The effects of an interspinous implant on the kinematics of the instrumented and adjacent levels in the lumbar spine

Interspinous-Interbody Fusion via a Strictly Lateral Surgical Approach: A Biomechanical Stabilization Comparison to Constructs Requiring Both Lateral and Posterior Approaches

Objective Lumbar fusion performed through lateral approaches is becoming more common. The interbody devices are generally supported by supplemental posterior fixation implanted through a posterior approach, potentially requiring a second incision and intraoperative repositioning of the patient. A minimally invasive lateral interspinous fixation device may eliminate the need for intraoperative repositioning and avoid disruption of the supraspinous ligament. The objective of this in vitrobiomechanical study was to investigate segmental multidirectional stability and maintenance of foraminal distraction of a lateral interspinous fixation device compared to commonly used pedicle screw and facet screw posterior fixation constructs when combined with lumbar interbody cages. Methods Six human cadaver lumbar spine specimens were subjected to nondestructive quasistatic loading in the following states: (1) intact; (2) interspinous fixation device alone and (3) with lateral interbody cage; (4) lateral lumbar interbody cage with bilateral pedicle screws; (5) lateral lumbar interbody cage with unilateral pedicle screws; and (6) lateral lumbar interbody cage with facet screws. Multidirectional pure bending in 1.5 Nm increments to 7.5 Nm, and 7.5 Nm flexion-extension bending with a 700 N compressive follower load were performed separately with optoelectronic segmental motion measurement. Relative angular motions of L2-L3, L3-L4, and L4-L5 functional spinal units were evaluated, and the mean instantaneous axis of rotation in the sagittal plane was calculated for the index level. Foraminal height was assessed during combined flexion-extension and compression loading for each test construct. Results All implant configurations significantly restricted flexion-extension motion compared with intact (p < 0.05). No significant differences were found in flexion-extension when comparing the different posterior implants combined with lateral lumbar interbody cages. All posterior fixation devices provided comparable neuroforaminal distraction and maintained distraction during flexion and extension. Conclusions When combinedwith lateral lumbar interbody cages, the minimally invasive lateral interspinous fixation device effectively stabilized the spine and maintained neuroforaminal distraction comparable to pedicle screw constructs or facet screws. These results suggest the lateral interspinous fixation device may provide a favorable alternative to other posterior systems that require patient repositioning during surgery and involve a greater disruption of native tissues.

Best Practices for Minimally Invasive Lumbar Spinal Stenosis Treatment 2.0 (MIST): Consensus Guidance from the American Society of Pain and Neuroscience (ASPN)

Introduction

Methods

Results

Discussion

Conclusion

Three-Dimensional Volumetric Changes and Clinical Outcomes after Decompression with DIAM™ Implantation in Patients with Degenerative Lumbar Spine Diseases

Background and objectives: The prevalence of degenerative lumbar spine diseases has increased. In addition to standard lumbar decompression and/or fusion techniques, implantation of interspinous process devices (IPDs) can provide clinical benefits in highly selected patients. However, changes in spinal structures after IPD implantation using magnetic resonance imaging (MRI) have rarely been discussed. This volumetric study aimed to evaluate the effect of IPD implantation on the intervertebral disc and foramen using three-dimensional assessment. Materials and Methods: We retrospectively reviewed patients with lumbar degenerative disc diseases treated with IPD implantation and foraminotomy and/or discectomy between January 2016 and December 2019. The mean follow-up period was 13.6 months. The perioperative lumbar MRI data were processed for 3D-volumetric analysis. Clinical outcomes, including the Prolo scale and visual analog scale (VAS) scores, and radiographic outcomes, such as the disc height, foraminal area, and translation, were analyzed. Results: Fifty patients were included in our study. At the one-year follow-up, the VAS and Prolo scale scores significantly improved (both p < 0.001). The disc height and foraminal area on radiographs also increased significantly, but with limited effects up to three months postoperatively. MRI revealed an increased postoperative disc height with a mean difference of 0.5 ± 0.1 mm (p < 0.001). Although the mean disc volume difference did not significantly increase, the mean foraminal volume difference was 0.4 ± 0.16 mm³ (p < 0.05). Conclusions: In select patients with degenerative disc diseases or lumbar spinal stenosis, the intervertebral foramen was enlarged, and disc loading was reduced after IPD implantation with decompression surgery. The 3D findings were compatible with the clinical benefits.

Stenosis of the vertebral canal of the lumbar spine

The overall incidence of symptomatic lumbar spinal stenosis is about 1015% among persons aged 5070 years. Due to the aging of the population, the incidence of this pathology is constantly growing. The desire of older patients to preserve their quality of life and their functional abilities, along with the improvement of surgical techniques, leads to an increase in the number of surgical interventions for lumbar stenosis. This publication describes the classification of spinal canal stenosis. The clinical picture of this disease has been studied in detail. A special attention is paid to such diagnostic methods as computed tomography (CT), radiography, CT-myelography, magnetic resonance imaging (MRI). Various methods of surgical treatment decompression and decompression-stabilization are described in detail.. The efficiency of various types of decompression operations are 7280%, the results of surgery not differing statistically between the types of decompression (hemilaminectomy, interlaminectomy). Decompression-stabilization operations are used for progressive degenerative spinal deformity, destabilization after the surgical treatment, and disruption of the vertebral-pelvic relations. Currently, the following types of stabilization are used in the lumbar stenosis surgery: ALIF, PLIF, PLF, TLIF, XLIF, OLIF, and transpedicular fixation. The rate of complications in the stabilizing interventions is 27.6%; after decompression operations 9.7%. The frequency of revision operations is also higher after stabilization 10.3%, while after decompression it is 6.5%, which makes us cautious about these types of interventions. Systems of interosseous fixation are also used in the treatment of lumbar stenosis. In the 14 years of followup after interosseous fixation and decompression in 142 patients, 30 (21.1%) patients underwent revision interventions, with chronic pain (38.5%) and disc herniation (42.3%) being the main indication for repeated surgery in 26 of them.

Efficacy of interspinous device on adjacent segment degeneration after single level posterior lumbar interbody fusion: a minimum 2-year follow-up

OBJECTIVE

Adjacent segment degeneration (ASD) is a well-known problem of posterior lumbar interbody fusion (PLIF). A device for interspinous assisted motion (DIAM) has been recently applied at the adjacent segment to pedicle screw instrumentation to create a dynamic transition zone. The aim of this study was to determine whether DIAM implantation at the adjacent segment could reduce the occurrence of radiologic and symptomatic ASD.

METHODS

This retrospective study reviewed 51 patients who underwent PLIF with or without DIAM between 2005 and 2016. They were followed up for more than 24 months. The mean follow-up was over 5 years. Fourteen patients underwent PLIF with DIAM implantation at the cephalad level (Group A) and 37 patients received PLIF only (Group B). In radiologic ASD, several parameters were measured using pre- and post-operative radiographs and magnetic resonance image for lumbar degenerative disease and paraspinal muscle. Visual analogue scale (VAS) and Roland-Morris Disability Questionnaire (RMDQ) scores of back and leg were used to investigate symptomatic ASD.

RESULTS

In postoperative radiographic changes, disc height narrowing and progression of spondylolisthesis at adjacent segment were significantly less in group A than those in group B (0.58 mm versus 1.17 mm, p = 0.038 and 0.30 mm versus 1.69 mm, p = 0.041, respectively). In clinical assessments, back VAS and RMDQ scores improved significantly more in group A (-4.07 versus -2.54, p = 0.029 and -7.57 versus -5.43, p = 0.016, respectively).

CONCLUSION

DIAM implantation with single-level PLIF could prevent disc height narrowing and progression of spondylolisthesis at adjacent segment. Clinically, DIAM implantation reduced back pain and disability. Therefore, DIAM implantation could help slow the progression of both radiologic and symptomatic ASD.

Biomechanics and Mechanism of Action of Indirect Lumbar Decompression and the Evolution of a Stand-alone Spinous Process Spacer

Objective

Objective Interspinous process spacers are used in the treatment of lumbar spinal stenosis by preventing extension at the implanted level and reducing claudication, which is a common symptom of lumbar spinal stenosis. This review assessed the current safety and performance of lumbar spinal stenosis treatments and the biomechanical effects of spinal position, range of motion, and the use of interspinous process spacers.

Method

Method EMBASE and PubMed were searched to find studies reporting on the safety and performance of nonsurgical treatment, including physical therapy and pharmacological treatment, and surgical treatment, including direct and indirect lumbar decompression treatment. Results were supplemented with manual searches to include studies reporting on the use of interspinous process spacers and the review of biomechanical testing performed on the Superion device.

Results

Results The effects of spinal position in extension and flexion have been shown to have an impact in the variation in dimensions of the spinal canal and foramina areas. Overall studies have shown that spinal positions from flexion to extension reduce the spinal canal and foramina dimensions and increase ligamentum flavum thickness. Biomechanical test data have shown that the Superion device resists extension and reduces angular movement at the implantation level and provides significant segmental stability.

Conclusions

Conclusions Superion interspinous lumbar decompression is a minimally invasive, low-risk procedure for the treatment of lumbar spinal stenosis, which has been shown to have a low safety profile by maintaining sagittal alignment, limiting the potential for device dislodgment or migration, and to preserve mobility and structural elements.

Interspinous Process Fixation Device Versus Extended Pedicle Screw Fixation for Symptomatic Adjacent Segment Disease: 3-Year Retrospective Study

OBJECTIVE

In the present study, we compared the clinical and radiographic outcomes of an interspinous process fixation device (IFD) with those of extended pedicle screw fixation (PSF) for symptomatic adjacent segment disease (ASD) after lumbar fusion.

METHODS

The data from 109 patients with ASD treated with IFD (n = 48) or extended PSF (n = 61) from January 2009 to January 2016 were reviewed retrospectively. The clinical outcomes were measured using a visual analog scale (VAS) and the Oswestry disability index. The radiographic outcomes included the fusion rate, incidence of cage subsidence, and additional radiographic ASD.

RESULTS

The mean incision length, operative time, blood loss, and length of hospital stay were significantly lower in the IFD group (P < 0.001). Postoperative back and leg pain were relieved in both groups (P < 0.001). The mean preoperative VAS scores were 8.3 ± 1.3 and 8.5 ± 1.1 in the IFD and PSF groups and had improved to 2.8 ± 1.1 and 2.7 ± 1.2 after 36 months, respectively (P < 0.001). At 36 months postoperatively, 10 of the 56 patients (17.9%) in the PSF group had developed additional radiographic ASD compared with 2 of 44 patients (4.5%) in the IFD group.

CONCLUSION

Our results have demonstrated that in the treatment of symptomatic ASD, comparable clinical and radiologic outcomes can be achieved using IFD, which has a shorter skin incision, shorter operative time, less intraoperative blood loss, and shorter hospital stay than the extended PSF technique. Although not statistically significant, the IFD resulted in a lower ASD incidence compare with the PSF technique. Thus, IFD might be an alternative surgical method for symptomatic ASD after lumbar spine fusion.

How I do it: step-by-step BacJac™ posterior interspinous spacer placement

BACKGROUND

BacJac™ is a posterior interspinous spacer for selected cases of degenerative lumbar spine diseases. It blocks the metameric vertebral segment in terminal extension, restoring foraminal heights.

METHODS

The authors provide a detailed step-by-step description of the surgical technique, shedding light on surgical tips and pitfalls of this procedure. An accurate pre-operative patient selection is analyzed, defining meticulously surgical indications. A high-quality video of the surgical procedure is provided.

CONCLUSION

BacJac™ interspinous device allows a safe, mini-invasive, and effective treatment of selected cases of degenerative lumbar spine disease.

Coflex interspinous implant placement leading to synovial cyst development: case report

Interspinous process devices (IPDs) have been developed as less-invasive alternatives to spinal fusion with the goal of decompressing the spinal canal and preserving segmental motion. IPD implantation is proposed to treat symptoms of lumbar spinal stenosis that improve during flexion. Recent indications of IPD include lumbar facet joint syndrome, which is seen in patients with mainly low-back pain. Long-term outcomes in this subset of patients are largely unknown. The authors present a previously unreported complication of coflex (IPD) placement: the development of a large compressive lumbar synovial cyst. A 64-year-old woman underwent IPD implantation (coflex) at L4-5 at an outside hospital for low-back pain that occasionally radiates to the right leg. Postoperatively, her back and right leg pain persisted and worsened. MRI was repeated and showed a new, large synovial cyst at the previously treated level, severely compressing the patient's cauda equina. Four months later, she underwent removal of the interspinous process implant, bilateral laminectomy, facetectomy, synovial cyst resection, interbody fusion, and stabilization. At the 3-month follow-up, she reported significant back pain improvement with some residual leg pain. This case suggests that facet arthrosis may not be an appropriate indication for placement of coflex.

Lumbar spinal stenosis: symptoms, diagnosis and treatment (meta-analysis of literature data)

Lumbar spinal stenosis is a disease in which degenerated discs, ligamentum flavum, facet joints, while aging, lead to a narrowing of the space around the neurovascular structures of the spine. This article presents a meta-analysis of literature data on epidemiology, causes, pathogenesis, diagnosis and various types of treatment of lumbar spinal stenosis.

Biomechanical analysis of a new lumbar interspinous device with optimized topology

Interspinous spacers used stand-alone preserve joint movement but provide little protection for diseased segments of the spine. Used as adjuncts with fusion, interspinous spacers offer rigid stability but may accelerate degeneration on adjacent levels. Our new device is intended to balance the stability and preserves motion provided by the implant. A new interspinous spacer was devised according to the results of topology optimization studies. Four finite element (FE) spine models were created that consisted of an intact spine without an implant, implantation of the novel, the device for intervertebral assisted motion (DIAM system), and the Dynesys system. All models were loaded with moments, and their range of motions (ROMs), peak disc stresses, and facet contact forces were analyzed. The limited motion segment ROMs, shielded disc stresses, and unloaded facet contact forces of the new devices were greater than those of the DIAM and Dynesys system at L3-L4 in almost all directions of movements. The ROMs, disc stresses, and facet contact forces of the new devices at L2-L3 were slightly greater than those in the DIAM system, but much lower than those in the Dynesys system in most directions. This study demonstrated that the new device provided more stability at the instrumented level than the DIAM system did, especially in lateral rotation and the bending direction. The device caused fewer adjacent ROMs, lower disc stresses, and lower facet contact forces than the Dynesys system did. Additionally, this study conducted topology optimization to design the new device and created a smaller implant for minimal invasive surgery.

How are adjacent spinal levels affected by vertebral fracture and by vertebroplasty? A biomechanical study on cadaveric spines

BACKGROUND CONTEXT

Spinal injuries and surgery may have important effects on neighboring spinal levels, but previous investigations of adjacent-level biomechanics have produced conflicting results. We use "stress profilometry" and noncontact strain measurements to investigate thoroughly this long-standing problem.

PURPOSE

This study aimed to determine how vertebral fracture and vertebroplasty affect compressive load-sharing and vertebral deformations at adjacent spinal levels.

STUDY DESIGN

We conducted mechanical experiments on cadaver spines.

METHODS

Twenty-eight cadaveric spine specimens, comprising three thoracolumbar vertebrae and the intervening discs and ligaments, were dissected from fourteen cadavers aged 67-92 years. A needle-mounted pressure transducer was used to measure the distribution of compressive stress across the anteroposterior diameter of both intervertebral discs. "Stress profiles" were analyzed to quantify intradiscal pressure (IDP) and concentrations of compressive stress in the anterior and posterior annulus. Summation of stresses over discrete areas yielded the compressive force acting on the anterior and posterior halves of each vertebral body, and the compressive force resisted by the neural arch. Creep deformations of vertebral bodies under load were measured using an optical MacReflex system. All measurements were repeated following compressive injury to one of the three vertebrae, and again after the injury had been treated by vertebroplasty. The study was funded by a grant from Action Medical Research, UK ($143,230). Authors of this study have no conflicts of interest to disclose.

RESULTS

Injury usually involved endplate fracture, often combined with deformation of the anterior cortex, so that the affected vertebral body developed slight anterior wedging. Injury reduced IDP at the affected level, to an average 47% of pre-fracture values (p<.001), and transferred compressive load-bearing from nucleus to annulus, and also from disc to neural arch. Similar but reduced effects were seen at adjacent (non-fractured) levels, where mean IDP was reduced to 73% of baseline values (p<.001). Vertebroplasty partially reversed these changes, increasing mean IDP to 76% and 81% of baseline values at fractured and adjacent levels, respectively. Injury also increased creep deformation of the vertebral body under load, especially in the anterior region where a 14-fold increase was observed at the fractured level and a threefold increase was observed at the adjacent level. Vertebroplasty also reversed these changes, reducing deformation of the anterior vertebral body (compared with post-fracture values) by 62% at the fractured level, and by 52% at the adjacent level.

CONCLUSIONS

Vertebral fracture adversely affects compressive load-sharing and increases vertebral deformations at both fractured and adjacent levels. All effects can be partially reversed by vertebroplasty.

Kinematic characteristics of lumbar spinous processes during axial rotation in patients with lumbar degenerative disc disease lateral lumbar interbody fusion and intervention

Background

Data about minimally invasive surgery for the treatment of patients with degenerative disc disease (DDD) has been reported. However, no quantitative knowledge about the biomechanical characteristics of the spinous processes in patients with DDD after operation was reported in the literature.

Methods

Fourteen adult patients with DDD at the L3-4 level were recruited and scanned using computed tomography (CT) to construct three-dimensional (3D) anatomical vertebral models of L2-5. These patients were asked to maintain four positions to acquire 6DOF data about the area of the spine being investigated (L2-5). Fluoroscopy was used to capture spinal motion. 6DOF data from the fluoroscopic images of the four positions was compared to evaluate the kinematics before operation and 6 months after direct lateral interbody fixation (DLIF).

Results

Altered kinematics were found mainly in rotation. For the images captured while patients were in the supine position, no significant differences were detected in different functional positions before and after operation. At other positions, the most kinematic involved level was the L3-4 level, which was followed by the L4-5 level. The range of flexion-extension motion at all levels decreased after operation (by an average of 1° to 7°) while different trends were found in left-right bending/rotation. Overall, after surgical treatment, functional activities were partially restored.

Conclusions

Overall the lumbar spinous processes (LSP) at each level responded differently, regarding rotation, before and after DLIF. This data provides new insights for the evaluation of function before and after surgical treatment in patients with LSP disease.

The Likelihood of Reaching Substantial Clinical Benefit After an Interlaminar Dynamic Spacer for Chronic Low Back Pain: A Clinical and Radiologic Analysis of a Prospective Cohort

OBJECTIVE

Chronic low back pain (CLBP) often causes disabling pain that impairs a patient's quality of life. Surgical treatment is recommended for patients who do not respond to conservative treatments lasting more than 6 months. The purpose of this study is to present results after the use of an interlaminar dynamic spacer for CLBP.

METHODS

We enrolled consecutive patients with CLBP irresponsive to more than 6 months of conservative treatment into the present study. Included patients underwent an interlaminar dynamic spacer insertion without direct decompression. We assessed radiographic parameters and health-related quality of life (HRQoL) data included visual analog scale back/leg pain and Oswestry Disability Index scores. Substantial clinical benefit achievement was assessed.

RESULTS

Thirty-five patients (average age, 47.8 years; 21 female) were included. The mean preoperative symptom duration was 29.6 months. Surgeries involved 1-level (n = 18) and 2-levels (n = 17) procedures. Operative levels included L4-5 (n = 8), L5-S1 (n = 10), L3-4-5 (n-2), and L4-5-S1 (n = 15). The average follow-up period was 16.6 months. After the procedure, all radiographic parameters (including disc height, segmental extension angle, and foraminal area) improved significantly. All preoperative HRQoL parameters improved significantly at the final follow-up. Substantial clinical benefit achievement was observed in 75.8% of the cases on the Oswestry Disability Index, and in 72.7% and 84.8% of the cases on the visual analog scale back and leg pain, respectively.

CONCLUSIONS

An interlaminar dynamic spacer significantly improves HRQoL scores in patients with CLBP who do not respond to conservative treatment. Although encouraging, these results should be confirmed with studies assessing a larger cohort and a longer follow-up.

Hybrid Rigid-Deformable Model for Prediction of Neighboring Intervertebral Disk Loads During Flexion Movement After Lumbar Interbody Fusion at L3-4 Level

Knowledge of spinal loads in neighboring disks after interbody fusion plays an important role in the clinical decision of this treatment as well as in the elucidation of its effect. However, controversial findings are still noted in the literature. Moreover, there are no existing models for efficient prediction of intervertebral disk stresses within annulus fibrosus (AF) and nucleus pulposus (NP) regions. In this present study, a new hybrid rigid-deformable modeling workflow was established to quantify the mechanical stress behaviors within AF and NP regions of the L1-2, L2-3, and L4-5 disks after interbody fusion at L3-4 level. The changes in spinal loads were compared with results of the intact model without interbody fusion. The fusion outcomes revealed maximal stress changes (10%) in AF region of L1-2 disk and in NP region of L2-3 disk. The minimal stress change (1%) is noted at the NP region of the L1-2 disk. The validation of simulation outcomes of fused and intact lumbar spine models against those of other computational models and in vivo measurements showed good agreements. Thus, this present study may be used as a novel design guideline for a specific implant and surgical scenario of the lumbar spine disorders.

Radioisotopic assessment of bone metabolism of the operated vertebra after inter-process stabilizer implantation in the lumbar segment of the spine

INTRODUCTION

Lack of efficacy of pharmacotherapy and physiotherapy in spinal pain syndrome is an indication for intervertebral stabilizer implantation between the processes in the lumbar segment of the spine.

MATERIAL AND METHODS

The group consisted of 32 patients qualified after radioisotopic single-photon emission computed tomography/computed tomography (SPECT/CT) examinations with assessment of bone metabolism and mineral density. For comparative purposes, the L2 vertebra was defined as normal. Parameters defined in the area of operated vertebrae were comparable to L2. Imaging examinations and a pain intensity test were performed before and 12 months after the procedure.

RESULTS

In SPECT, osteotropic isotope (OI) activity in spinous bodies and processes was close to L2 values. Density assessed in CT of analysed vertebrae was close to L2. In the control examination, activity of OI in spinous bodies and processes was higher in the procedure area. Under the stabilizer, there was a strong positive correlation with the L2 parameters. The differences were statistically significant (p = 0.0002). The increase of OI activity in the elements above the stabilizer was variable. In the control examination, there was higher density of spinous processes and bodies above and under the stabilizer. The difference, compared to the L2 density, was statistically significant.

CONCLUSIONS

The radioisotopic method with SPECT/CT allows for the precise assessment of bone metabolism in the spine. After the procedure, a negative correlation was observed between bone metabolism changes and pain intensity test results.

Two-Year Evaluation of the X-STOP Interspinous Spacer in Different Primary Patient Populations With Neurogenic Intermittent Claudication Because of Lumbar Spinal Stenosis

STUDY DESIGN

Multicenter, prospective single-arm study in patients diagnosed with neurogenic intermittent claudication because of lumbar spinal stenosis.

OBJECTIVE

To collect data from 2 different primary patient populations, new participants meeting entry criteria [Continued Access Program (CAP)], or subjects who had been randomly assigned to nonsurgical management in the pivotal Investigational Device Exemption study and failed to respond upon study completion [Crossover Study (COS)].

SUMMARY OF BACKGROUND DATA

The X-STOP interspinous spacer is a minimally invasive treatment option for neurogenic intermittent claudication shown to improve pain, physical functioning, and/or overall quality of life.

METHODS

Fifty-five subjects were enrolled, 42 in CAP and 13 in COS. Zurich Claudication Questionnaire (ZCQ) success rates were obtained based on the number of subjects achieving a threshold level of success. Mean SF-36 domain scores were compared with baseline using repeated measures analysis of variance.

RESULTS

Eighty percent of subjects completed the study. At 2 years, 26/43 subjects (60.5%) achieved clinically significant improvement in the Symptom Severity domain, 25/43 (58.1%) achieved clinically significant improvement in the Physical Function domain, and 31/44 (70.5%) achieved clinically significant improvement in the Patient Satisfaction domain of the ZCQ. Statistically significant improvement in mean scores was obtained in all physical domains of the SF-36 (with the exception of General Health) at 24 months. Mean improvement in ZCQ and SF-36 scores was not as pronounced in the COS cohort compared with the CAP cohort. The most frequently reported device-related or treatment-related adverse event was stenosis pain reported by 3 subjects.

CONCLUSIONS

Overall data are consistent with the randomized pivotal Investigational Device Exemption trial. On the basis of the COS cohort which was subject to several additional years of failed conservative treatment, overall success rates do not improve as greatly in patients with long-standing lumbar spinal stenosis symptoms.

Surgical and nonsurgical treatments for lumbar spinal stenosis

Lumbar spinal stenosis (LSS) is the most common indication for spinal surgery in older adults; however, the efficacy of surgery for LSS as compared to nonsurgical treatments remains unclear. Here, we reviewed numerous studies, including randomized control trails (RCTs), to compare nonsurgical and surgical treatments for LSS. The nonsurgical management of LSS includes medication, epidural injections, physiotherapy, lifestyle modification, and multidisciplinary rehabilitative approaches. Patients with LSS who do not improve after nonsurgical treatments are typically treated surgically using decompressive surgery, which has the strongest evidence base. Although decompressive surgical treatment is associated with modestly successful outcomes, it remains unclear whether decompression combined with fusion surgery results in clinical outcomes that are superior to those following decompression surgery alone. Future RCTs assessing the effectiveness of specific treatments based on high-quality scientific evidence are expected to aid clinical decision-making and improve treatment outcomes for LSS.

INTERSPINOUS SPACER IN PERSISTENT DISCOGENIC PAIN: PERCUTANEOUS APPROACH OR OPEN TECHNIQUE

ABSTRACT Objective: To compare the postoperative clinical course of placement of interspinous spacer with open technique (ISO) with percutaneous interspinous spacer (PIS). Methods: Quasi-experimental, longitudinal study of 42 patients with discogenic pain uncontrolled with analgesics, aged 35-55 years old, 21 women, and 21 men. Clinical history, location of pain, VAS scale before and after surgery, Oswestry Disability Index and Macnab modified scale at 6 months were used. Results: When performing quantitative analysis statistical significance (p = 0.0478, 0.0466, 0.0399) was demonstrated with Student's t test between the results according to VAS scale; in the qualitative analysis with the Oswestry index and Macnab modified scale it was demonstrated the hypothesis that the results is dependent of the surgical technique. Conclusions: According to the results, we can conclude that there is a statistically significant difference depending on the surgical technique used with respect to the rate of disability and functionality in daily life as well as in the improvement of pain symptoms.

Market approval processes for new types of spinal devices: challenges and recommendations for improvement

BACKGROUND

Spinal pathology and related symptoms are among the most common health problems and are associated with high health care costs and productivity losses. Due to the aging population, these costs are further increasing every year. Another important reason for the increasing costs is the market approval of new technologies, such as spinal devices that are usually more expensive than the existing technologies. Previous cases of medical device failure led to concern about possible deficiencies in the market approval process.

OBJECTIVE

The objective is to provide an overview of U.S. Food and Drug Administration (FDA) regulation regarding spinal implants to delineate the challenges and opportunities that spine surgery currently faces.

METHODS

In this paper, two cases of market entries of spinal devices are presented and evaluated to illustrate these deficiencies.

RESULTS

Spinal implant regulation is facing several challenges. New spinal devices should increase patient outcomes and safety at reasonable societal costs. The main challenge is to have a rigorous evaluation before dissemination, while still leaving room for innovative behavior that thrusts the healthcare practice forward.

CONCLUSION

We have provided recommendations to enhance spinal implant regulation and improve and ensure the patient's safety and the future of spine surgery.

Restoring lumbar spine stiffness using an interspinous implant in an ovine model of instability

BACKGROUND

The objective of this study was to determine the effect of an interspinous implant on lumbar spine stability and stiffness during dorsoventral loading.

METHODS

Twelve Merino lambs were mechanically tested in vivo. Oscillatory (2 Hz) loads were applied to L2 under load control while displacements were monitored. Tri-axial accelerometers further quantified adjacent L3-L4 accelerations. Dorsoventral lumbar spine stiffness and L3 and L4 dorsoventral and axial displacements were determined over six trials of 20 cycles of loading. Four conditions were examined: 1) initial intact, 2) following destabilization at L3-L4, 3) following the insertion of an InSwing(®) interspinous device at L3-L4, and 4) with the implant secured with a tension band. Comparisons were performed using a one-way ANOVA with repeated measures and post-hoc Bonferroni correction.

FINDINGS

Compared to the intact condition, destabilization significantly decreased lumbar stiffness by 4.5% (P=.001) which was only recovered by the interspinous device with tension band. The interspinous device caused a significant 9.75% (P=.001) increase in dorsoventral stiffness from destabilization that increased 14% with the tension band added (P=.001). The tension band was responsible for decreased displacements from the intact (P=.038), instability (P=.001), and interspinous device (P=.005) conditions. Dorsoventral L3-L4 motion significantly improved with the interspinous device (P=.01) and the addition of the tension band (P=.001). No significant differences in L3-L4 intersegmental stability were noted for axial motion in the sagittal plane.

INTERPRETATION

This ovine model provided objective in vivo biomechanical evidence of lumbar instability and its restoration by means of an interspinous implant during dorsoventral spinal loading.

Posterior dynamic stabilization in the lumbar spine - 24 months results of a prospective clinical and radiological study with an interspinous distraction device

Background

Interspinous distraction devices (IDD) are due to maintain or restore intersegmental range of motion (iROM) in a controlled fashion with the aim of stabilization the affected level dynamically. The following study is the first to present clinical and radiological data with the Wallis® spacer during a follow-up of 24 months.

Methods

Ten patients underwent posterior dynamic stabilization (PDS) of the lumbar spine with an IDD (Wallis® spacer) and were controlled clinically and radiologically after 3, 6, 12, and 24 months in a prospective study design. Pain intensity, functional disability and life quality were assessed by use of subjective scores. Motion analyses were performed with the help of lateral functional x-rays to determine the iROM of the operated segments and total ROM (tROM) of the lumbar spine. In addition, roentgen stereophotogrammetric analysis (RSA) was used to measure the iROM of the treated levels.

Results

During the postoperative course pain and disability most clinical scores were significantly improved. After 24 months we observed statistically significant reduction in back pain intensity with a mean value of 6.0 on visual analog scale (VAS) before surgery and of 2.7 at the latest evaluation. The leg pain was also decreased without statistical significance from 4.7 preoperatively to 2.1 at final follow-up. The functional disability according to Oswestry Disability Index (ODI) and Roland-Morris Disability Questionnaire (RM) was decreased both with statistical significance at all examination dates with a mean value in ODI of 40.0 % before operation and of 17.3 % after 2 years and an initial mean value in RM of 55.2 and of 23.5 % after latest follow-up. After 24 months, the results of the health related quality of life score also showed much better values with only two exceptions. The iROM of the treated levels was reduced during each follow-up examination with preserved residual mobility. Directly postoperatively and after 3 and 12 months intersegmental mobility was statistically significantly decreased with an average iROM of 6.62° before operation and of 2.69° few days after surgery, of 3.79° and 3.16° 3 and 12 months later. At 6 (4.37°) and 24 (4.01°) months follow-up iROM was also but not statistically significantly reduced. The mean tROM did not change significantly during all postoperative controls.

Conclusions

The radiological findings support the thesis of posterior dynamic stabilization by the used implant. The positive clinical findings should be interpreted with caution because of the limited number of patients and the missing control group.

Degenerative lumbar spinal stenosis treatment with Aperius™ PerCLID™ system and Falena® interspinous spacers: 1-year follow-up of clinical outcome and quality of life

PURPOSE

Evaluation of the efficacy of the Falena(®) and Aperius™ PerCLID™ interspinous devices in the treatment of degenerative lumbar spinal stenosis with neurogenic intermittent claudication refractory to conservative treatment.

MATERIALS AND METHODS

We retrospectively analyzed data from 24 patients (20 male and 4 female patients; 61 ± 7 years old), treated with an implantation of the AperiusTM PerCLID™ system, and from 35 patients (29 male and 6 female patients; 65 ± 9 years old) treated with the Falena(®) interspinous device.Patient pain intensity was evaluated by a 10-point visual analog scale (VAS), with a score (ranging from 0 = no pain to 10 = unbearable pain) that was collected before the procedure, at baseline; and at months 1, 6 and 12 after the interventional procedure. The assessment of quality of life (QOL) impairment was evaluated by the Oswestry Disability Index (ODI) questionnaire, which was administered beforehand at baseline; and at months 1, 6 and 12 after the interventional procedure. The vertebral canal area was measured by magnetic resonance imaging (MRI) scans before the treatment and at the one-year follow-up.

RESULTS

All patients completed the study with no complications. Both the Falena group and Aperius group of surgery patients showed a statistically significant reduction of their VAS and ODI scores at the 6- and 12-month follow-up (p < 0.0001). A statistically significant increase in the vertebral canal area was observed both in the group that received Falena (p < 0.0001) and in the group that received Aperius (p = 0.0003). At the 1-year follow-up, we observed that there was a higher increase of vertebral canal area in those patients whom were treated with the Falena device (p < 0.001).

CONCLUSIONS

The implantation of Falena(®) and Aperius™ PerCLID™ interspinous devices is an effective and safe procedure, in the medium term.

Management of lumbar spinal stenosis

Lumbar spinal stenosis (LSS) affects more than 200,000 adults in the United States, resulting in substantial pain and disability. It is the most common reason for spinal surgery in patients over 65 years. Lumbar spinal stenosis is a clinical syndrome of pain in the buttocks or lower extremities, with or without back pain. It is associated with reduced space available for the neural and vascular elements of the lumbar spine. The condition is often exacerbated by standing, walking, or lumbar extension and relieved by forward flexion, sitting, or recumbency. Clinical care and research into lumbar spinal stenosis is complicated by the heterogeneity of the condition, the lack of standard criteria for diagnosis and inclusion in studies, and high rates of anatomic stenosis on imaging studies in older people who are completely asymptomatic. The options for non-surgical management include drugs, physiotherapy, spinal injections, lifestyle modification, and multidisciplinary rehabilitation. However, few high quality randomized trials have looked at conservative management. A systematic review concluded that there is insufficient evidence to recommend any specific type of non-surgical treatment. Several different surgical procedures are used to treat patients who do not improve with non-operative therapies. Given that rapid deterioration is rare and that symptoms often wax and wane or gradually improve, surgery is almost always elective and considered only if sufficiently bothersome symptoms persist despite trials of less invasive interventions. Outcomes (leg pain and disability) seem to be better for surgery than for non-operative treatment, but the evidence is heterogeneous and often of limited quality.

Failure rates and complications of interspinous process decompression devices: a European multicenter study

OBJECT

Spacers placed between the lumbar spinous processes represent a promising surgical treatment alternative for a variety of spinal pathologies. They provide an unloading distractive force to the stenotic motion segment, restoring foraminal height, and have the potential to relieve symptoms of degenerative disc disease. The authors performed a retrospective, multicenter nonrandomized study consisting of 1108 patients to evaluate implant survival and failure modes after the implantation of 8 different interspinous process devices (IPDs).

METHODS

The medical records of patients who had undergone placement of an IPD were retrospectively evaluated, and demographic information, diagnosis, and preoperative pain levels were recorded. Preoperative and postoperative clinical assessments in the patients were based on the visual analog scale. A minimum of 3 years after IPD placement, information on long-term outcomes was obtained from additional follow-up or from patient medical and radiological records.

RESULTS

One thousand one hundred eight patients affected by symptomatic 1- or 2-level segmental lumbar spine degenerative disease underwent placement of an IPD. The complication rate was 7.8%. There were 27 fractures of the spinous process and 23 dura mater tears with CSF leakage. The ultimate failure rate requiring additional surgery was 9.6%. The reasons for revision, which always involved removal of the original implant, were acute worsening of low-back pain or lack of improvement (45 cases), recurrence of symptoms after an initial good outcome (42 cases), and implant dislocation (20 cases).

CONCLUSIONS

The IPD is not a substitute for a more invasive 3-column fusion procedure in cases of major instability and spondylolisthesis. Overdistraction, poor bone density, and poor patient selection may all be factors in the development of complications. Preoperatively, careful attention should be paid to bone density, appropriate implant size, and optimal patient selection.

Determination of the biomechanical effect of an interspinous process device on implanted and adjacent lumbar spinal segments using a hybrid testing protocol: a finite-element study

OBJECT

The authors evaluated the biomechanical effects of an interspinous process (ISP) device on kinematics and load sharing at the implanted and adjacent segments.

METHODS

A 3D finite-element (FE) model of the lumbar spine (L1–5) was developed and validated through comparison with published in vitro study data. Specifically, validation was achieved by a flexible (load-control) approach in 3 main planes under a pure moment of 10 Nm and a compressive follower load of 400 N. The ISP device was inserted between the L-3 and L-4 processes. Intact and implanted cases were simulated using the hybrid protocol in all motion directions. The resultant motion, facet load, and intradiscal pressure after implantation were investigated at the index and adjacent levels. In addition, stress at the bone-implant interface was predicted.

RESULTS

The hybrid approach, shown to be appropriate for adjacent-level investigations, predicted that the ISP device would decrease the range of motion, facet load, and intradiscal pressure at the index level relative to the corresponding values for the intact spine in extension. Specifically, the intradiscal pressure induced after implantation at adjacent segments increased by 39.7% and by 6.6% at L2–3 and L4–5, respectively. Similarly, facet loads at adjacent segments after implantation increased up to 60% relative to the loads in the intact case. Further, the stress at the bone-implant interface increased significantly. The influence of the ISP device on load sharing parameters in motion directions other than extension was negligible.

CONCLUSIONS

Although ISP devices apply a distraction force on the processes and prevent further extension of the index segment, their implantation may cause changes in biomechanical parameters such as facet load, intradiscal pressure, and range of motion at adjacent levels in extension.

Cost-effectiveness of three treatment strategies for lumbar spinal stenosis: Conservative care, laminectomy, and the Superion interspinous spacer

BACKGROUND

Lumbar spinal stenosis is a painful and debilitating condition resulting in healthcare costs totaling tens of billions of dollars annually. Initial treatment consists of conservative care modalities such as physical therapy, NSAIDs, opioids, and steroid injections. Patients refractory to these therapies can undergo decompressive surgery, which has good long-term efficacy but is more traumatic and can be associated with high post-operative adverse event (AE) rates. Interspinous spacers have been developed to offer a less-invasive alternative. The objective of this study was to compare the costs and quality adjusted life years (QALYs) gained of conservative care (CC) and decompressive surgery (DS) to a new minimally-invasive interspinous spacer.

METHODS

A Markov model was developed evaluating 3 strategies of care for lumbar spinal stenosis. If initial therapies failed, the model moved patients to more invasive therapies. Data from the Superion FDA clinical trial, a prospective spinal registry, and the literature were used to populate the model. Direct medical care costs were modeled from 2014 Medicare reimbursements for healthcare services. QALYs came from the SF-12 PCS and MCS components. The analysis used a 2-year time horizon with a 3% discount rate.

RESULTS

CC had the lowest cost at $10,540, while Spacers and DS were nearly identical at about $13,950. CC also had the lowest QALY increase (0.06), while Spacers and DS were again nearly identical (.28). The incremental cost-effectiveness ratios (ICER) for Spacers compared to CC was $16,300 and for DS was $15,200.

CONCLUSIONS

Both the Spacer and DS strategies are far below the commonly cited $50,000/QALY threshold and produced several times the QALY increase versus CC, suggesting that surgical care provides superior value (cost / effectiveness) versus sustained conservative care in the treatment of lumbar spinal stenosis.

Unconstrained testing of spine with bi-axial universal testing machine

BACKGROUND

In-vitro biomechanical assessment of the spine reveals significant information on the mechanics of spinal disorders, treatment methods, and surgical implants. Specialized devices for the evaluation of spine biomechanics have thus become popular. However, these devices might not be affordable for all research groups.

PURPOSE

The purpose of this study was to describe an apparatus to be attached to a standard bi-axial universal testing machine that would make unconstrained testing of the spine possible.

STUDY DESIGN/SETTING

A technical note on the definition of a spinal testing fixture with validation.

METHODS

Intact lumbosacral spines (T12-S1) were tested in sagittal and lateral bending and axial rotation. Three-dimensional interlevel rotations at each level (L1-4) were analyzed.

RESULTS

By comparison with the literature, we found that the new fixture was able to successfully produce reasonable relative rotation values for the lumbar spine.

CONCLUSIONS

We demonstrated that the low cost fixture allowed unconstrained (six degree of freedom, 6 DOF) testing of fresh-frozen cadaveric lumbar spine.

Clinical outcomes of a polyaxial interspinous fusion system

Background

Early interspinous process fixation constructs utilize rigid fixation plates with immobile spikes which increase the difficulty of device implantation when anatomic variations are encountered. Second generation systems have been designed with polyaxial properties with the goal of accommodating natural osseous anatomic variations to achieve optimal implant placement and fixation integrity. The purpose of this study was to evaluate clinical outcomes in patients treated with this device to supplement the biomechanical data from previous studies.

Methods

A retrospective, non-randomized, single-center chart review at or beyond the one year postoperative time point was conducted to collect preoperative and perioperative data on patients treated with a polyaxial intraspinous fixation system. A postoperative numerical pain rating scale and modified MacNab classification score were obtained from each patient in the cohort via phone survey.

Results

A total of 53 patients were included in the study. Median hospital stay was 2 days (range 1-7 days). There were no reported perioperative blood transfusions or cases of radiographic fracture/migration of the device at the 6 week post-operative time point. There was a significant improvement in pain index score in the overall patient study group and a satisfactory (excellent or good) MacNab result was obtained in 48% of all patients. Patients with preoperative pain scores greater than 8/10 reported more pain improvement than patients with preoperative pain scores less than 5 (0 points, p = 0.96, n = 8). Patients with a BMI less than 30 had significantly better MacNab outcome classifications than patients with a BMI greater than 30.

Conclusions

The polyaxial interspinous fusion system produces significant clinical improvement when employed to treat patients with stenosis, herniated disc, or low grade spondylolisthesis. This device can be implanted with a low complication rate and short postoperative hospital admission time. Patients with high pre-operative pain score and BMI under 30 can be predictors of better clinical outcome and should be considered prior to implantation.

Characterization of the behavior of a novel low-stiffness posterior spinal implant under anterior shear loading on a degenerative spinal model

PURPOSE

Dynamic implants have been developed to address potential adjacent level effects due to rigid instrumentation. Rates of revision surgeries may be reduced by using improved implants in the primary surgery. Prior to clinical use, implants should be rigorously tested ex vivo. The objective of our study was to characterize the load-sharing and kinematic behavior of a novel low-stiffness spinal implant.

METHODS

A human cadaveric model of degenerative spondylolisthesis was tested in shear. Lumbar functional spinal units (N = 15) were tested under a static 300 N axial compression force and a cyclic anterior shear force (5-250 N). Translation was tracked with a motion capture system. A novel implant was compared to three standard implants with shear stiffness ranging from low to high. All implants were instrumented with strain gauges to measure the supported shear force. Each implant was affixed to each specimen, and the specimens were tested intact and in two progressively destabilized states.

RESULTS

Specimen condition and implant type affected implant load-sharing and specimen translation (p < 0.0001). Implant load-sharing increased across all degeneration-simulating specimen conditions and decreased across the three standard implants (high- to low-stiffness). Translation increased with the three standard implants (trend). The novel implant behaved similarly to the medium-stiffness implant (p > 0.2).

CONCLUSIONS

The novel implant behaved similarly to the medium-stiffness implant in both load-sharing and translation despite having a different design and stiffness. Complex implant design and specimen-implant interaction necessitate pre-clinical testing of novel implants. Further in vitro testing in axial rotation and flexion-extension is recommended as they are highly relevant loading directions for non-rigid implants.

Percutaneous interspinous distraction device for the treatment of lumbar spinal canal stenosis: clinical and radiographic results at 2-year follow-up

Objective

To evaluate the effectiveness of the In- space (Synthes, Umkirch, Germany) and the correlation between radiographic parameters and clinical outcome in patients with lumbar spinal canal stenosis (LSS).

Methods

Between June 2009 and May 2013, 56 patients with LSS underwent In-space by one senior surgeon. All of the patients were evaluated both clinically and radiographic measurements before the procedure and each visit at the postoperative follow-up. Preoperative and postoperative X-ray imaging was performed before the procedure and at follow-up to assess the correlation with the clinical outcome. Radiological measurements and clinical outcomes were recorded to establish a relationship between the radiographic parameters and clinical outcome of this procedure. All patients had at least 2 years of follow-up.

Results

The mean VAS score of back pain decreased significantly (p < 0.05).

Conclusions

Our data suggest that percutaneous interspinous devices are a good alternative to treat LSS. The device offers significant decrease in back pain, leg pain and ODI score with 2-year lasting relief from symptoms. The increased intervertebral foramenal space explains the improvement of leg pain, but the mechanism of back pain relief remains unclear. A very weak correlation between the radiographic changes and improvement of pain was found.

Posterior Arch Augmentation (Spinoplasty) before and after Single and Double Interspinous Spacer Introduction at the Same Level: Preventing and Treating the Failure?

Lumbar spinal canal stenosis (LSCS) is one of the most common degenerative diseases in elderly patients. Failure of he treatment can occur, generally related to bone remodelling/fracture of spinous processes. PMMA augmentation of the posterior arch (spinoplasty, SP) has recently been proposed in case of neoplastic involvement. This study evaluated the efficacy of SP as a prophylactic treatment before introducing an interspinous spacer (IS). Moreover, we consider the possibility to treat patients who previously underwent IS implants with subsequent failure of the device, by introducing a second spacer at the same level, performing accessory SP. From January 2009 to September 2011, 174 patients with LSCS underwent CT-guided percutaneous IS implant in our department. From January 2011, all patients with osteoporosis underwent prophylactic SP before introducing the spacer. Moreover, in patients with re-stenosis related to bone remodelling and/or fracture, after strengthening the spinous processes with PMMA introduction, a second similar device was introduced to re-open the stenotic spinal canal. In patients with prophylactic treatment before spacer introduction, no restenosis occurred at three to 12 month follow-up. Patients who underwent second spacer implant at the same level after posterior arch augmentation again obtained a resolution of symptoms, and no further bone remodelling had occurred at follow-up controls. In conclusion, prophylactic SP prevents single spacer failure for bone remodelling/fracture, and allows failure repair by introducing a second spacer at the same level.

Interspinous device versus laminectomy for lumbar spinal stenosis: a comparative effectiveness study

BACKGROUND CONTEXT

Currently no studies directly compare effectiveness between interspinous devices (IDs) and laminectomy in lumbar spinal stenosis (LSS) patients.

PURPOSE

To compare reoperations, complications, and costs between LSS patients undergoing ID placement versus laminectomy.

STUDY DESIGN

Retrospective comparative study.

PATIENT SAMPLE

The MarketScan database (2007-2009) was queried for adults with LSS undergoing ID placement as a primary inpatient procedure.

OUTCOME MEASURES

Reoperation rates, complication rates, and costs.

METHODS

Each ID patient was matched with a laminectomy patient using propensity score matching. Reoperations, complications, and costs were analyzed in patients with at least 18 months postoperative follow-up. The authors did not receive funding from any external sources for this study.

RESULTS

Among 498 inpatients that underwent ID placement between 2007 and 2009; the average age was 73 years. The cumulative reoperation rates after ID at 12 and 18 months were 21% and 23%, respectively. The average inpatient hospitalization lasted 1.6 days with an associated cost of $17,432. Two propensity-matched cohorts of 174 patients that had undergone ID versus laminectomy were analyzed. Longer length of stay was observed in the laminectomy cohort (2.5 days vs. 1.6 days, p<.0001), whereas ID patients accrued higher costs at index hospitalization ($17,674 vs. $12,670, p=.0001). Index hospitalization (7.5% vs. 3.5%, p=.099) and 90-day (9.2% vs. 3.5%, p=.028) complications were higher in the laminectomy cohort compared with the ID cohort. The ID patients had significantly higher reoperation rates than laminectomy patients at 12 months follow-up (12.6% vs. 5.8%, p=.026) and incurred higher cumulative costs than laminectomy patients at 12 months follow-up ($39,173 vs. $34,324, p=.289).

CONCLUSIONS

Twelve-month reoperation rates and index hospitalization costs were significantly higher among patients who underwent ID compared with laminectomy for LSS.

Biomechanics of interspinous devices

A number of interspinous devices (ISD) have been introduced in the lumbar spine implant market. Unfortunately, the use of these devices often is not associated with real comprehension of their biomechanical role. The aim of this paper is to review the biomechanical studies about interspinous devices available in the literature to allow the reader a better comprehension of the effects of these devices on the treated segment and on the adjacent segments of the spine. For this reason, our analysis will be limited to the interspinous devices that have biomechanical studies published in the literature.

Minimally-invasive posterior lumbar stabilization for degenerative low back pain and sciatica. A review

The most diffused surgical techniques for stabilization of the painful degenerated and instable lumbar spine, represented by transpedicular screws and rods instrumentation with or without interbody cages or disk replacements, require widely open and/or difficult and poorly anatomical accesses. However, such surgical techniques and approaches, although still considered "standard of care", are burdened by high costs, long recovery times and several potential complications. Hence the effort to open new minimally-invasive surgical approaches to eliminate painful abnormal motion. The surgical and radiological communities are exploring, since more than a decade, alternative, minimally-invasive or even percutaneous techniques to fuse and lock an instable lumbar segment. Another promising line of research is represented by the so-called dynamic stabilization (non-fusion or motion preservation back surgery), which aims to provide stabilization to the lumbar spinal units (SUs), while maintaining their mobility and function. Risk of potential complications of traditional fusion methods (infection, CSF leaks, harvest site pain, instrumentation failure) are reduced, particularly transitional disease (i.e., the biomechanical stresses imposed on the adjacent segments, resulting in delayed degenerative changes in adjacent facet joints and discs). Dynamic stabilization modifies the distribution of loads within the SU, moving them away from sensitive (painful) areas of the SU. Basic biomechanics of the SU will be discussed, to clarify the mode of action of the different posterior stabilization devices. Most devices are minimally invasive or percutaneous, thus accessible to radiologists' interventional practice. Devices will be described, together with indications for patient selection, surgical approaches and possible complications.

Dynamic motion characteristics of the lower lumbar spine: implication to lumbar pathology and surgical treatment

PURPOSE

Many studies have reported on the segmental motion range of the lumbar spine using various in vitro and in vivo experimental designs. However, the in vivo weightbearing dynamic motion characteristics of the L4-5 and L5-S1 motion segments are still not clearly described in literature. This study investigated in vivo motion of the lumbar spine during a weight-lifting activity.

METHODS

Ten asymptomatic subjects (M/F: 5/5; age: 40-60 years) were recruited. The lumbar segment of each subject was MRI-scanned to construct 3D models of the L2-S1 vertebrae. The lumbar spine was then imaged using a dual fluoroscopic imaging system as the subject performed a weight-lifting activity from a lumbar flexion position (45°) to maximal extension position. The 3D vertebral models and the fluoroscopic images were used to reproduce the in vivo vertebral positions along the motion path. The relative translations and rotations of each motion segment were analyzed.

RESULTS

All vertebral motion segments, L2-3, L3-4, L4-5 and L5-S1, rotated similarly during the lifting motion. L4-5 showed the largest anterior-posterior (AP) translation with 2.9 ± 1.5 mm and was significantly larger than L5-S1 (p < 0.05). L5-S1 showed the largest proximal-distal (PD) translation with 2.8 ± 0.9 mm and was significantly larger than all other motion segments (p < 0.05).

CONCLUSIONS

The lower lumbar motion segments L4-5 and L5-S1 showed larger AP and PD translations, respectively, than the higher vertebral motion segments during the weight-lifting motion. The data provide insight into the physiological motion characteristics of the lumbar spine and potential mechanical mechanisms of lumbar disease development.

One-year follow-up of a series of 100 patients treated for lumbar spinal canal stenosis by means of HeliFix interspinous process decompression device

PURPOSE

New interspinous process decompression devices (IPDs) provide an alternative to conservative treatment and decompressive surgery for patients with neurogenic intermittent claudication (NIC) due to degenerative lumbar spinal stenosis (DLSS). HeliFix is a minimally invasive IPD that can be implanted percutaneously. This is a preliminary evaluation of safety and effectiveness of this IPD up to 12 months after implantation.

METHODS

After percutaneous implantation in 100 patients with NIC due to DLSS, data on symptoms, quality of life, pain, and use of pain medication were obtained for up to 12 months.

RESULTS

Early symptoms and physical function improvements were maintained for up to 12 months. Leg, buttock/groin, and back pain were eased throughout, and the use and strength of related pain medication were reduced. Devices were removed from 2% of patients due to lack of effectiveness.

CONCLUSIONS

Overall, in a period of up to 12-month follow-up, the safety and effectiveness of the HeliFix offered a minimally invasive option for the relief of NIC complaints in a high proportion of patients. Further studies are undertaken in order to provide insight on outcomes and effectiveness compared to other decompression methods and to develop guidance on optimal patient selection.

Controversies about interspinous process devices in the treatment of degenerative lumbar spine diseases: past, present, and future

A large number of interspinous process devices (IPD) have been recently introduced to the lumbar spine market as an alternative to conventional decompressive surgery in managing symptomatic lumbar spinal pathology, especially in the older population. Despite the fact that they are composed of a wide range of different materials including titanium, polyetheretherketone, and elastomeric compounds, the aim of these devices is to unload spine, restoring foraminal height, and stabilize the spine by distracting the spinous processes. Although the initial reports represented the IPD as a safe, effective, and minimally invasive surgical alternative for relief of neurological symptoms in patients with low back degenerative diseases, recent studies have demonstrated less impressive clinical results and higher rate of failure than initially reported. The purpose of this paper is to provide a comprehensive overview on interspinous implants, their mechanisms of action, safety, cost, and effectiveness in the treatment of lumbar stenosis and degenerative disc diseases.

Role of coflex as an adjunct to decompression for symptomatic lumbar spinal stenosis

STUDY DESIGN

Prospective cohort study.

PURPOSE

To assess whether additional implantation of Coflex following spinal decompression provided better clinical outcomes compared to decompression alone for symptomatic lumbar spinal stenosis (LSS) and to determine whether improvement in clinical outcomes correlated with changes in the radiological indices studied.

OVERVIEW OF LITERATURE

Literature on benefits of additional Coflex implantation compared to decompression alone for symptomatic LSS is limited.

METHODS

Patients with symptomatic LSS who met the study criteria were offered spinal decompression with Coflex implantation. Those patients who accepted Coflex implantation were placed in the Coflex group (n=22); while those opting for decompression alone, were placed in the comparison group (n=24). Clinical outcomes were assessed preoperatively, six-months, one-year and two-years postoperatively, using the Oswestry disability index, 100 mm visual analogue scale (VAS)-back pain and VAS-leg pain, and short form-36 (SF-36). Radiological indices (disc height, foraminal height and sagittal angle) were assessed preoperatively, six months, one year, and two years postoperatively.

RESULTS

Both groups showed statistically significant (p<0.001) improvement in all the clinical outcome indicators at all points in time as compared to the preoperative status. However, improvement in the Coflex group was significantly greater (p<0.001) than the comparison group. Changes in the radiological indices did not correlate significantly with the improvement in clinical outcome indicators.

CONCLUSIONS

Additional Coflex implantation after spinal decompression in symptomatic LSS offers better clinical outcomes than decompression alone in the short-term. Changes in radiological indices do not correlate with the improvements in clinical outcomes after surgery for symptomatic LSS.

Application of the restoring force method for identification of lumbar spine flexion-extension motion under flexion-extension moment

The restoring force method (RFM), a nonparametric identification technique established in applied mechanics, was used to maximize the information obtained from moment-rotation hysteresis curves under pure moment flexion-extension testing of human lumbar spines. Data from a previous study in which functional spine units were tested intact, following simulated disk injury, and following implantation with an interspinous process spacer device were used. The RFM was used to estimate a surface map to characterize the dependence of the flexion-extension rotation on applied moment and the resulting axial displacement. This described each spine response as a compact, reduced-order model of the complex underlying nonlinear biomechanical characteristics of the tested specimens. The RFM was applied to two datasets, and successfully estimated the flexion-extension rotation, with error ranging from 3 to 23%. First, one specimen, tested in the intact, injured, and implanted conditions, was analyzed to assess the differences between the three specimen conditions. Second, intact specimens (N = 12) were analyzed to determine the specimen variability under equivalent testing conditions. Due to the complexity and nonlinearity of the hysteretic responses, the mathematical fit of each surface was defined in terms of 16 coefficients, or a bicubic fit, to minimize the identified (estimated) surface fit error. The results of the first analysis indicated large differences in the coefficients for each of the three testing conditions. For example, the coefficient corresponding to the linear stiffness (a01) had varied magnitude among the three conditions. In the second analysis of the 12 intact specimens, there was a large variability in the 12 unique sets of coefficients. Four coefficients, including two interaction terms comprised of both axial displacement and moment, were different from zero (p < 0.05), and provided necessary quantitative information to describe the hysteresis in three dimensions. The results suggest that further work in this area has the potential to supplement typical biomechanical parameters, such as range of motion, stiffness, and neutral zone, and provide a useful tool in diagnostic applications for the reliable detection and quantification of abnormal conditions of the spine.

The effect of design parameters of interspinous implants on kinematics and load bearing: an in vitro study

INTRODUCTION

A number of concepts with controversy approaches are currently discussed for interspinous stabilization (IPS). However, comparative biomechanical studies among the different systems are rare. Nevertheless, it remains unclear which biomechanical characteristics are influenced by different design features of these implants, such as implant stiffness or an additional tension band. Therefore, the aim of the present study was to compare different interspinous implants to investigate the biomechanical impact of IPS implant design on intersegmental kinematics, such as range of motion, neutral zone, center of rotation (COR), as well as load transfer like intradiscal pressure (IDP), to gain additional experience for clinical indications and limitations.

MATERIAL AND METHOD

Twelve human lumbar spine specimens were tested in a spine loading apparatus. In vitro flexibility testing was performed by applying pure bending moments of 7.5 Nm without and with additional preload of 400 N in the three principal motion planes. Four interspinous implants, Coflex "COF" (Paradigm Spine, Germany), Wallis "WAL" (Abbott Laboratories, France), DIAM "DIA" (Sofamor Danek, France) and InterActiv (Aesculap AG, Germany) with two treatment options (without dorsal tensioning "IAO" and with dorsal tensioning "IAM") were consecutively tested in comparison to the native situation "NAT" and to a defect situation "DEF" of the functional spinal unit. The tested IPS devices are comprised of a compression stiffness range of 133 to 1,674 N/mm and a tensile stiffness range of 0-39 N/mm. Range of motion, neutral zone, center of rotation and intradiscal pressure were analyzed for all instrumentation steps and load cases.

CONCLUSION

For the IPS, we found a correlation between compression stiffness and stabilization in extension. Here, the system with the lowest stiffness, DIA, displayed nearly no stabilization of the treated segment, whereas the system with the highest stiffness, WAL and COF, was most pronounced. This applies also for the correlation between device stiffness and IDP. In flexion only the degree of stabilization is in correlation with the tensile stiffness, whereas the IDP stays constant and is not affected by the different tensile stiffness. IPS is not able to stabilize in the frontal and transversal plane. Furthermore IPS does not substantially alter the location of the COR.

Construcciones híbridas del raquis lumbosacro: trabajo preliminar - 20 casos

OBJETIVO: Presentar la filosofía utilizada y como y por qué decidimos proteger el nivel adyacente a una fusión. MÉTODOS: En el criterio de selección de 620 pacientes operados entre enero de 2007 y agosto de 2011 por patología degenerativa, inestabilidad y estenosis del conducto lumbosacro, se seleccionaron 30 pacientes con estadios de Pfirmann 3 y 4, de los cuales seis se perdieron en la consulta postoperatoria y cuatro rechazaron la terapéutica quirúrgica, quedando 20 pacientes que fueron intervenidos quirúrgicamente. La edad promedio de los pacientes fue de 46 años (rango: 22 a 71 años), siendo 11 hombres (55%) y 9 mujeres (45%). RESULTADOS: El seguimiento de los casos es de 6 meses a 2 años y hasta el momento no se evidenció empeoramiento clínicoo radiológico, ni aflojamiento de la instrumentación en ningún caso. CONCLUSIONES: Entendemos que la protección del nivel adyacente mediante el empleo de barras semirrígidas en PEEK sería una buena alternativa de protección debido a que no es necesario abordar el ligamento o los pedículos del nivel adyacente a la fusión.

Biomechanical analysis of an interspinous fusion device as a stand-alone and as supplemental fixation to posterior expandable interbody cages in the lumbar spine

OBJECT

In this paper the authors evaluate through in vitro biomechanical testing the performance of an interspinous fusion device as a stand-alone device, after lumbar decompression surgery, and as supplemental fixation to expandable cages in a posterior lumbar interbody fusion (PLIF) construct.

METHODS

Nine L3-4 human cadaveric spines were biomechanically tested under the following conditions: 1) intact/control; 2) L3-4 left hemilaminotomy with partial discectomy (injury); 3) interspinous spacer (ISS); 4) bilateral pedicle screw system (BPSS); 5) bilateral hemilaminectomy, discectomy, and expandable posterior interbody cages with ISS (PLIF-ISS); and 6) PLIF-BPSS. Each test consisted of 100 N of axial preload with ± 7.5 Nm of torque in flexion-extension, right/left lateral bending, and right/left axial rotation. Significant changes in range of motion (ROM), neutral zone stiffness (NZS), elastic zone stiffness (EZS), and energy loss (EL) were explored among conditions using nonparametric Friedman test and Wilcoxon signed-rank comparisons (p ≤ 0.05).

RESULTS

The injury increased ROM in flexion (p = 0.01), left bending (p = 0.03), and right/left rotation (p < 0.01) and also decreased NZS in flexion (p = 0.01) and extension (p < 0.01). Both the ISS and BPSS reduced flexion-extension ROM and increased flexion-extension stiffness (NZS and EZS) with respect to the injury and intact conditions (p < 0.05), but the ISS condition provided greater resistance than BPSS in extension for ROM, NZS, and EZS (p < 0.01). The BPSS increased the rigidity (ROM, NZS, and EZS) of the intact model in lateral bending and axial rotation (p ≤ 0.01), except in EZS for left rotation (p = 0.23, Friedman test). The incorporation of posterior cages marginally increased (p = 0.05) the EZS of the BPSS construct in flexion but these interbody devices provided significant stability to the ISS construct in lateral bending and axial rotation for ROM (p = 0.02), in lateral bending for NZS (p = 0.02), and in flexion/axial rotation for EZS (p ≤ 0.03); however, both PLIF constructs demonstrated equivalent ROM and stiffness (p ≥ 0.16), except in lateral bending where the PLIF-BPSS was more stable (p = 0.02). In terms of EL, the injury increased EL in flexion-extension (p = 0.02), the ISS increased EL for lateral bending and axial rotation (p ≤ 0.03), and the BPSS decreased EL in lateral bending (p = 0.02), with respect to the intact condition. The PLIF-ISS decreased lateral bending EL with respect to the ISS condition (p = 0.02), but not enough to be smaller or, at least, equivalent, to that of the PLIF-BPSS construct (p = 0.02).

CONCLUSIONS

The ISS may be a suitable device to provide immediate flexion-extension balance after a unilateral laminotomy, but the BPSS provides greater immediate stability in lateral bending and axial rotation motions. Both PLIF constructs performed equivalently in flexion-extension and axial rotation, but the PLIF-BPSS construct is more resistant to lateral bending motions. Further biomechanical and clinical evidence is required to strongly support the recommendation of a stand-alone interspinous fusion device or as supplemental fixation to expandable posterior interbody cages.

Interspinous distraction in lumbar spinal stenosis: a neurophysiological perspective

STUDY DESIGN

Prospective neurophysiological study.

OBJECTIVE

To identify and quantify the neurophysiological effects of interspinous distraction during spine surgery for lumbar spinal stenosis (LSS).

SUMMARY OF BACKGROUND DATA

Interspinous devices have been introduced as an alternative treatment of LSS in selected patients aiming at obtaining indirect decompression. Nevertheless, there is no data on the immediate neurophysiological effect of distraction.

METHODS

Thirty patients with LSS undergoing decompression (14 at single level, 16 at multiple levels) were enrolled, resulting in a total of 48 levels to be analyzed. Before decompression, calibrated incremental distraction simulating interspinous device implantation of 8, 10, 12, 14, and 16 mm was performed. Intraoperative motor evoked potentials were acquired before any distraction, during distraction at each incremental value and after bilateral decompression. We evaluated relative changes of motor evoked potentials normalized to hand muscles and related them to the number of affected levels, LSS radiological severity based on the A to D grading, lordosis, and disc height.

RESULTS

For single-level disease, 8-mm distraction and open decompression yielded similar improvement in motor evoked potentials not only in levels with morphological grades A or B, but also in levels with morphological grades C or D (i.e., severe or extreme stenosis) (P = 0.32). In contrast, distraction superior to 8 mm was less effective (P ≤ 0.05). In multiple-level stenosis, decompression was significantly more effective than any degree of distraction (P < 0.001). No correlation of those results to disc height or lordosis was observed. Using χ trend test to analyze the effect of distraction, a linear trend favoring moderate over severe stenotic morphology was observed (P = 0.0349).

CONCLUSION

Interspinous distraction of 8 mm is sufficient to replicate electrophysiological improvements obtained during full decompression even in severe single-level stenosis but not in multilevel disease. Interspinous distraction has therefore an immediately measurable neurophysiological effect.

LEVEL OF EVIDENCE

4.

Motion characteristics of the lumbar spinous processes with degenerative disc disease and degenerative spondylolisthesis

OBJECTIVE

Recently, interspinous process devices have attracted much attention since they can be implanted between the lumbar spinous processes (LSP) of patients with degenerative disc disease (DDD) and degenerative spondylolisthesis (DLS) using a minimally invasive manner. However, the motion characters of the LSP in the DLS and DDD patients have not been reported. This study is aimed at investigating the kinematics of the lumbar spinous processes in patients with DLS and DDD.

METHODS

Ten patients with DDD at L4-S1 and ten patients with DLS at L4-L5 were studied. The positions of the vertebrae (L2-L5) at supine, standing, 45° trunk flexion, and maximal extension positions were determined using MRI-based models and dual fluoroscopic images. The shortest ISP distances were measured and compared with those of healthy subjects that have been previously reported.

RESULTS

The shortest distance of the interspinous processes (ISP) gradually decreased from healthy subjects to DDD and to DLS patients when measured in the supine, standing, and extension positions. During supine-standing and flexion-extension activities, the changes in the shortest ISP distances in DDD patients were 2 ± 1.2 and 4.8 ± 2.1 mm at L4-L5; in DLS patients they were 0.5 ± 0.4 and 2.8 ± 1.7 mm at L4-L5, respectively. The range of motion is increased in DDD patients but decreased in DLS patients when compared with those of the healthy subjects. No significantly different changes were detected at L2-L3 and L3-L4 levels.

CONCLUSION

At the involved level, the hypermobility of the LSP was seen in DDD and hypomobility of the LSP in DLS patients. The data may be instrumental for improving ISP surgeries that are aimed at reducing post-operative complications such as bony fracture and device dislocations.