The influence of static axial torque in combined loading on intervertebral joint failure mechanics using a porcine model

Efficacy of a new protocol for the prevention of work-related musculoskeletal disorders in dental hygiene students: A pilot randomized controlled trial

OBJECTIVE

The purpose of this pilot randomized controlled trial (RCT) was to assess the efficacy of a new muscle stretching and strengthening protocol for the prevention of work-related musculoskeletal disorders (WMSD) in dental hygiene students.

METHODS

Students attending the 2nd and 3rd year of a Dental Hygiene Degree Course of a University Hospital were randomly allocated into treatment group (muscle stretching and strengthening sessions) and control group (no treatment). Nordic Musculoskeletal Questionnaire (NMQ), quality of life, the intensity of the pain and the Global Perceived Effect (GPE) Scale were assessed at the baseline (T0), after 4 weeks (T1) and after 16 weeks (T2).

RESULTS

Of 37 subjects screened for eligibility, 28 patients (aged 28.25 ± 8.89 years) were enrolled and divided into treatment and control groups. The NWQ showed significant between-group differences in the following regions from T0 to T2: neck (p = 0.0003), shoulders (p = 0.0057) and lower back (p = 0.0136). In terms of pain, a significant between-group difference was reported from T2 (p < 0.001). The GPE demonstrated that the average satisfaction related to the performed treatment was 1.4 ± 0.63.

CONCLUSION

The present pilot RCT demonstrated the efficacy of stretching associated with muscle strengthening in decreasing the risk of WMSD, especially for the neck, shoulders and lower back. The potential strength of this model is related to the possibility to perform stretching exercises chairside at work during scheduled breaks, in addition to complementary muscle strengthening sessions at home. Future RCTs are necessary to better investigate the role of this protocol for WMSD prevention.

An Assessment of Back and Shoulder Postures in Single-Handed Exertions: Expanding Ergonomic Reaching Guidelines to Consider Lumbar Spine Axial Twist

Occupational applicationsAcross a series of standing single-handed exertions performed at different lateral angles, distances, heights, and loads, lumbar axial twist exceeded an angular threshold of 9° in select exertions. Specifically, 9° of rightward axial twist was exceeded for all exertions performed laterally (90° from the body midline). Additionally, for those at the body midline, 9° of leftward axial twist was exceeded for upward exertions and exertions performed at far distances (tertiary reach envelope). Further, the data supports that for many exertions, lumbar flexion-extension and shoulder elevation would be unlikely to increase the potential for injury as angles remained within the in vivo lumbar neutral zone and were not considered overhead. Given the relationship between lateral hand exertions and lumbar axial twist, it is generally recommended that standing single-handed exertions not be performed beyond 60° from the midline. In addition to the current recommendations related to reach distance, future ergonomic reach envelope guidelines could benefit from incorporating recommendations on reach angle from the body midline.

Cervical Spine Motion Requirements From Night Vision Goggles May Play a Greater Role in Chronic Neck Pain than Helmet Mass Properties

BACKGROUND

Chronic Neck Pain (CNP) among rotary-wing aircrew is thought to stem from night vision goggles (NVG) and counterweight (CW) systems which displace the centre of mass of the head. This investigation aimed to quantify the loads acting on the neck as a function of movement magnitude (MM), helmet conditions, and movement axes in rapid movements.

METHODS

Cervical spine kinematics during rapid head repositioning tasks for flexion-extension (FE) and axial rotation (AR) movements were measured from 15 males and 15 females. Participants moved in either a 35° (Near MM) or 70° arc (Far MM), while donning a helmet, helmet with NVG, helmet with NVG and a typical CW, and a CW Liner (CWL). Measured EMG from three muscles bilaterally and used to drive a biomechanical model to quantify the compression and shear acting at the C5-C6 joint.

RESULTS

In AR, the NVGs were associated with the largest compression magnitudes, 252 (24) N. CW conditions decreased the maximum compression to 249 (53) N. For FE, the compression was 340 N for the Far MM trials and 246 N for Near MMs. Changing the helmet configuration only modestly influenced these magnitudes in FE.

CONCLUSION

Every 30° of MM increased compression by 57 to 105 N. The reduction of the moment of inertia by 16% in the CWL did not reduce reaction forces. Joint loads scaled proportionately with head-supported weight by a factor of 2.05. The magnitudes of loads suggest a cumulative loading pathway for CNP development.

The role of biomechanical factors in models of intervertebral disc degeneration across multiple length scales

Low back pain is the leading cause of disability, producing a substantial socio-economic burden on healthcare systems worldwide. Intervertebral disc (IVD) degeneration is a primary cause of lower back pain, and while regenerative therapies aimed at full functional recovery of the disc have been developed in recent years, no commercially available, approved devices or therapies for the regeneration of the IVD currently exist. In the development of these new approaches, numerous models for mechanical stimulation and preclinical assessment, including in vitro cell studies using microfluidics, ex vivo organ studies coupled with bioreactors and mechanical testing rigs, and in vivo testing in a variety of large and small animals, have emerged. These approaches have provided different capabilities, certainly improving the preclinical evaluation of these regenerative therapies, but challenges within the research environment, and compromises relating to non-representative mechanical stimulation and unrealistic test conditions, remain to be resolved. In this review, insights into the ideal characteristics of a disc model for the testing of IVD regenerative approaches are first assessed. Key learnings from in vivo, ex vivo, and in vitro IVD models under mechanical loading stimulation to date are presented alongside the merits and limitations of each model based on the physiological resemblance to the human IVD environment (biological and mechanical) as well as the possible feedback and output measurements for each approach. When moving from simplified in vitro models to ex vivo and in vivo approaches, the complexity increases resulting in less controllable models but providing a better representation of the physiological environment. Although cost, time, and ethical constraints are dependent on each approach, they escalate with the model complexity. These constraints are discussed and weighted as part of the characteristics of each model.

Porcine Functional Spine Unit in orthopedic research, a systematic scoping review of the methodology

Purpose

The aim of this study was to conduct a systematic scoping review of previous in vitro spine studies that used pig functional spinal units (FSU) as a model to gain an understanding of how different experimental methods are presented in the literature. Research guidelines are often used to achieve high quality in methods, results, and reports, but no research guidelines are available regarding in vitro biomechanical spinal studies.

Methods

A systematic scoping review approach and protocol was used for the study with a systematic search in several data bases combined with an extra author search. The articles were examined in multiple stages by two different authors in a blinded manner. Data was extracted from the included articles and inserted into a previously crafted matrix with multiple variables. The data was analyzed to evaluate study methods and quality and included 70 studies.

Results

The results display that there is a lack of consensus regarding how the material, methods and results are presented. Load type, duration and magnitude were heterogeneous among the studies, but sixty-seven studies (96%) did include compressive load or tension in the testing protocol.

Conclusions

This study concludes that an improvement of reported data in the present field of research is needed. A protocol, modified from the ARRIVE guidelines, regarding enhanced report-structure, that would enable comparison between studies and improve the method quality is presented in the current study. There is also a clear need for a validated quality-assessment template for experimental animal studies.

Examining the protective role of the posterior elements of the spine against endplate fractures in a porcine model

Previous studies have shown that the posterior elements/facet joints provide strength to the overall functional spine unit (FSU) by taking 3-25% of vertical compressive load off the intervertebral disc (IVD). However, little is known regarding whether this offloading has a protective effect against endplate fracture. Therefore, the purpose of this study was to investigate if the posterior elements provide a protective role to the endplate in porcine cervical spines under fracture-inducing conditions. Twenty-two cervical porcine FSUs (C5/6 level) were randomized into two groups: 1) a control group which had their posterior elements left intact (n = 11); 2) an experimental group which had the posterior elements removed (n = 11). Each FSU underwent a previously reported rapid IVD pressurization protocol in order to create endplate fractures. Briefly, hydraulic fluid was rapidly injected into the IVD via a standard inflation needle inserted through the anterior annulus which was connected to a hydraulic pump and pressure transducer. Post pressurization, each FSU was dissected to determine the presence and size of endplate fracture. Peak pressurization and rate of pressurization were not found to differ between intact and cut specimens (p = 0.313 and 0.101, respectively). In contrast, significantly, more cut FSUs sustained an endplate fracture (11/11) compared to intact FSUs (5/11); p = 0.012. Further, cut FSUs resulted in a fracture area 1.91 times greater in size compared to the fractures seen in the intact FSUs (p = 0.011). Therefore, posterior elements appear to decrease the risk and severity of endplate fracture.

Facet Tropism/Inclination and Its Association with Intervertebral Disc Herniation in the Lumbar Spine - A Radiological Evaluation

Objective  To assess the role of facet tropism (FT) in intervertebral disc prolapse. Methods  A total 98 patients with lower back pain were included in the study. Magnetic resonance imaging scans were performed and analyzed. The angles of the right and left facets were measured on the axial section. Patients without disc prolapse at the L3-L4, L4-L5 and L5-S1 levels act as controls for those with disc prolapse at the same levels. A statistical analysis was also performed. Results  The incidence of FT at the L3-L4 level was of 85.2% in patients with disc herniation ( n  = 27), and of 56.3% in the control group, which was statistically significant ( p  = 0.008). Similarly, at the L4-L5 level, incidence of FT among cases and controls was of 71.4% ( n  = 35) and 52.4% respectively ( p  = 0.066). At the L5-S1 the incidence was of 66% and 51% among cases and controls respectively ( p  = 0.13). Conclusion  We found a positive association between FT and disc herniation at the L3-L4 level, but no association at the L4-L5 and L5-S1 levels.

Feature Detection and Biomechanical Analysis to Objectively Identify High Exposure Movement Strategies When Performing the EPIC Lift Capacity test

Purpose The Epic Lift Capacity (ELC) test is used to determine a worker's maximum lifting capacity. In the ELC test, maximum lifting capacity is often determined as the maximum weight lifted without exhibiting a visually appraised "high-risk workstyle." However, the criteria for evaluating lifting mechanics have limited justification. This study applies feature detection and biomechanical analysis to motion capture data obtained while participants performed the ELC test to objectively identify aspects of movement that may help define "high-risk workstyle". Method In this cross-sectional study, 24 participants completed the ELC test. We applied Principal Component Analysis, as a feature detection approach, and biomechanical analysis to motion capture data to objectively identify movement features related to biomechanical exposure on the low back and shoulders. Principal component scores were compared between high and low exposure trials (relative to median exposure) to determine if features of movement differed. Features were interpreted using single component reconstructions of principal components. Results Statistical testing showed that low exposure lifts and lowers maintained the body closer to the load, exhibited squat-like movement (greater knee flexion, wider base of support), and remained closer to neutral posture at the low back (less forward flexion and axial twist) and shoulder (less flexion and abduction). Conclusions Use of feature detection and biomechanical analyses revealed movement features related to biomechanical exposure at the low back and shoulders. The objectively identified criteria could augment the existing scoring criteria for ELC test technique assessment. In the future, such features can inform the design of classifiers to objectively identify "high-risk workstyle" in real-time.

Spine biomechanical testing methodologies: The controversy of consensus vs scientific evidence

Biomechanical testing methodologies for the spine have developed over the past 50 years. During that time, there have been several paradigm shifts with respect to techniques. These techniques evolved by incorporating state-of-the-art engineering principles, in vivo measurements, anatomical structure-function relationships, and the scientific method. Multiple parametric studies have focused on the effects that the experimental technique has on outcomes. As a result, testing methodologies have evolved, but there are no standard testing protocols, which makes the comparison of findings between experiments difficult and conclusions about in vivo performance challenging. In 2019, the international spine research community was surveyed to determine the consensus on spine biomechanical testing and if the consensus opinion was consistent with the scientific evidence. More than 80 responses to the survey were received. The findings of this survey confirmed that while some methods have been commonly adopted, not all are consistent with the scientific evidence. This review summarizes the scientific literature, the current consensus, and the authors' recommendations on best practices based on the compendium of available evidence.

Facet Tropism in Lumbar Spine and Cervical Spine: A Systematic Review and Meta-Analysis

BACKGROUND

Facet tropism (FT) refers to the difference in the orientation of facet joints with respect to each other in the sagittal plane. FT leads to unequal biomechanical forces on facet joint and intervertebral disc during rotation and other physiologic movements. Most of the studies have reported the incidence of FT in the lumbar spine to vary between 40% and 70%, with L4-5 level being the most commonly afflicted level. The objective of this study was to find the association between FT and various lumbar and cervical degenerative disorders.

METHODS

A systematic search of PubMed was performed with the keywords "facet tropism" and "facet asymmetry." Data for meta-analysis were extracted from the studies to obtain pooled impact of FT on lumbar disc herniation (LDH) and lumbar degenerative spondylolisthesis (LDS).

RESULTS

Eighty-two articles were included in the systematic review and 18 studies had the required data to be included in the meta-analysis. The pooled standard mean difference between FT angles in patients with or without LDH was 0.31 with (P = 0.04). The pooled odds ratio for FT in patients with LDH was 3.27 with (P = 0.02). Subgroup analysis showed that there is no significant difference in the L3/4, L4/5, and L5S1 subgroups. The pooled standard mean difference between FT angles in patients with or without LDS was 0.54 (P = 0.009).

CONCLUSIONS

FT is significantly associated with LDH and LDS along with various other lumbar and cervical degenerative diseases.

The relationship between facet tropism and cervical disc herniation

Many studies have demonstrated the association between facet tropism and disc herniation in the lumbar spine. Some of them found that lumbar disc herniation was on the side of the more sagittal facet joint interface. However, little is understood about the association of facet tropism with disc herniation in the cervical spine. As the relationship between the facet orientation and the side of cervical disc herniation (CDH) is unclear, the purpose of this study is to investigate that relationship. Ninety-six patients with single-level CDH (C4-C5, C5-C6 or C6-C7) were included in the CDH group of this study. Another 50 age-matched and gender-matched healthy participants who accepted physical examinations were enrolled as the control group. The cervical facet angles of two sides were measured using axial computed tomography (CT). The intersection angle of the midsagittal line of the vertebra to the facet line represents the facet angle. Facet tropism was defined as the angular difference of 7º between the left and the right sides. Facet tropism angle was recorded as the absolute value of the difference of facet angles between two sides. There were 20 herniations at C4-C5 level, 50 herniations at C5-C6 level and 26 herniations at C6-C7 level. The present study showed that more cases in the CDH group had facet tropism than did those in the control group at C4-C5, C5-C6 and C6-C7 level (p = .021, p = .001, p = .015, respectively). The facet tropism angles in the CDH group were significantly bigger than those in the control group at C4-C5, C5-C6 and C6-C7 level (p = .001, p = .002, p = .028, respectively). In the CDH group, the facet angles on the herniated side were found to be significantly bigger than those on the healthy side at C4-C5, C5-C6 and C6-C7 level (p = .000, p = .000, p = .037, respectively). The findings of this present study suggest that facet tropism is associated with the disc herniation in the cervical spine. We also found that cervical disc herniates towards the side of the bigger facet angle with respect to the sagittal plane. There is a need for future studies to verify the biomechanical impact of facet tropism on CDH.

Mechanobiology of annulus fibrosus and nucleus pulposus cells in intervertebral discs

Low back pain (LBP) is a chronic condition that can affect up to 80% of the global population. It is the number one cause of disability worldwide and has enormous socioeconomic consequences. One of the main causes of this condition is intervertebral disc (IVD) degeneration. IVD degenerative processes and inflammation associated with it has been the subject of many studies in both tissue and cell level. It is believed that the phenotype of the resident cells within the IVD directly affects homeostasis of the tissue. At the same time, IVDs located between vertebral bodies of spine are under various mechanical loading conditions in vivo. Therefore, investigating how mechanical loading can affect the behaviour of IVD cells has been a subject of many research articles. In this review paper, following a brief explanation of the anatomy of the IVD and its resident cells, we compiled mechanobiological studies of IVD cells (specifically, annulus fibrosus and nucleus pulposus cells) and synthesized and discussed the key findings of the field.

Does facet tropism negatively affect the response to transforaminal epidural steroid injections? A prospective clinical study

OBJECTIVE

To examine the impact of the presence of facet tropism on the results of transforaminal epidural steroid injection for unilateral radicular pain induced by lumbar disc herniation.

MATERIALS AND METHODS

We included 112 patients diagnosed with unilateral, single-level lumbar disc herniation-induced radicular pain. Injection was planned at relevant levels. The patients were assessed using the Numerical Rating Scale, the Modified Oswestry Disability Index, and the Beck Depression Inventory before the injection and at hour 1, week 3, and month 3 after the injection. Presence of facet tropism was assessed by measuring the facet angles in the L3-4, L4-5, and L5-S1 segments of lumbar MRI T2 sequence axial section.

RESULTS

A significant decrease in the Numerical Rating Scale and an increase in the Modified Oswestry Disability Index scores were detected at all follow-ups in groups comprising 39 patients with and 61 without facet tropism (p < 0.05). On comparison, improvement in clinical parameters at week 3 and month 3 in the group without facet tropism was greater (p < 0.05). As treatment success is considered to be a ≥ 50% reduction in the Numerical Rating Scale scores, 55.2% of the patients attained treatment success at month 3. Further, although the treatment success rate in the group with facet tropism was 34.2%, it was 69% in that without facet tropism (p < 0.05).

CONCLUSION

Facet tropism correlates with less success of transforaminal epidural steroid injection; therefore, facet tropism may be a worthwhile measurement in a discussion with patients of the benefits of the procedure.

Incorporating loading variability into in vitro injury analyses and its effect on cumulative compression tolerance in porcine cervical spine units

During repetitive movement, low-back loading exposures are inherently variable in magnitude. The current study aimed to investigate how variation in successive compression exposures influences cumulative load tolerance in the spine. Forty-eight porcine cervical spine units were randomly assigned to one of six combinations of mean peak compression force (30%, 50%, 70% of the predicted tolerance) and loading variation (consistent peak amplitude, variable peak amplitude). Following preload and passive range-of-motion tests, specimens were positioned in a neutral posture and then cyclically loaded in compression until failure occurred or the maximum 12 h duration was reached. Specimens were dissected to classify macroscopic injury and measurements of cumulative load, cycles, and height loss sustained at failure were calculated. Statistical comparisons were made between loading protocols within each normalized compression group. A significant loading variation × compression interaction was demonstrated for cumulative load (p = 0.026) and cycles to failure (p = 0.021). Cumulative compression was reduced under all normalized compression loads (30% p = 0.016; 50% p = 0.030; 70% p = 0.020) when variable loading was incorporated. The largest reduction was by 33% and occurred in the 30% compression group. The number of sustained cycles was reduced by 31% (p = 0.017), 72% (p = 0.030), and 76% (p = 0.009) under normalized compression loads of 30%, 50%, and 70%, respectively. These findings suggest that variation in compression exposures interact to reduce cumulative compression tolerance of the spine and could elevate low-back injury risk during time-varying repetitive tasks.

Validation of an Ultrasound Protocol to Measure Intervertebral Axial Twist during Functional Twisting Movements in Isolated Functional Spinal Units

Ultrasound has potential for use in evaluation of bone and joint movement during axial twist of the lumbar spine both in vivo and in vitro. Such segmental rotations could then be measured under controlled external thoracic axial twist conditions and in response to mechanical loading. The purpose of this study was to measure vertebral segmental rotations in a porcine model of the human lumbar spine using an ultrasound imaging protocol and to validate use of this imaging technique with an optical motion capture system. In part 1, ultrasound transducer angle was confirmed to have no effect on sonogram point digitization. In part 2, 12 porcine functional spinal units were fixed to a mechanical testing system, and compression (15% of compressive tolerance), flexion-extension and axial twist (0°, 2°, 4° or 6°) were applied. Axial twist motion was tracked using an optical motion capture system and posterior surface ultrasound. Correlation between the two measurement systems was >0.903, and absolute system error was 0.01° across all flexion-extension postures. These findings indicate that ultrasound can be used to track axial twist motion in an in vitro spine motion segment and has the potential for use in vivo to evaluate absolute intervertebral axial twist motion.

The Effect of Axial Torsion on the Mechanical Properties of the Annulus Fibrosus

STUDY DESIGN

In-vitro study of the tissue mechanics of annulus fibrosus.

OBJECTIVE

To determine the effect of axial torsion on the mechanical properties of the inter- and intralamellar matrices.

SUMMARY OF BACKGROUND DATA

Axial torsion, when combined with repetitive flexion, has been associated with an increased risk of intervertebral disc herniation. However, the mechanisms behind this relationship are poorly understood.

METHODS

Bovine intervertebral discs (IVDs) from the caudal region were exposed to a combination of either 0° or 12° of static axial torsion and 0 N or 1000 N of compression for 2 hours in an attempt to created micro-damage to the IVD. Following the loading protocol, one multilayered sample and two single layer samples were dissected from the annulus fibrosus to undergo tensile testing of the inter- and intralamellar matrices. Histological staining was also performed.

RESULTS

The strength of the interlamellar matrix was not affected by axial torsion or compression, suggesting that torsion did not damage the interlamellar matrix. However, intralamellar matrix strength of samples exposed to axial torsion, regardless of compressive loading magnitude, was 48% lower than those from samples that were not exposed to torsion (P < 0.001). Similarly, intralamellar matrix stiffness of samples exposed to axial torsion was 42% lower than from samples that were not exposed to torsion (P = 0.010). Additionally, histological analysis demonstrated more disruption within individual lamellae of the samples exposed to axial torsion compared with samples that were not.

CONCLUSION

This study suggests that axial torsion damages the components of the intralamellar matrix as a result of the strain it puts on the matrix, thus making the intervertebral disc more susceptible to herniation.

LEVEL OF EVIDENCE

N/A.

Degenerative spondylolisthesis: a prospective cross-sectional cohort study on the role of weakened anterior abdominal musculature on causation

PURPOSE

Degenerative spondylolisthesis (DS) is a degenerative condition of the spine which, unlike others, is more common in a female population. Previous studies have highlighted possible causative factors such as facet tropism and pregnancy as reasons for this. This study sets out to assess the possible link between abdominal musculature and DS.

METHOD

A prospective cross-sectional cohort study in a single surgeon practice assessed all patients aged over 50 years attending for degenerative lumbar spinal complaints. Patient demographics, as well as the number of pregnancies, children, abdominal surgical procedures, were recorded.

RESULTS

We found 205 patients that met our inclusion criteria (98 Males/107 Females). Women with multiple pregnancies (p = 0.036) and abdominal surgeries (p = 0.021) were more likely to develop DS. Males with ventral hernias were more likely to have developed DS (p = 0.004).

CONCLUSION

This study highlights the important role that the abdominal musculature plays in stabilization of the spine and highlights its potential role as a factor in the development of DS. These slides can be retrieved under Electronic Supplementary Material.

Biomechanical Effects of Lateral Bending Position on Performing Cervical Spinal Manipulation for Cervical Disc Herniation: A Three-Dimensional Finite Element Analysis

Background

Most studies report that the common position of cervical spinal manipulation (CSM) for treating symptomatic cervical disc herniation (CDH) is lateral bending to the herniated side. However, the rationality of lateral bending position on performing CSM for CDH is still unclear.

Objective

The purpose of this study is to investigate the biomechanical effects of lateral bending position on performing CSM for CDH.

Methods

A finite element (FE) model of CDH (herniated on the left side) was generated in C5-6 segment based on the normal FE model. The FE model performed CSM in left lateral bending position, neutral position, and right lateral bending position, respectively. Cervical disc displacement, annulus fiber stress, and facet joint stress were observed during the simulation of CSM.

Results

The cervical disc displacement on herniated side moved forward during CSM, and the maximum forward displacements were 0.23, 0.36, and 0.45 mm in left lateral bending position, neutral position, and right lateral bending position, respectively. As the same trend of cervical disc displacement, the annulus fiber stresses on herniated side from small to large were 7.40, 16.39, and 22.75 MPa in left lateral bending position, neutral position, and right lateral bending position, respectively. However, the maximum facet stresses at left superior cartilage of C6 in left lateral bending position, neutral position, and right lateral bending position were 6.88, 3.60, and 0.12 MPa, respectively.

Conclusion

Compared with neutral position and right lateral bending position, though the forward displacement of cervical disc on herniated side was smaller in left lateral bending position, the annulus fiber stress on herniated side was declined by sharing load on the left facet joint. The results suggested that lateral bending to the herniated side on performing CSM tends to protect the cervical disc on herniated side. Future clinical studies are needed to verify that.

Static Compression Induces ECM Remodeling and Integrin α2β1 Expression and Signaling in a Rat Tail Caudal Intervertebral Disc Degeneration Model

STUDY DESIGN

A three-level rat tail caudal intervertebral disc (IVD) degeneration (IVDD) model was established to study effects of static compression on extracellular matrix (ECM) remodeling and integrin signaling in IVDs during IVDD.

OBJECTIVE

The aim of this study was to investigate the effect of compression force on ECM remodeling and integrin signaling in IVDs during IVDD.

SUMMARY OF BACKGROUND DATA

Integrins sense mechanical environment alteration via binding to ECM ligands and trigger intracellular signaling for pathological ECM remodeling during IVDD. However, the role of compression force in ECM remodeling and integrin signaling during IVDD remains elusive.

METHODS

Compared with the classical one-level rat tail IVDD model that exerts axial stress on the 8th to 9th caudal vertebral bodies, a three-level model was established by using an Ilizarov-type apparatus to exert stress on the 7th to 10th caudal vertebral bodies in rat tails for four weeks. To exclude side effects from surgical stab injury on manipulated discs, intact coccygeal (Co) disc Co8-9 was analyzed.

RESULTS

In three-level IVDD model, significant degeneration of the Co8-9 disc was observed. Quantitative real-time polymerase chain reaction (qRT-PCR) showed elevated mRNA expression of collagen types I, III, and V; matrix metalloproteinases (MMPs) 2, 3, 9, 13, 14; and decreased mRNA expression of collagen type II in Co8-9 disc. Compression loading altered the expression of integrin α2β1 (upregulated) and α10β1 (downregulated) in NP cells, and activated integrin downstream signaling. By contrast, one-level model showed more severe disc degeneration and ECM remodeling. Integrin α1, α2, α11, and β1 were upregulated, whereas α10 was downregulated. Similar activation of integrin signaling was observed.

CONCLUSION

Static compression altered collagen and MMP expression, and promoted β1 integrin expression and signaling in IVD. Compared with one-level rat tail IVDD model, three-level model showed milder effects on disc degeneration, ECM remodeling, and integrin expression, suggesting one-level model might involve other causes that induce IVDD via mechanisms independent of compression force.

LEVEL OF EVIDENCE

N/A.

Biomechanics of the human intervertebral disc: A review of testing techniques and results

Many experimental testing techniques have been adopted in order to provide an understanding of the biomechanics of the human intervertebral disc (IVD). The aim of this review article is to amalgamate results from these studies to provide readers with an overview of the studies conducted and their contribution to our current understanding of the biomechanics and function of the IVD. The overview is presented in a way that should prove useful to experimentalists and computational modellers. Mechanical properties of whole IVDs can be assessed conveniently by testing 'motion segments' comprising two vertebrae and the intervening IVD and ligaments. Neural arches should be removed if load-sharing between them and the disc is of no interest, and specimens containing more than two vertebrae are required to study 'adjacent level' effects. Mechanisms of injury (including endplate fracture and disc herniation) have been studied by applying complex loading at physiologically-relevant loading rates, whereas mechanical evaluations of surgical prostheses require slower application of standardised loading protocols. Results can be strongly influenced by the testing environment, preconditioning, loading rate, specimen age and degeneration, and spinal level. Component tissues of the disc (anulus fibrosus, nucleus pulposus, and cartilage endplates) have been studied to determine their material properties, but only the anulus has been thoroughly evaluated. Animal discs can be used as a model of human discs where uniform non-degenerate specimens are required, although differences in scale, age, and anatomy can lead to problems in interpretation.

Influence of Complex Loading Conditions on Intervertebral Disc Failure

STUDY DESIGN

High resolution imaging investigation of the failure of ovine lumbar intervertebral discs under complex loading.

OBJECTIVE

To investigate how different loading combinations influence the mechanism and extent of intervertebral disc failure.

SUMMARY OF BACKGROUND DATA

Even though there has been extensive research on how an intervertebral disc fails under various conditions, failure mechanisms remain unclear. In addition, the influence of different loading directions on the mode and extent of failure under complex loading was never systematically investigated.

METHODS

Thirty ovine lumbar spinal segments were loaded in a newly developed, dynamic, 6-degree-of-freedom (6-DOF) disc loading simulator under five combinations of the following loading parameters: 0°-13° flexion, 0°-10° lateral bending, 0°-4° axial rotation, 0-800 N axial compression. A total of 1000 cycles at 2 Hz were done. After testing, imaging of the discs was performed in an ultra-high field magnetic resonance imaging (11.7 T) scanner and with a micro-computed tomography scanner.

RESULTS

A total of 13 large endplate junction failures (EPJFs) occurred, of which all but one maintained an intact cartilaginous endplate. Ten out of 13 EPJFs occurred caudally. Four solely annulus failures occurred affecting only the outer posterior annulus. A herniation was not observed. The maximum moments measured in any group (median) were 52.5 N · m flexion, 16.5 N · m lateral bending, and 14.0 N · m axial rotation.

CONCLUSION

Complex loading protocols could lead to EPJFs (76%) and annulus failures (24%) in vitro. The combination of flexion, lateral bending, axial rotation, and axial compression bears the highest risk for caudal EPJF. Flexion without lateral bending and vice versa has the lowest risk for failure. Both axial compression and axial rotation seem to have a smaller influence than flexion and lateral bending. It seems that a herniation requires an additional failure of the cartilaginous endplate, likely initiated by further axial compressive load.

LEVEL OF EVIDENCE

4.

Numerical Prediction of the Mechanical Failure of the Intervertebral Disc under Complex Loading Conditions

Finite element modeling has been widely used to simulate the mechanical behavior of the intervertebral disc. Previous models have been generally limited to the prediction of the disc behavior under simple loading conditions, thus neglecting its response to complex loads, which may induce its failure. The aim of this study was to generate a finite element model of the ovine lumbar intervertebral disc, in which the annulus was characterized by an anisotropic hyperelastic formulation, and to use it to define which mechanical condition was unsafe for the disc. Based on published in vitro results, numerical analyses under combined flexion, lateral bending, and axial rotation with a magnitude double that of the physiological ones were performed. The simulations showed that flexion was the most unsafe load and an axial tensile stress greater than 10 MPa can cause disc failure. The numerical model here presented can be used to predict the failure of the disc under all loading conditions, which may support indications about the degree of safety of specific motions and daily activities, such as weight lifting.

ISSLS Prize Winner: Vibration Really Does Disrupt the Disc: A Microanatomical Investigation

STUDY DESIGN

Microstructural investigation of vibration-induced disruption of the flexed lumbar disc.

OBJECTIVE

The aim of the study was to explore micro-level structural damage in motion segments subjected to vibration at subcritical peak loads.

SUMMARY OF BACKGROUND DATA

Epidemiological evidence suggests that cumulative whole body vibration may damage the disc and thus play an important role in low back pain. In vitro investigations have produced herniations via cyclic loading (and cyclic with added vibrations as an exacerbating exposure), but offered only limited microstructural analysis.

METHODS

Twenty-nine healthy mature ovine lumbar motion segments flexed 7° and subjected to vibration loading (1300 ± 500 N) in a sinusoidal waveform at 5 Hz to simulate moderately severe physiologic exposure. Discs were tested either in the range of 20,000 to 48,000 cycles (medium dose) or 70,000 to 120,000 cycles (high dose). Damaged discs were analyzed microstructurally.

RESULTS

There was no large drop in displacement over the duration of both vibration doses indicating an absence of catastrophic failure in all tests. The tested discs experienced internal damage that included delamination and disruption to the inner and mid-annular layers as well as diffuse tracking of nucleus material, and involved both the posterior and anterior regions. Less frequent tearing between the inner disc and endplate was also observed. Annular distortions also progressed into a more severe form of damage, which included intralamellar tearing and buckling and obvious strain distortion around the bridging elements within the annular wall.

CONCLUSION

Vibration loading causes delamination and disruption of the inner and mid-annular layers and limited diffuse tracking of nucleus material. These subtle levels of disruption could play a significant role in initiating the degenerative cascade via micro-level disruption leading to cell death and altered nutrient pathways.

LEVEL OF EVIDENCE

5.

Is intervertebral disc pressure linked to herniation?: An in-vitro study using a porcine model

Approximately 40% of low back pain cases have been attributed to internal disc disruption. This disruption mechanism may be linked to intradiscal pressure changes, since mechanical loading directly affects the pressure and the stresses that the inner annulus fibrosus experiences. The objective of this study was to characterize cycle-varying changes in four dependent measures (intradiscal pressure, flexion-extension moments, specimen height loss, and specimen rotation angle) using a cyclic flexion-extension (CFE) loading protocol known to induce internal disc disruption. A novel bore-screw pressure sensor system was used to instrument 14 porcine functional spinal units. The CFE loading protocol consisted of 3600 cycles of flexion-extension range of motion (average 18.30 (SD 3.76) degrees) at 1Hz with 1500N of compressive load. On average, intradiscal pressure and specimen height decreased by 47% and 62%, respectively, and peak moments increased by 102%. From 900 to 2100 cycles, all variables exhibited significant changes between successive time points, except for the specimen posture at maximum pressure, which demonstrated a significant shift towards flexion limit after 2700 cycles. There were no further changes in pressure range after 2100 cycles, whereas peak moments and height loss were significantly different from prior time points throughout the CFE protocol. Twelve of the 14 specimens showed partial herniation; however, injury type was not significantly correlated to any of the dependent measures. Although change in pressure was not predictive of damage type, the increase in pressure range seen during this protocol supports the premise that repetitive combined loading (i.e., radial compression, tension and shear) imposes damage to the inner annulus fibrosus, and its failure mechanism may be linked to fatigue.

Working position influences the biomechanical demands on the lower back during dental hygiene

This investigation monitored the biomechanical demands on the lower back during simulated dental hygiene work. A total of 19 female, registered dental hygienists performed 30 continuous minutes of manual scaling (plaque removal) of a manikin's teeth while seated. We monitored the working location and orientation of the dental hygienists, with respect to the manikin, along with their spine kinematics, spine extensor muscle activities and seat pressure, throughout the 30 min. A clock representation was used to express the working location. The location significantly influenced the dental hygienists' pelvic orientation with respect to the manikin, spine posture, erector muscle activity and pressure distribution. Findings from this study suggest that the prevalence of lower back pain amongst dental hygienists may be directly related to low-level tonic activity of the spine's extensor musculature, and the combined flexed and axially rotated spine postures. Practitioner Summary: Low back pain (LBP) is prevalent in dental hygienists, yet occupational demand on the low back has not been investigated. Posture, muscle activity and seat pressure were monitored. Combined spine rotation and flexion, and tonic activity of the extensor musculature may be related to LBP in dental hygienists.

Aging and age related stresses: a senescence mechanism of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is a complicated process that involves both age-related change and tissue damage caused by multiple stresses. In a degenerative IVD, cellular senescence accumulates and is associated with reduced proliferation, compromised self-repair, increased inflammatory response, and enhanced catabolic metabolism. In this review, we decipher the senescence mechanism of IVD degeneration (IVDD) by interpreting how aging coordinates with age-related, microenvironment-derived stresses in promoting disc cell senescence and accelerating IVDD. After chronic and prolonged replication, cell senescence may occur as a natural part of the disc aging process, but can potentially be accelerated by growth factor deficiency, oxidative accumulation, and inflammatory irritation. While acute disc injury, excessive mechanical overloading, diabetes, and chronic tobacco smoking contribute to the amplification of senescence-inducing stresses, the avascular nature of IVD impairs the immune-clearance of the senescent disc cells, which accumulate in cell clusters, demonstrate inflammatory and catabolic phenotypes, deteriorate disc microenvironment, and accelerate IVDD. Anti-senescence strategies, including telomerase transduction, supply of growth factors, and blocking cell cycle inhibitors, have been shown to be feasible in rescuing disc cells from early senescence, but their efficiency for disc regeneration requires more in vivo validations. Guidelines dedicated to avoiding or alleviating senescence-inducing stresses might decelerate cellular senescence and benefit patients with IVD degenerative diseases.

A new dynamic six degrees of freedom disc-loading simulator allows to provoke disc damage and herniation

Purpose

The cause of disc herniation is not well understood yet. It is assumed that heavy lifting and extreme postures can cause small injuries starting either in the inner anulus or from the outside close to the endplate. Such injuries are accumulated over years until its structure is weakened and finally a single loading event leads to a sudden failure of the last few intact lamellae. This paper describes a novel, custom-developed dynamic 6-DOF disc-loading simulator that allows complex loading to provoke such disc damage and herniations.

Methods

The machine’s axes are driven by six independent servomotors providing high loads (10 kN axial compression, 2 kN shear, 100 Nm torque) up to 5 Hz. A positional accuracy test was conducted to validate the machine. Subsequently, initial experiments with lumbar ovine motion segments under complex loading were performed. After testing, the discs were examined in an ultra-high field MRI (11.7 T). A three-dimensional reconstruction was performed to visualise the internal disc lesions.

Results

Validation tests demonstrated positioning with an accuracy of ≤0.08°/≤0.026 mm at 0.5 Hz and ≤0.27°/≤0.048 mm at 3.0 Hz with amplitudes of ±17°/±2 mm. Typical failure patterns and herniations could be provoked with complex asymmetrical loading protocols. Loading with axial compression, flexion, lateral bending and torsion lead in 8 specimens to 4 herniated discs, two protrusions and two delaminations. All disc failures occurred in the posterior region of the disc.

Conclusion

This new dynamic disc-loading simulator has proven to be able to apply complex motion combinations and allows to create artificial lesions in the disc with complex loading protocols. The aim of further tests is to better understand the mechanisms by which disc failure occurs at the microstructural level under different loading conditions. Visualisation with ultra-high field MRI at different time points is a promising method to investigate the gradual development of such lesions, which may finally lead to disc failure. These kinds of experiments will help to better investigate the mechanical failure of discs to provide new insights into the initiation of intervertebral disc herniation. This device will also serve for many other applications in spine biomechanics research.

Duration-dependent influence of dynamic torsion on the intervertebral disc: an intact disc organ culture study

PURPOSE

Mechanical loading is an important parameter that alters the homeostasis of the intervertebral disc (IVD). Studies have demonstrated the role of compression in altering the cellular metabolism, anabolic and catabolic events of the disc, but little is known how complex loading such as torsion-compression affects the IVD cell metabolism and matrix homeostasis. Studying how the duration of torsion affects disc matrix turnover could provide guidelines to prevent overuse injury to the disc and suggest possible beneficial effect of torsion. The aim of the study was to evaluate the biological response of the IVD to different durations of torsional loading.

METHODS

Intact bovine caudal IVD were isolated for organ culture in a bioreactor. Different daily durations of torsion were applied over 7 days at a physiological magnitude (±2°) in combination with 0.2 MPa compression, at a frequency of 1 Hz.

RESULTS

Nucleus pulpous (NP) cell viability and total disc volume decreased with 8 h of torsion-compression per day. Gene expression analysis suggested a down-regulated MMP13 with increased time of torsion. 1 and 4 h per day torsion-compression tended to increase the glycosaminoglycans/hydroxyproline ratio in the NP tissue group.

CONCLUSIONS

Our result suggests that load duration thresholds exist in both torsion and compression with an optimal load duration capable of promoting matrix synthesis and overloading can be harmful to disc cells. Future research is required to evaluate the specific mechanisms for these observed effects.

Region specific response of intervertebral disc cells to complex dynamic loading: an organ culture study using a dynamic torsion-compression bioreactor

The spine is routinely subjected to repetitive complex loading consisting of axial compression, torsion, flexion and extension. Mechanical loading is one of the important causes of spinal diseases, including disc herniation and disc degeneration. It is known that static and dynamic compression can lead to progressive disc degeneration, but little is known about the mechanobiology of the disc subjected to combined dynamic compression and torsion. Therefore, the purpose of this study was to compare the mechanobiology of the intervertebral disc when subjected to combined dynamic compression and axial torsion or pure dynamic compression or axial torsion using organ culture. We applied four different loading modalities [1. control: no loading (NL), 2. cyclic compression (CC), 3. cyclic torsion (CT), and 4. combined cyclic compression and torsion (CCT)] on bovine caudal disc explants using our custom made dynamic loading bioreactor for disc organ culture. Loads were applied for 8 h/day and continued for 14 days, all at a physiological magnitude and frequency. Our results provided strong evidence that complex loading induced a stronger degree of disc degeneration compared to one degree of freedom loading. In the CCT group, less than 10% nucleus pulposus (NP) cells survived the 14 days of loading, while cell viabilities were maintained above 70% in the NP of all the other three groups and in the annulus fibrosus (AF) of all the groups. Gene expression analysis revealed a strong up-regulation in matrix genes and matrix remodeling genes in the AF of the CCT group. Cell apoptotic activity and glycosaminoglycan content were also quantified but there were no statistically significant differences found. Cell morphology in the NP of the CCT was changed, as shown by histological evaluation. Our results stress the importance of complex loading on the initiation and progression of disc degeneration.

ISSLS Prize winner: The anatomy of failure in lumbar disc herniation: an in vivo, multimodal, prospective study of 181 subjects

STUDY DESIGN

A prospective multimodal study including clinical, radiological, serial postcontrast magnetic resonance imaging, intraoperative findings, and histopathological study.

OBJECTIVE

To document in vivo, the site of anatomical failure in lumbar disc herniation (LDH).

SUMMARY OF BACKGROUND DATA

Although in vitro mechanical disruption studies have implicated both the endplate junction (EPJ) and the annulus fibrosus (AF) as the site of failure in LDH, there are no in vivo human studies to document the exact anatomy of failure.

METHODS

One hundred eighty-one consecutive patients requiring microdiscectomy at a single level formed the study group. The status of the endplate and AF in the operated level (study discs) and the other discs (control) were evaluated by plain radiograph, thin slice computed tomographic scan, plain and contrast magnetic resonance imaging, intraoperative examination, and histopathological analysis.

RESULTS

LDH due to EPJ failure (EPJF- type I herniation) was more common (117; 65%) than annulus fibrosis rupture. Herniated discs had a significantly higher incidence of EPJF than control discs (P < 0.0001). The EPJF was evident radiologically as vertebral corner defect in 30 patients, rim avulsion in 46, frank bony avulsions in 24, and avulsion at both upper and lower EP in 4. Thirteen discs with normal EP radiologically had cartilage or bone avulsion intraoperatively. Sixty-four discs (35%) had intact EP of which annular high intensity zone was found in 21 (11%), suggesting a disruption of AF (type II herniation). Postcontrast magnetic resonance image of 20 patients showed dye leak at the EPJ proving EPJF as main cause of LDH.

CONCLUSION

Our study provides the first in vivo evidence that LDH in humans is more commonly the result of EPJF than AF rupture and offers clinical validation of previous in vitro mechanical disruption studies. Future research must focus on the EPJ as a primary area of interest in LDH.

LEVEL OF EVIDENCE

N/A.

Low back pain development response to sustained trunk axial twisting

PURPOSE

To investigate if there is an effect of sustained trunk axial twisting on the development of low back pain.

METHODS

Sixteen male pain-free university students volunteered for this study. The trunk axial twisting was created by a torsion moment of 50 Nm for 10-min duration. The axial rotational creep was estimated by the transverse camera view directly on the top of the head. The visual analog scale in low back area was examined both in the initial and at the end of twisting. Each performed three trials of lumbar flexion-extension with the cycle of 5 s flexion and 5 s extension in standing before and after twisting. Surface electromyography from bilateral erector spinae muscles as well as trunk flexion performance was recorded synchronously in video camera. A one-way ANOVA with repeated measures was used to evaluate the effect of twist.

RESULTS

The results showed that there was a significant (p < 0.001) twist creep with rotational angle 10.5° as well as VAS increase with a mean value 45 mm. The erector spinae was active in a larger angle during flexion as well as extension after trunk axial twisting.

CONCLUSIONS

Sustained trunk axial twisting elicits significant trunk rotational creep. It causes the visual analog scale to have a significant increase, and causes erector spinae muscles to become active longer during anterior flexion as well as extension, which may be linked to the decrease of the tension ability of passive tissues in low back area, indicating a higher risk in developing low back pain.

Towards establishing an occupational threshold for cumulative shear force in the vertebral joint - an in vitro evaluation of a risk factor for spondylolytic fractures using porcine specimens

BACKGROUND

Injury models for spondylolytic fracture of the pars interarticularis have long considered repetitive shear loading as a risk factor without quantifying the relationship between shear force magnitude and fatigue life. This investigation sought to quantify the relationship using a basic in vitro approach.

METHODS

Thirty-two (16 C3-C4, 16 C5-C6) porcine cervical specimens were exposed to repetitive shear loading to 20%, 40%, 60%, or 80% of their calculated ultimate anterior shear failure tolerance. Shear force was cyclically applied at 1Hz for 21,600cycles or until bone failure was detected. Cumulative shear force and the number of cycles sustained until failure were calculated. Failure patterns were also documented.

FINDINGS

Cumulative shear and the number of cycles sustained prior to failure demonstrated a strong non-linearly decreasing relationship with increased force magnitude. In particular, sustained cumulative shear by the 40% group was 2.52 and 2.63MN∗s higher than for the 60% and 80% groups (P<0.0001). Despite undergoing an average of 230 more loading cycles, cumulative shear force sustained by the 60% group was not statistically different from the 80% group. Bilateral fractures of the cranial vertebra's pars interarticularis were most common, but less consistent at higher force magnitudes.

INTERPRETATION

Our investigation suggested that pars interarticularis damage may begin non-linearly accumulating with shear forces between 20% and 40% of failure tolerance (approximately 430 to 860N). Models of pars interarticularis injury and estimates of cumulative shear exposure may be enhanced from a tissue-based weighting method for low-back shear.

Association of facet tropism with lumbar disc herniation

PURPOSE

Facet tropism is defined as asymmetry between left and right facet joints and is postulated as a possible cause of disc herniation. In the present study, the authors used a 3-T MRI to investigate the association between facet tropism and lumbar disc herniation at a particular motion segment. They also examined whether the disc herniated towards the side of the more coronally oriented facet joint.

METHODS

Sixty patients (18-40 years) with single level disc herniation (L3-L4, L4-L5, or L5-S1) were included in the study. Facet angles were measured using MRI of 3-T using the method described by Karacan et al. Facet tropism was defined as difference of 10° in facet joint angles between right and left sides. Normal disc adjacent to the herniated level was used as control. We also examined if disc herniated towards the side of more coronally oriented facet.

RESULTS

Twenty-five herniations were at L4-L5 level and 35 at L5-S1. Statistical analysis was performed using the Fischer Exact Test. At L4-L5 level, 6/25 cases had tropism compared to 3/35 controls (p = 0.145). At L5-S1 level, 13/35 cases had tropism as compared to 1/21 controls (p = 0.0094). Of 19 cases having tropism, the disc had herniated towards the coronally oriented facet in six (p = 0.11).

CONCLUSION

The findings of the study suggest that facet tropism is associated with lumbar disc herniation at the L5-S1 motion segment but not at the L4-L5 level.

How do elliptical machines differ from walking: a study of torso motion and muscle activity

BACKGROUND

The elliptical trainer is a popular exercise modality, yet its effect on the lumbar spine is poorly understood. The purpose of this study was to analyze the effect of different hand positions, speed and stride lengths on spine kinematics and corresponding muscle activity while using the elliptical trainer, and compare with those demonstrated in normal walking.

METHODS

Electromyographic data was collected over 16 trunk and gluteal muscle sites on 40 healthy males (mean age (SD)=23(3)) while on the elliptical trainer. Two stride lengths (46, 66cm), 2 speeds (self-selected, 30% faster), and 3 hand positions (freehand, central bar, handles) were analyzed. Lumbar spine kinematics was calculated from data collected using a motion capture system. Results were compared to those found in walking using repeated measures ANOVA for each dependent variable with Bonferroni adjustments (P<0.004. Correlations were made between lumbar motion and various anthropometric measures.

FINDINGS

All significance levels comparing walking to elliptical varied according to stride length, speed and hand position. Average lumbar flexion angles and lumbar rotation were generally greater on the elliptical trainer, whereas walking produced more frontal motion. Total lumbar flexion/extension was similar between the two activities. Muscle activation patterns of the gluteal muscles were consistently higher on the elliptical, whereas the back extensors, latissimi and internal obliques were greater in only selected conditions.

INTERPRETATION

The various hand positions, speeds and stride lengths affect lumbar motion and muscle activity on the elliptical trainer, thus must be considered when incorporated into an exercise protocol.

Comparing lower lumbar kinematics in cyclists with low back pain (flexion pattern) versus asymptomatic controls--field study using a wireless posture monitoring system

The aim of this study was to examine lower lumbar kinematics in cyclists with and without non-specific chronic low back pain (NS-CLBP) during a cross-sectional cycling field study. Although LBP is a common problem among cyclists, studies investigating the causes of LBP during cycling are scarce and are mainly focussed on geometric bike-related variables. Until now no cycling field studies have investigated the relationship between maladaptive lumbar kinematics and LBP during cycling. Eight cyclists with NS-CLBP classified as having a 'Flexion Pattern' (FP) disorder and nine age- and gender-matched asymptomatic cyclists were tested. Subjects performed a 2 h outdoor cycling task on their personal race bike. Lower lumbar kinematics was measured with the BodyGuard™ monitoring system. Pain intensity during and after cycling was measured using a numerical pain rating scale. The NS-CLBP (FP) subjects were significantly more flexed at the lower lumbar spine during cycling compared to healthy controls (p = 0.018), and reported a significant increase in pain over the 2 h of cycling (p < 0.001). One-way repeated measures ANOVA revealed a significant main effect for group (p = 0.035, F = 5.546) which remained just significant when adding saddle angle as a covariate (p = 0.05, F = 4.747). The difference in posture between groups did not change over time. These findings suggest that a subgroup of cyclists with NS-CLBP (FP) demonstrate an underlying maladaptive motor control pattern resulting in greater lower lumbar flexion during cycling which is related to a significant increase in pain.

Relative importance of expertise, lifting height and weight lifted on posture and lumbar external loading during a transfer task in manual material handling

The objective of this study was to measure the effect size of three important factors in manual material handling, namely expertise, lifting height and weight lifted. The effect of expertise was evaluated by contrasting 15 expert and 15 novice handlers, the effect of the weight lifted with a 15-kg box and a 23-kg box and the effect of lifting height with two different box heights: ground level and a 32 cm height. The task consisted of transferring a series of boxes from a conveyor to a hand trolley. Lifting height and weight lifted had more effect size than expertise on external back loading variables (moments) while expertise had low impact. On the other hand, expertise showed a significant effect of posture variables on the lumbar spine and knees. All three factors are important, but for a reduction of external back loading, the focus should be on the lifting height and weight lifted.

PRACTITIONER SUMMARY

The objective was to measure the effect size of three important factors in a transfer of boxes from a conveyor to a hand trolley. Lifting height and weight lifted had more effect size than expertise on external back loading variables but expertise was a major determinant in back posture.

Complex loading affects intervertebral disc mechanics and biology

BACKGROUND

Complex loading develops in multiple spinal motions and in the case of hyperflexion is known to cause intervertebral disc (IVD) injury. Few studies have examined the interacting biologic and structural alterations associated with potentially injurious complex loading, which may be an important contributor to chronic progressive degeneration.

OBJECTIVE

This study tested the hypothesis that low magnitudes of axial compression loading applied asymmetrically can induce IVD injury affecting cellular and structural responses in a large animal IVD ex-vivo model.

METHODS

Bovine caudal IVDs were assigned to either a control or wedge group (15°) and placed in organ culture for 7 days under static 0.2MPa load. IVD tissue and cellular responses were assessed through confined compression, qRT-PCR, histology and structural and compositional measurements, including Western blot for aggrecan degradation products.

RESULTS

Complex loading via asymmetric compression induced cell death, an increase in caspase-3 staining (apoptosis), a loss of aggrecan and an increase in aggregate modulus in the concave annulus fibrosis. While an up-regulation of MMP-1, ADAMTS4, IL-1β, and IL-6 mRNA, and a reduced aggregate modulus were induced in the convex annulus.

CONCLUSION

Asymmetric compression had direct deleterious effects on both tissue and cells, suggesting an injurious loading regime that could lead to a degenerative cascade, including cell death, the production of inflammatory mediators, and a shift towards catabolism. This explant model is useful to assess how injurious mechanical loading affects the cellular response which may contribute to the progression of degenerative changes in large animal IVDs, and results suggest that interventions should address inflammation, apoptosis, and lamellar integrity.

The influence of torsion on disc herniation when combined with flexion

The role of torsion in the mechanical derangement of intervertebral discs remains largely undefined. The current study sought to investigate if torsion, when applied in combination with flexion, affects the internal failure mechanics of the disc wall when exposed to high nuclear pressure. Thirty ovine lumbar motion segments were each positioned in 2 degrees axial rotation plus 7 degrees flexion. Whilst maintained in this posture, the nucleus of each segment was gradually injected with a viscous radio-opaque gel, via an injection screw placed longitudinally within the inferior vertebra, until failure occurred. Segments were then inspected using micro-CT and optical microscopy in tandem. Five motion segments failed to pressurize correctly. Of the remaining 25 successfully tested motion segments, 17 suffered vertebral endplate rupture and 8 suffered disc failure. Disc failure occurred in mature motion segments significantly more often than immature segments. The most common mode of disc failure was a central posterior radial tear involving a systematic annulus-endplate-annulus failure pattern. The endplate portion of these radial tears often propagated contralateral to the direction of applied axial rotation, and, at the lateral margin, only those fibres inclined in the direction of the applied torque were affected. Apart from the 2 degrees of applied axial rotation, the methods employed in this study replicated those used in a previously published study. Consequently, the different outcome obtained in this study can be directly attributed to the applied axial rotation. These inter-study differences show that when combined with flexion, torsion markedly reduces the nuclear pressure required to form clinically relevant radial tears that involve cartilaginous endplate failure. Conversely, torsion appears to increase the disc wall's resistance to radial tears that do not involve cartilaginous endplate failure, effectively halving the disc wall's overall risk of rupture.

The influence of intervertebral disc shape on the pathway of posterior/posterolateral partial herniation

STUDY DESIGN

Basic scientific investigation employing the medical imaging techniques of contrast-enhanced plane film radiographs and computed tomography in addition to gross dissection techniques on a sample of spines.

OBJECTIVE

To document the specific posterior/posterolateral pathway of mechanically-induced intervertebral disc (IVD) herniation as the result of repetitive loading and disc geometry.

SUMMARY OF BACKGROUND DATA

In vitro cadaveric and animal investigations have indicated that the posterior/posterolateral aspects of the IVD are most susceptible to damage leading to herniation, and that cyclic bending is the most potent variable influencing herniation. The IVD in horizontal cross-section ranges in shape from ovoid to limacon (kidney-shaped) which influences stress distributions. The purpose of this investigation was to determine the role of the IVDs shape and size on influencing the pathway of herniation.

METHODS

Compressive loads (1472 N) in conjunction with 7000 repetitive cycles of flexion-extension were applied to 22 porcine motion segments. Computed tomography images and contrast-enhanced plane file radiographs, in addition to dissection techniques were used to evaluate the progression of herniations. A logistical regression assessed the links between endplate size and shape, and the probability of a specific herniation type (directionally diffuse or directionally concentrated).

RESULTS

A total of 18 out of the 22 specimens exhibited detectable anular damage in the posterior/posterior lateral direction. Of the 18 specimens, 17 were partial herniations while one incurred a full herniation. IVD shape was found to be predictive of the pathway of herniation (P = 0.0329); oval IVD shapes were more likely to herniate in a directionally diffuse manner (6/18), while limacon IVDs were more likely to herniate in a directionally concentrated manner (12/18).

CONCLUSION

The shape of the IVD appears to be predictive of the pathway of IVD herniation.