Intramuscular pressure in the erector spinae and intra-abdominal pressure related to posture and load

Muscle-driven forward dynamic active hybrid model of the lumbosacral spine: combined FEM and multibody simulation

Most spine models belong to either the musculoskeletal multibody (MB) or finite element (FE) method. Recently, coupling of MB and FE models has increasingly been used to combine advantages of both methods. Active hybrid FE-MB models, still rarely used in spine research, avoid the interface and convergence problems associated with model coupling. They provide the inherent ability to account for the full interplay of passive and active mechanisms for spinal stability. In this paper, we developed and validated a novel muscle-driven forward dynamic active hybrid FE-MB model of the lumbosacral spine (LSS) in ArtiSynth to simultaneously calculate muscle activation patterns, vertebral movements, and internal mechanical loads. The model consisted of the rigid vertebrae L1-S1 interconnected with hyperelastic fiber-reinforced FE intervertebral discs, ligaments, facet joints, and force actuators representing the muscles. Morphological muscle data were implemented via a semi-automated registration procedure. Four auxiliary bodies were utilized to describe non-linear muscle paths by wrapping and attaching the anterior abdominal muscles. This included an abdominal plate whose kinematics was optimized using motion capture data from upper body movements. Intra-abdominal pressure was calculated from the forces of the abdominal muscles compressing the abdominal cavity. For the muscle-driven approach, forward dynamics assisted data tracking was used to predict muscle activation patterns that generate spinal postures and balance the spine without prescribing accurate spinal kinematics. During calibration, the maximum specific muscle tension and spinal rhythms resulting from the model dynamics were evaluated. To validate the model, load cases were simulated from -10° extension to +30° flexion with weights up to 20 kg in both hands. The biomechanical model responses were compared with in vivo literature data of intradiscal pressures, intra-abdominal pressures, and muscle activities. The results demonstrated high agreement with this data and highlight the advantages of active hybrid modeling for the LSS. Overall, this new self-contained tool provides a robust and efficient estimation of LSS biomechanical responses under in vivo similar loads, for example, to improve pain treatment by spinal stabilization therapies.

Coordination Between Trunk Muscles, Thoracolumbar Fascia, and Intra-Abdominal Pressure Toward Static Spine Stability

STUDY DESIGN

Numerical in-silico human spine stability finite element analysis.

OBJECTIVE

The purpose of this study was to investigate the contribution of major torso tissues toward static spine stability, mainly the thoracolumbar fascia (TLF), abdominal wall with its intra-abdominal pressure (IAP), and spinal muscles inclusive of their intramuscular pressure.

SUMMARY OF BACKGROUND DATA

Given the numerous redundancies involved in the spine, current methodologies for assessing static spinal stability are limited to specific tissues and could lead to inconclusive results. A three-dimensional finite element model of the spine, with structured analysis of major torso tissues, allows for objective investigation of static spine stability.

METHODS

A novel previously fully validated spine model was employed. Major torso tissues, mainly the muscles, TLF, and IAP were individually, and in combinations, activated under a 350N external spine perturbation. The stability contribution exerted by these tissues, or their ability to restore the spine to the unperturbed position, was assessed in different case-scenarios.

RESULTS

Individual activations recorded significantly different stability contributions, with the highest being the TLF at 75%. Combined or synergistic activations showed an increase of up to 93% stability contribution when all tissues were simultaneously activated with a corresponding decrease in the tensile load exerted by the tissues themselves.

CONCLUSION

This investigation demonstrated torso tissues exhibiting different roles toward static spine stability. The TLF appeared able to dissipate and absorb excessive loads, the muscles acted as antagonistic to external perturbations, and the IAP played a role limiting movement. Furthermore, the different combinations explored suggested an optimized engagement and coordination between different tissues to achieve a specific task, while minimizing individual work.Level of Evidence: N/A.

Development and validation of a timely and representative finite element human spine model for biomechanical simulations

Numerous spine Finite Element (FE) models have been developed to assess spinal tolerances, spinal loadings and low back pain-related issues. However, justified simplifications, in terms of tissue decomposition and inclusion, for such a complex system may overlook crucial information. Thus, the purpose of this research was to develop and validate a comprehensive and representative spine FE model inclusive of an accurate representation of all major torso elements. A comprehensive model comprised of 273 tissues was developed via a novel FE meshing method to enhance computational feasibility. A comprehensive set of indirect validation tests were carried out to validate every aspect of the model. Under an increasing angular displacement of 24°-41°, the lumbar spine recorded an increasing moment from 5.5 to 9.3 Nm with an increase in IVD pressures from 0.41 to 0.66 MPa. Under forward flexion, vertical vertebral displacements simulated a 6% and 13% maximum discrepancy for intra-abdominal and intramuscular pressure results, all closely resembling previously documented in silico measured values. The developed state-of-the-art model includes most physiological tissues known to contribute to spinal loadings. Given the simulation's accuracy, confirmed by its validation tests, the developed model may serve as a reliable spinal assessment tool.

Is the Agricultural Work a Risk Factor for Koreans Elderly Spinal Sagittal Imbalance?

Objective

A primary degenerative sagittal imbalance has been considered because of unique lifestyles such as the prolonged crouched posture during agricultural work and performing activities of daily living on the floor. Previous papers have reported that sagittal imbalance disease is often seen distinctly in the farming districts of “oriental” countries such as Korea and Japan. However, this finding was only evaluated with the use of X-ray, and other factors such as magnetic resonance imaging (MRI), muscle volume, compression fracture, and laboratory results were not considered. Thus, using these, we evaluate the agricultural work-associated factors for Korean elderly spinal sagittal imbalance.

Methods

We recruited 103 Korean participants who had a sagittal vertical axis (SVA) of >5 cm in this Korean Elderly Sagittal Imbalance Cohort Study. The following were evaluated : radiological parameters, MRI, compression fracture, vitamin D, parathyroid hormone, C-terminal telopeptide, osteocalcin, bone mineral density and muscle fatty change, muscle volume, and health-related quality of life from patients’ survey. Moreover, in this survey, the farmers’ annual working hours were investigated. Subsequently, we analyzed the associated factors for spinal sagittal imbalance depending on occupation.

Results

A total of 46 participants were farmers, and the others were housewives, sellers, and office workers. The farmer group had more SVA (141 vs. 99 mm, p=0.001) and pelvic tilt (31° vs. 24°, p=0.004) and lesser lumbar lordosis (20° vs. 30°, p=0.009) and thoracic kyphosis (24° vs. 33°, p=0.03) than non-farmer group. A significantly positive correlation was noted between the working hour and SVA in the farmer group (p=0.014). The visual analogue scale score for back pain (8.26 vs. 6.96, p=0.008) and Oswestry Disability Index (23.5 vs. 19.1, p=0.003) in the farmer group were higher than that in the non-farmer group, but the Short Form-36 score was not significantly different between the two groups. The Mini-Mental State Exam score was significantly lower in the farmer group than in the non-farmer group (24.85 vs. 26.98, p=0.002).

Conclusion

The farmer group had more sagittal imbalance and back pain in proportion to the working hours even though the muscle and bone factors and general laboratory condition were not significantly different between the two groups. These results supported that the long hours spent in the crouched posture while performing agricultural work were a risk factor for severe sagittal imbalance.

Age and gender related neuromuscular pattern during trunk flexion-extension in chronic low back pain patients

BACKGROUND

The root mean square surface electromyographic activity of lumbar extensor muscles during dynamic trunk flexion and extension from standing has repeatedly been recommended to objectively assess muscle function in chronic low back pain patients. However, literature addressing older patients is sparse. This cross sectional study sought to examine differences in neuromuscular activation between age groups (>60 versus 40-60 versus <40 years) and sexes during a standardized trunk flexion-extension task.

METHODS

A total of 216 patients (62 older, 84 middle-aged, 70 younger) performed maximum trunk extensions followed by trunk flexion extension testing thereby holding static positions at standing, half, and full trunk flexion. The lumbar extensor muscle activity and 3d-accelerometric signals intended to monitor hip and trunk position angles were recorded from the L5 (multifidus) and T4 (semispinalis thoracis) levels. Permutation ANOVA with bootstrapped confidence intervals were performed to examine for age and gender related differences. Ridge-regressions investigated the impact of physical-functional and psychological variables to the half flexion relaxation ratio (i.e. muscle activity at the half divided by that in maximum flexion position).

RESULTS

Maximum back extension torque was slightly but significantly higher in youngest compared to oldest patients if male and females were pooled. Normalized RMS-SEMG revealed highest lumbar extensor muscle activity at standing in the oldest and the female groups. Patients over 60 years showed lowest activity changes from standing to half (increments) and from half to the maximum flexion position (decrements) leading to a significantly lower half flexion relaxation ratio compared to the youngest patients. These oldest patients demonstrated the highest hip and lowest lumbothoracic changes of position angles. Females had higher regional hip and gross trunk ranges of movement compared to males. Lumbothoracic flexion and the muscle activity at standing had a significant impact on the half flexion relaxation ratio.

CONCLUSIONS

The neuromuscular activation pattern and the kinematics in this trunk flexion-extension task involving static half flexion position changed according to age and sex. The test has a good potential to discriminate between impaired and unimpaired neuromuscular regulation of back extensors in cLBP patients, thereby allowing the design of more individualized exercise programs.

The prevalence and risk factors of low back pain in rural community residents of Korea

STUDY DESIGN

A community-based, cross-sectional study that is part of the prospective Korean Health and Genome Study.

OBJECTIVE

To determine the prevalence of low back pain (LBP) among middle-aged and elderly rural community residents in Korea and to examine the relevant risk factors, including activities reflecting the Asian lifestyle, and the relationship between radiographical features of degenerative changes in the lumbar spine and LBP.

SUMMARY OF BACKGROUND DATA

The prevalence and implication of LBP among the elderly, particularly Asians, are under-represented in previous reports.

METHODS

Data for LBP were collected for 4181 subjects from a rural farming community. The point and cumulative lifetime prevalences of LBP were obtained in addition to measurement of the severity of LBP. Lateral lumbar spine radiographs were obtained according to a standard protocol.

RESULTS

The mean age of the study subjects was 56 years and 55% were women. The lifetime prevalence of LBP was 61.3%, with women having a higher prevalence. The point and 6-month prevalences were also higher among women. The lifetime, point, and 6-month prevalences increased with age in both sexes, except for lifetime prevalence in men. The prevalence of LBP of grade 3 or more was significantly higher in women and increased significantly with age, particularly in women. Both lifetime and point of prevalence of LBP were significantly associated with age, female sex, and time spent squatting. After adjusting for age and sex, the presence of disc space narrowing, osteophytes, and advanced Kellgren-Lawrence grade in lumbar radiograph was associated with LBP.

CONCLUSION

The prevalence of LBP is comparable between these Korean community residents and other population groups. Risk factors associated with LBP included advanced age, female sex, squatting, the presence of osteophytes, joint space narrowing, and advanced Kellgren-Lawrence grading on lumbar radiograph.

Effect of the intra-abdominal pressure and the center of segmental body mass on the lumbar spine mechanics - a computational parametric study

Determination of physiological loads in human lumbar spine is critical for understanding the mechanisms of lumbar diseases and for designing surgical treatments. Computational models have been used widely to estimate the physiological loads of the spine during simulated functional activities. However, various assumptions on physiological factors such as the intra-abdominal pressure (IAP), centers of mass (COMs) of the upper body and lumbar segments, and vertebral centers of rotation (CORs) have been made in modeling techniques. Systematic knowledge of how these assumptions will affect the predicted spinal biomechanics is important for improving the simulation accuracy. In this paper, we developed a 3D subject-specific numerical model of the lumbosacral spine including T12 and 90 muscles. The effects of the IAP magnitude and COMs locations on the COR of each motion segment and on the joint/muscle forces were investigated using a global convergence optimization procedure when the subject was in a weight bearing standing position. The data indicated that the line connecting the CORs showed a smaller curvature than the lordosis of the lumbar spine in standing posture when the IAP was 0 kPa and the COMs were 10 mm anterior to the geometric center of the T12 vertebra. Increasing the IAP from 0 kPa to 10 kPa shifted the location of CORs toward the posterior direction (from 1.4 ± 8.9 mm anterior to intervertebral disc (IVD) centers to 40.5 ± 3.1 mm posterior to the IVD centers) and reduced the average joint force (from 0.78 ± 0.11 Body weight (BW) to 0.31 ± 0.07 BW) and overall muscle force (from 349.3 ± 57.7 N to 221.5 ± 84.2 N). Anterior movement of the COMs from -30 mm to 70 mm relative to the geometric center of T12 vertebra caused an anterior shift of the CORs (from 25.1 ± 8.3 mm posterior to IVD centers to 7.8 ± 6.2 mm anterior to IVD centers) and increases of average joint forces (from 0.78 ± 0.1 BW to 0.93 ± 0.1 BW) and muscle force (from 348.9 ± 47.7 N to 452.9 ± 58.6 N). Therefore, it is important to consider the IAP and correct COMs in order to accurately simulate human spine biomechanics. The method and results of this study could be useful for designing prevention strategies of spinal injuries and recurrences, and for enhancing rehabilitation efficiency.

Chronic lumbar paraspinal compartment syndrome: a case report and review of the literature

A 25-year-old male weightlifter felt increasing intractable low back pain during training but denied any acute injury. The physical examination, blood parameters, radiographs and MRI were unremarkable. He had been treated non-operatively by various means, with only temporary relief. The pressures in the lumbar paraspinal compartment were abnormally high and he was treated by surgical decompression. This gave rapid relief, he returned to training, and one year later the pain had not recurred.

Creation of an asymmetrical gradient of back muscle activity and spinal stiffness during asymmetrical hip extension

BACKGROUND

Low back pain is often associated with increased spinal stiffness which thought to arise from increased muscle activity. Unfortunately, the association between paraspinal muscle activity and paraspinal stiffness, as well as the spatial distribution of this relation, is unknown. The purpose of this investigation was to employ new technological developments to determine the relation between spinal muscle contraction and spinal stiffness over a large region of the lumbar spine.

METHODS

Thirty-two male subjects performed graded isometric prone right hip extension at four different exertion levels (0%, 10%, 25% and 50% of the maximum voluntary contraction) to induce asymmetric back muscle activity. The corresponding stiffness and muscle activity over bilateral paraspinal lumbar regions was measured by indentation loading and topography surface electromyography, respectively. Paraspinal stiffness and muscle activity were then plotted and their correlation was determined.

FINDINGS

Data from this study demonstrated the existence of an asymmetrical gradient in muscle activation and paraspinal stiffness in the lumbar spine during isometric prone right hip extension. The magnitude and scale of the gradient increased with the contraction force. A positive correlation between paraspinal stiffness and paraspinal muscle activity existed irrespective of the hip extension effort (Pearson correlation coefficient, range 0.566-0.782 (P<0.001)).

INTERPRETATION

Our results demonstrate the creation of an asymmetrical gradient of muscle activity and paraspinal stiffness during right hip extension. Future studies will determine if alterations in this gradient may possess diagnostic or prognostic value for patients with low back pain.

Muscle oxygenation and intramuscular pressure related to posture and load in back muscles

BACKGROUND CONTEXT

There is little information about the simultaneous changes of intramuscular pressure (IMP) and oxygen saturation (StO(2)) of the paraspinal muscle under various conditions of posture and load.

PURPOSE

To measure simultaneously and compare IMP and StO(2) across a range of static trunk postures commonly observed during normal work tasks.

STUDY DESIGN

A prospective study using a repeated-measure design in clinical setting.

PATIENT SAMPLE

Sixteen healthy young men with no history of back pain.

OUTCOME MEASURES

Simultaneous measurements of IMP by a flexible slit catheter and StO(2) by near infrared spectroscopy of the multifidus muscle were performed.

METHODS

The two measures were taken in six static posture tasks: standing upright and bending forward with and without load (20kg), bending backward and during a sustained isometric contraction (ie, Sorensen test). To compare the influence of the tasks on IMP and StO(2) variables, a one-way variance analysis with repeated measures was used. Spearman's rank correlation coefficient (rho) was determined between the two variables for each posture task.

RESULTS

We observed only a moderate but significant correlation between IMP and StO(2) values in upright standing and a trend in bending forward positions with load (p<.05). IMP increased in the bending backward position and showed the greatest increase during the Sorensen test. StO(2) decreased significantly during the Sorensen test, in the bending forward position with and without load bearing but did not in bending backward.

CONCLUSION

The simultaneous recording of IMP and StO(2) of the multifidus muscle allows a deeper insight of physiological events during various trunk postures. In the mutifidus muscle, there is no evident linear relationship between IMP and StO(2) values in various static postures of the trunk in young males. This preliminary study shows that IMP may play a role on StO(2) only in some circumstances, such as a prolonged endurance test or in a bending forward position with a significant load bearing.

Low intervertebral disc height in postmenopausal women with osteoporotic vertebral fractures compared to hormone-treated and untreated postmenopausal women and premenopausal women without fractures

OBJECTIVE

To assess the intervertebral disc height in postmenopausal women with osteoporotic vertebral fractures.

METHODS

A total of 203 women were recruited from a bone densitometer directory. The disc heights measured were those between the 12th thoracic and 3rd lumbar vertebrae. The discs were assigned the symbols D, whereby D(1) refers to the disc between the 12th thoracic and 1st lumbar vertebrae. The disc height of the group of women (n = 38) with osteoporotic vertebral fractures was compared to the disc heights of hormone-treated women (n = 47), untreated postmenopausal women (n = 77) and another group of premenopausal women (n = 41).

RESULTS

The total disc height (D(1) - D(3)) (mean +/- standard deviation) in the fracture group was 1.58 +/- 0.1 cm, significantly lower (p < 0.0001) than in the untreated group (1.82 +/- 0.06 cm), which in turn was significantly (p < 0.0001) lower than in the hormone-treated group (2.15 +/- 0.08 cm) and in the premenopausal group (2.01 +/- 0.09 cm).

CONCLUSION

The fracture group was noted to have the lowest intervertebral disc height compared to the other three groups. The hormone-treated and the premenopausal women had the highest disc heights recorded. These results may be due to the effect that the menopause and senescence have on the discal connective tissue components. This may lead to loss of the shock-absorbing properties of the intervertebral disc and an altered discoid shape, influencing the occurrence of osteoporotic vertebral body fractures.

The effect of muscle relaxant on the paraspinal muscle blood flow: a randomized controlled trial in patients with chronic low back pain

STUDY DESIGN

A randomized controlled trial.

OBJECTIVE

To investigate the effect of muscle relaxant for muscle blood flow at the trunk muscle in patients with chronic low back pain (LBP).

SUMMARY OF BACKGROUND DATA

Paraspinal muscle function is widely believed to play a role and considered to be of etiologic significance in LBP, and intramuscular pressure increases and blood flow decreases in the flexion position. Decrease in oxygenated hemoglobin at the trunk muscle is seen in patients with LBP.

METHODS

A total of 74 male patients with LBP lasting more than 6 months were randomized to 3 treatment groups: (1) physical therapy only (control) (n = 25), (2) administration of eperisone hydrochloride (EMPP) for 4 weeks (n = 24), and (3) McKenzie therapy (n = 25). The primary outcome variables, observed at 2 and 4 weeks, are the Japanese Orthopedic Association LBP score, visual analogue scale (VAS), Faces Pain Scale-Revised, and SF-36. Intramuscular oxygenation was evaluated using near-infrared spectroscopy during lumbar extension and flexion, and oxygenated hemoglobin and deoxygenated hemoglobin were compared.

RESULTS

VAS was significantly lower at 4 weeks in the McKenzie group than in the control group. There were no significant changes at 2 weeks in all parameters, however, the relative change of oxygenated hemoglobin during lumbar extension at 4 weeks was significantly higher in the EMPP group when compared with the other 2 groups. The relative change of deoxygenated hemoglobin during lumbar flexion showed a significant difference at 4 weeks in the EMPP group when compared with the control group.

CONCLUSION

Administration of EMPP for 4 weeks improved the LBP in VAS, though not as effective as McKenzie therapy. Our data demonstrated the effects of eperisone hydrochloride on paraspinal muscle hemodynamics improving intramuscular oxygenation during lumbar extension and flexion in patients with chronic LBP.

Estabilização segmentar da coluna lombar nas lombalgias: uma revisão bibliográfica e um programa de exercícios

No tratamento de lombalgias, exercícios tradicionais de fortalecimento dos músculos abdominais e extensores do tronco têm sido alvo de críticas por submeter a coluna vertebral a altas cargas de trabalho, aumentando o risco de nova lesão. Estudos recentes comprovam a eficácia da estabilização segmentar como tratamento para a lombalgia, sendo menos lesiva por ser realizada em posição neutra. Pesquisas sugerem que, sem a ativação correta dos estabilizadores profundos do tronco, as recidivas do quadro álgico são notadas com muita freqüência. Este estudo procedeu à revisão da literatura sobre o tratamento das lombalgias mediante estabilização da coluna e propõe exercícios para seu tratamento baseados na estabilização segmentar lombar. Na base PubMed, por meio dos descritores estabilização lombar, multífido lombar, transverso do abdome e os equivalentes em inglês, foram selecionados 47 artigos e livros publicados entre 1984 e 2006. A literatura estabelece um elo entre lombalgia e escasso controle dos músculos profundos do tronco, em especial o multífido lombar e o transverso do abdome; estudos também indicam os músculos quadrado lombar e diafragma como estabilizadores lombares. Propõem-se assim exercícios de contrações isométricas sincronizadas, sutis e específicas, que atuam diretamente no alívio da dor por meio do aumento da estabilidade do segmento vertebral.

In vivo erector spinae muscle blood volume and oxygenation measures during repetitive incremental lifting and lowering in chronic low back pain participants

STUDY DESIGN

A case control study.

OBJECTIVES

Using metabolic gas analysis and near infrared spectroscopy, a comparison was made between healthy controls and chronic low back pain (LBP) participants on cardiorespiratory, erector spinae muscle blood volume, and oxygenation responses, and these variables were used to determine factors that best predict peak oxygen consumption (VO2peak).

SUMMARY OF BACKGROUND DATA

To date, it is unknown how the cardiorespiratory and erector spinae muscles of chronic LBP persons respond to repetitive incremental lifting and lowering. With the advent of near infrared spectroscopy technology, it is now possible to noninvasively examine erector spinae muscle oxygen supply and utilization in vivo. Thus, by using metabolic gas analysis and near infrared spectroscopy technology simultaneously, it is now possible to compare the cardiorespiratory and erector spinae muscle responses of chronic LBP participants to that of healthy controls (no history of LBP) during incremental work to volitional fatigue.

METHODS

Thirty-four participants with chronic LBP and 34 healthy controls completed the repetitive incremental lifting and lowering (2.25 kg x min) protocol from floor to table (height 76 cm) at 10 lifts . min to voluntary fatigue.

RESULTS

The healthy controls had significantly greater VO2peak (mL x kg x min) and VO2peak (mL x kgLBM x min), peak mass lifted, test duration, and breathing frequency. Furthermore, healthy controls showed significantly greater change in muscle oxygenation and faster one-half recovery times. Multiple regression analysis indicated that approximately 97% of the variance in absolute VO2peak was predicted by cardiorespiratory variables in both groups, while muscle oxygenation aided in predicting VO2peak relative in the LBP participants.

CONCLUSIONS

The results indicated that the chronic LBP participants demonstrated a reduced cardiorespiratory and erector spinae muscle response during repetitive incremental lifting and lowering to volitional fatigue as compared to the healthy controls.

Intramuscular hemodynamics in bilateral erector spinae muscles in symmetrical and asymmetrical postures with and without loading

BACKGROUND

Although attention has been paid to the relationship between the changes in blood circulation in erector spinae muscles and back pain, little is known about their hemodynamics in several various comparable postures with and without loading. Studies on hemodynamics of erector spinae muscles using near-infrared spectroscopy have been performed on subjects and patients mainly in forward flexion positions.

METHODS

Two near-infrared spectroscopes were used to measure oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin in bilateral erector spinae muscles at L2-3 in subjects in 9 postures, and holding no load, 10 kg or 20 kg in maximum flexed and lateral bending. Those three values in each posture and loading condition were expressed as a percentage of their corresponding values obtained in the standing upright position, and designated and statistically analyzed as %Oxy-Hb, %Deoxy-Hb and %Total-Hb, respectively.

FINDINGS

%Total-Hb and %Oxy-Hb in maximum flexion were the most decreased. In maximum lateral bending, %Oxy-Hb only in the contralateral erector spinae muscles was decreased. When the load was 20 kg, the decreases in %Oxy-Hb were the largest in maximum flexion and lateral bendings.

INTERPRETATION

Using two near-infrared spectroscopes allowed us to measure simultaneously the hemodynamics of bilateral muscles. They demonstrated different responses in each side. Asymmetrical posture and loading were accompanied by asymmetrical changes of the bilateral erector spinae muscles. Stretched muscle had less blood volume and oxygenation, both of which decreased with increasing load. These results showed that these postures and conditions might lead to fatigue of the ES muscles.

Role of intra-abdominal pressure in the unloading and stabilization of the human spine during static lifting tasks

The role of intra-abdominal pressure (IAP) in unloading the spine has remained controversial. In the current study, a novel kinematics-based approach along with a nonlinear finite-element model were iteratively used to calculate muscle forces, spinal loads, and stability margin under prescribed postures and loads measured in in vivo studies. Four coactivity levels (none, low, moderate, and high) of abdominal muscles (rectus abdominis, external oblique, and internal oblique) were considered concurrently with a raise in IAP from 0 to 4 kPa when lifting a load of 180 N in upright standing posture and to 9 kPa when lifting the same load in forward trunk flexions of 40 degrees and 65 degrees. For comparison, reference cases with neither abdominal coactivity nor IAP were investigated as well. A raise in IAP unloaded and stabilized the spine when no coactivity was considered in the foregoing abdominal muscles for all lifting tasks regardless of the posture considered. In the upright standing posture, the unloading action of IAP faded away even in the presence of low level of abdominal coactivity while its stabilizing action continued to improve as abdominal coactivity increased to moderate and high levels. For lifting in forward-flexed postures, the unloading action of IAP disappeared only with high level of abdominal coactivities while its stabilizing action deteriorated as abdominal coactivities increased. The unloading and stabilizing actions of IAP, hence, appear to be posture and task specific.

The influence of non-specific low back pain on pressure pain thresholds and disability

The purpose of this study was to investigate the pressure pain thresholds (PPTs) with respect to the Erector spinae and the hip muscles in 87 patients with subacute non-specific low back pain (LBP) and to evaluate the relationship between the PPTs and disability. In order to establish reference values, 64 healthy subjects were examined with respect to PPTs and used as a control group against the group of LBP patients. The mean PPT values of the Erector spinae and the hip at all examined points of the LBP group were significantly lower (p<0.001) in comparison to the PPT values of the healthy group. An exceptionally high difference (2.7 kg/cm2) was found at the L3 Erector spinae level. The correlation between having LBP or not in the whole group (n=151) and PPT, was highest at the L3 level of the Erector spinae (r=-0.710, p<0.001). When the group of patients with LBP was divided into two subgroups in terms of having an Oswestry disability index (ODI) lower than 40 ("moderate LBP disability") or an ODI higher than 40 ("severe LBP disability") it was surprising to notice that there was no significant difference between the PPTs of the Erector spinae and the hip musculature. This study has shown the possibility of the existence of muscular disorder in the lumbar part of the Erector spinae in patients with non-specific low back pain, but also reveals the strong inter-individual differences in muscular fibrosis sensitivity and pain behaviour related to gender.

Anterior thoracic posture increases thoracolumbar disc loading

In the absence of external forces, the largest contributor to intervertebral disc (IVD) loads and stresses is trunk muscular activity. The relationship between trunk posture, spine geometry, extensor muscle activity, and the loads and stresses acting on the IVD is not well understood. The objective of this study was to characterize changes in thoracolumbar disc loads and extensor muscle forces following anterior translation of the thoracic spine in the upright posture. Vertebral body geometries (C2 to S1) and the location of the femoral head and acetabulum centroids were obtained by digitizing lateral, full-spine radiographs of 13 men and five women volunteers without previous history of back pain. Two standing, lateral, full-spine radiographic views were obtained for each subject: a neutral-posture lateral radiograph and a radiograph during anterior translation of the thorax relative to the pelvis (while keeping T1 aligned over T12). Extensor muscle loads, and compression and shear stresses acting on the IVDs, were calculated for each posture using a previously validated biomechanical model. Comparing vertebral centroids for the neutral posture to the anterior posture, subjects were able to anterior translate +101.5 mm+/-33.0 mm (C7-hip axis), +81.5 mm+/-39.2 mm (C7-S1) (vertebral centroid of C7 compared with a vertical line through the vertebral centroid of S1), and +58.9 mm+/-19.1 mm (T12-S1). In the anterior translated posture, disc loads and stresses were significantly increased for all levels below T9. Increases in IVD compressive loads and shear loads, and the corresponding stresses, were most marked at the L5-S1 level and L3-L4 level, respectively. The extensor muscle loads required to maintain static equilibrium in the upright posture increased from 147.2 N (mean, neutral posture) to 667.1 N (mean, translated posture) at L5-S1. Compressive loads on the anterior and posterior L5-S1 disc nearly doubled in the anterior translated posture. Anterior translation of the thorax resulted in significantly increased loads and stresses acting on the thoracolumbar spine. This posture is common in lumbar spinal disorders and could contribute to lumbar disc pathologies, progression of L5-S1 spondylolisthesis deformities, and poor outcomes after lumbar spine surgery. In conclusion, anterior trunk translation in the standing subject increases extensor muscle activity and loads and stresses acting on the intervertebral disc in the lower thoracic and lumbar regions.

Relationship between the thickness and hemodynamics of the erector spinae muscles in various lumbar curvatures

BACKGROUND

There is little information about the relationship between the changes of hemodynamics and the morphologic changes of the erector spinae muscle.

METHODS

Fifty healthy male volunteers participated. Ultrasonography was used to measure muscle thickness, and near-infrared spectroscopy was used to measure tissue blood volume and its oxygenation in the erector spinae muscle at L3 in six different relaxed trunk postures (flexed 20 degrees , flexed 40 degrees, flexed maximum, neutral posture, extended 20 degrees, and extended maximum of the lumbar spine). We also evaluated the reproducibility of the near-infrared spectroscopy measurements.

FINDINGS

Near-infrared spectroscopy gave highly reproducible measurements. The thickness of the erector spinae muscle and the total and oxygenated hemoglobin were simultaneously increased during relaxed extension and decreased during relaxed flexion. Changes in the thickness of the erector spinae muscle with various lumbar curvature were similar in pattern to the changes in tissue blood volume and its oxygenation.

INTERPRETATION

The erector spinae muscles' thickness, tissue blood volume, and its oxygenation are simultaneously increased during relaxed extension and decreased during relaxed flexion, as demonstrated by non-invasive near-infrared spectroscopy and ultrasonography. These findings might afford a better understanding of the pathomechanics of posture-related back symptoms.

RELEVANCE

The erector spinae muscles' thickness, tissue blood volume, and its oxygenation are simultaneously increased during relaxed extension and decreased during relaxed flexion, as shown by non-invasive near-infrared spectroscopy and ultrasonography. Changes in hemodynamics and morphology of the erector spinae muscles in asymptomatic subjects are given for further research on the pathomechanism of back pain.

Treatment of a Case of Subacute Lumbar Compartment Syndrome Using the Graston Technique

OBJECTIVE

To discuss subacute lumbar compartment syndrome and its treatment using a soft tissue mobilization technique.

CLINICAL FEATURES

A patient presented with low back pain related to exercise combined with prolonged flexion posture. The symptoms were relieved with rest and lumbar extension. The patient had restrictive lumbar fascia in flexion and rotation and no neurological deficits.

INTERVENTION AND OUTCOME

The restrictive lumbar posterior fascial layers and adjoining restrictive fascia (thoracic, gluteal, hamstring) were treated with a form of instrument-assisted soft tissue mobilization called the Graston technique. Restoration of fascial extensibility and resolution of the complaint occurred after 6 treatment visits.

CONCLUSIONS

The posterior spinal fascial compartments may be responsible for intermittent lower back pain. Functional clinical tests can be employed to determine whether the involved fascia is abnormally restrictive. Treatment directed at the restrictive fascia using this soft tissue technique may result in improved fascial functional testing and reduction of symptoms.

Intramuscular pressure, tissue oxygenation and EMG fatigue measured during isometric fatigue-inducing contraction of the multifidus muscle

Simultaneous measurement of intramuscular pressure (IMP), tissue oxygen partial pressure (pO(2)) and EMG fatigue parameters in the multifidus muscle during a fatigue-inducing sustained muscular contraction. The study investigated the following hypotheses: (1) Increases in IMP result in tissue hypoxia; (2) Tissue hypoxia is responsible for loss of function in the musculature. The nutrient supply to muscle during muscle contraction is still not fully understood. It is assumed that muscle contraction causes increased tissue pressure resulting in compromised perfusion and tissue hypoxia. This tissue hypoxia, in turn, leads to muscle fatigue and therefore to loss of function. To the authors' knowledge, no study has addressed IMP, pO(2) and EMG fatigue parameters in the same muscle to gain a deeper sight into muscle perfusion during contraction. As back muscles need to have a constant muscular tension to maintain trunk stability during stance and locomotion, muscle fatigue due to prolonged contraction-induced hypoxia could be an explanation for low back pain. Sixteen healthy subjects performed an isometric muscular contraction exercise at 60% of maximum force until the point of localized muscular fatigue. During this exercise, the individual changes of IMP, pO(2) and the median frequency (MF) of the surface EMG signal of the multifidus muscle were recorded simultaneously. In 12 subjects with a documented increase in intramuscular pressure, only five showed a decrease in tissue oxygen partial pressure, while this parameter remained unchanged in six other subjects and even increased in one. A fall in tissue pO(2) was associated with a drop in MF in only five subjects, while there was no correlation between these parameters in the other 11 subjects. To summarize, an increase in IMP correlated with a decrease in pO(2) and a drop in MF in only five out of 16 subjects. High intramuscular pressure values are not always associated with a hypoxia in muscle tissue. Tissue hypoxia is not automatically associated with a median frequency shift in the EMG signal's power spectrum.

Simultaneous measurement of intramuscular pressure and surface electromyography of the multifidus muscle

The anatomic proof of a spinal compartment and the clinical symptoms of compartment syndrome in patients with chronic back pain are inconsistent with the rarely met measuring criteria of intramuscular pressure (IMP). Previous studies assume a dependence of the IMP on spinal alignment (degree of lumbar spine flexion) and the degree of muscle activation. The significance of these disturbance variables in the interpretation of IMP could explain the above discrepancy. This study therefore investigates the influence of both a 30% increase in trunk flexion and alterations in muscle contraction from 100% to 60%. Sixteen healthy subjects participated in the study. The IMP and mean rectified amplitude of the multifidus surface EMG signal were determined at rest and 0 degrees and approximately 30 degrees of lumbar spine flexion, and they were compared. Subsequently, both parameters were measured during both 100% and 60% maximal voluntary contraction (MVC) of the muscle and then correlated. During rest and 0 degrees flexion, the median IMP was 9.3 mmHg (range 0.0-22.5) while the median mean rectified amplitude (MRA) of the EMG signal was 1.98 microV (range 1.32-7.38). In 30 degrees flexion, the median IMP went up to 24.3 mmHg (range 1.4-97.3) with hardly any increase in the median MRA of 2.32 microV (range 1.20-9.72). Under 60% MVC, the median IMP rose to 186.6 mmHg (range 15.4-375.4) and the median MRA to 21.02 microV (range 4.63-43.63). During 100% MVC, the median MRA increased to 34.38 microV (range 12.99-102.54) while the median IMP rose to 273.4 mmHg (range 90.4-395.1). Spearman's rank correlation coefficient for the IMP and MRA quotients of the 100/60% MVC values was r= -0.21. To sum up, it can be said that IMP was subject to great interindividual variation in all the experiments. This parameter is highly dependent on spinal alignment and muscular activity. Further studies are needed so that the IMP can be interpreted properly when diagnosing a chronic compartment of the erector spinae muscles.

Use of ultrasonography to evaluate thickness of the erector spinae muscle in maximum flexion and extension of the lumbar spine

STUDY DESIGN

An observational study of the changes in thickness of the erector spinae (ES) muscle in three different trunk postures.

OBJECTIVE

To use ultrasonography to evaluate the thickness of the ES muscle in three different trunk postures.

BACKGROUND

Although there has been extensive study of the morphology of the ES muscle during prolonged trunk flexion, we have little information about the changes in thickness of these muscles in various postures of the lumbar spine. Ultrasonography has never been used to measure the thickness of ES muscle.

METHODS

We studied 30 volunteers with no history of lower back problems. We used ultrasonography to measure the thickness of the ES muscle at each lumbar level (L1, L2, L3, L4, and L5) in maximum flexion, neutral posture, and maximum extension. We tested the reliability of this method by evaluating intraobserver and interobserver differences in 13 subjects.

RESULT

The high correlation between intraobserver and interobserver measurements in the 13 subjects demonstrated that the method provides sufficient reproducibility. When the trunk was flexed maximally, the thickness of the ES muscle was significantly decreased at each lumbar vertebral level. When the trunk was extended maximally, the thickness of the ES muscle was significantly increased at each lumbar vertebral level.

CONCLUSION

The thickness of the ES muscle decreases as the lumbar spine flexes and increases as it extends. We used ultrasonography successfully for quantitative evaluation of changes in thickness of the ES muscle with postural changes in the lumbar spine.

A review of anatomical and mechanical factors affecting vertebral body integrity

Background: The aetiology of osteoporotic vertebral fracture is multifactorial and may be conceptualised using a systems framework. Previous studies have established several correlates of vertebral fracture including reduced vertebral cross-sectional area, weakness in back extensor muscles, reduced bone mineral density, increasing age, worsening kyphosis and recent vertebral fracture. Alterations in these physical characteristics may influence biomechanical loads and neuromuscular control of the trunk and contribute to changes in subregional bone mineral density of the vertebral bodies. Methods: This review discusses factors that have received less attention in the literature, which may contribute to the development of vertebral fracture. A literature review was conducted using electronic databases including Medline, Cinahl and ISI Web of Science to examine the potential contribution of trabecular architecture, subregional bone mineral density, vertebral geometry, muscle force, muscle strength, neuromuscular control and intervertebral disc integrity to the aetiology of osteoporotic vertebral fracture. Interpretation: A better understanding of factors such as biomechanical loading and neuromuscular control of the trunk may help to explain the high incidence of subsequent vertebral fracture after sustaining an initial vertebral fracture. Consideration of these issues may be important in the development of prevention and management strategies.

Tissue adaptation to physical stress: a proposed "Physical Stress Theory" to guide physical therapist practice, education, and research

The purpose of this perspective is to present a general theory--the Physical Stress Theory (PST). The basic premise of the PST is that changes in the relative level of physical stress cause a predictable adaptive response in all biological tissue. Specific thresholds define the upper and lower stress levels for each characteristic tissue response. Qualitatively, the 5 tissue responses to physical stress are decreased stress tolerance (eg, atrophy), maintenance, increased stress tolerance (eg, hypertrophy), injury, and death. Fundamental principles of tissue adaptation to physical stress are described that, in the authors' opinion, can be used to help guide physical therapy practice, education, and research. The description of fundamental principles is followed by a review of selected literature describing adaptation to physical stress for each of the 4 main organ systems described in the Guide to Physical Therapist Practice (ie, cardiovascular/pulmonary, integumentary, musculoskeletal, neuromuscular). Limitations and implications of the PST for practice, research, and education are presented.

Sensory-motor control of the lower back: implications for rehabilitation

Although low back pain (LBP) is a widespread and disabling health problem, there is a lack of evidence based medicine with respect to its treatment and rehabilitation. A major reason for this is the poor understanding of the underlying mechanisms of the LBP syndromes. In an attempt to fill this gap, the present review article provides an overview of the sensory-motor control aspects of trunk stabilization and postural control of the trunk, and how they may relate to the evolution of LBP. In particular, the anatomy and physiology of the sensory-motor control mechanisms of the trunk muscles that contribute to general and segmental stability of the lumbar spine will be elucidated. Furthermore, a brief overview of current theories of postural control will be provided with respect to spinal stabilization. Finally, a concept of the pathophysiological changes within the sensory-motor control mechanisms of the lumbar spine in the presence of muscle injury and pain will be presented. The impact of pain and muscle injury on the muscular support for the lumbar motion segment will be discussed along with the deficits in neuromuscular control in LBP patients with decreased segmental lumbar stability.

Intermittent isometric fatigue study of the lumbar multifidus muscle in four-point kneeling: an intra-rater reliability investigation

Back muscle endurance is considered important in low back pain (LBP) rehabilitation. Specific training of multifidus may also be necessary to restore normal low back function. The reliability of surface electromyogram (EMG) to assess endurance of the multifidus muscle during intermittent isometric exercise was evaluated. Multifidus endurance was monitored in the four-point kneeling exercise position using the power spectral analysis method. Twenty healthy volunteers were tested on three separate occasions. Subjects performed repeat 10 s high-intensity voluntary contractions of multifidus for 3 min. The median frequency (MF) and the integrated-rectified (I-R) EMG signal displayed the fatigue pattern of multifidus. Intraclass correlation coefficients indicated fair-good reproducibility for MF (0.48-0.67) but poor reliability for IR-EMG. In conclusion, problems concerning functional testing protocols for the back muscles remain and careful development is necessary for more realistic rehabilitation monitoring.