Effects of motion segment level, Pfirrmann intervertebral disc degeneration grade and gender on lumbar spine kinematics

Prevalence, distribution characteristic and risk factors of lumbar vertebral axial rotation in patients with lumbar disc herniation: a retrospective study

This retrospective study aimed to investigate the impact of lumbar disc herniation (LDH) on vertebral axial rotation (VAR) in the lumbar spine, focusing on both close and distant neighboring vertebrae. A total of 516 patients with LDH and an equal number of healthy individuals were included in the study, matched for age and gender. The degree of axial rotation for each lumbar spine vertebra was assessed using the Nash-Moe index. The results revealed that the prevalence of VAR in the lumbar spine was significantly higher in the LDH group compared to the Control group (65.7% vs 46.7%, P < 0.001). Among the LDH group, the L2 vertebra had the highest frequency of VAR (49.5%), followed by L1 (45.1%), and then L3 to L5 (33.6%, 8.9%, 3.1%, respectively). A similar pattern was observed in the Control group (L2, 39.8%; L1, 34.6%; L3, 23.2%; L4, 3.1%; L5, 0.8%). Furthermore, the study found that disc herniation was associated with a higher incidence of VAR not only in close neighboring vertebrae but also in distant neighboring vertebrae. This indicates that the biomechanical influence of LDH extends beyond just the immediate adjacent vertebrae. To identify potential risk factors for VAR in LDH patients, multivariate analysis was performed. The results revealed that age was an independent risk factor for VAR (OR 1.022, 95% CI [1.011, 1.034], P < 0.001). However, the duration of symptoms and presence of back pain were not found to be significant risk factors for VAR.

Injectable hydrogel induces regeneration of naturally degenerate human intervertebral discs in a loaded organ culture model

Low back pain resulting from disc degeneration is a leading cause of disability worldwide. However, to date few therapies target the cause and fail to repair the intervertebral disc (IVD). This study investigates the ability of an injectable hydrogel (NPgel), to inhibit catabolic protein expression and promote matrix expression in human nucleus pulposus (NP) cells within a tissue explant culture model isolated from degenerate discs. Furthermore, the injection capacity of NPgel into naturally degenerate whole human discs, effects on mechanical function, and resistance to extrusion during loading were investigated. Finally, the induction of potential regenerative effects in a physiologically loaded human organ culture system was investigated following injection of NPgel with or without bone marrow progenitor cells. Injection of NPgel into naturally degenerate human IVDs increased disc height and Young's modulus, and was retained during extrusion testing. Injection into cadaveric discs followed by culture under physiological loading increased MRI signal intensity, restored natural biomechanical properties and showed evidence of increased anabolism and decreased catabolism with tissue integration observed. These results provide essential proof of concept data supporting the use of NPgel as an injectable therapy for disc regeneration. STATEMENT OF SIGNIFICANCE: Low back pain resulting from disc degeneration is a leading cause of disability worldwide. However, to date few therapies target the cause and fail to repair the intervertebral disc. This study investigated the potential regenerative properties of an injectable hydrogel system (NPgel) within human tissue samples. To mimic the human in vivo conditions and the unique IVD niche, a dynamically loaded intact human disc culture system was utilised. NPgel improved the biomechanical properties, increased MRI intensity and decreased degree of degeneration. Furthermore, NPgel induced matrix production and decreased catabolic factors by the native cells of the disc. This manuscript provides evidence for the potential use of NPgel as a regenerative biomaterial for intervertebral disc degeneration.

Epidemiology of Modic changes in dogs: Prevalence, possible risk factors, and association with spinal phenotypes

Background

Chronic low back pain, a leading contributor to disease burden worldwide, is often caused by intervertebral disc (IVD) degeneration. Modic changes (MCs) are MRI signal intensity changes due to lesions in vertebral bone marrow adjacent to degenerated IVDs. Only a few studies described the histopathological changes associated with MC to date. MC type 1 is suggested to be associated with bone marrow infiltration of fibrovascular tissue, type 2 with fatty infiltration, and type 3 with bone sclerosis in humans.

Methods

This study investigated whether the dog can be a valuable animal model to research MCs, by examining the prevalence, imaging, and histological characteristics of lumbar MCs in dogs (340 dogs, 2496 spinal segments).

Results

Logistic regression analysis indicated that the presence of lumbosacral MCs was associated with age and disc herniation (annulus fibrosis protrusion and/or nucleus pulposus extrusion). According to MRI analysis, MCs were mostly detected at the lumbosacral junction in dogs. Most signal intensity changes represented MC type 3, while previous spinal surgery seemed to predispose for the development of MC type 1 and 2. Histological analysis (16 dogs, 39 spinal segments) indicated that IVDs with MCs showed more histopathological abnormalities in the endplate and vertebral bone marrow than IVDs without MCs. Mostly chondroid proliferation in the bone marrow was encountered, while the histologic anomalies described in humans associated with MCs, such as fibrovascular or fatty infiltration, were scarcely detected.

Conclusions

Dogs spontaneously develop MCs, but may exhibit other pathological processes or more chronic bone marrow pathologies than humans with MCs. Therefore, more research is needed to determine the translatability of the MCs encountered in dog low-back-pain patients.

Role of Apparent Diffusion Coefficient in Evaluating Degeneration of the Intervertebral Disc: A Narrative Review

Degeneration of the lumbar intervertebral disc is the most common cause of lower back pain. It is directly related to daily activities, mechanical stress, and other biological factors. We use imaging modalities to assess the degree of disc degeneration, out of which magnetic resonance imaging (MRI) is the most popular non-invasive modality. It is believed that early changes in disc degeneration are due to the biochemical events in the disc and can be evaluated by sequences in MRI involving the diffusion of water molecules. The apparent diffusion coefficient (ADC) is one such sequence that captures the signals based on the diffusion of water molecules. Ten articles were chosen from PubMed and Google Scholar using the MeSH terms 'lumbar spine degeneration' and 'apparent diffusion coefficient'. This review article has summarized various studies intending to gain a better understanding of the biochemical events leading to the development of disc degeneration. This study has also gathered the role of various sequences in MRI that can quantitatively assess disc degeneration.

Detection of Imperceptible Intervertebral Disc Fissures in Conventional MRI-An AI Strategy for Improved Diagnostics

Annular fissures in the intervertebral discs are believed to be closely related to back pain. However, no sensitive non-invasive method exists to detect annular fissures. This study aimed to propose and test a method capable of detecting the presence and position of annular fissures in conventional magnetic resonance (MR) images non-invasively. The method utilizes textural features calculated from conventional MR images combined with attention mapping and artificial intelligence (AI)-based classification models. As ground truth, reference standard computed tomography (CT) discography was used. One hundred twenty-three intervertebral discs in 43 patients were examined with MR imaging followed by discography and CT. The fissure classification model determined the presence of fissures with 100% sensitivity and 97% specificity. Moreover, the true position of the fissures was correctly determined in 90 (87%) of the analyzed discs. Additionally, the proposed method was significantly more accurate at identifying fissures than the conventional radiological high-intensity zone marker. In conclusion, the findings suggest that the proposed method is a promising diagnostic tool to detect annular fissures of importance for back pain and might aid in clinical practice and allow for new non-invasive research related to the presence and position of individual fissures.

TAK-242 treatment and its effect on mechanical properties and gene expression associated with IVD degeneration in SPARC-null mice

PURPOSE

Intervertebral disc (IVD) degeneration is accompanied by mechanical and gene expression changes to IVDs. SPARC-null mice display accelerated IVD degeneration, and treatment with (toll-like receptor 4 (TLR4) inhibitor) TAK-242 decreases proinflammatory cytokines and pain. This study examined if chronic TAK-242 treatment impacts mechanical properties and gene expression associated with IVD degeneration in SPARC-null mice.

METHODS

Male and female SPARC-null and WT mice aged 7-9 months were given intraperitoneal injections with TAK-242 or an equivalent saline vehicle for 8 weeks (3x/per week, M-W-F). L2-L5 spinal segments were tested in cyclic axial tension and compression. Gene expression analysis (RT-qPCR) was performed on male IVD tissues using Qiagen RT2 PCR arrays.

RESULTS

SPARC-null mice had decreased NZ length (p = 0.001) and increased NZ stiffness (p < 0.001) compared to WT mice. NZ length was not impacted by TAK-242 treatment (p = 0.967) despite increased hysteresis energy (p = 0.024). Tensile stiffness was greater in SPARC-null mice (p = 0.018), and compressive (p < 0.001) stiffness was reduced from TAK-242 treatment in WT but not SPARC-null mice (p = 0.391). Gene expression analysis found upregulation of 13 ECM and 5 inflammatory genes in SPARC-null mice, and downregulation of 2 inflammatory genes after TAK-242 treatment.

CONCLUSIONS

TAK-242 had limited impacts on SPARC-null mechanical properties and did not attenuate NZ mechanical changes associated with IVD degeneration. Expression analysis revealed an increase in ECM and inflammatory gene expression in SPARCnull mice with a reduction in inflammatory expression due to TAK-242 treatment. This study provides insight into the role of TLR4 in SPARC-null mediated IVD degeneration.

Impact of Variations in Water Concentration on the Nanomechanical Behavior of Type I Collagen Microfibrils in Annulus Fibrosus

Radial variation in water concentration from outer to inner lamellae is one of the characteristic features of annulus fibrosus (AF). In addition, water concentration changes are also associated with intervertebral disc (IVD) degeneration. Such changes alter the chemo-mechanical interactions among the biomolecular constituents at molecular level, affecting the load-bearing nature of IVD. This study investigates mechanistic impacts of water concentration on the collagen type I microfibrils in AF using molecular dynamics simulations. Results show, in axial tension, that increase in water concentration (WC) from 0% to 50% increases the elastic modulus from 2.7 GPa to 3.9 GPa. This is attributed to combination of shift in deformation from backbone straightening to combined backbone stretching- intermolecular sliding and subsequent strengthening of tropocollagen-water (TC-water-TC) interfaces through water bridges and intermolecular electrostatic attractions. Further increase in WC to 75% reduces the modulus to 1.8 GPa due to shift in deformation to polypeptide straightening and weakening of TC-water-TC interface due to reduced electrostatic attraction and increase in the number of water molecules in a water bridge. During axial compression, increase in WC to 50% results in increase in modulus from 0.8 GPa to 4.5 GPa. This is attributed to the combination of the development of hydrostatic pressure and strengthening of the TC-water-TC interface. Further increase in WC to 75% shifts load-bearing characteristic from collagen to water, resulting in a decrease in elastic modulus to 2.8 GPa. Such water-mediated alteration in load-bearing properties acts as foundations toward AF mechanics and provides insights toward understanding degeneration-mediated altered spinal stiffness.

Patient-Specific Variations in Local Strain Patterns on the Surface of a Trussed Titanium Interbody Cage

Introduction: 3D printed trussed titanium interbody cages may deliver bone stimulating mechanobiological strains to cells attached at their surface. The exact size and distribution of these strains may depend on patient-specific factors, but the influence of these factors remains unknown. Therefore, this study aimed to determine patient-specific variations in local strain patterns on the surface of a trussed titanium interbody fusion cage.

Materials and Methods: Four patients eligible for spinal fusion surgery with the same cage size were selected from a larger database. For these cases, patient-specific finite element models of the lumbar spine including the same trussed titanium cage were made. Functional dynamics of the non-operated lumbar spinal segments, as well as local cage strains and caudal endplate stresses at the operated segment, were evaluated under physiological extension/flexion movement of the lumbar spine.

Results: All patient-specific models revealed physiologically realistic functional dynamics of the operated spine. In all patients, approximately 30% of the total cage surface experienced strain values relevant for preserving bone homeostasis and stimulating bone formation. Mean caudal endplate contact pressures varied up to 10 MPa. Both surface strains and endplate contact pressures varied more between loading conditions than between patients.

Conclusions: This study demonstrates the applicability of patient-specific finite element models to quantify the impact of patient-specific factors such as bone density, degenerative state of the spine, and spinal curvature on interbody cage loading. In the future, the same framework might be further developed in order to establish a pipeline for interbody cage design optimizations.

Characteristics of lumbar disc degeneration and risk factors for collapsed lumbar disc in Korean farmers and fishers

Background

Few studies have investigated the risk factors for lumbar intervertebral disc degeneration among hard physical workers involved in heavy lifting. In this study, we aimed to identify the characteristics of lumbar intervertebral disc degeneration and evaluate the relationship between collapsed lumbar disc and potential risk factors in farmers and fishers.

Methods

This study included 203 farmers (103 men and 100 women) and 166 fishers (95 men and 71 women) aged 40–69 years who had undergone lumbar magnetic resonance imaging and were enrolled in the Korea Farmer's Knee Cohort and the Jeonnam Fishers' Cohort. We evaluated each of the 5 lumbar discs using the Pfirrmann grading system and classified collapsed lumbar intervertebral disc (cLD) as a case with ≥ 1 grade 5 at any disc level. We investigated potential risk factors, such as gender, age, body mass index (BMI), working hours per day, working months per year, and cumulative heavy lifting working time (CLWT). The odds ratios (ORs) and their corresponding 95% confidence intervals (CIs) were calculated.

Results

The prevalence of cLD was 19.8% (23.7% among fishers, 21.2% among fishers with farming, and 17.2% among farmers). cLD correlated with factors such as age and occupation. Gender, CLWT and the working time matrix were not significantly associated with cLD. The OR of cLD adjusted by gender, age, BMI, and working time matrix was 1.26 (95% CI: 0.69–2.30) for ≥ 5,000 hours CLWT compared to that for < 2,000 hours CLWT. The OR of cLD adjusted by gender, age, BMI, CLWT, and working time matrix was 2.08 (95% CI: 1.06–4.06) for fishers compared to that for farmers.

Conclusions

Heavy lifting did not show a significant association with cLD in farmers and fishers. However, there is possibility that fishers are at a higher risk of lumbar disc collapse than farmers.

Biomechanical effects of lumbar fusion surgery on adjacent segments using musculoskeletal models of the intact, degenerated and fused spine

Adjacent segment disorders are prevalent in patients following a spinal fusion surgery. Postoperative alterations in the adjacent segment biomechanics play a role in the etiology of these conditions. While experimental approaches fail to directly quantify spinal loads, previous modeling studies have numerous shortcomings when simulating the complex structures of the spine and the pre/postoperative mechanobiology of the patient. The biomechanical effects of the L4–L5 fusion surgery on muscle forces and adjacent segment kinetics (compression, shear, and moment) were investigated using a validated musculoskeletal model. The model was driven by in vivo kinematics for both preoperative (intact or severely degenerated L4–L5) and postoperative conditions while accounting for muscle atrophies. Results indicated marked changes in the kinetics of adjacent L3–L4 and L5–S1 segments (e.g., by up to 115% and 73% in shear loads and passive moments, respectively) that depended on the preoperative L4–L5 disc condition, postoperative lumbopelvic kinematics and, to a lesser extent, postoperative changes in the L4–L5 segmental lordosis and muscle injuries. Upper adjacent segment was more affected post-fusion than the lower one. While these findings identify risk factors for adjacent segment disorders, they indicate that surgical and postoperative rehabilitation interventions should focus on the preservation/restoration of patient’s normal segmental kinematics.

Age-related change in shear elastic modulus of the thoracolumbar multifidus muscle in healthy Beagle dogs using ultrasound shear wave elastography

Background

Multifidus muscle stiffness decreases in patients with lumbar intervertebral disk herniation; however, age-related changes in humans have not been reported.

Objectives

The reliability of ultrasound shear wave elastography in dogs, and changes in the shear elastic modulus of the thoracolumbar multifidus muscle with aging in dogs, were investigated.

Methods

Twelve beagle dogs were divided into 2 groups based on the age of onset of intervertebral disk herniation: young (aged not exceeding 2 years; 1.3 ± 0.6 years old, n = 5) and adult (4.9 ± 1.2 years old, n = 7). The shear elastic modulus of the multifidus muscle, from the thirteenth thoracic spine to the fourth lumbar spine, was measured using ultrasound shear wave elastography. The length, cross-sectional area and muscle to fat ratio of the multifidus muscle, and the grade of intervertebral disk degeneration, were assessed using radiographic and magnetic resonance imaging examinations.

Results

The length and cross-sectional area of the multifidus muscle increased caudally. In the young group, the shear elastic modulus of the multifidus muscle of the thirteenth thoracic spine was less than that of the third lumbar spine. In the adult group, the shear elastic modulus of the multifidus muscle of first and third lumbar spine was lower than that of the same site in the young group.

Conclusions

Ultrasound can be used to measure shear wave elastography of the thoracolumbar multifidus in dogs. If the multifidus muscle stiffness decreases, we should consider age-related change.

Region- and degeneration dependent stiffness distribution in intervertebral discs derived by shear wave elastography

Information on the local stiffness characteristics of the intervertebral disc (IVD) is crucial for the understanding of its structure-function properties in health and disease and may improve numerical modeling. Previous studies have attempted to map local tissue stiffness by sectioning the disc and performing mechanical testing on these discrete tissue units, which is technically challenging and may bias the results. Shear wave elastography (SWE) represents a nondestructive alternative that can provide spatially continuous elasticity estimates. We investigated the feasibility of SWE for human intervertebral disc elasticity mapping in a laboratory setting. To this end, global spinal segment mechanical behavior was determined in 6 loading directions and served as ground truth data for the validation of the approach. Subsequently, the cranial spinal vertebra was removed and shear wave elastographic scans of the IVD were acquired. SWE-measurements were reconstructed into three-dimensional elastographic maps, discretized into distinct IVD regions and correlated with global segment mechanical parameters. SWE-derived Young's modulus estimates were compared among different regions and as a function of their state of degeneration. We found annulus shear wave speed to be moderately correlated with segment mechanical behavior irrespective of the loading direction whereas shear wave speed in the nucleus pulposus showed a very weak association (mean (SD) absolute Pearson correlation coefficients: 0.51 (0.14) and 0.17 (0.12), respectively). Young's modulus mapping of the intervertebral disc revealed stiffness to be highest in the ventral annulus with a stiffness decrease both circumferentially towards the dorsal aspect as well as towards the center of the disc. SWE hence provides a valid alternative to disc sectioning and piecewise mechanical testing.

Effect of an Adjustable Hinged Carbon Fiber Operating Table on the Coronal Alignment of the Lumbar Spine During Oblique Lateral Interbody Fusion

OBJECTIVE

We sought to measure the coronal alignment of the lumbar spine of patients in the right lateral decubitus position on a hinged Jackson operating table with the following 3 table positions: neutral and right and left 20-degree flexion.

METHODS

We analyzed the data of 23 patients who underwent OLIF. Spinal alignment was quantified using the coronal Cobb angle from L1 to S1, measured on anterior-posterior radiographs obtained preoperatively, after induction of anesthesia, with patients in the right lateral decubitus position, for the following 3 positions of the Jackson hinged operating table: neutral, right 20-degree flexion, and left 20-degree flexion. The Cobb angle at each position, the change in the Cobb angle, and the effective range of motion (%) were obtained from neutral to right and left 20-degree flexion. Alignment was compared between the 3 positions, and the range of motion was compared between men and women.

RESULTS

The Cobb angle was different in all 3 positions of the table (P < 0.0001): -7.0 ± 8.7°, neutral; 2.8 ± 7.6°, right 20-degree flexion; and -14.7 ± 7.8°, left 20-degree flexion. The change in Cobb angle and the effective range of motion were greater in women (10.9 ± 2.8° and 55%) than in men (6.7 ± 5.8° and 34%) from the neutral to right 20-degree flexion position (P = 0.0298).

CONCLUSIONS

The coronal alignment of the lumbar spine of patients in the right lateral decubitus position on a flat operating table (neutral position) was convex. The right 20-degree flexion position of the hinged operating table yielded less coronal plane lumbar spine deformity, with greater deformity in women.

Characterization of chondroitinase-induced lumbar intervertebral disc degeneration in a sheep model intended for assessing biomaterials

Intervertebral disc (IVD) degeneration (IVDD) leads to structural and functional changes. Biomaterials for restoring IVD function and promoting regeneration are currently being investigated; however, such approaches require validation using animal models that recapitulate clinical, biochemical, and biomechanical hallmarks of the human pathology. Herein, we comprehensively characterized a sheep model of chondroitinase-ABC (ChABC) induced IVDD. Briefly, ChABC (1 U) was injected into the L_1/2 , L_2/3 , and L_3/4 IVDs. Degeneration was assessed via longitudinal magnetic resonance (MR) and radiographic imaging. Additionally, kinematic, biochemical, and histological analyses were performed on explanted functional spinal units (FSUs). At 17-weeks, ChABC treated IVDs demonstrated significant reductions in MR index (p = 0.030) and disc height (p = 0.009) compared with pre-operative values. Additionally, ChABC treated IVDs exhibited significantly increased creep displacement (p = 0.004) and axial range of motion (p = 0.007) concomitant with significant decreases in tensile (p = 0.034) and torsional (p = 0.021) stiffnesses and long-term viscoelastic properties (p = 0.016). ChABC treated IVDs also exhibited a significant decrease in NP glycosaminoglycan: hydroxyproline ratio (p = 0.002) and changes in microarchitecture, particularly in the NP and endplates, compared with uninjured IVDs. Taken together, this study demonstrated that intradiscal injection of ChABC induces significant degeneration in sheep lumbar IVDs and the potential for using this model in evaluating biomaterials for IVD repair, regeneration, or fusion.

The degenerative lumbar disc: not a disease, but still an important consideration for OMPT practice: a review of the history and science of discogenic instability

BACKGROUND

A recent AAOMPT position paper was published that opposed the use of the term 'degenerative disc disease' (DDD), in large part because it appears to be a common age-related finding. While common, there are significant physiologic and biomechanical changes that occur as a result of discogenic degeneration, which are relevant to consider during the practice of manual therapy.

METHODS

A narrative review provides an overview of these considerations, including a historical perspective of discogenic instability, the role of the disc as a pain generator, the basic science of a combined biomechanical and physiologic cycle of degeneration and subsequent discogenic instability, the influence of rotation on the degenerative segment, the implications of these factors for manual therapy practice, and a perspective on an evidence-based treatment approach to patients with concurrent low back pain and discogenic degeneration.

CONCLUSIONS

As we consider the role of imaging findings such as DDD, we pose the following question: Do our manual interventions reflect the scientifically proven biomechanical aspects of DDD, or have we chosen to ignore the helpful science as we discard the harmful diagnostic label?

Variations Among Human Lumbar Spine Segments and Their Relationships to In Vitro Biomechanics: A Retrospective Analysis of 281 Motion Segments From 85 Cadaveric Spines

Background

Biomechanical properties of intact spinal motion segments are used to establish baseline values during in vitro studies evaluating spinal surgical techniques and implants. These properties are also used to validate computational models (ie, patient-specific finite element models) of human lumbar spine segments. Our laboratory has performed a large number of in vitro mechanical studies of lumbar spinal segments, using a consistent methodology. This provides extensive biomechanical data for a large number of intact motion segments, along with donor demographic variables, bone mineral density (BMD) measurements, and geometric properties. The objective of this study was to analyze how donor demographics, BMD, and geometric properties of cadaveric lumbar spine segments affect motion segment flexibility, including the range of motion (ROM), lax zone (LZ), and stiff zone (SZ), to help improve our understanding of spinal biomechanics.

Methods

A retrospective study examined the relationships between the biomechanical properties of 281 lumbar motion segments from 85 human cadaveric spines, donor demographic variables (age, sex, weight, height, and body mass index), and specimen measurements (vertebral body height, intervertebral disc height, and BMD).

Results

Statistical correlation and regression analyses showed that the flexibility of a lumbar motion segment is affected by lumbar level, donor age, sex, and weight as well as the intervertebral disc height, vertebral body height, and bone quality. Increased disc height was associated with decreased ROM (axial rotation), decreased LZ (flexion-extension and axial rotation), and increased SZ (flexion-extension and lateral bending) in the male group, but increased ROM (lateral bending) in the female group. Increased vertebral body height correlated with increased LZ (lateral bending) in the female group. Increased BMD correlated with decreased ROM overall.

Conclusions

Biomechanical measurements from flexibility testing of cadaveric lumbar spine segments are significantly correlated with donor demographics and specimen measurements. Many of these correlations are sex-dependent.

Arp2/3 inactivation causes intervertebral disc and cartilage degeneration with dysregulated TonEBP-mediated osmoadaptation

Extracellular matrix and osmolarity influence the development and homeostasis of skeletal tissues through Rho GTPase-mediated alteration of the actin cytoskeleton. This study investigated whether the actin-branching Arp2/3 complex, a downstream effector of the Rho GTPases Cdc42 and Rac1, plays a critical role in maintaining the health of matrix-rich and osmotically loaded intervertebral discs and cartilage. Mice with constitutive intervertebral disc- and cartilage-specific deletion of the critical Arp2/3 subunit Arpc2 (Col2-Cre; Arpc2fl/fl) developed chondrodysplasia and spinal defects. Since these mice did not survive to adulthood, we generated mice with inducible Arpc2 deletion in disc and cartilage (Acan-CreERT2; Arpc2fl/fl). Inactivation of Arp2/3 at skeletal maturity resulted in growth plate closure, loss of proteoglycan content in articular cartilage, and degenerative changes in the intervertebral disc at 1 year of age. Chondrocytes with Arpc2 deletion showed compromised cell spreading on both collagen and fibronectin. Pharmacological inhibition of Cdc42 and Arp2/3 prevented the osmoadaptive transcription factor TonEBP/NFAT5 from recruiting cofactors in response to a hyperosmolarity challenge. Together, these findings suggest that Arp2/3 plays a critical role in cartilaginous tissues through the regulation of cell-extracellular matrix interactions and modulation of TonEBP-mediated osmoadaptation.

MODIFICATION OF THE SPINOPELVIC PARAMETERS WITH SURGICAL POSITIONING AND THE ROLE OF THE HIP

ABSTRACT Post-operative lumbar pain is related to alterations in the sagittal and spinopelvic parameters. A lumbar fusion that fails to maintain, or that worsens the physiological lordosis alters the sagittal balance. Objective: To analyze spinopelvic variation in different surgical positions. Methods: A prospective, analytical and comparative study of spinograms, lumbosacral radiographs in the surgical position over a 4-pole quadratus lumborum, and lumbosacral radiographs with quadratus lumborum and support in the knees. A sample of 129 patients, of both sexes, aged between 18 and 60 years, and presenting with lower back pain. Lumbar Lordosis (LL), Pelvic Tilt (PT), Pelvic Incidence (PI) and Sacral Slope (SS) were measured. Results: PI was the most stable parameter. With quadratus lumborum, a slight increase in PT, a decrease in SS and a significant reduction in LL were found. With quadratus lumborum and support in the knees, a decrease in PT and a slight increase in SS were found, while the LL value remained similar to that of the spinogram. Conclusion: The intraoperative position with hip flexion of between 40° and 45° over quadratus lumborum reduced LL to 10.52° in men and 16.21° in women, increased PT, and decreased SS. The intraoperative position with hip flexion of between 0° and 10° showed the same values as the reference spinogram. Level of Evidence II; Prospective comparative study.

TonEBP-deficiency accelerates intervertebral disc degeneration underscored by matrix remodeling, cytoskeletal rearrangements, and changes in proinflammatory gene expression

The tonicity-responsive enhancer binding protein (TonEBP) plays an important role in intervertebral disc and axial skeleton embryogenesis. However, the contribution of this osmoregulatory transcription factor in postnatal intervertebral disc homeostasis is not known in vivo. Here, we show for the first time that TonEBP-deficient mice have pronounced age-related degeneration of the intervertebral disc with annular and endplate herniations. Using FTIR-imaging spectroscopy, quantitative immunohistochemistry, and tissue-specific transcriptomic analysis, we provide morphological and molecular evidence that the overall phenotype is driven by a replacement of water-binding proteoglycans with fibrocartilaginous matrix. Whereas TonEBP deficiency in the AF compartment caused tissue fibrosis associated with alterations in actin cytoskeleton and adhesion molecules, predominant changes in pro-inflammatory pathways were seen in the NP compartment of mutants, underscoring disc compartment-specific effects. Additionally, TonEBP-deficient mice presented with compromised trabecular bone properties of vertebrae. These results provide the first in vivo support to the long-held hypothesis that TonEBP is crucial for postnatal homeostasis of the spine and controls a multitude of functions in addition to cellular osmoadaptation.

Biomechanical properties in motion of lumbar spines with degenerative scoliosis

Degenerative lumbar scoliosis presumably alters spinal biomechanics, but a lack of quantitative reference measurements of these spines exists. We aimed to assess the biomechanical properties of spines with degenerative scoliosis, and to relate these to intervertebral disc degeneration (DD) and Cobb angle. Secondly, we compared these results to previous measurements of non-scoliotic spines. Ten cadaveric spines (Th12-L5, mean age 82 ± 11 years) with Cobb angle ≥10° and apex at L3 were acquired. Three loading cycles (-4 to 4 Nm) were applied in flexion/extension (FE), lateral bending (LB), and axial rotation (AR). The range of motion (ROM), neutral zone (NZ) stiffness, NZ ROM, elastic zone (EZ) stiffness and hysteresis were calculated for each motion segment in the loading direction. ROM was calculated in coupled directions, expressed as a percentage of rotation in the loaded direction. For Th12-L5, there was a ROM (degrees ± SD) of 14.9 ± 6.5 in FE, 14.9 ± 7.8 in LB, and 10.2 ± 5.5 in AR. The median (Nm/degree (Q1;Q3)) NZs was 0.24 (0.19;0.35) in FE, 0.25 (0.22;0.42) in LB, and 0.49 (0.33;0.99) in AR. Greater coupled motions related to higher Cobb angle, especially during AR on segments around the apex (FE: ρ = 0.539, p = 0.021 and LB: ρ = 0.821, p = 0.000). DD correlated to lower ROM and increased NZs on L2-L3 in FE (ρ = -0.721, p = 0.028 and ρ = 0.694, p = 0.038, respectively). Compared to non-scoliotic spines, smaller ROM in FE (p = 0.030) was found. This study describes the biomechanical properties of lumbar spines with degenerative scoliosis. Compared to non-scoliotic spines, they tended to be stiffer and exhibited smaller ROM in FE. DD only affected the ROM and NZs of the segments around the apex.

Lumbar spinal canal stenosis in patients with diffuse idiopathic skeletal hyperostosis: Surgical outcomes after posterior decompression surgery without spinal instrumentation

BACKGROUND

To evaluate surgical outcomes after posterior decompression surgery for lumbar spinal canal stenosis (LSS) in patients with diffuse idiopathic skeletal hyperostosis (DISH).

METHODS

The patients (n = 184; 132 males and 52 females; mean age 72.0 years; mean follow-up 30.7 months) who underwent posterior decompression surgery for LSS were identified and classified as either DISH (D) or non-DISH (N) based on whole spine radiograph findings. Data on age, gender, American Society of Anesthesiologists (ASA) classification, operation time, and estimated blood loss, were evaluated, while radiographic parameters were measured from radiographs obtained pre- and post-operatively.

RESULTS

Mean age and ASA classification were comparable between the two groups, while the proportion of males was significantly higher in the D group (87.5%) than in the N group (67.6%) (p = 0.016). Further, mean operation time was longer in the D group (89.0 min) than in the N group (73.7 min) (p = 0.036) and mean estimated blood loss was larger in the D group (98.7 g) than in the N group (51.9 g) (p = 0.006). At two years after surgery, the development of anterior translation was significantly higher in the D group (33.3%) than in the N group (17.3%) (p = 0.021). Improvements in ODI and SF-8 after the surgery were better in the N group than in the D group.

CONCLUSIONS

Compared to LSS patients without DISH who also underwent posterior decompression surgery for LSS, surgery in patients with DISH was characterized by greater blood loss, longer operation time, increased translation at the decompressed segment, and poor recovery.

Sex Differences in Rat Intervertebral Disc Structure and Function Following Annular Puncture Injury

STUDY DESIGN

A rat puncture injury intervertebral disc (IVD) degeneration model with structural, biomechanical, and histological analyses.

OBJECTIVE

To determine if males and females have distinct responses in the IVD after injury.

SUMMARY OF BACKGROUND DATA

Low back pain (LBP) and spinal impairments are more common in women than men. However, sex differences in IVD response to injury have been underexplored, particularly in animal models where sex differences can be measured without gender confounds.

METHODS

Forty-eight male and female Sprague Dawley rats underwent sham, single annular puncture with tumor necrosis factor α (TNFα) injection (1×), or triple annular puncture with TNFα injection (3×) surgery. Six weeks after surgery, lumbar IVDs were assessed by radiologic IVD height, spinal motion segment biomechanical testing, histological degeneration grading, second harmonic generation (SHG) imaging, and immunofluorescence for fibronectin and α-smooth muscle actin.

RESULTS

Annular puncture injuries significantly increased degenerative grade and IVD height loss for males and females, but females had increased degeneration grade particularly in the annulus fibrosus (AF). Despite IVD height loss, biomechanical properties were largely unaffected by injury at 6 weeks. However, biomechanical measures sensitive to outer AF differed by sex after 3× injury-male IVDs had greater torsional stiffness, torque range, and viscoelastic creep responses. SHG intensity of outer AF was reduced after injury only in female IVDs, suggesting sex differences in collagen remodeling. Both males and females exhibited decreased cellularity and increased fibronectin expression at injury sites.

CONCLUSION

IVD injury results in distinct degeneration and functional healing responses between males and females. The subtle sex differences identified in this animal model suggest differences in response to IVD injury that might explain some of the variance observed in human LBP, and demonstrate the need to better understand differences in male and female IVD degeneration patterns and pain pathogenesis.

LEVEL OF EVIDENCE

N/A.

The biomechanical effect of single-level laminectomy and posterior instrumentation on spinal stability in degenerative lumbar scoliosis: a human cadaveric study

OBJECTIVEDegenerative lumbar scoliosis, or de novo degenerative lumbar scoliosis, can result in spinal canal stenosis, which is often accompanied by disabling symptoms. When surgically treated, a single-level laminectomy is performed and short-segment posterior instrumentation is placed to restore stability. However, the effects of laminectomy on spinal stability and the necessity of placing posterior instrumentation are unknown. Therefore, the aim of this study was to assess the stability of lumbar spines with degenerative scoliosis, characterized by the range of motion (ROM) and neutral zone (NZ) stiffness, after laminectomy and placement of posterior instrumentation.METHODSTen lumbar cadaveric spines (T12-L5) with a Cobb angle ≥ 10° and an apex on L3 were included. Three loading cycles were applied per direction, from -4 Nm to 4 Nm in flexion/extension (FE), lateral bending (LB), and axial rotation (AR). Biomechanical evaluation was performed on the native spines and after subsequent L3 laminectomy and the placement of posterior L2-4 titanium rods and pedicle screws. Nonparametric and parametric tests were used to analyze the effects of laminectomy and posterior instrumentation on NZ stiffness and ROM, respectively, both on an individual segment's motion and on the entire spine section. Spearman's rank correlation coefficient was used to study the correlation between disc degeneration and spinal stability.RESULTSThe laminectomy increased ROM by 9.5% in FE (p = 0.04) and 4.6% in LB (p = 0.01). For NZ stiffness, the laminectomy produced no significant effects. Posterior instrumentation resulted in a decrease in ROM in all loading directions (-22.2%, -24.4%, and -17.6% for FE, LB, and AR, respectively; all p < 0.05) and an increase in NZ stiffness (+44.7%, +51.7%, and +35.2% for FE, LB, and AR, respectively; all p < 0.05). The same changes were seen in the individual segments around the apex, while the adjacent, untreated segments were mostly unaffected. Intervertebral disc degeneration was found to be positively correlated to decreased ROM and increased NZ stiffness.CONCLUSIONSLaminectomy in lumbar spines with degenerative scoliosis did not result in severe spinal instability, whereas posterior instrumentation resulted in a rigid construct. Also, prior to surgery, the spines already had lower ROM and higher NZ stiffness in comparison to values shown in earlier studies on nonscoliotic spines of the same age. Hence, the authors question the clinical need for posterior instrumentation to avoid instability.

Diffusion based MR measurements correlates with age-related changes in human intervertebral disks

BACKGROUND

Understanding the association between MR parameters and age related deterioration in human intervertebral disks forms an important step in the development of clinical diagnostic protocols for disk disease.

METHODS

Ten unfixed thoracic and lumbar cadaver disk joints, age 37-81 years were imaged at 9.4 T using T2 relaxation (CPMG) and ADC (DWI spin echo) MR protocols. For each MR parameter, spatial maps were computed from the axial images, with the AF and NP segmented based on the T2 maps. Linear regression tested for the correlation between mean and variance (COV) of T2 and ADC with age in the disk, nucleus and annulus, and the effect of thoracic vs. lumbar spine on these correlations.

FINDINGS

In the disk, age negatively correlated with mean ADC (P < 0.001) and positively with COV of ADC (P < 0.001) and T2 (P < 0.05). Age was negatively correlated with mean T2 (P < 0.01), mean ADC (P < 0.001) and positively with COV of ADC (P < 0.001) and T2 (P < 0.05) in the NP and positively correlated with mean T2 (P < 0.05), COV of ADC (P < 0.01) and T2 (P < 0.05) and negatively with mean ADC (P < 0.05) in the AF. Compared to thoracic disks, lumbar disks showed higher mean ADC (P < 0.05), lower mean T2 (P < 0.001) and higher COV of ADC (P < 0.01) and T2 (P < 0.05).

INTERPRETATION

Compared to T2, MR diffusion was a more sensitive measure of age mediated changes in disk tissues. Strong differences in the association of MR parameters with age between the lumbar and thoracic suggest that mechanical environment effects tissue specific MR parameters' association with age.

Age-related changes in trunk muscle activity and spinal and lower limb kinematics during gait

The influence of age on spinal muscle activation patterns and its relation to kinematics is poorly understood. We aimed at understanding age-related changes to spine and trunk muscle activity in addition to spinal and lower limb kinematics during treadmill walking under various conditions. An observational study was conducted evaluating asymptomatic young (n = 10; 3F, 7M; 26.3±2.5yrs) and older (n = 9; 3F, 6M; 67.1±4.2yrs) adults’ treadmill walking at 2km/h and 4km/h, each at 0, 1, 5, and 10% inclination. Unilateral (right side) electromyography (EMG) was recorded from deep and superficial multifidus (intramuscular) and erector spinae and abdominal obliques (surface); trunk and leg kinematics were also measured. Muscle activity was characterised by peak amplitude and duration of activity, and the time-point of peak amplitude in the gait cycle (0–100%). Peak activation in older adults was lower for the superficial multifidus (p<0.0001) and higher for the thoracolumbar (p<0.001) and lumbar erector spinae (p<0.01). The duration of activation was longer in older adults for all muscles (p<0.05) except the superficial multifidus, and longer during faster walking for all participants. The time-point of peak amplitude in the gait cycle was earlier in older participants for the external obliques (p<0.05). Walking speed appeared to influence muscle activity more than inclination. Older adults used less spine, trunk and lower limb motion, except at the ankle. Age-related differences within multifidus and between paravertebral and trunk muscles were inconsistent. Walking at 4km/h at 5–10% inclination may specifically target the lumbar paravertebral muscles.

Bone morphogenetic protein 2 alleviated intervertebral disc degeneration through mediating the degradation of ECM and apoptosis of nucleus pulposus cells via the PI3K/Akt pathway

The present study aimed to explore the underlying mechanisms of bone morphogenetic protein 2 (BMP2) in alleviating intervertebral disc degeneration (IDD). A rat puncture IDD model was constructed, and the rats were randomly divided into six groups: Control; IDD (model); IDD+PBS [containing 1010 adeno‑associated virus serotype 2 (AAV)]; and IDD + AAV2‑BMP2 (106, 108 and 1010). IL‑1β was used to treat primary nucleus pulposus (NP) cells to mimic IDD in vitro. The effects of BMP2 in IDD were determined by magnetic resonance imaging (MRI), hematoxylin and eosin staining and Alcian Blue staining in vivo. The levels of collagen II, aggrecan, transcription factor SOX9 (SOX9) and matrix metalloproteinase 13 (MMP‑13) were examined using western blot analysis and reverse transcription quantitative polymerase chain reaction (RT‑qPCR) in NP tissues and cells. The expression of C‑telopeptide of type II collagen (CTX‑II) in the sera or cell supernatants was determined by ELISA. In addition, the levels of phosphorylation of phosphoinositide 3‑kinase (PI3K) and protein kinase B (Akt), and the levels of apoptosis‑associated proteins and apoptosis ratio of NP cells were also determined by western blot analysis and flow cytometry, respectively. LY29400, an inhibitor of PI3K, was used to additionally confirm the signal pathway mechanism of BMP2 treatment in IDD. BMP2 significantly extended the interval between discs and alleviated the fibrous ring rupture and the decrease in the levels of glycoproteins in IDD rats, as determined by MRI and histological staining. Additionally, BMP2 treatment significantly upregulated the levels of collagen II, aggrecan and SOX9, but downregulated the levels of MMP‑13 and CTX‑II in IDD rats and NP cells in a dose‑dependent manner. Concurrently, recombinant human (rh)BMP2 pretreatment also significantly decreased the apoptosis ratio of interleukin (IL)‑1β‑treated NP cells via downregulating the level of cleaved caspase‑3 and upregulating the level of uncleaved poly (adenosine 5'‑diphosphate‑ribose) polymerase. It was demonstrated that rhBMP2 also significantly decreased the inflammatory response in NP tissues and cells, based on levels of IL‑6, TNF‑α and IL‑10. In addition, rhBMP2 inhibited cell apoptosis via upregulating the phosphorylation levels of the PI3K/Akt signaling pathway, and LY29400 pretreatment inhibited the effects of BMP2 in IL‑1β treated NP cells. BMP2 alleviated IDD via the PI3K/Akt signaling pathway by inhibiting NP cell apoptosis and decreasing the levels of matrix proteins.

A novel in vivo large animal model of lumbar spinal joint degeneration

BACKGROUND CONTEXT

Degenerative disc disease (DDD) is a common, widespread socioeconomic problem. Appropriate large animal models of DDD are required for improved understanding and to serve as preclinical test beds for therapeutic strategies.

PURPOSE

To evaluate the effects of short and medium duration immobilization on the sheep lumbar intervertebral disc (IVD) and facet joints (FJs), and to establish a large animal model for DDD research.

STUDY DESIGN

An in vivo sheep model evaluating the effect of short- and medium-term immobilization on disc degeneration.

METHODS

Eighteen sheep were equally randomized into three groups: short-term (6-week) immobilization (n=6), medium-term (26-week) immobilization (n=6), and control (no surgery) (n=6). Immobilization of L3-L4 was achieved with pedicle screw and rod implantation, the IVD was kept intact, and the annulus and end plates were not disrupted. The IVD and FJs were assessed with planar radiography, computerized tomography (CT), magnetic resonance imaging (MRI), pure moment biomechanical testing, and histologic analysis.

RESULTS

Disc height was reduced for 6- and 26-week immobilization groups. The MRI and histologic analysis demonstrated significant disc degeneration for both immobilized groups compared with control, but no statistical difference was detected between short- and medium-term duration. Progressive degenerative changes in FJs were observed with micro-CT and histologic end points. Immobilization significantly reduced lateral bending and flexion-extension range of motion.

CONCLUSIONS

The mechanical environment set up by immobilization alone is capable of inducing lumbar disc degeneration at both 6 and 26 weeks in sheep. Longer duration immobilization did not advance disc degeneration process beyond of that found with short duration. The present model produces a degenerative disc with intact annulus and without acute injury, more closely representing the scenario common in human disc degeneration. This provides a suitable large animal in vivo model for the evaluation of the new therapies for disc degeneration. Further studies would do well to examine the effect of remobilization after immobilization in this model.

The degeneration of adjacent intervertebral discs negatively influence union rate of osteoporotic vertebral fracture: A multicenter cohort study

BACKGROUND

With the increasing aging population in developed countries, there has been an associated increased prevalence of osteoporotic vertebral fracture (OVF). Many previous reports have attempted to predict the risk of delayed union associated with OVF. However, the role of endplate failure and the degeneration of adjacent intervertebral discs, and their association with delayed union has received little attention. The aim of this study was to evaluate the endplate fracture and disc degeneration rank as risk factors for delayed union.

MATERIALS AND METHODS

Two hundred and eighteen consecutive patients with fresh OVF were enrolled in the study. MRI and X-ray were performed at the time of enrollment and at the 6 months follow-up. The MR images were used to assess the degeneration grade of adjacent intervertebral discs (using the modified Pfirrmann grading system), and endplate failure. Supine and weight-bearing radiographs were used to define angular motion and compression ratio of the anterior vertebral body wall.

RESULTS

A total of 139 patients (112 female, 27 male) completed the 6 month follow-up (a 65.1% follow-up rate). The study revealed 27 cases of delayed union (19.4%). A healthier adjacent caudal disc with low grade degeneration was found to be associated with an increased risk of delayed union (P = 0.008). Bi-endplate injury and significant compression of the anterior vertebral body wall were significantly associated with delayed union (P = 0.019, and P = 0.001 respectively). Rapid progression of the adjacent cranial disc degeneration was observed at the end of the 6 month follow-up period (P = 0.001).

CONCLUSION

Modified Pfirrmann grading system revealed that a healthier adjacent intervertebral disc at the caudal level and bi-endplate fracture were significantly associated with an increased risk of delayed union. These findings may influence the management strategy for patients with OVF.

Is intervertebral disc degeneration related to segmental instability? An evaluation with two different grading systems based on clinical imaging

Background Several in vitro studies investigated how degeneration affects spinal motion. However, no consensus has emerged from these studies. Purpose To investigate how degeneration grading systems influence the kinematic output of spinal specimens. Material and Methods Flexibility testing was performed with ten human T12-S1 specimens. Degeneration was graded using two different classifications, one based on X-ray and the other one on magnetic resonance imaging (MRI). Intersegmental rotation (expressed by range of motion [ROM] and neutral zone [NZ]) was determined in all principal motion directions. Further, shear translation was measured during flexion/extension motion. Results The X-ray grading system yielded systematically lesser degeneration. In flexion/extension, only small differences in ROM and NZ were found between moderately degenerated motion segments, with only NZ for the MRI grading reaching statistical significance. In axial rotation, a significant increase in NZ for moderately degenerated segments was found for both grading systems, whereas the difference in ROM was significant only for the MRI scheme. Generally, the relative increases were more pronounced for the MRI classification compared to the X-ray grading scheme. In lateral bending, only relatively small differences between the degeneration groups were found. When evaluating shear translations, a non-significant increase was found for moderately degenerated segments. Motion segment segments tended to regain stability as degeneration progressed without reaching the level of statistical significance. Conclusion We found a fair agreement between the grading schemes which, nonetheless, yielded similar degeneration-related effects on intersegmental kinematics. However, as the trends were more pronounced using the Pfirrmann classification, this grading scheme appears superior for degeneration assessment.

Effect of an Adjustable Hinged Operating Table on Lumbar Lordosis During Lumbar Surgery

STUDY DESIGN

Prospective observational study.

OBJECTIVES

Quantify the amount of lumbar lordosis achieved on a hinged operative table in neutral, flexion, and extension.

SUMMARY OF BACKGROUND DATA

Hinged operative tables may allow surgeons to adjust lumbar spine positioning intraoperatively. The amount of lumbar lordosis in neutral, flexion, and extension positions has not been quantified prospectively using a hinged table.

METHODS

Thirty patients undergoing elective lumbar surgery were enrolled. Standing x-rays taken in neutral, maximal flexion, and maximal extension were obtained. After prone positioning on a hinged operative table, x-rays in neutral, maximal flexion, and maximal extension were taken. Total lumbar lordosis was calculated for all six images by two physicians. Disc degeneration was graded using Pfirrmann grades.

RESULTS

Lumbar lordosis on the operative table was 56.5 ± 2.1, 43.6 ± 2.2, 63.2 ± 2.0 compared with 46.9 ± 3.1, 33.2 ± 2.8, 52.3 ± 3.3 on the standing films in neutral, flexion, and extension, respectively. Average flexion (12.9 ± 1.1) and extension (6.7 ± 1.2) were significantly different from neutral on the table (P < 0.001). Lumbar lordosis was significantly higher on the operative table (P < 0.001). Total range of motion was 19.6 ± 1.9 on the table and 19.1 ± 2.0 with standing (P = 0.42). Average Pfirrmann disc grade was 2.77 ± 0.10 that did not correlate with range of motion (P = 0.40).

CONCLUSION

In this cohort, the hinged operative table allowed for a physiologic arc of motion of nearly 20 from flexion to extension. A considerable amount of lumbar sagittal motion can be obtained on hinged operative tables without decreasing overall lumbar lordosis below physiologic levels.

LEVEL OF EVIDENCE

3.

Multi-segmental thoracic spine kinematics measured dynamically in the young and elderly during flexion

In contrast to the cervical and lumbar region, the normal kinematics of the thoracic spine have not been thoroughly investigated. The aim of this study was to characterize normal multi-segmental continuous motion of the whole thoracolumbar spine, during a flexion maneuver, in young and elderly subjects. Forty-two healthy volunteers were analyzed: 21 young (age=27.00±3.96) and 21 elderly (age=70.1±3.85). Spinal motion was recorded with a motion-capture system and analyzed using a 3rd order polynomial function to approximate spinal curvature throughout the motion sequence. The average motion profiles of the two age groups were characterized. Flexion timing of the thoracic region of the spine, as compared to the lumbar spine and hips, was found to be different in the two age groups (p=0.011): a delayed/sequential motion type was observed in most of the young, whereas mostly a simultaneous motion pattern was observed in the elderly subjects. A similar trend was observed in flexion of the lower thoracic segments (p=0.017). Differences between age groups were also found for regional and segmental displacements and velocities. The reported characterization of the thoracic spine kinematics may in the future support identification of abnormal movement or be used to improve biomechanical models of the spine.

MR Elastography-derived Stiffness: A Biomarker for Intervertebral Disc Degeneration

Purpose To determine the repeatability of magnetic resonance (MR) elastography-derived shear stiffness measurements of the intervertebral disc (IVD) taken throughout the day and their relationship with IVD degeneration and subject age. Materials and Methods In a cross-sectional study, in vivo lumbar MR elastography was performed once in the morning and once in the afternoon in 47 subjects without current low back pain (IVDs = 230; age range, 20-71 years) after obtaining written consent under approval of the institutional review board. The Pfirrmann degeneration grade and MR elastography-derived shear stiffness of the nucleus pulposus and annulus fibrosus regions of all lumbar IVDs were assessed by means of principal frequency analysis. One-way analysis of variance, paired t tests, concordance and Bland-Altman tests, and Pearson correlations were used to evaluate degeneration, diurnal changes, repeatability, and age effects, respectively. Results There were no significant differences between morning and afternoon shear stiffness across all levels and there was very good technical repeatability between the morning and afternoon imaging results for both nucleus pulposus (R = 0.92) and annulus fibrosus (R = 0.83) regions. There was a significant increase in both nucleus pulposus and annulus fibrosus MR elastography-derived shear stiffness with increasing Pfirrmann degeneration grade (nucleus pulposus grade 1, 12.5 kPa ± 1.3; grade 5, 16.5 kPa ± 2.1; annulus fibrosus grade 1, 90.4 kPa ± 9.3; grade 5, 120.1 kPa ± 15.4), and there were weak correlations between shear stiffness and age across all levels (R ≤ 0.32). Conclusion Our results demonstrate that MR elastography-derived shear stiffness measurements are highly repeatable, weakly correlate with age, and increase with advancing IVD degeneration. These results suggest that MR elastography-derived shear stiffness may provide an objective biomarker of the IVD degeneration process. ^© RSNA, 2017 Online supplemental material is available for this article.

The segment-dependent changes in lumbar intervertebral space height during flexion-extension motion

Objectives

Many studies have investigated the kinematics of the lumbar spine and the morphological features of the lumbar discs. However, the segment-dependent immediate changes of the lumbar intervertebral space height during flexion-extension motion are still unclear. This study examined the changes of intervertebral space height during flexion-extension motion of lumbar specimens.

Methods

First, we validated the accuracy and repeatability of a custom-made mechanical loading equipment set-up. Eight lumbar specimens underwent CT scanning in flexion, neural, and extension positions by using the equipment set-up. The changes in the disc height and distance between adjacent two pedicle screw entry points (DASEP) of the posterior approach at different lumbar levels (L3/4, L4/5 and L5/S1) were examined on three-dimensional lumbar models, which were reconstructed from the CT images.

Results

All the vertebral motion segments (L3/4, L4/5 and L5/S1) had greater changes in disc height and DASEP from neutral to flexion than from neutral to extension. The change in anterior disc height gradually increased from upper to lower levels, from neutral to flexion. The changes in anterior and posterior disc heights were similar at the L4/5 level from neutral to extension, but the changes in anterior disc height were significantly greater than those in posterior disc height at the L3/4 and L5/S1 levels, from neutral to extension.

Conclusions

The lumbar motion segment showed level-specific changes in disc height and DASEP. The data may be helpful in understanding the physiologic dynamic characteristics of the lumbar spine and in optimising the parameters of lumbar surgical instruments.

Cite this article: M. Fu, Q. Ye, C. Jiang, L. Qian, D. Xu, Y. Wang, P. Sun, J. Ouyang. The segment-dependent changes in lumbar intervertebral space height during flexion-extension motion. Bone Joint Res 2017;6:245–252. DOI: 10.1302/2046-3758.64.BJR-2016-0245.R1.

Moderately degenerated lumbar motion segments: Are they truly unstable?

The two main load bearing tissues of the intervertebral disc are the nucleus pulposus and the annulus fibrosus. Both tissues are composed of the same basic components, but differ in their organization and relative amounts. With degeneration, the clear distinction between the two tissues disappears. The changes in biochemical content lead to changes in mechanical behaviour of the intervertebral disc. The aim of the current study was to investigate if well-documented moderate degeneration at the biochemical and fibre structure level leads to instability of the lumbar spine. By taking into account biochemical and ultrastructural changes to the extracellular matrix of degenerating discs, a set of constitutive material parameters were determined that described the individual tissue behaviour. These tissue biomechanical models were then used to simulate dynamic behaviour of the degenerated spinal motion segment, which showed instability in axial rotation, while a stabilizing effect in the other two principle bending directions. When a shear load was applied to the degenerated spinal motion segment, no sign of instability was found. This study found that reported changes to the nucleus pulposus and annulus fibrosus matrix during moderate degeneration lead to a more stable spinal motion segment and that such biomechanical considerations should be incorporated into the general pathophysiological understanding of disc degeneration and how its progress could affect low back pain and its treatments thereof.