These analyses support the superiority of this IPD over conservative care for moderate back pain in appropriately selected patients. FDA DEVICE/DRUG STATUS DIAM™ Spinal Stabilization System (Investigational/Not approved)

Polyetheretherketone (PEEK) Rods for Lumbar Fusion: A Systematic Review and Meta-Analysis.

The purpose of this systematic review is to evaluate the safety and effectiveness of polyetheretherketone (PEEK) rod systems in patients receiving lumbar interbody fusion treatment. Meta-analyses of relevant clinical data were also conducted when possible. Relevant studies were identified by searching the PubMed, EMBASE, and Cochrane Library databases. Clinical studies evaluating the safety and/or effectiveness of the PEEK rod spinal stabilization system in patients receiving lumbar spinal fusion procedure were included. Studies regarding dynamic stabilization and hybrid stabilization (fixed and dynamic; eg, topping-off technique) were not included in this analysis. The analyses included patients who had a lumbar fusion procedure with PEEK rods or titanium rods as a control reference (only for controlled studies). Fusion success, functional and pain improvement, and safety data were evaluated, if reported. The search yielded 5 studies (1 prospective and 4 retrospectives) that included 177 participants (156 received PEEK rods, and 21 received titanium rods). Meta-analysis of interbody fusion success rate in PEEK rod patients yields the estimate of 95.6% (confidence interval: 91.6% to 98.4%). Functional outcomes in PEEK rod patients demonstrated clinically significant improvement when comparing postoperative to preoperative scores, with an average improvement of 67.4% ± 8.5%. Similarly, pain improvement was clinically significant with an average visual analog scores-back pain and visual analog scores-leg pain improvement percentages of 68.9% ± 8.6% and 76.6% ± 1.5%, respectively. Rod fracture was not reported in any of the studies. The rates of screw fracture and loosening were 3/114 (2.6%) and 1/50 (2.0%), respectively. In the controlled study, no statistically significant difference was reported in the fusion success rate, function improvement, pain improvement, or device-related events between subjects treated with PEEK rods and the subjects treated with titanium rods. Experience with PEEK rod systems has shown satisfactory clinical outcomes. Therefore, these results support the use of PEEK rod systems as supplemental fixation during lumbar fusion procedures.

Vertebral body spread in thoracolumbar burst fractures can predict posterior construct failure

Background ContextThe load sharing classification (LSC) laid foundations for a scoring system able to indicate which thoracolumbar fractures, after short-segment posterior-only fixations, would need longer instrumentations or additional anterior supports. PurposeWe analyzed surgically treated thoracolumbar fractures, quantifying the vertebral body's fragment displacement with the aim of identifying a new parameter that could predict the posterior-only construct failure. Study DesignThis is a retrospective cohort study from a single institution. Patient SampleOne hundred twenty-one consecutive patients were surgically treated for thoracolumbar burst fractures. Outcome MeasuresGrade of kyphosis correction (GKC) expressed radiological outcome; Oswestry Disability Index and visual analog scale were considered. MethodsOne hundred twenty-one consecutive patients who underwent posterior fixation for unstable thoracolumbar burst fractures were retrospectively evaluated clinically and radiologically. Supplementary anterior fixations were performed in 34 cases with posterior instrumentation failure, determined on clinic-radiological evidence or symptomatic loss of kyphosis correction. Segmental kyphosis angle and GKC were calculated according to the Cobb method. The displacement of fracture fragments was obtained from the mean of the adjacent end plate areas subtracted from the area enclosed by the maximum contour of vertebral fragmentation. The “spread” was derived from the ratio between this subtraction and the mean of the adjacent end plate areas. Analysis of variance, Mann-Whitney, and receiver operating characteristic were performed for statistical analysis. The authors report no conflict of interest concerning the materials or methods used in the present study or the findings specified in this paper. No funds or grants have been received for the present study. ResultsThe spread revealed to be a helpful quantitative measurement of vertebral body fragment displacement, easily reproducible with the current computed tomography (CT) imaging technologies. There were no failures of posterior fixations with preoperative spreads <42% and losses of correction (LOC)<10°, whereas spreads >62.7% required supplementary anterior supports whenever LOC>10° were recorded. Most of the patients in a “gray zone,” with spreads between 42% and 62.7%, needed additional anterior supports because of clinical-radiological evidence of impending mechanical failures, which developed independently from the GKC. Preoperative kyphosis (p<.001), load sharing score (p=.002), and spread (p<.001) significantly affected the final surgical treatment (posterior or circumferential). ConclusionsTwenty-two years after the LSC, both improvements in spinal stabilization systems and software imaging innovations have modified surgical concepts and approach on spinal trauma care. Spread was found to be an additional tool that could help in predicting the posterior construct failure, providing an objective preoperative indicator, easily reproducible with the modern viewers for CT images.

Herniectomy versus herniectomy with the DIAM spinal stabilization system in patients with sciatica and concomitant low back pain: results of a prospective randomized controlled multicenter trial.

To investigate the short and medium term efficacy and patient outcomes of DIAM spinal stabilization system on back pain, disability, leg pain and quality of life. 165 patients were enrolled; 146 patients with a single level disc herniation (L2 to L5) were randomized: 75 investigational (herniectomy and DIAM) and 71 control (herniectomy alone) treated and followed up for 24months. Significant improvements overtime (P<0.001) in both groups but not significantly differentbetween groups for visual analog scale (VAS) back pain at 6months (investigational -3.97±2.55 vs control-3.37±3.15, P=0.228) and Oswestry Disability Index (ODI) at 12months (-38.55±20.10 vs -37.19±22.61, P=0.719). For both outcomes, there was no statistically significant difference between the groups, at all postoperative time points. Although the enrolment ended before the intended sample size (308 patients) was reached, the number of patients reaching the VAS back pain minimally clinically important difference (MCID) of ≥2.2 at 6months was higher in the investigational (79.4% vs control 57.1%, P=0.008). These results were sustained throughout 24months (82.8 vs 64.4%, P<0.05). In average, surgical duration (P<0.001), blood loss (P=0.029) and skin incision (P<0.001) in the investigational were 10min longer, 22.5ml greater and 2.0cm wider than control group (median values). Improved tertiary outcomes from BL to 24 mo in both groups (investigational vs control): VAS leg pain (mean decrease -6.41±2.57 to -6.41 vs -5.61±to -3.30); improved quality of life (SF-36: 20.68±9.44 vs 16.90±10.74); pain medication reduction: 56.7 vs 47.9%; return to work: 45.7 vs 38.0%. Adverse event rates: 68.5% investigational and 66.2% control. This is the first randomized controlled trial to report equivalent efficacy and safety of herniectomy with or without DIAM spinal stabilizing device. Leg pain, back pain and the level of disability were not significantly different between groups; however, number of patients reaching the MCID for back pain was significantly higher in the investigational group at 6 through 24months.

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.

Long-term reduction in pain and disability after surgery with the interspinous device for intervertebral assisted motion (DIAM) spinal stabilization system in patients with low back pain: 4-year follow-up from a longitudinal prospective case series

Patients with low back pain (LBP) suffer chronic disability. In 40% of LBP patients degenerative disc disease (DDD) seems to be the cause. This prospective case series assessed the efficacy of the interspinous device for intervertebral assisted motion (DIAM™) in patients with LBP resulting from DDD. All patients were initially assessed by physical examinations, magnetic resonance imaging, dynamic X-rays and provocative discography. Eligible patients (n=52) had LBP for a minimum of 4months, and received surgery with the DIAM™ system 2-4weeks after diagnosis. Patients were evaluated pre-/post-operatively for pain severity using a visual analogue scale (VAS), and for dysfunction and disability with the Roland-Morris Disability Questionnaire (RMDQ). VAS and RMDQ score changes were assessed using the appropriate contrasts and Bonferroni-corrected P values. As a result, significant (P<0.0001) pain score reductions were observed between baseline values, and 2 (3.7, 95% CI 3.1; 4.2) and 48 (3.1, 95% CI 2.5; 3.6) months follow-up (intent-to-treat population). Disability scores were significantly (P<0.0001) reduced between baseline and 2 (8.6, 95% CI 7.4; 9.9) and 48 (7.5, 95% CI 6.1; 8.9) months. Disability scores were similar from months 2 to 48. At 48months, 67.3% of patients reached the minimum clinically important difference (MCID; ≥1.5-unit improvement) in VAS score and 78.9% of patients reached the MCID (≥30% improvement) in RMDQ score. No complications were associated with surgery. In conclusion, patients with LBP treated with the interspinous DIAM™ system showed significant and clinically meaningful improvements in pain and disability for up to 4years.

Spine stability after implantation of an interspinous device: an in vitro and finite element biomechanical study

Interspinous devices are widely used for the treatment of lumbar stenosis. The DIAM spinal stabilization system (Medtronic, Ltd.) is an interspinous implant made of silicone and secured in place with 2 laces. The device can be implanted via posterior access with the sacrifice of the supraspinous ligament (SSL) or via lateral access with preservation of the ligament. The aim of the present work was to evaluate the role of the laces, the SSL, and the device size and positioning to determine the device's ability in reducing segmental lordosis and in stabilizing motion. Biomechanical tests were performed in flexion and extension on 8 porcine spines implanted with the DIAM either with or without the laces and the SSL. A finite element model of the human L4-5 spine segments was also created and used to test 2 sizes of the device implanted in 2 different positions in the anteroposterior direction. Implantation of the DIAM induced a shift toward kyphosis in the neutral position. Laces, the SSL, and device size and placement had a significant influence on the neutral position, the stiffness of the implanted spine, and the positions of the instantaneous centers of rotation. The shift of the neutral position toward kyphosis may be beneficial in reducing symptoms of spinal stenosis such as radicular pain, sensation disturbance, and loss of strength in the legs. The authors recommend preservation of the SSL and the use of the fixation laces, given their relevant mechanical role. Choosing the proper device size and placement should be achieved by using a correct surgical technique.

Preclinical evaluation of the Dynesys posterior spinal stabilization system: a nonhuman primate model

Background context Posterior dynamic spinal stabilization systems are intended to restore near-normal biomechanical function of the spine without inducing unnatural stresses to the spinal elements or eliciting a histopathological response. These devices must resist loosening within the challenging biomechanical environment of the lumbar spine. Purpose To determine the biomechanical effects of the Dynesys dynamic stabilization system (Zimmer, Inc., Warsaw, IN, USA) in the acute postoperative period and after 6 and 12 months in vivo; to examine the facet joints at the same postoperative intervals for signs of degeneration; and to measure the incidence of screw loosening after in vivo loading. Study design/setting This was an in vitro and in vivo animal survival study. Methods Fourteen baboons were used. Eight animals underwent survival surgery to implant a posterior dynamic stabilization system spanning two lumbar levels. Six animals were sacrificed acutely, and their spines were biomechanically tested in the intact condition and with instrumentation implanted as described above. Six animals in the survival group were sacrificed at 6 months postoperatively and two animals at 12 months postoperatively. Their spines were biomechanically tested with instrumentation in situ and explanted. The facets were then processed using undecalcified technique. Microradiographs of the facets were examined for signs of arthrosis, inflammation, and degenerative changes. Results The range of flexion-extension motion for the acute group of instrumented spines was 27% of the intact condition. After 6 months with instrumentation in situ, flexion-extension was 56% of the intact condition. After 12 months with instrumentation in situ, flexion-extension was 70% of the intact condition. With instrumentation explanted, flexion-extension at 6 and 12 months was not different from the intact condition (p>.05). Similar results were observed for lateral bending. There were no significant differences in axial rotation between any groups at any time point (p>.05). The facet joints at the operative and adjacent levels exhibited normal articular cartilage at both the 6- and 12-month postoperative time points. There was no evidence of facet arthrosis in any animal. At 6 months postoperatively, 0 of 36 screws exhibited radiolucency at the bone-metal interface. At 12 months postoperatively, 3 of 12 screws exhibited radiolucency. Conclusions After 12 months in vivo, spinal motions were stabilized by the dynamic instrumentation system. No facet arthrosis was observed at 6 and 12 months postoperatively. Explantation of the instrumentation restored motion to intact levels. A 25% rate of screw loosening (3 of 12 screws) was observed at the 12-month postoperative time point.

Biomechanics of the Lumbar Spine After Dynamic Stabilization

Target of the study was to predict the biomechanics of the instrumented and adjacent levels due to the insertion of the DIAM spinal stabilization system (Medtronic Ltd). For this purpose, a 3-dimensional finite element model of the intact L3/S1 segment was developed and subjected to different loading conditions (flexion, extension, lateral bending, axial rotation). The model was then instrumented at the L4/L5 level and the same loading conditions were reapplied. Within the assumptions of our model, the simulation results suggested that the implant caused a reduction in range of motion of the instrumented level by 17% in flexion and by 43% in extension, whereas at the adjacent levels, no significant changes were predicted. Numerical results in terms of intradiscal pressure, relative to the intact condition, predicted that the intervertebral disc at the instrumented level was unloaded by 27% in flexion, by 51% in extension, and by 6% in axial rotation, while no variations in pressure were caused by the device in lateral bending. At the adjacent levels, a change of relative intradiscal pressure was predicted in extension, both at the L3/L4 level, which resulted unloaded by 26% and at the L5/S1 level, unloaded by 8%. Furthermore, a reduction in terms of principal compressive stress in the annulus fibrosus of the L4/L5 instrumented level was predicted, as compared with the intact condition. These numerical predictions have to be regarded as a theoretical representation of the behavior of the spine, because any finite element model represents only a simplification of the real structure.

Changes in Intradiscal Pressures due to More Compliant Spinal Stabilization System

Dynamic stabilization of the lumbar spine has gained increasingly popularity. These nonfusion systems are alleged to maintain or restore the intradiscal pressure to magnitudes of the intact spine and have little negative effect on the adjacent segments to the stabilized one. Compliant Nitinol alloy (Ni-Ti) has been used in the manufacture of the rods of the dynamic stabilization systems. In this study, we investigated a dynamic stabilization system with its coiled rods made of Nitinol alloy. Four porcine lumbar spines (T12-L6) were prepared: intact, fixed by a conventional rigid fixation system, fixed by a dynamic stabilization system with 2-coiled rods, fixed by a dynamic stabilization system with 3-coiled rods. Intradiscal pressures were measured at all levels before and after insertion of the implant. Our results show that the rigid stabilization system resulted in great changes of disc pressure in flexion and extension regardless of spinal levels. However, Intradiscal pressures (IDPs) remained relatively unchanged in models fixed by the dynamic stabilization systems. Changes in intradiscal pressure can lead to altered metabolism within the disc, with potential long-term disc degeneration. These results suggest that the dynamic stabilization systems are superior over traditional fusion implants in maintaining the intradiscal pressure to the intact level at surgical level and adjacent level and can therefore be considered as an alternative method to fusion surgery in these indications while the intradical pressure is preserved.

The Dynesys Lumbar Spinal Stabilization System

We present the positional magnetic resonance imaging findings of a prospective case series of patients undergoing surgery with the Dynesys spinal stabilization device (Zimmer, Inc., Warsaw, IN). To explore the biomechanical impact of the Dynesys device in vivo. Spinal fusion surgery is widely used for painful degenerative conditions of the lumbar spine that have not responded to conservative measures. It often produces good outcomes but can be associated with adjacent segment hypermobility that may lead to further degeneration and pain. Previous cadaveric biomechanical studies claim that the Dynesys Dynamic Spinal Stabilization System allows some lumbar movement, behaving similar to a normal spine in extension but similar to rigid fixation in flexion. Twenty-four patients with dominant low back pain, with or without leg pain, were treated with the Dynesys. All patients underwent positional magnetic resonance imaging before surgery and 9 months after surgery. Measurements were made to assess the differences at the operated level, adjacent level, and whole lumbar spine. There was a statistically significant reduction in flexion-extension range of movement of both the whole lumbar spine by 13.37 degrees (P = 0.002) and at the instrumented segments by 4.08 degrees (P < 0.001) following surgery. There was an insignificant reduction in range of movement at the level above instrumentation (P = 0.807). Mean anterior disc height at the instrumented level reduced by 0.7 mm following insertion of the Dynesys (P < 0.027). Mean posterior disc height reduced by 0.3 mm (P = 0.453). In a neutral posture, the Dynesys had no significant impact on lordosis or inclination of operated or adjacent levels. Contrary to cadaveric study findings, the Dynesys appears to restrict extension more than flexion with respect to a neutral posture. In vivo, the Dynesys Stabilization System allows movement at the instrumented level, albeit reduced, with no significant increased mobility at the adjacent segments. There was reduction of the anterior disc height without a significant increase of the posterior disc height.

Basic scientific considerations in total disc arthroplasty

Background context Total disc arthroplasty serves as the next frontier in the surgical management of intervertebral discogenic pathology. Purpose As we move from an era of interbody spinal arthrodesis to one in which segmental motion is preserved, this promising new technology offers increasing clinical and research challenges in the areas of spinal kinematics, histologic osseointegration at the prosthetic–bone interface and the effects of particulate wear debris. Study design The primary focus of this paper is to provide a methodologic basis to investigate the spinal kinematics, histologic osseointegration and particulate wear debris after total disc arthroplasty by using in vitro and in vivo models. Methods Part I: Using an in vitro cadaveric model, multidirectional flexibility testing evaluated the functional unit kinematics under the following L4–L5 reconstruction conditions: 1) intact spine, 2) Charité disc prosthesis, 3) BAK cages, 4) BAK cages+ISOLA pedicle screw or rod fixation (anteroposterior). Part II: A total of 27 mature baboons (n=27, Papio cynocephalus) underwent L5–L6 total disk replacement procedures to investigate the biomechanical, histochemical and biologic ingrowth characteristics of two different lumbar disc prostheses (AcroFlex and Charité) for total disc arthroplasty. Functional spinal unit fusion status was assessed by using radiographic analysis, biomechanical testing, undecalcified histopathologic and histomorphometric analyses. Part III: Using a total of 50 New Zealand white rabbits, this investigation served to quantify the neural and systemic tissue histopathologic response, after epidural application of four different types of spinal instrumentation particulate wear debris: 1) sham (control) (n=10), 2) stainless steel 316LVM (n=10), 3) titanium alloy Ti-6AL-4V (n=10), 4) cobalt chrome alloy (n=10) and 5) ultrahigh molecular weight polyethylene (UHMWPE) (n=10). Results In vitro multidirectional flexibility testing demonstrates the operative and adjacent level motion-preserving properties of total disc arthroplasty versus interbody arthrodesis cages and pedicle screw spinal instrumentation. To this end, disc replacement preserves the normal centrode or locus of intervertebral rotation at the operative and adjacent intervertebral spinal levels compared with conventional stabilization implants. On the basis of nonhuman primate modeling in the current studies, porous titanium interface surfaces afforded the greatest percentage of trabecular ingrowth at the prosthesis–end plate interface. In vivo segmental motion under multidirectional testing was preserved with the Charité device and slightly diminished with the AcroFlex implants. The porous ingrowth coverage at the bone–metal interface was more favorable for total disk replacement (range, 40% to 50%) compared with that reported for cementless total joint components in the appendicular skeleton (range, 10% to 30%). Direct epidural application of spinal instrumentation particulate wear debris elicits a chronic histiocytic reaction localized primarily within the epidural fibrous layers. Moreover, particles have the capacity to diffuse intrathecally, eliciting a macrophage and cytokine response within the epidural tissues, cerebrospinal fluid and spinal cord itself. Overall, on the basis of the postoperative time periods evaluated, no evidence was observed of an acute neural or systemic histopathologic response to the materials included in the current project. Conclusion The implementation of dynamic spinal stabilization systems for fusionless correction of spinal deformity, dynamic posterior stabilization and total disc arthroplasty necessitates improved understanding with regard to spinal kinematics, patterns and mechanisms of histologic osseointegration and the neurohistopathologic response to particulate wear debris. Collectively, the current studies provide a methodologic basis to comprehensively evaluate these three areas.

The effect of titanium stabilization rods on spinal cord radiation dose

The purpose of this study was to investigate the dosimetric effect of a titanium-rod spinal stabilization system on surrounding tissue, especially the spinal cord. Ion chamber dosimetry was performed for 6- and 18-MV photon beams in a water phantom containing a titanium-rod spinal stabilization system. Isodose curves were obtained in the phantom with and without rods. To assess the ability of a treatment planning system to reproduce the effects of the stabilization system on the radiation dose delivered to surrounding tissue, dose distributions were calculated after appropriate modifications were made in the computed tomography number-to-density conversion table to account for the increased density of the titanium rods. The resultant heterogeneity-corrected plans were compared with uncorrected plans. At a 7-cm depth in the water phantom, corresponding to the depth of the spinal cord, the beam was attenuated by 4% under the rods alone and by 13% rods under the rods with screws for the 6-MV photon beam as compared with curves generated in the absence of rods. The beam was attenuated by 3% and 11%, respectively, for the 18-MV beam. Using anteroposterior (18-MV) and posteroanterior (6-MV) photon beams, with and without heterogeneity correction for the rods, the corrected isodose plan showed an approximately 2% beam attenuation 4 cm anterior to the rods as compared with the uncorrected plan. No significant difference in the spinal cord dose was observed between the 2 plans, however. The titanium-rod spinal stabilization system tested in this study caused a decrease in the dose delivered distal to the rods but did not significantly affect the dose delivered to the spinal cord.

V-5-71 - A new spinal stabilization system: Anterior intercorporal fixation with the türkmen device. Cadaver study

V-5-71 - A new spinal stabilization system: Anterior intercorporal fixation with the türkmen device. Cadaver study