Circadian variation in human stature

The role of the nucleus pulposus in intervertebral disc recovery: Towards improved specifications for nucleus replacement devices

Nucleus replacement devices (NRDs) have potential to treat degenerated or herniated intervertebral discs (IVDs). However, IVD height loss is a post-treatment complication. IVD height recovery involves the nucleus pulposus (NP), but the mechanism of this in response to physiological loads is not fully elucidated. This study aimed to characterise the non-linear recovery behaviour of the IVD in intact, post-nuclectomy, and post-NRD treatment states, under physiological loading. 36 bovine IVDs (12 intact, 12 post-nuclectomy, 12 post-treatment) underwent creep-recovery protocols simulating Sitting, Walking or Running, followed by 12 h of recovery. A rheological model decoupled the fluid-independent (elastic, fast) and fluid-dependent (slow) recovery phases. In post-nuclectomy and post-treatment groups, nuclectomy efficiency (ratio of NP removed to remaining NP) was quantified following post-test sectioning. Relative to intact, post-nuclectomy recovery significantly decreased in Sitting (-0.3 ± 0.4 mm, p < 0.05) and Walking (-0.6 ± 0.3 mm, p < 0.001) coupled with significant decreases to the slow response (p < 0.05). Post-nuclectomy, the fast and slow responses negatively correlated with nuclectomy efficiency (p < 0.05). In all protocols, the post-treatment group performed significantly worse in recovery (-0.5 ± 0.3 mm, p < 0.01) and the slow response (p < 0.05). Results suggest the NP mainly facilitates slow-phase recovery, linearly dependent on the amount of NP present. Failure of this NRD to recover is attributed to poor fluid imbibition. Additionally, unconfined NRD performance cannot be extrapolated to the in vitro response. This knowledge informs NRD design criteria to provide high osmotic pressure, and encourages testing standards to incorporate long-term recovery protocols.

Recruiting participants for ergonomic research using self-reported stature and body mass

BACKGROUND

A valid distribution of key anthropometric parameters among participants is often a perquisite of ergonomics research.

OBJECTIVE

In this paper, we investigated the accuracy of self-reported stature and body mass of the population in the Netherlands.

METHODS

Data from 4 experiments was synthesized where in each experiment, participants self-reported their stature and body mass prior to being measured, of which they were not notified before.

RESULTS

Statistical analysis of 249 records indicated that on average, participants overreported their stature by 1.31 cm and underreported their mass by 1.45 kg. This is especially true for people with a BMI≥25.

CONCLUSION

Two models were proposed to adjust the self-reported stature and body mass for ergonomic researchers in a survey or recruitment. Limitations in using the models are highlighted as well.

The Radial Bulging and Axial Strains of Intervertebral Discs during Creep Obtained with the 3D-DIC System

Creep-associated changes in disc bulging and axial strains are essential for the research and development of mechano-bionic biomaterials and have been assessed in various ways in ex vivo creep studies. Nonetheless, the reported methods for measurement were limited by location inaccuracy, a lack of synchronousness, and destructiveness. To this end, this study focuses on the accurate, synchronous, and noninvasive assessment of bugling and strains using the 3D digital image correlation (3D-DIC) system and the impact of creep on them. After a preload of 30 min, the porcine cervical discs were loaded with different loads for 4 h of creep. Axial strains and lateral bulging of three locations on the discs were synchronously measured. The three-parameter solid model and the newly proposed horizontal asymptote models were used to fit the acquired data. The results showed that the load application reduced disc strains by 6.39% under 300 N, 11.28% under 400 N, and 12.59% under 500 N. Meanwhile, the largest protrusion occurred in the middle of discs with a bugling of 1.50 mm, 1.67 mm, and 1.87 mm. Comparison of the peer results showed that the 3D-DIC system could be used in ex vivo biomechanical studies with reliability and had potential in the assessment of the mechanical behavior of novel biomaterials. The phenomenon of the largest middle protrusion enlightened further the strength of spinal implants in this area. The mathematical characterizations of bulging and strains under different loads yielded various model parameters, which are prerequisites for developing implanted biomaterials.

Soccer coaches vs. sport science and medicine staff: who can more accurately predict the skeletal age of high-level youth soccer players?

Biological maturity is an important aspect in the context of talent identification and development processes within elite youth soccer players. The aim of this study was to investigate the accuracy of soccer coaches (SC) as well as sports science and medicine staff (SSMS) to predict the skeletal age of high-level youth soccer players. We also aimed to evaluate the inter-rater reliability of the skeletal age predictions among the SC and SSMS. Skeletal ages were collected for 89 male academy soccer players registered for the U12 to U16 age groups at a professional German Bundesliga club. In addition, 12 SC and five SSMS provided their skeletal age predictions for each player of their respective age group. Standardised mean differences and equivalence testing were performed between actual and predicted skeletal ages. Intra-class correlations (ICC) were calculated to assess the inter-rater reliability. For the SC, differences between predicted and actual skeletal ages were trivial and equivalent to zero for the U12, U14, and entire sample, while for the SSMS, standardised mean differences ranged from trivial to small for all age groups and the entire sample. ICC for skeletal age predictions for the entire sample was good among the SC and excellent among the SSMS, but was somewhat lower when age groups were analysed separately. While, on average, predictions were close to the actual skeletal age, SC were slightly more accurate than the SSMS. However, variability among the SSMS was large on an individual level.

Short-Term Bone Healing Response to Mechanical Stimulation-A Case Series Conducted on Sheep

It is well known that mechanical stimulation promotes indirect fracture healing by triggering callus formation. We investigated the short-term response of healing tissue to mechanical stimulation to compare the changes in tissue stiffness during stimulation and resting phases in a preclinical case-series. Four sheep underwent a tibial osteotomy and were instrumented with a custom-made active fixator which applied a mechanical stimulation protocol of 1000 cycles/day, equally distributed over 12 h, followed by 12 h of rest. During each cycle, a surrogate metric for tissue stiffness was measured, enabling a continuous real-time monitoring of the healing progression. A daily stiffness increase during stimulation and an increase during resting were evaluated for each animal. One animal had to be excluded from the evaluation due to technical reasons. For all included animals, the stiffness began to increase within the second week post-op. A characteristic pattern was observed during daily measurements: the stiffness dropped considerably within the first stimulation cycles followed by a steady rise throughout the rest of the stimulation phase. However, for all included animals, the average daily stiffness increase within the first three weeks post operation was larger during resting than during stimulation (Sheep I: 16.9% vs. -5.7%; Sheep II: 14.7% vs. -1.8%; Sheep III: 8.9% vs. 1.6%). A continuous measurement of tissue stiffness together with a controlled fracture stimulation enabled the investigation of the short-term effects of specific stimulatory parameters, such as resting periods. Resting was identified as a potentially determining factor for bone healing progression. Optimizing the ratio between stimulation and resting may contribute to more robust fracture healing in the future.

A cross-sectional analysis of the muscle strength, spinal shrinkage, and recovery during a working day of military police officers

OBJECTIVE

Military personnel has a large prevalence of back pain, especially those involved in patrolling routines, as they wear heavy protective equipment. Patrolling includes long periods of sustaining the protective equipment in a sitting or in a motor vehicle (motorcycle or car). Thus, understanding spinal loading of military police officers after patrolling by car (CAR; n = 14), motorcycle (MOT; n = 14), and administrative (ADM; n = 14) routines is relevant to establish preventive strategies.

METHODS

The torque of the trunk and working and anthropometric characteristics were assessed to explain spinal loading using stature variation measures. Precise stature measures were performed before and after a 6 h journey (LOSS) and 20 min after a resting posture (RECOV). The trunk extensor (PTE BM-1 ) and flexor (PTF BM-1 ) muscles' isometric peak torque were measured before the working journey.

RESULTS

The LOSS was similar between CAR and MOT (4.8 and 5.8 mm, respectively) after 6 h of patrolling. The ADM presented the lowest LOSS (2.8 mm; P < .05). No changes in RECOV between groups were observed (P > .05). Vibration may explain the greater spinal loading involved in patrolling in comparison to the ADM. A GLM analysis revealed that BMI was the only explanatory factor for stature loss. No independent variables explained RECOV. The ability of the trunk muscles to produce force did not influence LOSS or RECOV.

CONCLUSIONS

Military police officers involved in patrolling may require greater post-work periods and strategies designed to reduce the weight of the protective apparatus to dissipate spinal loading. The external load used in patrolling is a relevant spinal loading factor.

Spinal sagittal alignment, spinal shrinkage and back pain changes in office workers during a workday

Purpose. Prolonged sitting is a risk factor for the appearance of lower back pain during work. The aim of this study was to observe changes in spinal sagittal alignment, height and the perception of back pain in office workers during a workday. Materials and methods. Forty-one office workers (20 women) were enrolled into a cross-sectional study. Height, sitting height and degrees of thoracic kyphosis and lumbar lordosis as well as perceived neck pain, lower back pain and upper back pain were determined, before and after an 8-h workday. Results. At the end of the day, workers had a significant decrease (p = 0.000) in height and sitting height, and upper back pain increased significantly (p = 0.023). In men, spinal shrinkage correlated with neck pain (r = 0.410, p = 0.027), and lumbar lordosis degrees in women correlated negatively with upper back pain at the end of the day (r = -0.440, p = 0.012). Conclusions. Spinal shrinkage equally affects men and women who perform the same work. There are no changes in spinal sagittal alignment throughout the workday in office workers. Office workers show significantly increased pain in the upper back at the end of the day.

The circadian rhythm in intervertebral disc degeneration: an autophagy connection

There is one circadian clock in the central nervous system and another in the peripheral organs, and the latter is driven by an autoregulatory molecular clock composed of several core clock genes. The height, water content, osmotic pressure and mechanical characteristics of intervertebral discs (IVDs) have been demonstrated to exhibit a circadian rhythm (CR). Recently, a molecular clock has been shown to exist in IVDs, abolition of which can lead to stress in nucleus pulposus cells (NPCs), contributing to intervertebral disc degeneration (IDD). Autophagy is a fundamental cellular process in eukaryotes and is essential for individual cells or organs to respond and adapt to changing environments; it has also been demonstrated to occur in human NPCs. Increasing evidence supports the hypothesis that autophagy is associated with CR. Thus, we review the connection between CR and autophagy and the roles of these mechanisms in IDD.

Intervertebral disc swelling maintains strain homeostasis throughout the annulus fibrosus: A finite element analysis of healthy and degenerated discs

Tissues in the intervertebral disc have a large capacity to absorb water, partially due to the high glycosaminoglycan (GAG) content, which decreases linearly from the nucleus pulposus (NP) in the center to the outer annulus. Our recent work showed that fiber network and GAG distribution contributes to development of residual stresses and strains that were compressive in the inner annulus to tensile in the outer annulus. GAG loss in the inner annulus, as observed with early to moderate degeneration, reduced swelling capacity and circumferential-direction stress by over 50%. However, our previous model was not capable of evaluating interactions between the NP and annulus fibrosus (AF) during swelling. In this study, we evaluated the effect of degeneration (GAG content or swelling capacity) on residual stress development throughout the disc. Simulations of moderate to severe degeneration showed a 40% decrease in NP swelling capacity, with a 25% decrease in AF and cartilaginous endplate swelling. Together, these changes in tissue swelling resulted in a decrease in NP pressure (healthy = 0.21 MPa; severe degeneration = 0.03 MPa) that was comparable to observations in human discs. There was a 60% decrease in circumferential-direction residual deformations with early degeneration. Radial-direction stretch switched from compressive to tensile with degeneration, which may increase the risk for tears or delamination. Degeneration had a significant impact on residual stress/stretch and fiber stretch in the posterior AF, which is important for understanding herniation risk. In conclusion, degenerative changes in disc geometry and intradiscal deformations was recreated by only altering NP and AF GAG composition. Since most computational models simulate degeneration by altering material stiffness, this work highlights the importance of directly simulating biochemical composition and distribution to study disc biomechanics with degeneration. STATEMENT OF SIGNIFICANCE: Tissues in the intervertebral disc have a large swelling capacity, due to its high glycosaminoglycan content. Our recent work demonstrated the importance of fiber network and glycosaminoglycan distribution residual stresses and strains development. In this study, we evaluated the effect of swelling on intradiscal deformations between the nucleus pulposus and annulus fibrosus. We also investigated the effect of degenerative glycosaminoglycan loss on swelling-based intradiscal deformations of the intact disc and its subcomponents. Decreases in nucleus glycosaminoglycan content resulted in morphological changes observed with degenerated discs and may help to explain mechanisms behind the increases in annular tears and mechanical dysfunction with degeneration.

Changes in Spinal Height After Manual Axial Traction or Side Lying: A Clinical Measure of Intervertebral Disc Hydration Using Stadiometry

OBJECTIVES

The purpose of this study was to determine the immediate effects of a manual therapy technique consisting of axial traction compared with side lying on increased spine height after sustained loading.

METHODS

Twenty-one asymptomatic participants were included. Participants either received manual therapy technique consisting of manual axial traction force for 2 consecutive rounds of 3 minutes or sustained side lying for 10 minutes. Spine height was measured using a commercially available stadiometer. Spinal height change was determined from measurements taken after loaded walking and measurements taken after manual therapy. A paired t test was performed to determine if a manual therapy technique consisting of axial traction increased spinal height after a period of spinal loading.

RESULTS

A significant increase in height was found after both manual therapy technique and sustained side lying (P < .0001). The mean height gain was 8.60 mm using 3-dimensional axial separation.

CONCLUSION

This study is an initial attempt at evaluating the biomechanical effects of manual therapy technique consisting of axial traction. Both manual axial traction force and sustained side-lying position were equally effective for short-term change in spine height after a loaded walking protocol among healthy asymptomatic individuals. This study protocol may help to inform future studies that evaluate spine height after loading.

Acute effect of full time office work in real environment on postural actions and lumbar range of motion

INTRODUCTION

Prolonged sitting is often proposed as a risk factor for low back pain development. The purpose of this study was to evaluate the acute effect of full time office work on sensorimotor trunk functions.

METHODS

Seventeen healthy office workers participated in the study. Maximal lumbar flexion range of motion, anticipatory postural adjustments and postural reflex reactions were tested before and after full time office work in a real life environment.

RESULTS

There were longer onset latencies of postural reflexive reactions and decreased response amplitudes of anticipatory postural adjustments after full time office work, but these were significant only for the obliquus externus abdominis muscle. No changes in lumbar range of motion was found.

CONCLUSION

To our knowledge this is the first study that evaluates the effect of full time office work on postural actions and lumbar RoM. We found an absence of normal human circadian flexibility in the lumbar spine and some changes in postural actions. We propose that active trunk stiffness increase to compensate for decreased passive stiffness after prolonged seated work. Further studies are needed to confirm this assumption.

Bayesian modeling predicts age and sex are not required for accurate stature estimation from femoral length

Despite the recognized flaws in applying traditional stature estimation equations such as those of Trotter and Gleser (1952) [5] to a contemporary population, there are currently no available alternatives for stature estimation in Australia that address these limitations. Post mortem computed tomography (PMCT) DICOM scans of the left and right femora were acquired from 76 Australian deceased individuals aged 17-76 years for metric analysis. Femoral bicondylar length, femoral epicondylar breadth and anterior-posterior (AP) diameter, medial-lateral (ML) diameter, circumference and cortical area at the femoral midshaft were measured on three-dimensional (3D) models to build statistical models for estimating stature. In addition, Australian individuals aged 16-63 years (n=111) were measured in standing and supine positions to aid in the adjustment of supine stature of deceased individuals utilized in this study to standing stature. The results of this preliminary evaluation strongly indicate that the optimal model for estimating stature includes bicondylar femoral length and epicondylar breadth, that the effect of sex as an independent variable is very low, and there is limited practical benefit in including age in the estimation of stature. Our study indicates that the Australian population sampled represents a small yet significant shift in stature from the original Trotter and Gleser sample. Additionally, in the case of fragmentary remains, it was found that epicondylar breadth and AP diameter had the highest probability of accurate stature estimation in the absence of bicondylar femoral length. As stature forms a significant component of a biological profile and therefore aids in the personal identification of human remains, it is important that forensic anthropologists utilize the most accurate methodologies available. Stature estimation of Australian individuals is therefore achieved with higher accuracy through utilizing the femoral equations proposed in this study.

Factors influencing diurnal variation in height among adults

This study evaluates height loss during the day in light of variables assessable through participant self-report. Participants were 19 female and 15 male staff and students who met with us twice with a mean interval between measurement sessions of 6.96h (SD=0.86). Hypotheses were evaluated using two-stage least squares regression analysis (SYSTAT 10). Males and females lost similar amounts of height between sessions (male,x¯=6.9mm;female,x¯=7.4mm). Among factors considered to impact overall height loss, sleep duration (Adj. R²=0.181, p=0.022) and height (Adj. R²=0.121, p=0.048) were useful in univariate analyses, though they were not significant in any models that included variables other than sex. Judging from log-transformed BMI variation, heavier males and females lost more height (F_{(2, 31)}=4.59, Adj. R²=0.179, p=0.018). Among factors anticipated to reduce height loss by acting prior to morning measurements, only time spent walking was significantly associated (β=2.6±0.8mm, t=3.16, p=0.004) when included as a predictor along with sex (p=0.17) and log-BMI (p=0.003). This model explained about 38% of height loss variance. None of the factors considered as potentially acting between measurement sessions showed statistically significant influences when included in the model just described, though predictor coefficients were in the anticipated direction. Results suggest that self-reported activities may be an important supplement to anthropometric studies, both for planning and later evaluation, particularly in large studies.

Determining the reliability of a custom built seated stadiometry set-up for measuring spinal height in participants with chronic low back pain

Indirect measurement of disc hydration can be obtained through measures of spinal height using stadiometry. However, specialised stadiometers for this are often custom-built and expensive. Generic wall-mounted stadiometers alternatively are common in clinics and laboratories. This study examined the reliability of a custom set-up utilising a wall-mounted stadiometer for measurement of spinal height using custom built wall mounted postural rods. Twelve participants with non-specific chronic low back pain (CLBP; females n = 5, males n = 7) underwent measurement of spinal height on three separate consecutive days at the same time of day where 10 measurements were taken at 20 s intervals. Comparisons were made using repeated measures analysis of variance for 'trial' and 'gender'. There were no significant effects by trial or interaction effects of trial x gender. Intra-individual absolute standard error of measurement (SEM) was calculated for spinal height using the first of the 10 measures, the average of 10 measures, the total shrinkage, and the rate of shrinkage across the 10 measures examined as the slope of the curve when a linear regression was fitted. SEMs were 3.1 mm, 2.8 mm, 2.6 mm and 0.212, respectively. Absence of significant differences between trials and the reported SEMs suggests this custom set-up for measuring spinal height changes is suitable use as an outcome measure in either research or clinical practice in participants with CLBP.

The poro-elastic behaviour of the intervertebral disc: A new perspective on diurnal fluid flow

Diurnal disc height changes, due to fluid in- and outflow, are in equilibrium while daytime spinal loading is twice as long as night time rest. A direction-dependent permeability of the endplates, favouring inflow over outflow, reportedly explains this; however, fluid flow through the annulus fibrosus should be considered. This study investigates the fluid flow of entire intervertebral discs. Caprine discs were preloaded in saline for 24h under four levels of static load. Under sustained load, we modulated the disc׳s swelling pressure by exchanging saline for demineralised water (inflow) and back to saline (outflow), both for 24h. We measured disc height creep and used stretched exponential models to determine time-constants. During inflow disc height increased in relation to applied load, and during outflow disc height decreased to preload levels. When comparing in- and outflow phases, there was no difference in creep, and time-constants were similar indicating no direction-dependent resistance to fluid flow in the entire intervertebral disc. Results provoked a new hypothesis for diurnal fluid flow: in vitro time-constants for loading are shorter than for unloading and in vivo daytime loading is twice as long as night time unloading, i.e. in diurnal loading the intervertebral disc is closer to loading equilibrium than to unloading equilibrium. Per definition, fluid flow is slower close to equilibrium than far from equilibrium; therefore, as diurnal loading occurs closer to loading equilibrium, fluid inflow during night time unloading can balance fluid outflow during daytime loading, despite a longer time-constant.

Spinal height change in response to sustained and repetitive prone lumbar extension after a period of spinal unloading

OBJECTIVE

The purpose of this study was to investigate if differences in spinal height changes in healthy individuals were observed after a period of spinal unloading using repetitive as compared with sustained lumbar extension exercises.

METHODS

This study used a pretest, posttest, crossover design. Asymptomatic participants were recruited using convenience sampling. Thirty-two participants (15 male; 17 female) without back pain were included in the data analysis (mean, 24.4 years; range, 20-41 years). Participants performed sustained or repetitive prone lumbar extension exercises after 1 hour of sustained spinal unloading. Spinal height was measured using a stadiometer before and after the repetitive and sustained prone lumbar extension exercises.

RESULTS

Paired t tests revealed no significant difference in spine height after repetitive (P = .774) or sustained (P = .545) prone lumbar extension after a period of spinal unloading. No significant difference between spinal height changes occurred between sustained (mean [SD], -0.28 [2.59] mm) and repetitive (mean [SD], -0.12 [2.42] mm) lumbar extension (P = .756).

CONCLUSION

In this group of asymptomatic individuals, sustained and repetitive lumbar extension exercises did not appear to affect spinal height after a period of spinal unloading.

Circadian variation in human flexibility and grip strength

The main aim of this study was to monitor changes in joint flexibility over 24 hours in 25 subjects. Measurements of finger tip to floor, lumbar flexion, lumbar extension, passive straight leg raising and glenohumeral lateral rotation at 90° abduction were taken every two hours during the 24 hour cycle. The presence of circadian rhythms in flexibility were established by graphical analysis of the results. These were shown to exist in all measurements, the most strong being finger tip to floor and most weak glenohumeral lateral rotation. The study also investigated grip strength over 24 hours and disclosed a circadian pattern in which there was a considerable fall in strength during the early hours and a rapid rise after 0600 hours.

Non-Gaussian diffusion-weighted imaging for assessing diurnal changes in intervertebral disc microstructure

PURPOSE

To investigate the use of non-Gaussian diffusion-weighted imaging (q-space imaging [QSI]) to estimate diurnal changes in intervertebral disc (IVD) microstructure.

MATERIALS AND METHODS

IVDs of 15 male subjects (mean age, 27.3 years; mean body mass index, 22.50 kg/m(2) ) were investigated once in the morning, less than 30 min after rising, and a second time in the evening after at least 10 h of normal physical activity, using 3 Tesla (T) MR imaging. T2 mapping and QSI data values (apparent diffusion coefficient [ADC], root mean square displacement [RMSD], and apparent kurtosis coefficient [AKC]) were calculated and compared between the morning and evening imaging sessions.

RESULTS

The T2, ADC, and RMSD values showed a significant decrease in the evening (175.8 ± 49.5 ms, 1.56 ± 0.32 10(-3) mm(2) /s and 40.0 ± 3.0 μm, respectively; P < 0.05 for all values; paired t-test), when compared with the morning values (226.5 ± 83.8 ms, 1.69 ± 0.29 10(-3) mm(2) /s and 45.2 ± 2.9 μm, respectively). The AKC value showed a significant increase in the evening (0.67 ± 0.08), when compared with the morning value (0.58 ± 0.04; P < 0.05).

CONCLUSION

The RMSD and AKC values obtained from QSI analysis may be biomarkers for IVD diurnal microstructural changes.

Estimation bias: body mass and body height in endurance athletes

Body Mass Index is associated with endurance performance in athletes. Reported and measured values of body mass and body height in 1,618 endurance athletes (1,358 men, 260 women) showed that men and women both underestimated their body mass and overestimated their body height, leading to an underestimation of Body Mass Index. There were age and sex differences in estimates of height and weight; for both women and men, underestimation of Body Mass Index amounted to 0.4 kg/m2. Master athletes tended to underestimate their body mass and overestimate their body height thus leading to significant differences between estimated and measured Body Mass Index. However, the magnitude of underestimation of BMI probably has a negligible influence on performance predictions. The differences between measured and estimated body mass, height, and BMI were within the range of normal daily variation, and for body height even within the precision of the measurement (0.5 cm).

Is the ovine intervertebral disc a small human one? A finite element model study

The sheep is one of the most frequently used animal models for experimental intervertebral disc research questions. Although there are large differences in size between human and ovine discs, recent in vivo and in vitro studies indicate similarities in the internal disc stresses. The present finite element model study, therefore, intended to detect the parameters that, despite the different geometry, ensure mechanical comparability between both species. At first, a finite element model of the human L4-L5 lumbar intervertebral disc was developed. The predicted displacement and nucleus pressure response were validated with experimental in vivo and in vitro data. Starting with adapting the model geometry from the human to the ovine disc, several material and biochemical parameters, which might contribute to the preservation of the mechanical disc response across both species, were successively adapted to ovine properties. Replacing the geometry yielded a substantially higher disc stiffness and lower nucleus pressure compared to in vitro measurements performed on ovine discs. Additional reduction of annulus and nucleus elasticity led to an improved correlation between model predictions and measurements. Changes in the glycosaminoglycan content and endplate permeability improved the predicted pressure, but only slightly affected the displacement response. Only the combination of all parameters resulted in a good agreement between the predictions and measurements. This study demonstrated that there are profound differences between model predictions and in vitro results if an ovine simulation is run with human material properties. However, once the species-specific material properties are included, the predictions fit the in vitro results. Therefore, it seems that the human and ovine disc is functionally adapted to produce similar internal stresses, despite the large variation in geometry.

In vitro and in silico investigations of disc nucleus replacement

Currently, numerous hydrogels are under examination as potential nucleus replacements. The clinical success, however, depends on how well the mechanical function of the host structure is restored. This study aimed to evaluate the extent to and mechanisms by which surgery for nucleus replacements influence the mechanical behaviour of the disc. The effects of an annulus defect with and without nucleus replacement on disc height and nucleus pressure were measured using 24 ovine motion segments. The following cases were considered: intact; annulus incision repaired by suture and glue; annulus incision with removal and re-implantation of nucleus tissue repaired by suture and glue or plug. To identify the likely mechanisms observed in vitro, a finite-element model of a human disc (L4-L5) was employed. Both studies were subjected to physiological cycles of compression and recovery. A repaired annulus defect did not influence the disc behaviour in vitro, whereas additional nucleus removal and replacement substantially decreased disc stiffness and nucleus pressure. Model predictions demonstrated the substantial effects of reductions in replaced nucleus water content, bulk modulus and osmotic potential on disc height loss and pressure, similar to measurements. In these events, the compression load transfer in the disc markedly altered by substantially increasing the load on the annulus when compared with the nucleus. The success of hydrogels for nucleus replacements is not only dependent on the implant material itself but also on the restoration of the environment perturbed during surgery. The substantial effects on the disc response of disruptions owing to nucleus replacements can be simulated by reduced nucleus water content, elastic modulus and osmotic potential.

Musculoskeletal myths

This paper discusses a number of common myths in the musculoskeletal pain management and rehabilitation/athletic development fields. The origins or rationale for these beliefs are reviewed. New scientific evidence disputing or refuting the myth is then presented followed by and explanation and evidence for an updated perspective.

Recommendations for management of uncomplicated back pain in the workers' compensation system: a focus on functional restoration

OBJECTIVE

To present recommendations for conservative strategies to improve the management of uncomplicated back pain and to evaluate the financial crisis currently facing the workers' compensation system due in part to rapidly rising medical costs.

BACKGROUND

Medical costs in the workers' compensation system have risen at an alarming rate placing a tremendous burden on the cost of doing business in the United States. Historically, treatment for back pain in the United States has been a pathology-based approach; the literature supports a functional restorative approach for clinical efficacy and cost effectiveness.

DESIGN

Narrative overview of the literature.

METHODS

Computerized databases were searched for relevant literature in the English language from the years 1994-2004, including: Alternative Health Watch; Cochrane Database of Systematic Reviews; Pre-CINAHL; CINAHL; MEDLINE; AgeLine; SPORT Discus. A narrative synthesis of the literature was written from retrieved articles.

DISCUSSION

A history and overview of the workers' compensation system is presented. Concerns regarding rising medical costs and recommendations for strategies to improve cost and quality of care with an emphasis on ergonomic and functional restoration recommendations are made.

CONCLUSION

A percentage of costs in the workers' compensation system go towards treating uncomplicated back pain; recurrences and chronicity of back pain are key contributors to these costs, which are currently increasing. Ergonomic advice plays a key role in helping the patient with musculoskeletal injuries heal faster and prevent costly flare-ups. Conservative care, which includes chiropractic manipulation, ergonomic recommendations, and exercise rehabilitation with an emphasis on coordination and endurance training, is supported by the literature as a possible method of cost containment.

Diurnal variation in stature: do those with chronic low-back pain differ from asymptomatic controls?

BACKGROUND

Stature loss is a commonly used measure of spinal load. The aim of this study was to investigate the pattern of diurnal stature change in those with and without chronic low-back pain, over a 24-h period.

METHODS

Eight participants with chronic low-back pain (age 24.6 (SD 4.3) years, height 1.76 (SD 0.08) m, body mass 72.8 (SD 11.1) kg) and eight controls (age 21.8 (SD 2.0) years, height 1.75 (SD 0.10) m, body mass 71.8 (SD 11.6) kg) participated in this investigation. Twenty-four stature measurements were performed over a 24-h period.

FINDINGS

The trough to peak variation in stature of 17.9 mm (low-back pain group) and 17.6mm (control group) did not differ between groups (P>0.05). Both groups experienced greatest stature change in the 1st hour after rising (31.3% [low-back pain] and 44.6% [control] of total stature change). At approximately 18:00h the LBP group reached a plateau whilst the control group continued to lose stature. Between 14:00 and 18:00h both groups demonstrated a previously unreported recovery of stature. A significant correlation was found between low-back discomfort and stature change in the low-back pain group only.

INTERPRETATION

No significant difference existed between groups in relation to total stature loss; however the low-back pain group appeared to reach their nadir earlier, possibly exposing other spinal structures to loading for a greater duration. This is supported by the relationship found between stature loss and discomfort. The reversal in stature loss in the afternoon may be of clinical significance and warrants further investigation.

Simulation of inhomogeneous rather than homogeneous poroelastic tissue material properties within disc annulus and nucleus better predicts cervical spine response: a C3-T1 finite element model analysis under compression and moment loadings

STUDY DESIGN

A finite element (FE) modeling of homogeneous and inhomogeneous poroelastic tissue material properties within disc anulus fibrosus (AF) and nucleus pulposus (NP).

OBJECTIVE

To test the hypothesis that simulation of inhomogeneous poroelastic tissue material properties within AF and NP quadrants, rather than homogeneous properties within regions of AF and NP without quadrants, would better predict the cervical spine biomechanics.

SUMMARY OF BACKGROUND DATA

In order to represent tissue swelling and creep deformation behavior more physiologically in FE models, disc poroelastic tissue material properties should be modeled appropriately. Past studies show an existence of inhomogeneous rather than homogeneous nature of the tissue properties in various quadrants of AF and NP, and this has been simulated in a single-segment FE lumbar model with only compression analysis. This article simulated these tissue properties in a multisegmental cervical spine and reported the results of both compression and moment loads.

METHODS

Two three-dimensional FE models of a C3-T1 segment were developed. Model I included homogeneous poroelastic tissue properties in AF and NP, whereas Model II included inhomogeneous poroelastic tissue properties in AF and NP quadrants. Biomechanical responses of the FE models under diurnal compression and moment loads were compared with corresponding in vivo published studies.

RESULTS

Model II with disc quadrant-based inhomogeneous poroelastic tissue properties predicted better, mainly in flexion and extension, than the Model I with homogeneous tissue properties when compared with the corresponding in vivo results, thereby confirming the current study hypothesis. Inhomogeneous tissue properties govern segmental behavior mainly during sagittal plane motions, with a root-mean-square difference of nearly 50% across the motion segments.

CONCLUSION

The current data justify the need to simulate inhomogeneous tissue properties within disc quadrants for any FE model analysis. Model II can be further used to understand the biomechanical effects of quadrant-based degenerative poroelastic tissue properties on cervical spine behavior. Future experiments are necessary to support the current study results.

Relative contributions of strain-dependent permeability and fixed charged density of proteoglycans in predicting cervical disc biomechanics: a poroelastic C5-C6 finite element model study

Disc swelling pressure (P(swell)) facilitated by fixed charged density (FCD) of proteoglycans (P(fcd)) and strain-dependent permeability (P(strain)) are of critical significance in the physiological functioning of discs. FCD of proteoglycans prevents any excessive matrix deformation by tissue stiffening, whereas strain-dependent permeability limits the rate of stress transfer from fluid to solid skeleton. To date, studies involving the modeling of FCD of proteoglycans and strain-dependent permeability have not been reported for the cervical discs. The current study objective is to compare the relative contributions of strain-dependent permeability and FCD of proteoglycans in predicting cervical disc biomechanics. Three-dimensional finite element models of a C5-C6 segment with three different disc compositions were analyzed: an SPFP model (strain-dependent permeability and FCD of proteoglycans), an SP model (strain-dependent permeability alone), and an FP model (FCD of proteoglycans alone). The outcomes of the current study suggest that the relative contributions of strain-dependent permeability and FCD of proteoglycans were almost comparable in predicting the physiological behavior of the cervical discs under moment loads. However, under compression, strain-dependent permeability better predicted the in vivo disc response than that of the FCD of proteoglycans. Unlike the FP model (least stiff) in compression, motion behavior of the three models did not vary much from each other and agreed well within the standard deviations of the corresponding in vivo published data. Flexion was recorded with maximum P(fcd) and P(strain), whereas minimum values were found in extension. The study data enhance the understanding of the roles played by the FCD of proteoglycans and strain-dependent permeability and porosity in determining disc tissue swelling behavior. Degenerative changes involving strain-dependent permeability and/or loss of FCD of proteoglycans can further be studied using an SPFP model. Future experiments are necessary to support the current study results.

Reduction in segmental flexibility because of disc degeneration is accompanied by higher changes in facet loads than changes in disc pressure: a poroelastic C5-C6 finite element investigation

BACKGROUND CONTEXT

Nerve fiber growth inside the degenerative intervertebral discs and facets is thought to be a source of pain, although there may be several other pathological and clinical reasons for the neck pain. It, however, remains difficult to decipher how much disc and facet joints contribute to overall degenerative segmental responses. Although the biomechanical effects of disc degeneration (DD) on segmental flexibility and posterior facets have been reported in the lumbar spine, a clear understanding of the pathways of degenerative progression is still lacking in the cervical spine.

PURPOSE

To test the hypothesis that after an occurrence of degenerative disease in a cervical disc, changes in the facet loads will be higher than changes in the disc pressure.

STUDY DESIGN

To understand the biomechanical relationships between segmental flexibility, disc pressure, and facet loads when the C5-C6 disc degenerates.

METHODS

A poroelastic, three-dimensional finite element (FE) model of a normal C5-C6 segment was developed and validated. Two degenerated disc models (moderate and severe) were built from the normal disc model. Biomechanical responses of the three FE models (normal, moderate, and severe) were further studied under diurnal compression (at the end of the daytime activity period) and moment loads (at the end of 5 seconds) in terms of disc height loss, angular motions, disc pressure, and facet loads (average of right and left facets).

RESULTS

Disc deformation under compression and segmental rotational motions under moment loads for the normal disc model agreed well with the corresponding in vivo studies. A decrease in segmental flexibility because of DD is accompanied by a decrease in disc pressure and an increase in facet loads. Biomechanical effects of degenerative disc changes are least in flexion. Segmental flexibility changes are higher in extension, whereas changes in disc pressure and facet loads are higher in lateral bending and axial rotation, respectively.

CONCLUSIONS

The results of the present study confirmed the hypothesis of higher changes in facet loads than in disc pressure, suggesting posterior facets are more affected than discs because of a decrease in degenerative segmental flexibility. Therefore, a degenerated disc may increase the risk of overloading the posterior facet joints. It should be clearly noted that only after degeneration simulation in the disc, we recorded the biomechanical responses of the facets and disc. Therefore, our hypothesis does not suggest that facet joint osteoarthritis may occur before degeneration in the disc. Future cervical spine-based experiments are warranted to verify the conclusions presented in this study.

Patterns of height changes in anterior and posterior cervical disc regions affects the contact loading at posterior facets during moderate and severe disc degeneration: a poroelastic C5-C6 finite element model study

STUDY DESIGN

Biomechanical roles of anterior and posterior portions of the disc (AD and PD, respectively) in governing posterior facets (PF) behavior of a C5-C6 motion segment.

OBJECTIVE

To understand how height patterns (loss and gain) at AD and PD affects the PF contact loading during moderate and severe grades of cervical disc degeneration (DD).

SUMMARY OF BACKGROUND DATA

PF overloading and degeneration after degenerative disc height loss is a clinical concern. This may occur because of a decrease in facet joints space, causing elevated PF contact forces. During a physiologic motion, axial disc height patterns at AD and PD affects the spacing and overlapping of articulating PF surfaces. The question arises as to what percentage of deformation and/or elongation at AD and PD is contributing to a corresponding increase and/or decrease in PF contact loading.

METHODS

A poroelastic, three-dimensional finite element model of a C5-C6 segment with a normal (grade I) disc was used after validation. Two degenerated disc models were developed from the normal disc model: moderate (combined effect of Thompson disc grades II and III) and severe (combined effect of Thompson disc grades IV and V). The models were analyzed under compression, flexion, and extension. Height patterns (loss and gain) at AD and PD, and PF loading were calculated for each model.

RESULTS

PF loading increased with PD height loss, and further increased with AD height gain. In moderate DD, PF loading was more affected by PD height loss than AD height gain, whereas in severe DD, it was more affected by AD height gain than PD height loss.

CONCLUSION

The current study conclusions suggest a possible mechanism for PF loading through loss and gain in the AD and PD heights during moderate and severe grades of DD. Further cervical spine based biomechanical investigations are suggested to verify our findings.

Restoration of disk height through non-surgical spinal decompression is associated with decreased discogenic low back pain: a retrospective cohort study

BACKGROUND

Because previous studies have suggested that motorized non-surgical spinal decompression can reduce chronic low back pain (LBP) due to disc degeneration (discogenic low back pain) and disc herniation, it has accordingly been hypothesized that the reduction of pressure on affected discs will facilitate their regeneration. The goal of this study was to determine if changes in LBP, as measured on a verbal rating scale, before and after a 6-week treatment period with non-surgical spinal decompression, correlate with changes in lumbar disc height, as measured on computed tomography (CT) scans.

METHODS

A retrospective cohort study of adults with chronic LBP attributed to disc herniation and/or discogenic LBP who underwent a 6-week treatment protocol of motorized non-surgical spinal decompression via the DRX9000 with CT scans before and after treatment. The main outcomes were changes in pain as measured on a verbal rating scale from 0 to 10 during a flexion-extension range of motion evaluation and changes in disc height as measured on CT scans. Paired t-test or linear regression was used as appropriate with p < 0.05 considered to be statistically significant.

RESULTS

We identified 30 patients with lumbar disc herniation with an average age of 65 years, body mass index of 29 kg/m2, 21 females and 9 males, and an average duration of LBP of 12.5 weeks. During treatment, low back pain decreased from 6.2 (SD 2.2) to 1.6 (2.3, p < 0.001) and disc height increased from 7.5 (1.7) mm to 8.8 (1.7) mm (p < 0.001). Increase in disc height and reduction in pain were significantly correlated (r = 0.36, p = 0.044).

CONCLUSIONS

Non-surgical spinal decompression was associated with a reduction in pain and an increase in disc height. The correlation of these variables suggests that pain reduction may be mediated, at least in part, through a restoration of disc height. A randomized controlled trial is needed to confirm these promising results.

CLINICAL TRIAL REGISTRATION NUMBER

NCT00828880.

Response analysis of the lumbar spine during regular daily activities--a finite element analysis

A non-linear poroelastic finite element model of the lumbar spine was developed to investigate spinal response during daily dynamic physiological activities. Swelling was simulated by imposing a boundary pore pressure of 0.25 MPa at all external surfaces. Partial saturation of the disc was introduced to circumvent the negative pressures otherwise computed upon unloading. The loading conditions represented a pre-conditioning full day followed by another day of loading: 8h rest under a constant compressive load of 350 N, followed by 16 h loading phase under constant or cyclic compressive load varying in between 1000 and 1600 N. In addition, the effect of one or two short resting periods in the latter loading phase was studied. The model yielded fairly good agreement with in-vivo and in-vitro measurements. Taking the partial saturation of the disc into account, no negative pore pressures were generated during unloading and recovery phase. Recovery phase was faster than the loading period with equilibrium reached in only approximately 3h. With time and during the day, the axial displacement, fluid loss, axial stress and disc radial strain increased whereas the pore pressure and disc collagen fiber strains decreased. The fluid pressurization and collagen fiber stiffening were noticeable early in the morning, which gave way to greater compression stresses and radial strains in the annulus bulk as time went by. The rest periods dampened foregoing differences between the early morning and late in the afternoon periods. The forgoing diurnal variations have profound effects on lumbar spine biomechanics and risk of injury.

Effect of time of day on the vertical spinal creep response

Vertical spinal creep (VSC) is height loss during sustained postures over a set period of time. While total stature has been demonstrated to decrease throughout the day, whether a diurnal effect applies to the VSC response has not been reported. The aim of this study was to investigate whether time of day had an effect on the magnitude of the VSC response in young subjects asymptomatic for musculoskeletal pathologies. The VSC response was recorded over 25 min while subjects remained seated on the stadiometer, at three times (morning, midday and afternoon) on the same day, in 48 asymptomatic volunteers aged 20-39 years. While no significant differences were calculated for the magnitude of the VSC responses on the three occasions of testing, differences in magnitude of VSC response may have been confounded by preloading activities. Where magnitude of the VSC response is the primary outcome measure, measurement protocols should control preloading activities and continue to conduct measurements at the same time of day, until further studies conclusively refute the existence of a diurnal effect.

Using "spinal shrinkage" as a trigger for motivating students to learn about obesity and adopt a healthy lifestyle

Obesity is a global problem; however, relatively little attention is directed toward preparing and inspiring students of medicine and allied medical sciences to address this serious matter. Students are not routinely exposed to the assessment methods for obesity, its overall prevalence, causative factors, short- and long-term consequences, and its management by lifestyle modification. This physiology laboratory exercise involving students of medicine (n = 106) was developed to 1) introduce medical students to methods of obesity assessment and to differentiate between general and abdominal obesity, 2) generate an interest and sensitivity about obesity, and 3) stimulate thinking about modification of their lifestyle in relation to eating habits, weight control, and physical activity. Spinal shrinkage (the difference between the standing height of a person and his/her recumbent length) was used as an immediate observable parameter to demonstrate the effect of adiposity. Spinal shrinkage is recognized as an index of the compressive forces acting on the spine and is related to body mass index. A positive correlation (r = 0.365, P < 0.05) was observed between body mass index and spinal shrinkage. A questionnaire was used to assess student responses to this exercise. Students were motivated to engage in more physical activity (74%), adopt healthier eating (63%), and enhance their knowledge about obesity (67%). They expressed keen interest in the laboratory exercise and found the sessions enjoyable (91%). The laboratory exercise proved to be a success in motivating the students to actively learn and inquire about obesity and to adopt a healthier lifestyle.

Stature loss and recovery following a period of loading: effect of time of day and presence or absence of low back pain

BACKGROUND

Stature reductions in asymptomatic individuals, caused by a set load, are lower later in the day when stature is in the trough of diurnal variation; hence most stature reduction investigations are conducted in the morning. Recent evidence suggests that it is not the reductions in stature, but the recovery of stature, that is of greatest importance. The aim of this investigation was to establish whether stature recovery is also affected by time of day and to determine if any differences exist between a chronic low back pain and asymptomatic group.

METHODS

Eleven chronic low back pain participants (age=32.8 SD 7.9 yrs, mass=74.4 SD 14.2 kg and height=1.73 SD 0.07 m) and 11 asymptomatic participants (age=31.0 SD 6.3 yrs, body mass=72.6 SD 11.5 kg and height=1.76 SD 0.09 m) underwent two 20 min loaded walking tasks (10% body mass), one in the morning (09:00) and one in the afternoon (14:00), followed by a 20 min unloaded recovery period. Measurements of stature were obtained throughout.

FINDINGS

The asymptomatic group experienced significantly less stature reduction (P=0.05; ES=1.1) and greater stature recovery (P=0.02; ES=0.9) in the afternoon compared to the morning. The chronic low back pain group experienced a similar pattern to the asymptomatic group, however no significant difference between sessions for changes in stature was evident P=0.07.

INTERPRETATION

Further investigations of stature recovery should be restricted to the morning when comparing individuals with and without chronic low back pain, as time of day appeared to have effect on stature recovery, particularly in the asymptomatic group. Time dependent differences in stature change between these two populations warrants further investigation.

Spinal unloading after abdominal exercises

BACKGROUND

Intervertebral discs are exposed to compressive forces, which produces fluid loss. This loss decreases disc height, spinal length and consequently overall stature. The loss of stature has been associated with spine loading and low back pain. Abdominal exercises increase intra-abdominal pressure and unload the spine. The purpose of this study was to identify if abdominal exercises may produce acute spinal unloading compared to a known unloading position.

METHODS

Nine subjects performed a loading protocol and an unloading protocol on three experimental sessions. The loading protocol consisted of three sets of military press, while three unloading protocols were: three sets of regular abdominal exercises, three sets of abdominal exercises performed in an inclined board or an unloading resting posture.

FINDINGS

Abdominal exercises showed a greater recovery (mean (SD)) (regular=87.8 (20.4)%; inclined=70.1 (14.5)%) in comparison to the resting position (Fowler=33.6 (14.1)%), although no significant differences were found between abdominal exercises in stature recovery (P=0.07).

INTERPRETATION

Abdominal exercises may be introduced between sets of resistance training to decrease the negative effect of compressive forces imposed during such highly stressing activities. Further studies are required to confirm the proposed underlying mechanisms.

Intervertebral disc recovery after dynamic or static loading in vitro: is there a role for the endplate?

In vivo studies on disc mechanics show loss of fluid from the intervertebral disc (IVD) during loading and full recovery during rest. Previous work indicated that in vitro recovery is hampered after static loading. The aim of the present study was to investigate the role of the endplate after dynamic and static loading on mechanical recovery in vitro. Lumbar spines (caprine) were obtained from the local slaughterhouse and stored frozen. Twenty-four intervertebral discs were thawed and subjected to a compression test in a saline bath (37 degrees C). The discs were pre-loaded at 20 N for 15 min. Three 15-min loading cycles (static: 2.0 MPa or dynamic: average load 2.0 MPa at 0.5 Hz) were applied, each followed by a 30-min period of unloading (20 N). After this protocol, the endplates of half of the discs were blocked with silicone paste and the long-term recovery protocol was applied; the discs were subjected to a single loading cycle (15 min of static or dynamic loading) followed by 10h of unloading at 20 N. All specimens showed a net loss of height and a gain in stiffness during the first part of the test. Eventually, height and stiffness were restored during a long-term recovery test. The difference in recovery between blocked and free endplates was marginal. If fluid flow plays a role during recovery in vitro, the role of the endplate appears to be limited. Our findings show no influence of loading type on recovery in vitro.

Effects of loading on spinal shrinkage in males of different age groups

A reduction in stature (shrinkage) has been used as a measure of the load on the spine. Musculoskeletal effects of ageing may influence individual responses to compressive loading on the spine and the resultant loss in stature. The aim was to apply the technique of precision stadiometry for assessment of spinal shrinkage in a comparison of responses of two different age groups performing a regimen of circuit weight training. In all, 20 subjects (10 aged 18-25 and 10 aged 47-60 years) participated in the study. Each performed two sets of a 12-station circuit of exercises, the loading being established relative to individual capabilities. Recovery procedures using a semi-supine posture intervened between the two sets and again post-exercise; altogether seven measures of change in stature were obtained using precision stadiometry. The two groups showed a similar pattern of spinal shrinkage, losses in stature being greater for the first set compared to the later set of exercises. Subjects gained height whilst in the formal recovery posture, but responses were inconsistent during warm-up, cool-down and active recovery. Irrespective of age, the spine was less responsive to loading as the duration of activity was increased. It was concluded that provided loading is related to individual capability, healthy older operators are not necessarily compromised by their age in activities that include handling and lifting weights.

Changes in stature and spine kinematics during a loaded walking task

The aim of the present study was to quantify the kinematics of the spine and stature loss induced by the asymmetric load carriage. Six healthy males with no history of low-back disorders walked at their self-selected pace for 8,500 m with and without a standard Royal Mail bag (model MB36) containing 17.5% of the participant's body mass. The load was reduced gradually during the task. The loaded condition produced a stature loss double that observed in the unloaded condition. Increased forward leaning (up to 6 degrees ) and lateral bending of the spine (up to 12 degrees ) was observed with load. Thoracic adjustments occurred in the sagittal plane, changes in the lumbar area occurred in the frontal plane. The data provided evidence against mailbags designs in which the workers cannot alternate the side of the mailbag.

Body mass as a factor in stature change

BACKGROUND

Back pain is a common condition which has been described as a serious public health problem. Spinal shrinkage has been used as an index of spinal loading in a range of tasks. Epidemiological evidence shows that body mass index (BMI: 30 kg/m(2)) is related to the development of low back pain however, no studies have described the stature change patterns of obese individuals. This study aimed to compare changes in stature after an exercise task in obese and non-obese individuals.

METHODS

Twenty volunteers were divided into two equal groups; obese: BMI>30 kg/m(2), non-obese: BMI<25 kg/m(2). Stature was measured at 3 min intervals during a 30 min walking task and a 30 min standing recovery period. Tests were performed on two occasions, once with participants loaded during the walking task (10% body mass) and once unloaded. The influence of obesity and load condition on the magnitude and rate of stature change were compared by a two-way ANOVA:

FINDINGS

In both groups the stature loss was greater in the loaded than unloaded condition (mean (SD)) (6.52 (1.45)mm and 3.55 (0.93)mm non-obese; 8.49 (1.75)mm and 7.02 (1.32)mm obese: P=0.016). The obese presented a greater reduction in stature in both task conditions. The obese group were unable to recover stature regardless of the task condition during the recovery period (loaded: 0.06 (0.3)mm; unloaded: 0.32 (0.6)mm; P=0.013).

INTERPRETATION

It was concluded that the acute response of the spine to loading may represent a risk factor for low back pain in the obese, in addition to the chronic adaptations previously reported. A greater period of recovery may be necessary for obese individuals to re-establish intervertebral disc height. These findings may help to explain the high incidence of back disorders in obese individuals.

Flow-related mechanics of the intervertebral disc: the validity of an in vitro model

STUDY DESIGN

An in vitro mechanical study on porcine motion segments.

OBJECTIVES

To test the validity of in vitro studies of the flow-related mechanics of the intervertebral disc and, in particular, to investigate whether fluid flows back into the disc during unloading after a loading cycle.

SUMMARY OF BACKGROUND DATA

In vivo studies show both the inflow and outflow of fluid in the intervertebral disc. The resistance to flow out of the disc is higher than to inflow. The fluid flow is regulated via unbalance between the external load and the osmotic pressure of the nucleus pulposus.

MATERIALS

There were 8 porcine lumbar motion segments (without posterior elements) and 8 isolated discs tested in a physiologic saline bath (39 degrees C). The specimens were preloaded at 0.025 MPa for 15 minutes. Three 15-minute loading periods at 2.0 MPa were applied, each followed by an unloading period of 30 minutes. Loads, axial displacements, and nucleus pressure were recorded online.

RESULTS

Over the 3 loading and unloading periods, all specimens showed a net loss of height and mass. The time series of specimen height during the 3 unloading periods showed virtually identical responses. The pressure in the nucleus decreased in the subsequent loading periods and showed no increase during unloading.

CONCLUSION

The data show the limitations of an in vitro model for studying fluid flow-related intervertebral disc mechanics. During loading, outflow of fluid occurred, but inflow appears to be virtually absent during unloading. Poro-elastic behavior cannot be reproduced in an in vitro model.

Spinal shrinkage and recovery in women with and without low back pain

OBJECTIVES

To assess the behavior of the spinal column after loading in participants with and without low back pain (LBP) using spinal shrinkage measurements as a criterion and to analyze the relations among spinal shrinkage, recovery, and LBP.

DESIGN

A case-control study with repeated measures.

SETTING

University department with recruitment from primary care.

PARTICIPANTS

Convenience sample of 31 women (15 with chronic, nondisabling LBP [LBP group]; 16 with no history of low back disorders [control group]).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE

Changes in body length as determined by using a stadiometer.

RESULTS

The spinal shrinkage induced by the exercise was similar ( P >.05) in both groups (control group, mean +/- standard deviation of -3.99+/-1.13 mm; LBP group, -4.16+/-1.54 mm). Differences in spinal length were found after 20 minutes in the recovery position ( P <.05). The control group was able to recover stature to a greater extent (111.2%+/-13.6%) than the LBP group ( P <.05), which was unable to regain stature beyond baseline (57.5%+/-25.1%). A negative correlation was found between regaining stature and low back pain ( r =-.52, P <.05).

CONCLUSIONS

Participants with LBP were unable to recover stature to the same extent as controls. We suggest that LBP is related to the diminished ability to recover rather than to the magnitude of the spinal shrinkage imposed during the task.

Lumbar spine disc height and curvature responses to an axial load generated by a compression device compatible with magnetic resonance imaging

STUDY DESIGN

Axial load-dependent changes in the lumbar spine of supine healthy volunteers were examined using a compression device compatible with magnetic resonance imaging.

OBJECTIVE

To test two hypotheses: Axial loading of 50% body weight from shoulder to feet in supine posture 1) simulates the upright lumbar spine alignment and 2) decreases disc height significantly.

SUMMARY OF BACKGROUND DATA

Axial compression on the lumbar spine has significantly narrowed the lumbar dural sac in patients with sciatica, neurogenic claudication or both.

METHODS

Using a device compatible with magnetic resonance imaging, the lumbar spine of eight young volunteers, ages 22 to 36 years, was axially compressed with a force equivalent to 50% of body weight, approximating the normal load on the lumbar spine in upright posture. Sagittal lumbar magnetic resonance imaging was performed to measure intervertebral angle and disc height before and during compression.

RESULTS

Each intervertebral angle before and during compression was as follows: T12-L1 (-0.8 degrees +/- 2.5 degrees and -1.5 degrees +/- 2.6 degrees ), L1-L2 (0.7 degrees +/- 1.4 degrees and 3.3 degrees +/- 2.9 degrees ), L2-L3 (4.7 degrees +/- 3.5 degrees and 7.3 degrees +/- 6 degrees ), L3-L4 (7.9 degrees +/- 2.4 degrees and 11.1 degrees +/- 4.6 degrees ), L4-L5 (14.3 degrees +/- 3.3 degrees and 14.9 degrees +/- 1.7 degrees ), L5-S1 (25.8 degrees +/- 5.2 degrees and 20.8 degrees +/- 6 degrees ), and L1-S1 (53.4 degrees +/- 11.9 degrees and 57.3 degrees +/- 16.7 degrees ). Negative values reflect kyphosis, and positive values reflect lordosis. A significant difference between values before and during compression was obtained at L3-L4 and L5-S1. There was a significant decrease in disc height only at L4-L5 during compression.

CONCLUSIONS

The axial force of 50% body weight in supine posture simulates the upright lumbar spine morphologically. No change in intervertebral angle occurred at L4-L5. However, disc height at L4-L5 decreased significantly during compression.