The myth of lumbar instability: the importance of abnormal loading as a cause of low back pain

Chronology of disc degeneration and facet joint arthritis in lumbar spine is variable - A CT based cross-sectional study

BACKGROUND

The notion that disc degeneration (DD) always precedes facet joint arthritis (FJA) has held sway for many decades. However, it is not always the case. We hypothesized that DD is not always the first offender studied the prevalence of isolated DD and isolated FJA in the lumbar spine.

METHODS

Inter-vertebral discs and bilateral facet joints of lumbar spines of 135 participants were graded. The participants were divided into one of the four categories. 'No degeneration,' 'Isolated disc degeneration without facet joint arthritis,' 'Combined disc degeneration and facet joint arthritis,' and 'Isolated facet joint arthritis without disc degeneration.' Multivariate logistic regression analysis was done to evaluate the predictive factors for spinal degeneration using FJA as a dependent variable while age, sex, BMI, smoking history, and DD as predictor variables.

RESULTS

The majority of participants had isolated FJA 64 (47.4%). Combined DD and FJA were noted in 32 (23.7%), isolated DD in 8 (5.9%), while 31(23%) had no degeneration. Only age was found to be significantly contributing to the prediction model in multivariate analysis.

CONCLUSION

Our study shows that spinal degeneration may begin either in the disc or in the facet joints depending upon the aetiological factors. It is a vicious circle that may be entered at any point, FJA or DD.

Degenerative Lumbar Spine Disease: Imaging and Biomechanics

Chronic low back pain (CLBP) is one of the most common diagnoses encountered when considering years lived with disability. The degenerative changes of the lumbar spine include a wide spectrum of morphological modifications visible on imaging, some of them often asymptomatic or not consistent with symptoms. Phenotyping by considering both clinical and imaging biomarkers can improve the management of CLBP. Depending on the clinical presentation, imaging helps determine the most likely anatomical nociceptive source, thereby enhancing the therapeutic approach by targeting a specific lesion. Three pathologic conditions with an approach based on our experience can be described: (1) pure painful syndromes related to single nociceptive sources (e.g., disk pain, active disk pain, and facet joint osteoarthritis pain), (2) multifactorial painful syndromes, representing a combination of several nociceptive sources (such as lumbar spinal stenosis pain, foraminal stenosis pain, and instability pain), and (3) nonspecific CLBP, often explained by postural (muscular) syndromes.

Robot for Ligament Tensioning and Assessment of Spinal Stability

STUDY DESIGN

An in vitro human cadaveric biomechanics study.

OBJECTIVE

A proof-of-concept study to quantify whether or not differences in segmental mobility associated with spinal instability could be detected by a robotic distraction system.

METHODS

Testing was performed in fresh human cadaveric tissue. A prototype Robotic Middle Column Distractor was attached unilaterally to the pedicles of L3-4. Distraction forces up to 150 N were applied first in the intact state, and following discectomy of L3-4. Motions were recorded by time-indexed visual and fluoroscopic images, and analyzed to measure actual motions achieved. Functions of the robot unit were monitored during the procedure and evaluated qualitatively.

RESULTS

A difference of 2.5 mm in z-axis motion was detected at 150 N load between the intact and post-discectomy states. The robot coupled with the image analysis method was able to clearly detect the difference between the intact ("stable") and post-discectomy ("unstable") spine. Data analysis of fluoroscopic images taken during the procedure showed greater motion than perceived by the investigators from qualitative review of visual data. All monitored robot functions performed within design parameters without error.

CONCLUSION

The study demonstrates the feasibility and utility of utilizing an intraoperative robotic distractor to measure the amount of spinal mobility present at a level. This could lead to an important clinical tool for both diagnostic functions as well as operative assist functions.

Axial Spondyloarthritis is associated with changes in lumbosacral loading during daily activities

BACKGROUND

There is currently little insight in lumbar spine loading during activities of daily living in patients with axial spondyloarthritis. Furthermore, it is unclear how inflammation or ankylosis-related mobility limitations in patients with axial spondyloarthritis affect lumbosacral loading, and if lumbar movement profiles have an effect on lumbosacral loading as well. Therefore, the aim of this study is to get more insight in the differences in peak and cumulative lumbosacral loading in patients with axial spondyloarthritis during activities of daily living.

METHODS

Three-dimensional motion analysis with integrative force-plates was used to calculate peak lumbosacral moment (peak loading) and lumbosacral moment impulse (cumulative loading), of 19 patients with axial spondyloarthritis and 23 healthy controls during forward bending, sit-to-stand and two lifting tasks (symmetric/asymmetric). We compared inflammatory (n = 7) and ankylosed (n = 12) patients with axial spondyloarthritis and controls. Patients were also classified into Flexion or Lordotic profile.

FINDINGS

Both inflammatory and ankylosed patients generated significantly larger lumbosacral moment impulses than healthy controls in all movements, except during sit-to-stand, where the inflammatory group showed larger moment impulse than both other two groups. Patients with a Lordotic profile showed lowered peak lumbosacral moments and moment impulses compared to those with a Flexion profile.

INTERPRETATION

Both inflammatory and ankylosed patients experienced more cumulative loading depending on the activity. But our findings suggest that classification of patients into different movement profiles might be more interesting to clinically target specific loading adaptations related to pain and fear of movement.

Correlation between kinematic sagittal parameters of the cervical lordosis or head posture and disc degeneration in patients with posterior neck pain

The purpose of this retrospective cross-sectional study was to examine the degrees of the cervical disc degeneration and the parameters of cervical sagittal balance in plain radiographs, representing cervical lordosis or head posture in subjects with posterior neck pain. A total of 113 patients with posterior neck pain with or without radiating pain were analyzed. The kinematic sagittal parameters of cervical radiographs were obtained at the occipito-cervical (O-C2) angle, sagittal Cobb's angles of C1-C2, C2-C7, and sagittal vertical axis (SVA) of C1-C7 and C2-C7. Cervical disc degeneration was evaluated using the sum of Pfirrmann grades and total modified Matsumoto scores calculated from MRI of the cervical spine. A significant positive correlation was found for the C2-C7 angle using the sum of the Pfirrmann grades and total modified Matsumoto scores, whereas the O-C2 angle and the C1-C2 angle were negatively correlated. The sagittal cervical parameters representing cervical kyphosis and jaw lifting posture were found to be significantly correlated with the degree of cervical disc degeneration. These findings suggest that the loss of the natural sagittal lordosis of the cervical spine may contribute to the progression of disc degeneration, rather than the forward head posture.

Center of rotation locations during lumbar spine movements: a scoping review protocol

OBJECTIVE

The objective of this review is to identify and map current literature describing the center of rotation locations and migration paths during lumbar spine movements.

INTRODUCTION

Altered lumber spine kinematics has been associated with pain and injury. Intervertebral segments' center of rotations, the point around which spinal segments rotate, are important for determining the features of lumbar spine kinematics and the potential for increased injury risk during movements. Although many studies have investigated the center of rotations of humans' lumbar spine, no review has summarized and organized the state of the science related to center of rotation locations and migration paths of the lumbar spine during lumbar spine movements.

INCLUSION CRITERIA

This review will consider studies that include human lumbar spines of any age and condition (e.g. heathy, pathological) during lumbar spine movements. Quantitative study designs, including clinical, observational, laboratory biomechanical experimental studies, mathematical and computer modeling studies will be considered. Only studies published in English will be included, and there will be no limit on dates of publication.

METHODS

PubMed, MEDLINE, Embase, the Cochrane Library Controlled Register of Trials, CINAHL, ACM Digital Library, Compendex, Inspec, Web of Science, Scopus, Google Scholar, and dissertation and theses repositories will be searched. After title and abstract screening of identified references, two independent reviewers will screen the full-text of identified studies and extract data. Data will be summarized and categorized, and a comprehensive narrative summary will be presented with the respective results.

Schmorl Node-A Cause of Acute Thoracic Pain: A Case Report and Pathophysiological Mechanism

Purpose

We report a case of a patient with an acute symptomatic Schmorl node (SN) that spontaneously resolved with characteristic imaging findings. The extensive hematological investigations also allow some insight as to the likely pathophysiology of the painful lesion.

Methods

Case report of an acute symptomatic SN.

Results

A fit and athletic 44-year-old female participant in a competitive paddling event developed atypical thoracic pain and was admitted for further investigation. Normal blood results included complete blood cell count, clotting, and D-dimer. Creatine phosphokinase was 63 U/L (reference < 167 U/L) and troponin I levels were not raised. Her only hematological abnormality was an elevated C-reactive protein (CRP) at 60.2 mg/L (reference < 5 mg/L). Magnetic resonance imaging (MRI) scan showed signal hyperintensity involving T7 vertebral body, surrounding an enlarged SN. Patient was given oral nonsteroidal anti-inflammatory drugs, opioid analgesia, and gradually mobilized. After 3 days, the pain had sufficiently subsided and CRP was 17.8 mg/L. Follow-up MRI scan showed some reduction in the T2 hyperintensity and size of the intraosseous herniation. Patient gradually returned to full activities and had no recurrence of symptoms. MRI scan 8 months after the initial scan showed almost complete resolution of the T2 hyperintensity and pan-vertebral marrow edema.

Conclusion

Symptomatic SN should be part of the differential diagnosis of unexplained thoracolumbar pain. Modality of choice for diagnosis would be MRI. Once diagnosed, several treatment options are available with the most likely being spontaneous resolution of symptoms and bone healing within a few months. The conservative approach is recommended when the symptoms can be medically well controlled.

Lumbar rocking test: A new clinical test for predicting lumbar instability

Purpose

Significant number of low back pain is caused by spinal instability. Clinical and radiological tests are used to diagnose lumbar instability, but the practical utility of clinical tests has not been studied extensively. Hence, it was decided to study lumbar rocking test and passive lumbar extension (PLE) clinical tests to identify their accuracy for lumbar instability, in comparison to the radiological assessment.

Materials and Methods

This cross-sectional prospective study was conducted in 2017 at an Indian tertiary care center, after Ethics Committee approval. No financial transection involved anywhere at any stage of the study. Patients of 30-65 years having low back pain were included following informed consent. Clinical tests conducted were rocking test and PLE tests. All patients were subjected to a neutral anteroposterior, lateral and flexion-extension X-rays of lumbosacral spine. The association between clinical tests and lumbar instability was represented by Chi-square analysis. The rest of the findings were represented as descriptive statistics.

Results

Fifty patients enrolled in the study, of which 28 (56%) were females. On X-rays, the maximum angular rotation and sagittal translation were seen at L5-S1 level. 35 (70%) and 46 (92%) patients showed positive PLE and rocking test, respectively. Significant association (P < 0.05) was seen between rocking test and lumbar instability. The sensitivity of rocking test was 95.56% and positive predictive value as 93.47%.

Conclusion

Clinical tests can be used effectively for the diagnosis of lumbar spine instability. Rocking test was found to be accurate and sensitive for detecting subtle lumbar instability.

Effect of disc degeneration on the mechanical behavior of the human lumbar spine: a probabilistic finite element study

BACKGROUND CONTEXT

Intervertebral disc degeneration has been subject to numerous in vivo and in vitro investigations and numerical studies during recent decades, reporting partially contradictory findings. However, most of the previous studies were limited in the number of specimens investigated and, therefore, could not consider the vast variety of the specimen geometries, which are likely to strongly influence the mechanical behavior of the spine.

PURPOSE

To complement the understanding of the mechanical consequences of disc degeneration, whereas considering natural variations in the major spinal geometrical parameters.

DESIGN/SETTING

A probabilistic finite element study.

METHODS

A parametric finite element model of a human L4-L5 motion segment considering 40 geometrical parameters was developed. One thousand individual geometries comprising four degeneration grades were generated in a probabilistic manner, and the influence of the severity of disc degeneration on the mechanical response of the motion segment to different loading conditions was statistically evaluated.

RESULTS

Variations in the individual structural parameters resulted in marked variations in all evaluated parameters within each degeneration grade. Nevertheless, the effect of degeneration in almost all evaluated response values was statistically significant. With degeneration, the intradiscal pressure progressively decreased. At the same time, the facet loads increased and the ligament tension was reduced. The initially nonlinear load-deformation relationships became linear whereas the segment stiffness increased.

CONCLUSIONS

Results indicate significant stiffening of the motion segment with progressing degeneration and gradually increasing loading of the facets from nondegenerated to moderately degenerated conditions along with a significant reduction of the ligament tension in flexion.

Stand-alone lumbar cage subsidence: A biomechanical sensitivity study of cage design and placement

BACKGROUND AND OBJECTIVE

Spinal degeneration and instability are commonly treated with interbody fusion cages either alone or supplemented with posterior instrumentation with the aim to immobilise the segment and restore intervertebral height. The purpose of this work is to establish a tool which may help to understand the effects of intervertebral cage design and placement on the biomechanical response of a patient-specific model to help reducing post-surgical complications such as subsidence and segment instability.

METHODS

A 3D lumbar functional spinal unit (FSU) finite element model was created and a parametric model of an interbody cage was designed and introduced in the FSU. A Drucker-Prager Cap plasticity formulation was used to predict plastic strains and bone failure in the vertebrae. The effect of varying cage size, cross-sectional area, apparent stiffness and positioning was evaluated under 500 N preload followed by 7.5 Nm multidirectional rotation and the results were compared with the intact model.

RESULTS

The most influential cage parameters on the FSU were size, curvature congruence with the endplates and cage placement. Segmental stiffness was higher when increasing the cross-sectional cage area in all loading directions and when the cage was anteriorly placed in all directions but extension. In general, the facet joint forces were reduced by increasing segmental stiffness. However, these forces were higher than in the intact model in most of the cases due to the displacement of the instantaneous centre of rotation. The highest plastic deformations took place at the caudal vertebra under flexion and increased for cages with greater stiffness. Thus, wider cages and a more anteriorly placement would increase the volume of failed bone and, therefore, the risk of subsidence.

CONCLUSIONS

Cage geometry plays a crucial role in the success of lumbar surgery. General considerations such as larger cages may be applied as a guideline, but parameters such as curvature or cage placement should be determined for each specific patient. This model provides a proof-of-concept of a tool for the preoperative evaluation of lumbar surgical outcomes.

Biomechanical effect of interspinous process distraction height after lumbar fixation surgery: An in vitro model

Pedicle screw fixation may induce abnormal activity at adjacent segment and accelerate the degeneration of lumbar vertebrae. Dynamic stabilizers could provide an intermediate solution between conservative treatment and fusion surgery. Lumbar vertebral segment cephalad to instrumented fixation was the most common localization of adjacent segment degeneration. The aim of this study is to explore the use of interspinous process devices in the lumbar vertebral segment cephalad to fixation segment in changing the mechanical distribution and limiting abnormal activity of the spine. Eight specimens were tested in the following groups: intact group, instability group (bilateral facetectomy at L3-L4), fixation group (bilateral facetectomy and pedicle screw fixation at L3-L4), and hybrid fixation group (fixation at L3-L4 and simulating interspinous device implantation of 6, 8, 10, 12, 14, 16, and 18 mm at L2-L3). Range of motion, motion of vertebral body, and strain distribution change were recorded. The range of motion in extension with 16- and 18-mm hybrid constructs was significantly lower than intact, instability, and fixation groups. In flexion and lateral bending, the strain values of L4 inferior articular process with 18-mm hybrid construct have a significant difference compared with other groups. In axial rotation, under the condition of a contralateral state, the strain values of L2 superior articular process with 18-mm hybrid construct have a significant difference compared with intact and fixation groups. The strain value of the L4 inferior articular process had negative correlation with height distraction in three dimensions, except extension. A negative correlation between the strain value of the L2 superior articular process and distraction height was found in contralateral bending and contralateral axial rotation. Interspinous process devices above the fixation segment can change the mechanical distribution of the spine and limit activity in some of the segments of the spine, which may delay the degeneration of the adjacent segment.

Chronic low back pain and its association with lumbar vertebrae and intervertebral disc changes in adults. A case control study

AIM

This study was done to determine the association between chronic low back pain and vertebral fractures, intervertebral disc space (IDS) narrowing, vertebral osteophytes and spondylolisthesis among adults.

METHOD

This case control study was done in Sri Lanka. Cases were patients with low back pain and controls were without low back pain. Postero-anterior and lateral radiographs of lumbar sacral spine of both groups were studied. To detect vertebral fractures in fourth and fifth lumbar vertebrae, anterior and posterior heights of vertebrae were measured using a Vernier caliper and antero-posterior ratio (A/P) was calculated. Having an A/P ratio value of < 0.89 was considered as a vertebral fracture. Presence of disc space narrowing, vertebral osteophytes and spondylolisthesis was assessed by two radiologists working independently. Bivariate and logistic regression analysis was done to find associations.

RESULTS

There were 140 cases and 140 controls. Mean (SD) age for cases was 51.6 (17) years. Mean (SD) age for controls was 50 (15) years. Females made up 62% of cases and controls. Fifth lumbar vertebral fracture (odds ratio [OR] = 10.2; P = 0.001), fourth lumbar vertebral fracture (OR = 2.5; P = 0.017) and IDS narrowing (OR = 4.15, P = 0.009) had a significant association with low back pain and vertebral osteophytes and spondylolisthesis did not have a significant association with low back pain.

CONCLUSION

Only vertebral fractures and IDS narrowing had a significant association with chronic low back pain.

Cranio-caudal asymmetries in trabecular architecture reflect vertebral fracture patterns

Clinically, vertebral fractures often occur in the upper lumbar spine and involve the superior endplate of a vertebra (which is immediately caudal to a disc). Knowledge that the cranial endplate of a disc is thicker and has greater bone mineral density (BMD) than the corresponding caudal endplate helps to explain this phenomenon. In this study, we investigated structural differences in vertebral trabeculae on either side of a lumbar disc to provide further insight into vertebral fracture risk. As the focus is trabecular difference within a spinal motion segment, we define cranial and caudal vertebral trabeculae relative to the disc. Ninety-two spinal motion segments from 46 cadaveric lumbar spines (males, mean age 50years, range 21-63years) were studied. Disc narrowing on radiography and spread of barium sulfate (BaSO₄) on discography were measured to indicate disc degeneration. Micro-computed tomography (μCT) images were obtained at a resolution of 82μm for each vertebra and processed to include only vertebral trabeculae. Using image processing, the vertebral trabeculae were divided into superior and inferior halves, and then into central and peripheral regions which were approximately opposite to the disc pulposus and annulus, and further into anterior and posterior sub-regions. Microarchitecture measurements for each vertebral region were obtained to determine the differences between the cranial and caudal trabeculae (relative to disc) and their associations with age and disc degeneration within each spinal motion segment. Data from the upper (L1/2-L3/4) and lower (L4/5) lumbar segments were analyzed separately. In the upper lumbar region, the trabeculae cranial to a disc on average had 5.3% greater BMD and trabecular bone volume, 3.6% greater trabecular number, 9.7% greater connectivity density, and 3.7% less trabecular separation than the corresponding caudal trabeculae (P<0.05 for all). Similar trends were observed in peripheral, anterior and posterior regions, but not in central region. No structural difference was observed in the trabeculae of L4/5 segment. Structural asymmetries of vertebral trabeculae were not associated with age, disc degeneration, or disc narrowing. Vertebral trabecular parameters cranial to the disc were greater than caudally in the upper but not in the lower lumbar region. Findings further explain why vertebral fractures are more common in the upper lumbar region and more frequently involve the endplate caudal to a disc.

Complications associated with the Dynesys dynamic stabilization system: a comprehensive review of the literature

The Dynesys dynamic stabilization system is an alternative to rigid instrumentation and fusion for the treatment of lumbar degenerative disease. Although many outcomes studies have shown good results, currently lacking is a comprehensive report on complications associated with this system, especially in terms of how it compares with reported complication rates of fusion. For the present study, the authors reviewed the literature to find all studies involving the Dynesys dynamic stabilization system that reported complications or adverse events. Twenty-one studies were included for a total of 1166 patients with a mean age of 55.5 years (range 39-71 years) and a mean follow-up period of 33.7 months (range 12.0-81.6 months). Analysis of these studies demonstrated a surgical-site infection rate of 4.3%, pedicle screw loosening rate of 11.7%, pedicle screw fracture rate of 1.6%, and adjacent-segment disease (ASD) rate of 7.0%. Of studies reporting revision surgeries, 11.3% of patients underwent a reoperation. Of patients who developed ASD, 40.6% underwent a reoperation for treatment. The Dynesys dynamic stabilization system appears to have a fairly similar complication-rate profile compared with published literature on lumbar fusion, and is associated with a slightly lower incidence of ASD.

Paraspinal Muscle Spindle Response to Intervertebral Fixation and Segmental Thrust Level During Spinal Manipulation in an Animal Model

STUDY DESIGN

In vivo cat model study.

OBJECTIVE

To determine whether intervertebral facet joint fixation and segmental thrust level alter paraspinal muscle spindle activity during simulated spinal manipulation.

SUMMARY OF BACKGROUND DATA

Intervertebral motion is commonly assessed by manual therapy practitioners during clinical evaluation and treatment. Mechanoreceptor activity elicited during spinal manipulation has been theorized as a potential mechanism of its efficacy. The degree to which intervertebral fixation and segmental thrust level alter paraspinal muscle spindle activity during high velocity low amplitude spinal manipulation (HVLA-SM) is unclear.

METHODS

Intervertebral fixation was created by inserting facet screws through the left L(5-6) and L(6-7) and left L(4-5), L(5-6), and L(6-7) facet joints of a cat spine. Changes in the mean instantaneous frequency of L6 muscle spindle discharge were determined during 5 HVLA-SM thrust durations (0-control, 75, 100, 150, 250 ms) delivered at the L4 or L6 spinous process in each of the 3 conditions within the same preparation: laminectomy-only (surgical control; n = 23), L(5-6) and L(6-7) fixations (n = 20), and L(4-5), L(5-6), and L(6-7) fixations (n = 7). Comparisons were made between thrust levels, thrust durations, and spinal joint conditions using a linear mixed model.

RESULTS

Insertion of facet screws compared with laminectomy-only significantly increased (P < 0.001) lumbar spinal stiffness during L6 HVLA-SM. Compared with laminectomy-only, both the 2 facet screw (100 ms; P < 0.05) and 3 screw conditions [75 ms and 100 ms (P < 0.001), 150 ms (P < 0.005), and 250 ms (P < 0.05)] significantly decreased L6 spindle response during the L6 HVLA-SM. HVLA-SM-delivered 2 segments rostral to the level of muscle spindle input significantly decreases spindle response compared with HVLA-SM-delivered at-level; however, nontarget HVLA-SM still elicits 60% to 80% of at-level muscle spindle response.

CONCLUSION

Intervertebral fixation decreases paraspinal muscle spindle response during L6 HVLA-SM in a cat model. Whereas HVLA-SM target accuracy maximizes spindle response, nontarget HVLA-SM still elicits substantial levels of muscle spindle activity.

LEVEL OF EVIDENCE

N/A.

3D point cloud in the evaluation of processes that generate instability of the lumbar spine

OBJECTIVE: To integrate patients with lumbar instability in a multisensor platform in the process of assessment and diagnosis, assigning quantitative parameters for the sagittal balance (SB) and muscle function. METHODS: Experimental study involving adult patients diagnosed with diseases that cause alterations in the SB, that were or were not submitted to surgery with posterior instrumentation and fusion. Each patient underwent anthropometric measurements in body composition scale; a kinesiological analysis using a multisensor platform consisting of depth camera to static/dynamic analysis for the quantitative measurement of SB, and surface electromyography to capture the level of abdominal and lumbar muscles activation and through flexion and extension. RESULTS: Seven adult patients: five females (62.5%)and two men (37.5%) with a mean age 48 years. Images with depth cameras resulted in a SB of from -6.4 to +5.3cm (average -5.7cm). In individuals with positive sagittal balance the percentage of activation (PA) of the abdominal muscles was 58.5% and the lower back lumbar was 75.25%; patients with negative SB integrated the PA of the abdominal muscles of 70.25% and lumbar of 65%; the patient with neutral SB exhibited activation of the abdominal muscles of 87.75% and lumbar muscles of 78.25%. CONCLUSIONS: We observed a trend towards positive SB in patients with overweight and obesity by BMI, as well as increased activation of the abdominal muscles. The multi sensor platform is a useful tool for the diagnosis and prognosis of diseases involving sagittal imbalance.

Spinal pain

The spinal pain, and expecially the low back pain (LBP), represents the second cause for a medical consultation in primary care setting and a leading cause of disability worldwide [1]. LBP is more often idiopathic. It has as most frequent cause the internal disc disruption (IDD) and is referred to as discogenic pain. IDD refers to annular fissures, disc collapse and mechanical failure, with no significant modification of external disc shape, with or without endplates changes. IDD is described as a separate clinical entity in respect to disc herniation, segmental instability and degenerative disc desease (DDD). The radicular pain has as most frequent causes a disc herniation and a canal stenosis. Both discogenic and radicular pain also have either a mechanical and an inflammatory genesis. For to be richly innervated, facet joints can be a direct source of pain, while for their degenerative changes cause compression of nerve roots in lateral recesses and in the neural foramina. Degenerative instability is a common and often misdiagnosed cause of axial and radicular pain, being also a frequent indication for surgery. Acute pain tends to extinguish along with its cause, but the setting of complex processes of peripheral and central sensitization may influence its evolution in chronic pain, much more difficult to treat. The clinical assessment of pain source can be a challenge because of the complex anatomy and function of the spine; the advanced imaging methods are often not sufficient for a definitive diagnosis because similar findings could be present in either asymptomatic and symptomatic subjects: a clinical correlation is always mandatory and the therapy cannot rely uniquely upon any imaging abnormalities. Purpose of this review is to address the current concepts on the pathophysiology of discogenic, radicular, facet and dysfunctional pain, focusing on the role of the imaging in the diagnostic setting, to potentially address a correct approach also to minimally invasive interventional techniques. Special attention will be done to the discogenic pain, actually considered as the most frequent cause of chronic low back pain.

The Michel Benoist and Robert Mulholland yearly European Spine Journal Review: a survey of the "surgical research" articles in the European Spine Journal 2014

This is a review of some 50 papers published in the European Spine Journal in the year 2014. They are selected on the basis that the author felt they were significant contributions to the spinal literature in that year. A brief precis is provided of each paper, and each is accompanied by a short discussion explaining its importance and relevance.

The basis of mechanical instability in degenerative disc disease: a cadaveric study of abnormal motion versus load distribution

STUDY DESIGN

A biomechanical study in cadaveric lumbar spine.

OBJECTIVE

To establish the basis of mechanical stability in degenerative disc disease from the relationship between range of motion (ROM), neutral zone motion (NZ), intradiscal pressure profile, and instantaneous axis or rotation (IAR) in advancing grades of disc degeneration.

SUMMARY OF BACKGROUND DATA

The basis of mechanical instability in lumbar disc degeneration remains poorly understood. Controversy exists between abnormal motion and abnormal loading theories.

METHODS

Thirty-nine lumbar motion segments were graded for staging of disc degeneration with magnetic resonance scan. These specimens were tested for ROM and NZ in a 6 df spine simulator, with 7.5 N·m unconstrained, cyclical loading. Continuous tracking of IAR was derived from ROM data. Intradiscal pressure profiles were determined using needle-mounted pressure transducer, drawn across the disc space under constant loading.

RESULTS

The ROM showed insignificant change, but a trend of increase from grade I through III and a decrease with advanced degeneration. NZ increased significantly with advancing disc degeneration. Intradiscal pressure profile showed an even distribution of the load in normal discs but a depressurized nucleus and irregular spikes of excessive loading, with advancing degeneration. The IAR showed a smooth excursion in normal versus irregular jerky excursion in degenerated discs, without significant change in excursion. The center of rotation, derived from IAR, showed significantly increased vertical translation with advancing degeneration, indicating an abnormal quality of motion.

CONCLUSION

The study established a basis of mechanical instability in the lumbar spine with advancing disc degeneration as an abnormal quality of motion represented by variation in IAR and center of rotation, increased NZ motion without any increase in quantity of motion, and abnormal load distribution across the disc space with spikes of high load amidst depressurized nucleus. The study cannot identify clinical instability but finds an association between the abnormal motions and the abnormal load distribution in mechanical instability.

LEVEL OF EVIDENCE

N/A.

Intervertebral disc regeneration: from the degenerative cascade to molecular therapy and tissue engineering

Low back pain is one of the major health problems in industrialized countries, as a leading source of disability in the working population. Intervertebral disc degeneration has been identified as its main cause, being a progressive process mainly characterized by alteration of extracellular matrix composition and water content. Many factors are involved in the degenerative cascade, such as anabolism/catabolism imbalance, reduction of nutrition supply and progressive cell loss. Currently available treatments are symptomatic, and surgical procedures consisting of disc removal are often necessary. Recent advances in our understanding of intervertebral disc biology led to an increased interest in the development of novel biological treatments aimed at disc regeneration. Growth factors, gene therapy, stem cell transplantation and biomaterials-based tissue engineering might support intervertebral disc regeneration by overcoming the limitation of the self-renewal mechanism. The aim of this paper is to overview the literature discussing the current status of our knowledge from the degenerative cascade of the intervertebral disc to the latest molecular, cell-based therapies and tissue-engineering strategies for disc regeneration.

Pelvic incidence and lumbar spine instability correlations in patients with chronic low back pain

Purpose

Many factors such as lumbar instability and spinopelvic alignment are associated with low back pain. Our purpose was to analyze the pelvic incidence - one of spinopelvic alignment parameters- and spine instability correlations in patients with chronic low back pain.

Methods

Fifty-two patients suffering from chronic low back pain entered this case control study. Lateral spine radiography was taken from patients. pelvic incidence and L3, L4 and L5‘s vertebral body width were measured for all patients, and lumbar instability was evaluated in 3 different levels: L5-S1, L4-L5 and L3-L4.

Results

Thirty-two patients having lumbar instability formed group A and 20 patients without lumbar spine instability allocated to group B. Average age, mean weight, height, body mass index and mean vertebral width of both groups did not differ meaningfully. Pelvic incidence‘s mean amounts set to 53.9 in group B and 57.7 in group A without any significant difference; but pelvic incidence was significantly lower in patients with lumbar instability of L5-S1 origin (P=0.01).

Conclusions

Overall, pelvic incidence did not differ between two groups. However, separate evaluation of each level revealed lumbar instability of L5-S1 segment to be associated with lower pelvic incidence.

Late infections after dynamic stabilization of the lumbar spine with Dynesys

INTRODUCTION

Dynamic stabilization of the spine was developed as an alternative to rigid fusion in chronic back pain to reduce the risk of adjacent segment degeneration. Dynamic neutralization system (Dynesys, Zimmer CH) is one of the most popular systems available, but some midterm studies show revision rates as high as 30 %. Some late infectious complications in our patients prompted us to review them systematically. Propionibacterium recently has been shown to cause subtle infections of prosthetic material.

MATERIALS AND METHODS

Here, we report on a consecutive series of 50 Dynesys implants. In a median follow-up of 51 months (range 0-91), we identified 12 infectious and 11 non-infectious complications necessitating reoperation or removal of the implant in 17 patients.

RESULTS

Material infections occurred after a median of 52 months (2-77) and were due to Propionibacterium alone (n = 4) or in combination (n = 3) in seven out of 11 patients. Clinical presentation combines new or increasing pain associated with signs of screw loosening on conventional X-rays; however, as many as 73.5 % of patients present some degree of screw loosening without being at all symptomatic of infection.

CONCLUSION

The high rate of late infections with low-grade germs and the frequency of screw loosening signs made us suspect a lack of integration at the bone-screw interface. Surgeons should be suspicious if the patient presents a combination of new or increasing pain and signs of screw loosening, and aggressive revision is recommended in these cases.

A combined numerical and experimental technique for estimation of the forces and moments in the lumbar intervertebral disc

Evaluation of the loads on lumbar intervertebral discs (IVD) is critically important since it is closely related to spine biomechanics, pathology and prosthesis design. Non-invasive estimation of the loads in the discs remains a challenge. In this study, we proposed a new technique to estimate in vivo loads in the IVD using a subject-specific finite element (FE) model of the disc and the kinematics of the disc endplates as input boundary conditions. The technique was validated by comparing the forces and moments in the discs calculated from the FE analyses to the in vitro experiment measurements of three corresponding lumbar discs. The results showed that the forces and moments could be estimated within an average error of 20%. Therefore, this technique can be a promising tool for non-invasive estimation of the loads in the discs and may be extended to be used on living subjects.

The effect of degenerative morphological changes of the intervertebral disc on the lumbar spine biomechanics: a poroelastic finite element investigation

Intervertebral disc degeneration involves changes in the spinal anatomical structures. The mechanical relevance of the following changes was investigated: disc height, endplate sclerosis, disc water content, permeability and depressurisation. A poroelastic nonlinear finite element model of the L4-L5 human spine segments was employed. Loads represented a daily cycle (500 N compression combined with flexion-extension motion for 16 h followed by 200 N compression for 8 h). In non-degenerative conditions, the model predicted a diurnal axial displacement of 1.32 mm and a peak intradiscal pressure of 0.47 MPa. Axial displacement, facet force and range of motion in flexion-extension are decreased by decreasing disc height. By decreasing the initial water content, axial displacement, facet force and fluid loss were all reduced. Endplate sclerosis did not have a significant influence on the calculated results. Depressurisation determined an increase of the disc effective stress, possibly inducing failure. Degenerative instability was not calculated in any simulations.

In vivo preclinical evaluation of the influence of osteoporosis on the anchorage of different pedicle screw designs

We investigate the anchorage of pedicle screws with different surface treatments in osteoporotic bone. Eight ewes were divided into two groups of four animals each: four sheep underwent bilateral ovariectomy (OVX Group), whereas the operation was simulated in the remaining group (SHAM Group). Eighteen months after the first operation, the Dynesys(®) System was fitted to the sheep using pedicle screws with three different surface treatments: untreated, rough blasted (uncoated) and bioactive coated (bioactive). Uncoated screws showed a significantly higher bone ingrowth value compared with the untreated screws in the OVX group (9.3%, p < 0.005) and a significantly lower bone ingrowth value in the SHAM group (-11.0%, p < 0.05). Furthermore, the bioactive pedicle screws had a significant lower bone ingrowth value than the untreated screws in the SHAM group (-12.1%, p < 0.05). These results suggest that both tested surface treatments of pedicular screws may provide an advantage in terms of bone quality and osseointegration, when implanted in osteoporotic vertebrae.

Correlação entre instabilidade radiográfica e presença do sinal de modic

OBJETIVOS: Este artigo tem por objetivo avaliar a presença de alterações do platô vertebral (Modic) e a sua associação com a instabilidade demonstrada nas radiografias em flexo-extensão e neutra no plano sagital. MÉTODOS: Análise seccional dos estudos de imagens realizados no serviço de radiologia do Hospital Mãe de Deus em Porto Alegre (RS), entre o período de julho de 2008 e fevereiro de 2010, em 115 pacientes. Foram analisados os segmentos de L1 a S1, num total de 575 segmentos nos exames radiográficos e de ressonância nuclear magnética. RESULTADOS: Analisou-se 115 pacientes sendo 59 (51,30%) do sexo feminino e 56 (48,70%) do sexo masculino. A idade variou de 13 anos e seis meses a 81 anos e dois meses com uma média de 43 anos e oito meses. Com os critérios utilizados, observou-se 224 segmentos instáveis e 351 segmentos estáveis. O Modic I apresentou-se em sete segmentos instáveis e em 22 segmentos estáveis. Quanto à prevalência, o segmento L4-L5 foi o mais instável, correspondendo por 32,58% de todos os segmentos instáveis. CONCLUSÃO: Este artigo refuta a idéia de que as alterações de Modic tipo I estejam associadas a segmentos instáveis.

Back pain is associated with changes in loading pattern throughout forward and backward bending

STUDY DESIGN

Experimental study to determine the kinetics of the lumbar spine (LS) and hips during forward and backward bending.

OBJECTIVE

To investigate the effects of back pain, with and without a positive straight leg raise (SLR) sign, on the loading patterns in the LS and hip during forward and backward bending.

SUMMARY OF BACKGROUND DATA

Forward and backward bending are important components of many functional activities and are part of routine clinical examination. However, there is a little information about the loading patterns during forward and backward bending in people with back pain with or without a positive SLR sign.

METHODS

Twenty asymptomatic participants, 20 back pain participants, and 20 participants with back pain and a positive SLR sign performed 3 continuous cycles of forward and backward bending. Electromagnetic sensors were attached to body segments to measure their kinematics while 2 nonconductive force plates gathered ground reaction force data. A biomechanical model was used to determine the loading pattern in LS and hips.

RESULTS

Although the loading on the LS at the end of the range decreased significantly, the loading at the early and middle ranges of forward bending actually increased significantly in people with back pain, especially in those with positive SLR sign. This suggests that resistance to movement is significantly increased in people with back pain during this movement.

CONCLUSION

This study suggested that it is not sufficient to study the spine at the end of range only, but a complete description of the loading patterns throughout the range is required. Although the maximum range of motion of the spine is reduced in people with back pain, there is a significant increase in the moment acting through the range, particularly in those with a positive SLR sign.

The restoration of lumbar intervertebral disc load distribution: a comparison of three nucleus replacement technologies

STUDY DESIGN

A validated L3-L4 nonlinear finite element model was used to evaluate strain and pressure in the surrounding structures for 4 nucleus replacement technologies.

OBJECTIVE

The objective of the current study was to compare subsidence and anular damage potential between 4 current nucleus replacement technologies. It was hypothesized that a fully conforming nucleus replacement would minimize the risk of both subsidence and anular damage.

SUMMARY OF BACKGROUND DATA

Nucleus pulposus replacements are emerging as a less invasive alternative to total disc replacement and fusion as a solution to degenerative intervertebral discs. Multiple technologies have been developed and are currently undergoing clinical investigation.

METHODS

The testing conditions were applied by excavating the nucleus of the intact model and virtually implanting models representing the various nucleus replacement technologies. The implants consisted of a conforming injectable polyurethane (E = 4 MPa), soft hydrogel (E = 4 MPa), stiff hydrogel (E = 20 MPa), and polyether-etherketone (PEEK) on PEEK articulating designs. The model was exercised in flexion, extension, lateral bending, axial rotation (7.5 Nm with 450 N preload), and compression (1000 N). Vertebral body strain, anular maximum shear strain, endplate contact pressure, anulus-implant contact pressure, and bone remodeling stimulus were reported.

RESULTS

The PEEK implant induced strain maxima in the vertebral bodies with associated endplate contact pressure concentrations. For the PEEK and hydrogel implants, areas of nonconformity with the endplate indicated adjacent bone resorption. Lack of conformity between the implant and inner anulus for the PEEK and hydrogel implants resulted in inward anular bulging with associated increased maximum shear strain. The conforming polyurethane implant maintained outward bulging of the inner anular wall and indicated no bone resorption or stress shielding adjacent to the implant.

CONCLUSION

A fully conforming nucleus replacement resulted in a decreased propensity for subsidence, anular bulging, and further degeneration of the anulus when compared with nonconforming implants.

Effect of nucleus replacement device properties on lumbar spine mechanics

STUDY DESIGN

A validated nonlinear three-dimensional finite element model of a single lumbar motion segment (L3-L4) was used to evaluate a range of moduli for ideally conforming nucleus replacement devices.

OBJECTIVE

The objective of the current study was to determine the biomechanical effects of nucleus replacement technology for a variety of implant moduli. We hypothesized that there would be an optimal modulus for a nucleus replacement that would provide loading in the surrounding bone and anulus similar to the intact state.

SUMMARY OF BACKGROUND DATA

Nucleus pulposus replacements are interventional therapies that restore stiffness and height to mildly degenerated intervertebral discs. Currently a wide variety of nucleus replacement technologies with a large range of mechanical properties are undergoing preclinical testing.

METHODS

A finite element model of L3-L4 was created and validated using range of motion, disc pressure, and bony strains from previously published data. The intact model was altered by changing the mechanical properties of the nucleus pulposus to represent a wide range of nucleus replacement technologies (E = 0.1, 1, 4, and 100 MPa). All of the models were exercised in compression, flexion, extension, lateral bending, and axial rotation. Vertebral body strain, peak anulus fibrosus shear strain, initial bone remodeling stimulus, range of motion, and center of rotation were analyzed.

RESULTS

A nucleus replacement modulus of 1 and 4 MPa resulted in vertebral body strains similar to the intact model. The softest device indicated increased loading in the AF and bone resorption adjacent to the implant. Areas of strain maxima and bone formation were observed adjacent to the implant for the stiffest device.

CONCLUSION

The current study predicted an optimal nucleus replacement of 1 to 4 MPa. An overly stiff implant could result in subsidence, which would preclude the benefit of disc height increase or restoration. Conversely, an overly soft implant could accelerate a degenerative cascade in the anulus.

The implications of stress patterns in the vertebral body under axial support of an artificial implant

Clinical studies show an association between changed load patterns both in the disc and its adjacent vertebral body, with painful degenerated discs. This suggests that failure to restore the normal loading pattern on implantation of a disc replacement could be a cause of lower clinical success rate. In the present study the variations of load patterns in the vertebra after disc implantation was studied using a simplified finite element models of natural and artificial discs. The effect of implant size and presence of voids at the implant-bony endplate interface were studied, for the worst case scenario of no bone remodelling. An altered stress pattern was observed in the vertebrae of implanted segments. The use of smaller size implants and presence of voids at the interface caused localized stress concentration in the endplate and adjacent cancellous bone. The study results support the hypothesis that current implants fail to restore normal loading patterns in the vertebral body, and the localized high stress regions could be the source of pain, and the cause of low success rate of TDRs.

Radiographic parameters of segmental instability in lumbar spine using kinetic MRI

OBJECTIVE

To investigate the effectiveness of radiographic parameters on segmental instability in the lumbar spine using Kinetic magnetic resonance imaging (MRI).

METHODS

Segmental motion, defined as excessive (more than 3 mm) translational motion from flexion to extension, was investigated in 309 subjects (927 segments) using Kinetic MRI. Radiographic parameters which can help indicate segmental instability include disc degeneration (DD), facet joint osteoarthritis (FJO), and ligament flavum hypertrophy (LFH). These three radiographic parameters were simultaneously evaluated, and the combinations corresponding to significant segmental instability at each level were determined.

RESULTS

The overall incidence of segmental instability was 10.5% at L3-L4, 16.5% at L4-L5, and 7.3% at L5-S1. DD and LFH at L3-L4 and FJO and LFH at L4-L5 were individually associated with segmental instability (p<0.05). At L4-L5, the following combinations had a higher incidence of segmental instability (p<0.05) when compared to other segments : (1) Grade IV DD with grade 3 FJO, (2) Grade 2 or 3 FJO with the presence of LFH, and (3) Grade IV DD with the presence of LFH. At L5-S1, the group with Grade III disc and Grade 3 FJO had a higher incidence of segmental instability than the group with Grade I or II DD and Grade 1 FJO.

CONCLUSION

This study showed that the presences of either Grade IV DD or grade 3 FJO with LFH at L4-L5 were good indicators for segmental instability. Therefore, using these parameters simultaneously in patients with segmental instability would be useful for determining candidacy for surgical treatment.

Influence of single-level lumbar degenerative disc disease on the behavior of the adjacent segments--a finite element model study

The current study investigated mechanical predictors for the development of adjacent disc degeneration. A 3-D finite element model of a lumbar spine was modified to simulate two grades of degeneration at the L4-L5 disc. Degeneration was modeled by changes in geometry and material properties. All models were subjected to follower preloads of 800N and moment loads in the three principal directions of motion using a hybrid protocol. Degeneration caused changes in the loading and motion patterns of the segments above and below the degenerated disc. At the level (L3-L4) above the degenerated disc, the motion increased due to moderate degeneration by 21% under lateral bending, 26% under axial rotation and 28% under flexion/extension. At the level (L5-S1) below the degenerated disc, motion increased only during lateral bending by 20% due to moderate degeneration. Both the L3-L4 and L5-S1 segment showed a monotonic increase in both the maximum von Mises stress and shear stress in the annulus as degeneration progressed for all loading directions, expect extension at L3-L4. The most significant increase in stress was observed at the L5-S1 level during axial rotation with nearly a ten-fold increase in the maximum shear stress and 103% increase in the maximum von Mises stress. The L5-S1 segment also showed a progressive increase in facet contact force for all loading directions with degeneration. Nucleus pressure did not increase significantly for any loading direction at either the caudal or cephalic adjacent segment. Results suggest that single-level degeneration can increase the risk for injury at the adjacent levels.

Total disc replacement positioning affects facet contact forces and vertebral body strains

STUDY DESIGN

A validated nonlinear three-dimensional finite element (FE) model of a single lumbar motion segment (L3-L4) was used to evaluate the effects of total disc replacement (TDR). The model was implanted with a fixed-bearing TDR (ProDisc-L) at 2 surgically relevant positions and exercised about the 3 anatomic axes. Facet forces, range of motion (RoM), and vertebral body strains were evaluated.

OBJECTIVE

The objective of the current study was to evaluate how TDR implantation and positioning affects facet joint forces and vertebral body strains. We hypothesized that facet contact forces (FCFs) would increase with TDR to compensate for the loss of periprosthetic load-bearing structures, and that vertebral body strains would increase in the region around the metallic footplates.

SUMMARY OF BACKGROUND DATA

TDR has the potential to replace fusion as the gold standard for the treatment of painful degenerative disc disease. However, complications after TDR include index level facet arthrosis and implant subsidence. Alterations in facet and vertebral body loading after TDR and their dependence on implant positioning are not fully understood.

METHODS

An FEM of L3-L4 was created and validated using RoM, disc pressure, and bony strains from previously published data. A TDR was incorporated into the L3-L4 spine model. All models were subjected to a compressive follower load of 500 N and moments of 7.5 Nm about the 3 anatomic axes.

RESULTS

Overall RoM and FCFs tended to increase with TDR. FCFs increased by an order of magnitude during flexion. Posterior placement of the device resulted in an unloading of the facets during extension. Areas of strain maxima were observed in the anterior portion of the vertebral body during flexion after TDR. The area of initial bone resorption signal under the metal footplate was greater when the device was anteriorly placed.

CONCLUSION

The current study predicted a decrease in segmental rotational stiffness resulting from TDR. This resulted from the removal of load bearing soft tissue structures, and caused increased loading in the facets. Additionally, vertebral body strains were generally higher after TDR, and tended to increase with decreased rotational stiffness. Posterior placement of the device provided a more physiologic load transfer to the vertebral body.