The Components of Lumbar Motor Control Are Not Inter-related.

OBJECTIVES: To verify the relationship between the indicators of components of lumbar motor control and determine the factors related to the indicators to each of these components. METHODS: Twenty-five healthy university students were included in the study. The lumbar spine and hip kinematic parameters of posterior/anterior pelvic tilt (mobility and smoothness), ball catching (reactivity), and forward/backward rocking (adaptive stability) were measured as indicators of lumbar motor control. Lumbar proprioception, trunk muscle strength, and lower trunk muscle thickness were also measured. Kinematic parameters of the lumbar spine and hip were measured using a small accelerometer. The data verified the relevance of indicators of lumbar motor control and the relationship with relevant factors. RESULTS: No significant correlations were found for most lumbar motor control indicators. Lumbar proprioception and rectus abdominis muscle thickness were identified as relevant indicators of lumbar motor control. CONCLUSIONS: Each component of lumbar motor control is independent and must be evaluated for the component whose function is required. Additionally, some components of lumbar motor control are associated with lumbar proprioception and rectus abdominis muscle thickness; thus, evaluation of these components is necessary when evaluating lumbar motor control.

Restricting lumbar spine flexion redistributes and changes total mechanical energy expenditure during lifting.

Minimizing lumbar spine flexion during lifting requires greater lower extremity joint motion. However, the effects of these kinematic changes on lumbar and lower extremity joint kinetics are unknown. Further, it is unclear whether the distribution of biomechanical demands throughout the lumbar spine and lower extremity during lumbar spine flexion restricted lifting are modulated by task factors like lift origin height and object mass. This study examined the influence of restricting lumbar spine flexion during lifting on the distribution of biomechanical demands, operationalized as mechanical energy expenditure (MEE), across the lumbar spine and lower extremity joints during lifting tasks. Twenty participants performed a series of lifting tasks that varied by lift origin height, object mass and presence or absence of lumbar spine motion restricting harness. MEE was quantified for the lumbar spine and lower extremity joints and summed across all joints to represent the total MEE. Distributions of MEE were compared across combinations of the three task factors. Total MEE was greater when lifting with restricted spine motion (p < 0.001). MEE was redistributed away from the lumbar spine and predominantly to the hips in the spine restricted conditions (p < 0.001). The nature and magnitude of this effect was modulated by lift origin height for the lumbar spine (p < 0.001) and hips (p < 0.001). Findings demonstrated that biomechanical demands can be shifted from the lumbar spine to the lower extremity when lifting with restricted spine flexion, which might help mitigate overuse injuries through coordinative variability.

Regional structure-function relationships of lumbar cartilage endplates.

Cartilage endplates (CEPs) act as protective mechanical barriers for intervertebral discs (IVDs), yet their heterogeneous structure-function relationships are poorly understood. This study addressed this gap by characterizing and correlating the regional biphasic mechanical properties and biochemical composition of human lumbar CEPs. Samples from central, lateral, anterior, and posterior portions of the disc (n = 8/region) were mechanically tested under confined compression to quantify swelling pressure, equilibrium aggregate modulus, and hydraulic permeability. These properties were correlated with CEP porosity and glycosaminoglycan (s-GAG) content, which were obtained by biochemical assays of the same specimens. Both swelling pressure (142.79 ± 85.89 kPa) and aggregate modulus (1864.10 ± 1240.99 kPa) were found to be regionally dependent (p = 0.0001 and p = 0.0067, respectively) in the CEP and trended lowest in the central location. No significant regional dependence was observed for CEP permeability (1.35 ± 0.97 * 10-16 m4/Ns). Porosity measurements correlated significantly with swelling pressure (r = -0.40, p = 0.0227), aggregate modulus (r = -0.49, p = 0.0046), and permeability (r = 0.36, p = 0.0421), and appeared to be the primary indicator of CEP biphasic mechanical properties. Second harmonic generation microscopy also revealed regional patterns of collagen fiber anchoring, with fibers inserting the CEP perpendicularly in the central region and at off-axial directions in peripheral regions. These results suggest that CEP tissue has regionally dependent mechanical properties which are likely due to the regional variation in porosity and matrix structure. This work advances our understanding of healthy baseline endplate biomechanics and lays a groundwork for further understanding the role of CEPs in IVD degeneration.

Sagittal spinal curvatures of young adults in the context of their self-reported physical activity and somatic parameters.

The objective of this study was to assess the thoracic kyphosis (ThKA) and lumbar lordosis (LLA) in healthy young adults and to investigate potential relationships between spinal curvatures, self-reported physical activity (PA), and somatic parameters. The study included 380 female students and 211 male students aged 20.7 ± 1.5 years. The ThKA and LLA were measured using a Plurimeter-V gravity inclinometer. The level of PA was estimated using the International Physical Activity Questionnaire. ThKA was lower in women compared to men, while LLA was higher in women than in men (p < 0.0001). Female students reported lower PA than male students (p < 0.001). Female students with ThKA within normal values reported a significantly higher amount of low-intensity PA compared to those with ThKA below or above the norm. A correlation was found between ThKA and body mass index (BMI), body adiposity index (BAI), WC, and fat percentage (rho < 0.2), whereas LLA showed correlations with BMI, BAI, waist circumference, and fat percentage (rho < 0.2). Among male students, a correlation was found between LLA and BMI as well as WC (rho < 0.2). Maintaining a healthy body composition may be instrumental in mitigating the risk of developing spinal curvature abnormalities.

Biomechanical repercussion of sitting posture on lumbar intervertebral discs: A systematic review.

BACKGROUND: The static sitting position contributes to increased pressure on the lumbar intervertebral disc, which can lead to dehydration and decreased disc height. OBJECTIVE: To systematically investigate the of sitting posture on degeneration of the lumbar intervertebral disc. MATERIALS AND METHODS: One researcher carried out a systematic literature search of articles with no language or time limits. Studies from 2006 to 2018 were found. The searches in all databases were carried out on January 28, 2022, using the following databases: Pubmed, Scopus, Embase, Cochrane, and Physiotherapy Evidence Database (PEDro) databases, and for the grey literature: Google scholar, CAPES Thesis and Dissertation Bank, and Open Grey. The acronym PECOS was used to formulate the question focus of this study: P (population) - male and female subjects; E (exposure) - sitting posture; C (comparison) - other posture or sitting posture in different periods; O (outcomes) - height and degeneration of the lumbar intervertebral disc(s), imaging exam; and S (study) - cross-sectional and case control. RESULTS: The risk of bias was in its moderate totality in its outcome: height and degeneration of the lumbar intervertebral disc(s) - imaging. Of the four selected studies, three found a decrease in the height of the disc(s) in sitting posture. CONCLUSION: The individual data from the manuscripts suggest that the sitting posture causes a reduction in the height of the lumbar intervertebral disc. It was also concluded that there is a need for new primary studies with a more in-depth design and sample size.

Traditional versus dynamic sitting: Lumbar spine kinematics and pain during computer work and activity guided tasks.

Dynamic sitting may mitigate low back pain during prolonged seated work. The current study compared pelvis and lumbar spine kinematics, pain, and work productivity, in traditional and dynamic sitting. Sixteen participants completed three 20-min blocks of computer work and activity guided tasks in a traditional office chair or backless and multiaxial rotating seat pan while kinematics were measured from accelerometers on the low back. Pain ratings were recorded on a visual analogue scale every 10 min. Similar pelvis and lumbar kinematics emerged when performing computer work in traditional and dynamic sitting. Pelvis and lumbar sagittal and frontal plane shifts and fidgets were largest for dynamic sitting in the activity guided tasks. Buttocks pain was higher in dynamic sitting, but low back pain and work productivity were unaffected. Dynamic sitting increased spine movement during activity guided tasks, without negatively impacting lumbar kinematics, low back pain, or productivity during seated computer work.

Simulation of cancer progression in bone by a virtual thermal flux with a case study on lumbar vertebrae with multiple myeloma.

BACKGROUND: Two main problems examining the mechanism of cancer progression in the tissues using the computational models are lack of enough knowledge on the effective factors for such events in vivo environments and lack of specific parameters in the available computational models to simulate such complicated reactions. METHODS: In this study, it was tried to simulate the progression of cancerous lesions in the bone tissues by an independent parameter from the anatomical and physiological characteristics of the tissues, so to degrade the orthotropic mechanical properties of the bone tissues, a virtual temperature was determined to be used by a well-known framework for simulation of damages in the composite materials. First, the reliability of the FE model to simulate hyperelastic response in the intervertebral discs (IVDs) and progressive failure in the bony components were verified by simulation of some In-Vitro tests, available in the literature. Then, the progression of the osteolytic damage was simulated in a clinical case with multiple myeloma in the lumbar vertebrae. RESULTS: The FE model could simulate stress-shielding and diffusion of lesion in the posterior elements of the damaged vertebra which led to spinal stenosis. The load carrying shares associated with the anterior half and the posterior half of the examined vertebral body and the posterior elements were estimated equal to 41 %, 47 % and 12 %, respectively for the intact condition, that changed to 14 %, 16 % and 70 %, when lesion occupied one third of the vertebral body. CONCLUSION: Correlation of the FE results with the deformation shapes, observed in the MRIs for the clinical case study, indicated appropriateness of the procedure, proposed for simulation of the progressive osteolytic damage in the vertebral segments. The future studies may follow simulation of tumor growth for various metastatic tissues using the method, established here.

Gender differences in spinal mobility during postural changes: a detailed analysis using upright CT.

Lumbar spinal alignment is crucial for spine biomechanics and is linked to various spinal pathologies. However, limited research has explored gender-specific differences using CT scans. The objective was to evaluate and compare lumbar spinal alignment between standing and sitting CT in healthy individuals, focusing on gender differences. 24 young and 25 elderly males (M) and females (F) underwent standing and sitting CT scans to assess lumbar spinal alignment. Parameters measured and compared between genders included lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI), lordotic angle (LA), foraminal height (FH), and bony boundary area (BBA). Females showed significantly larger changes in SS and PT when transitioning from standing to sitting (p = .044, p = .038). A notable gender difference was also observed in the L4-S LA among the elderly, with females showing a significantly larger decrease in lordotic angle compared to males (- 14.1° vs. - 9.2°, p = .039*). Females consistently exhibited larger FH and BBA values, particularly in lower lumbar segments, which was more prominent in the elderly group (M vs. F: L4/5 BBA 80.1 mm2 [46.3, 97.8] vs. 109.7 mm2 [74.4, 121.3], p = .019 in sitting). These findings underline distinct gender-related variations in lumbar alignment and flexibility, with a focus on noteworthy changes in BBA and FH in females. Gender differences in lumbar spinal alignment were evident, with females displaying greater pelvic and sacral mobility. Considering gender-specific characteristics is crucial for assessing spinal alignment and understanding spinal pathologies. These findings contribute to our understanding of lumbar spinal alignment and have implications for gender-specific spinal conditions and treatments.

Biomechanical analysis of different back-supporting exoskeletons regarding musculoskeletal loading during lifting and holding.

Industrial back support exoskeletons (BSEs) are a promising approach to addressing low back pain (LBP) which still affect a significant proportion of the workforce. They aim to reduce lumbar loading, the main biomechanical risk factor for LBP, by providing external support to the lumbar spine. The aim of this study was to determine the supporting effect of one active (A1) and two passive (P1 and P2) BSEs during different manual material handling tasks. Kinematic data and back muscle activity were collected from 12 subjects during dynamic lifting and static holding of 10 kg. Mean and peak L5/S1 extension moments, L5/S1 compression forces and muscle activation were included in the analysis. During dynamic lifting all BSEs reduced peak (12-26 %) and mean (4-17 %) extension moments and peak (10-22 %) and mean (4-15 %) compression forces in the lumbar spine. The peak (13-28 %) and mean (4-32 %) activity of the back extensor muscles was reduced accordingly. In the static holding task, analogous mean reductions for P1 and P2 of L5/S1 extension moments (12-20 %), compression forces (13-23 %) and muscular activity (16-23 %) were found. A1 showed a greater reduction during static holding for extension moments (46 %), compression forces (41 %) and muscular activity (54 %). This pronounced difference in the performance of the BSEs between tasks was attributed to the actuators used by the different BSEs.

Evaluation of trunk muscle coactivation predictions in multi-body models.

Musculoskeletal simulations with muscle optimization aim to minimize muscle effort, hence are considered unable to predict the activation of antagonistic muscles. However, activation of antagonistic muscles might be necessary to satisfy the dynamic equilibrium. This study aims to elucidate under which conditions coactivation can be predicted, to evaluate factors modulating it, and to compare the antagonistic activations predicted by the lumbar spine model with literature data. Simple 2D and 3D models, comprising of 2 or 3 rigid bodies, with simple or multi-joint muscles, were created to study conditions under which muscle coactivity is predicted. An existing musculoskeletal model of the lumbar spine developed in AnyBody was used to investigate the effects of modeling intra-abdominal pressure (IAP), linear/cubic and load/activity-based muscle recruitment criterion on predicted coactivation during forward flexion and lateral bending. The predicted antagonist activations were compared to reported EMG data. Muscle coactivity was predicted with simplified models when multi-joint muscles were present or the model was three-dimensional. During forward flexion and lateral bending, the coactivation ratio predicted by the model showed good agreement with experimental values. Predicted coactivation was negligibly influenced by IAP but substantially reduced with a force-based recruitment criterion. The conditions needed in multi-body models to predict coactivity are: three-dimensionality or multi-joint muscles, unless perfect antagonists. The antagonist activations are required to balance 3D moments but do not reflect other physiological phenomena, which might explain the discrepancies between model predictions and experimental data. Nevertheless, the findings confirm the ability of the multi-body trunk models to predict muscle coactivity and suggest their overall validity.

Exploring the Influence of Facet Orientation and Tropism on Neutral Zone Properties.

Lumbar spine pathologies have been linked independently to both neutral zone (NZ) properties and facet joint anatomical characteristics; however, the effect of facet joint orientation (FO) and tropism (FT) on NZ properties remains unclear. The aim of the present study was to investigate how axial plane FO and FT relate to NZ range and stiffness in the human lumbar spine and porcine cervical spine. Seven human lumbar functional spine units (FSUs) and 94 porcine cervical FSUs were examined. FO and FT were measured, and in vitro mechanical testing was used to determine anterior-posterior (AP) and flexion-extension (FE) NZ range and stiffness. FO and FT were found to have no significant relationship with AP and FE NZ range. Increases in FT were associated with greater FE and AP NZ stiffness in human FSUs, with no FT-NZ stiffness relationship observed in porcine specimens. A significant relationship (p < 0.001) between FO and FE NZ stiffness was observed for both porcine and human FSUs, with a more sagittal orientation of the facet joints being associated with decreased FE NZ stiffness. Given the link between NZ stiffness and pathological states of the lumbar spine, further research is warranted to determine the practical significance of the observed facet joint anatomical characteristic-NZ property relationship.

The relationship between bone strain index, bone mass, microarchitecture and mechanical behavior in human vertebrae: an ex vivo study.

The aim of this study was to determine whether the Bone Strain Index (BSI), a recent DXA-based bone index, is related to bone mechanical behavior, microarchitecture and finally, to determine whether BSI improves the prediction of bone strength and the predictive role of BMD in clinical practice. PURPOSE: Bone Strain Index (BSI) is a new DXA-based bone index that represents the finite element analysis of the bone deformation under load. The current study aimed to assess whether the BSI is associated with 3D microarchitecture and the mechanical behavior of human lumbar vertebrae. METHODS: Lumbar vertebrae (L3) were harvested fresh from 31 human donors. The anteroposterior BMC (g) and aBMD (g/cm2) of the vertebral body were measured using DXA, and then the BSI was automatically derived. The trabecular bone volume (Tb.BV/TV), trabecular thickness (Tb.Th), degree of anisotropy (DA), and structure model index (SMI) were measured using µCT with a 35-µm isotropic voxel size. Quasi-static uniaxial compressive testing was performed on L3 vertebral bodies under displacement control to assess failure load and stiffness. RESULTS: The BSI was significantly correlated with failure load and stiffness (r = -0.60 and -0.59; p < 0.0001), aBMD and BMC (r = -0.93 and -0.86; p < 0.0001); Tb.BV/TV and SMI (r = -0.58 and 0.51; p = 0.001 and 0.004 respectively). After adjustment for aBMD, the association between BSI and stiffness, BSI and SMI remained significant (r = -0.51; p = 0.004 and r = -0.39; p = 0.03 respectively, partial correlations) and the relation between BSI and failure load was close to significance (r = -0.35; p = 0.06). CONCLUSION: The BSI was significantly correlated with the microarchitecture and mechanical behavior of L3 vertebrae, and these associations remained statistically significant regardless of aBMD.

Overloading effect on the osmo-viscoelastic and recovery behavior of the intervertebral disc.

In vitro studies investigating the effect of high physiological compressive loads on the intervertebral disc mechanics as well as on its recovery are rare. Moreover, the osmolarity effect on the disc viscoelastic behavior following an overloading is far from being studied. This study aims to determine whether a compressive loading-unloading cycle exceeding physiological limits could be detrimental to the cervical disc, and to examine the chemo-mechanical dependence of this overloading effect. Cervical functional spine units were subjected to a compressive loading-unloading cycle at a high physiological level (displacement of 2.5 mm). The overloading effect on the disc viscoelastic behavior was evaluated through two relaxation tests conducted before and after cyclic loading. Afterward, the disc was unloaded in a saline bath during a rest period, and its recovery response was assessed by a third relaxation test. The chemo-mechanical coupling in the disc response was further examined by repeating this protocol with three different saline concentrations in the external fluid bath. It was found that overloading significantly alters the disc viscoelastic response, with changes statistically dependent on osmolarity conditions. The applied hyper-physiological compressive cycle does not cause damage since the disc recovers its original viscoelastic behavior following a rest period. Osmotic loading only influences the loading-unloading response; specifically, increasing fluid osmolarity leads to a decrease in disc relaxation after the applied cycle. However, the disc recovery is not impacted by the osmolarity of the external fluid.

Tactile localization accuracy at the low back.

Localizing tactile stimulation is an important capability for everyday function and may be impaired in people with persistent pain. This study sought to provide a detailed description of lumbar spine tactile localization accuracy in healthy individuals. Sixty-nine healthy participants estimated where they were touched at nine different points, labelled in a 3 × 3 grid over the lumbar spine. Mislocalization between the perceived and actual stimulus was calculated in horizontal (x) and vertical (y) directions, and a derived hypotenuse (c) mislocalization was calculated to represent the direct distance between perceived and actual points. In the horizontal direction, midline sites had the smallest mislocalization. Participants exhibited greater mislocalization for left- and right-sided sites, perceiving sites more laterally than they actually were. For all vertical values, stimulated sites were perceived lower than reality. A greater inaccuracy was observed in the vertical direction. This study measured tactile localization for the low back utilizing a novel testing method. The large inaccuracies point to a possible distortion in the underlying perceptual maps informing the superficial schema; however, further testing comparing this novel method with an established tactile localization task, such as the point-to-point method, is suggested to confirm these findings.

Effects of open and minimally invasive Transforaminal Lumbar Interbody Fusion (TLIF) surgical techniques on mechanical behaviour of fused L3-L4 FSU: A comparative finite element study.

For predicting the biomechanical effects of the fusion procedure, finite element (FE) analysis is widely used as a preclinical tool. Although several FE studies examined the efficacies of various fusion surgical techniques, comparative studies on Open and minimally invasive (MIS) transforaminal lumbar interbody fusion (TLIF) procedures incorporating a follower coordinate system have not been investigated yet. The current FE study evaluates the ranges of motion (ROM) and load distributions of Open-TLIF and MIS-TLIF implanted models, under physiological loading such as compression, flexion, extension and lateral bending. The most noteworthy finding from the investigation is that both the fusion procedures significantly reduced the ROMs of the implanted segment (L3-L4) and full model (L1-L5) by at least 89 % and 44 %, respectively, compared to the intact model. For all loading situations, over 95 % of the implanted models' cancellous bone volume was subjected to von Mises strains ranging from 0.0003 to 0.005. The maximum von Mises strain was observed to be localized on a small amount of cancellous bone volume (<5 %). The likelihood of adjacent segment degeneration is higher in the case of MIS-TLIF due to the higher stress (22-53 MPa) and strain (0.018-0.087) noticed on the upper facet of the L3 vertebra.

Effect of low back pain on the kinetics and kinematics of the lumbar spine - a combined in vivo and in silico investigation.

Lifting is a significant risk factor for low back pain (LBP). Different biomechanical factors including spinal loads, kinematics, and muscle electromyography (EMG) activities have previously been investigated during lifting activities in LBP patients and asymptomatic individuals to identify their association with LBP. However, the findings were contradictory and inconclusive. Accurate and subject-specific prediction of spinal loads is crucial for understanding, diagnosing, planning tailored treatments, and preventing recurrent pain in LBP patients. Therefore, the present study aimed to estimate the L5-S1 compressive and resultant shear loads in 19 healthy and 17 non-specific chronic LBP individuals during various static load-holding tasks (holding a 10 kg box at hip, chest, and head height) using full-body and personalized musculoskeletal models driven by subject-specific in vivo kinematic/kinetic, EMG, and physiological cross-sectional areas (PCSAs) data. These biomechanical characteristics were concurrently analyzed to identify potential differences between the two groups. Statistical analyses showed that LBP had almost no significant effect on the range of motion (trunk, lumbar, pelvis), PCSA, and EMG. There were no significant differences (p > 0.05) in the predicted L5-S1 loads. However, as the task became more demanding, by elevating the hand-load from hip to head, LBP patients experienced significant increases in both compressive (33 %, p = 0.00) and shear (25 %, p = 0.02) loads, while asymptomatic individuals showed significant increases only in compressive loads (30 %, p = 0.01). This suggests that engaging in more challenging activities could potentially magnify the effect of LBP on the biomechanical factors and increase their discrimination capacity between LBP and asymptomatic individuals.

Geometric determinants of the mechanical behavior of image-based finite element models of the intervertebral disc.

The intervertebral disc is an important structure for load transfer through the spine. Its injury and degeneration have been linked to pain and spinal fractures. Disc injury and spine fractures are associated with high stresses; however, these stresses cannot be measured, necessitating the use of finite element (FE) models. These models should include the disc's complex structure, as changes in disc geometry have been linked to altered mechanical behavior. However, image-based models using disc-specific structures have yet to be established. This study describes a multiphasic FE modeling approach for noninvasive estimates of subject-specific intervertebral disc mechanical behavior based on medical imaging. The models (n = 22) were used to study the influence of disc geometry on the predicted global mechanical response (moments and forces), internal local disc stresses, and tractions at the interface between the disc and the bone. Disc geometry was found to have a strong influence on the predicted moments and forces on the disc (R2 = 0.69-0.93), while assumptions regarding the side curvature (bulge) of the disc had only a minor effect. Strong variability in the predicted internal disc stresses and tractions was observed between the models (mean absolute differences of 5.1%-27.7%). Disc height had a systematic influence on the internal disc stresses and tractions at the disc-to-bone interface. The influence of disc geometry on mechanics highlights the importance of disc-specific modeling to estimate disc injury risk, loading on the adjacent vertebral bodies, and the mechanical environment present in disc tissues.

Replicating spine loading during functional and daily activities: An in vivo, in silico, in vitro research pipeline.

Lifestyle heavily influences intervertebral disc (IVD) loads, but measuring in vivo loads requires invasive methods, and the ability to apply these loads in vitro is limited. In vivo load data from instrumented vertebral body replacements is limited to patients that have had spinal fusion surgery, potentially resulting in different kinematics and loading patterns compared to a healthy population. Therefore, this study aimed to develop a pipeline for the non-invasive estimation of in vivo IVD loading, and the application of these loads in vitro. A full-body Opensim model was developed by adapting and combining two existing models. Kinetic data from healthy participants performing activities of daily living were used as inputs for simulations using static optimisation. After evaluating simulation results using in vivo data, the estimated six-axis physiological loads were applied to bovine tail specimens. The pipeline was then used to compare the kinematics resulting from the physiological load profiles (flexion, lateral bending, axial rotation) with a simplified pure moment protocol commonly used for in vitro studies. Comparing kinematics revealed that the in vitro physiological load protocol followed the same trends as the in silico and in vivo data. Furthermore, the physiological loads resulted in substantially different kinematics when compared to pure moment testing, particularly in flexion. Therefore, the use of the presented pipeline to estimate the complex loads of daily activities in different populations, and the application of those loads in vitro provides a novel capability to deepen our knowledge of spine biomechanics, IVD mechanobiology, and improve pre-clinical test methods.

Prediction of trunk muscle activation and spinal forces in adolescent idiopathic scoliosis during simulated trunk motion: A musculoskeletal modelling study.

Due to lack of reference validation data, the common strategy in characterizing adolescent idiopathic scoliosis (AIS) by musculoskeletal modelling approach consists in adapting structure and parameters of validated body models of adult individuals with physiological alignments. Until now, only static postures have been replicated and investigated in AIS subjects. When aiming to simulate trunk motion, two critical factors need consideration: how distributing movement along the vertebral motion levels (lumbar spine rhythm), and if neglecting or accounting for the contribution of the stiffness of the motion segments (disc stiffness). The present study investigates the effect of three different lumbar spine rhythms and absence/presence of disc stiffness on trunk muscle imbalance in the lumbar region and on intervertebral lateral shear at different levels of the thoracolumbar/lumbar scoliotic curve, during simulated trunk motions in the three anatomical planes (flexion/extension, lateral bending, and axial rotation). A spine model with articulated ribcage previously developed in AnyBody software and adapted to replicate the spinal alignment in AIS subjects is employed. An existing dataset of 100 subjects with mild and moderate scoliosis is exploited. The results pointed out the significant impact of lumbar spine rhythm configuration and disc stiffness on changes in the evaluated outputs, as well as a relationship with scoliosis severity. Unfortunately, no optimal settings can be identified due to lack of reference validation data. According to that, extreme caution is recommended when aiming to adapt models of adult individuals with physiological alignments to adolescent subjects with scoliotic deformity.

Effect of muscular fatigue on the cumulative lumbar damage during repetitive lifting task: a comparative study of damage calculation methods.

Several methods have been put forward to quantify cumulative loads; however, limited evidence exists as to the subsequent damages and the role of muscular fatigue. The present study assessed whether muscular fatigue could affect cumulative damage imposed on the L5-S1 joint. Trunk muscle electromyographic (EMG) activities and kinematics/kinetics of 18 healthy male individuals were evaluated during a simulated repetitive lifting task. A traditional EMG-assisted model of the lumbar spine was modified to account for the effect of erector spinae fatigue. L5-S1 compressive loads for each lifting cycle were estimated based on varying (i.e. actual), fatigue-modified, and constant Gain factors. The corresponding damages were integrated to calculate the cumulative damage. Moreover, the damage calculated for one lifting cycle was multiplied by the lifting frequency, as the traditional approach. Compressive loads and the damages obtained through the fatigue-modified model were predicted in close agreement with the actual values. Similarly, the difference between actual damages and those driven by the traditional approach was not statistically significant (p = 0.219). However, damages based on a constant Gain factor were significantly greater than those based on the actual (p = 0.012), fatigue-modified (p = 0.017), and traditional (p = 0.007) approaches.Practitioner summary: In this study, we managed to include the effect of muscular fatigue on cumulative lumbar damage calculations. Including the effect of muscular fatigue leads to an accurate estimation of cumulative damages while eliminating computational complexity. However, using the traditional approach also appears to provide acceptable estimates for ergonomic assessments.