Regressions for estimating muscle parameters in the thoracic and lumbar trunk for use in musculoskeletal modeling

Comparing spinal loads in individuals with unilateral transtibial amputation with and without chronic low back pain: An EMG-informed approach

Chronic low back pain (cLBP) is highly prevalent after lower limb amputation (LLA), likely due in part to biomechanical factors. Here, three-dimensional full-body kinematics and kinetics during level-ground walking, at a self-selected and three controlled speeds (1.0, 1.3, and 1.6 m/s), were collected from twenty-one persons with unilateral transtibial LLA, with (n = 9) and without cLBP (n = 12). Peak compressive, mediolateral, and anteroposterior L5-S1 spinal loads were estimated from a full-body, transtibial amputation-specific OpenSim model and compared between groups. Predicted lumbar joint torques from muscle activations were compared to inverse dynamics and predicted and measured electromyographic muscle activations were compared for model evaluation and verification. There were no group differences in compressive or anterior shear forces (p > 0.466). During intact stance, peak ipsilateral loads increased with speed to a greater extent in the cLBP group vs. no cLBP group (p=0.023), while during prosthetic stance, peak contralateral loads were larger in the no cLBP group (p=0.047) and increased to a greater extent with walking speed compared to the cLBP group (p=0.008). During intact stance, intact side external obliques had higher activations in the no cLBP group (p=0.039), and internal obliques had higher activations in the cLBP group at faster walking speeds compared to the no cLBP group. Predicted muscle activations demonstrated similar activation patterns to electromyographic-measured activations (r = 0.56-0.96), and error between inverse dynamics and simulated spinal moments was low (0.08 Nm RMS error). Persons with transtibial LLA and cLBP may adopt movement strategies during walking to reduce mediolateral shear forces at the L5-S1 joint, particularly as walking speed increases. However, future work is needed to understand the time course from pain onset to chronification and the cumulative influence of increased spinal loads over time.

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.

Assessment of a fully-parametric thoraco-lumbar spine model generator with articulated ribcage

The present paper describes a novel user-friendly fully-parametric thoraco-lumbar spine CAD model generator including the ribcage, based on 22 independent parameters (1 posterior vertebral body height per vertebra + 4 sagittal alignment parameters, namely pelvic incidence, sacral slope, L1-L5 lumbar lordosis, and T1-T12 thoracic kyphosis). Reliable third-order polynomial regression equations were implemented in Solidworks to analytically calculate 56 morphological dependent parameters and to automatically generate the spine CAD model based on primitive geometrical features. A standard spine CAD model, representing the case-study of an average healthy adult, was then created and positively assessed in terms of spinal anatomy, ribcage morphology, and sagittal profile. The immediate translation from CAD to FEM for relevant biomechanical analyses was successfully demonstrated, first, importing the CAD model into Abaqus, and then, iteratively calibrating the constitutive parameters of one lumbar and three thoracic FSUs, with particular interest on the hyperelastic material properties of the IVD, and the spinal and costo-vertebral ligaments. The credibility of the resulting lumbo-sacral and thoracic spine FEM with/without ribcage were assessed and validated throughout comparison with extensive in vitro and in vivo data both in terms of kinematics (range of motion) and dynamics (intradiscal pressure) either collected under pure bending moments and complex loading conditions (bending moments + axial compressive force).

Using inertial measurement units to estimate spine joint kinematics and kinetics during walking and running

Optical motion capture (OMC) is considered the best available method for measuring spine kinematics, yet inertial measurement units (IMU) have the potential to collect data outside the laboratory. When combined with musculoskeletal modeling, IMU technology may be used to estimate spinal loads in real-world settings. To date, IMUs have not been validated for estimates of spinal movement and loading during both walking and running. Using OpenSim Thoracolumbar Spine and Ribcage models, we compare IMU and OMC estimates of lumbosacral (L5/S1) and thoracolumbar (T12/L1) joint angles, moments, and reaction forces during gait across six speeds for five participants. For comparisons, time series are ensemble averaged over strides. Comparisons between IMU and OMC ensemble averages have low normalized root mean squared errors (< 0.3 for 81% of comparisons) and high, positive cross-correlations (> 0.5 for 91% of comparisons), suggesting signals are similar in magnitude and trend. As expected, joint moments and reaction forces are higher during running than walking for IMU and OMC. Relative to OMC, IMU overestimates joint moments and underestimates joint reaction forces by 20.9% and 15.7%, respectively. The results suggest using a combination of IMU technology and musculoskeletal modeling is a valid means for estimating spinal movement and loading.

Predicted vs. measured paraspinal muscle activity in adolescent idiopathic scoliosis patients: EMG validation of optimization-based musculoskeletal simulations

Musculoskeletal (MSK) models offer great potential for predicting the muscle forces required to inform more detailed simulations of vertebral endplate loading in adolescent idiopathic scoliosis (AIS). In this work, simulations based on static optimization were compared with in vivo measurements in two AIS patients to determine whether computational approaches alone are sufficient for accurate prediction of paraspinal muscle activity during functional activities. We used biplanar radiographs and marker-based motion capture, ground reaction force, and electromyography (EMG) data from two patients with mild and moderate thoracolumbar AIS (Cobb angles: 21° and 45°, respectively) during standing while holding two weights in front (reference position), walking, running, and object lifting. Using a fully automated approach, 3D spinal shape was extracted from the radiographs. Geometrically personalized OpenSim-based MSK models were created by deforming the spine of pre-scaled full-body models of children/adolescents. Simulations were performed using an experimentally controlled backward approach. Differences between model predictions and EMG measurements of paraspinal muscle activity (both expressed as a percentage of the reference position values) at three different locations around the scoliotic main curve were quantified by root mean square error (RMSE) and cross-correlation (XCorr). Predicted and measured muscle activity correlated best for mild AIS during object lifting (XCorr's ≥ 0.97), with relatively low RMSE values. For moderate AIS as well as the walking and running activities, agreement was lower, with XCorr reaching values of 0.51 and comparably high RMSE values. This study demonstrates that static optimization alone seems not appropriate for predicting muscle activity in AIS patients, particularly in those with more than mild deformations as well as when performing upright activities such as walking and running.

Dependence of trunk muscle size and position on age, height, and weight in a multi-ethnic cohort of middle-aged and older men and women

Trunk muscle size and location relative to the spine are key factors affecting their capacity to assist in trunk movement, strength, and function. There remains limited information on how age, weight and height affect these measurements across multiple spinal levels, and prior studies had limited samples in terms of size and ethnicity. In this study, we measured trunk muscles in coronal plane slices at T4 - L4 of CT scans acquired in 507 participants, aged 40-90 years, from the community-based Framingham Heart Study. Mixed-effects linear regressions, stratified by sex, determined the contributions of age, height and weight, to muscle cross-sectional area (CSA), the distance from the vertebral body centroid (CD), and the in-plane angle of the line between the vertebral body and the muscle centroids (CA). Muscle CSA decreased with higher age by an average of -0.8% per year, but weight (average 0.8% per kg) and height (average -0.05% per cm) had mixed results, with both positive and negative effects depending on muscle group and level. Muscle CD increased with weight by an average of 0.3% per kg, but had mixed effects for age (average 0.8% per year) and height (average 0.1% per cm). Muscle CA had mixed associations with age (average 0.05% per year), weight (average 0.01% per kg) and height (average -0.05% per cm). A prediction program created with these results provides a simple approach for estimating probable values for trunk muscle size and position in the absence of medical imaging.

Using static postures to estimate spinal loading during dynamic lifts with participant-specific thoracolumbar musculoskeletal models

Static biomechanical simulations are sometimes used to estimate in vivo kinetic demands because they can be solved efficiently, but this ignores any potential inertial effects. To date, comparisons between static and dynamic analyses of spinal demands have been limited to lumbar joint differences in young males performing sagittal lifts. Here we compare static and dynamic vertebral compressive and shear force estimates during axial, lateral, and sagittal lifting tasks across all thoracic and lumbar vertebrae in older men and women. Participant-specific thoracolumbar full-body musculoskeletal models estimated vertebral forces from recorded kinematics both with and without consideration of dynamic effects, at an identified frame of peak vertebral loading. Static analyses under-predicted dynamic compressive and resultant shear forces, by an average of about 16% for all three lifts across the thoracic and lumbar spine but were highly correlated with dynamic forces (average r² > .95). The study outcomes have the potential to enable standard clinical and occupational estimates using static analyses.

A computational method for estimating trunk muscle activations during gait using lower extremity muscle synergies

One of the surgical treatments for pelvic sarcoma is the restoration of hip function with a custom pelvic prosthesis after cancerous tumor removal. The orthopedic oncologist and orthopedic implant company must make numerous often subjective decisions regarding the design of the pelvic surgery and custom pelvic prosthesis. Using personalized musculoskeletal computer models to predict post-surgery walking function and custom pelvic prosthesis loading is an emerging method for making surgical and custom prosthesis design decisions in a more objective manner. Such predictions would necessitate the estimation of forces generated by muscles spanning the lower trunk and all joints of the lower extremities. However, estimating trunk and leg muscle forces simultaneously during walking based on electromyography (EMG) data remains challenging due to the limited number of EMG channels typically used for measurement of leg muscle activity. This study developed a computational method for estimating unmeasured trunk muscle activations during walking using lower extremity muscle synergies. To facilitate the calibration of an EMG-driven model and the estimation of leg muscle activations, EMG data were collected from each leg. Using non-negative matrix factorization, muscle synergies were extracted from activations of leg muscles. On the basis of previous studies, it was hypothesized that the time-varying synergy activations were shared between the trunk and leg muscles. The synergy weights required to reconstruct the trunk muscle activations were determined through optimization. The accuracy of the synergy-based method was dependent on the number of synergies and optimization formulation. With seven synergies and an increased level of activation minimization, the estimated activations of the erector spinae were strongly correlated with their measured activity. This study created a custom full-body model by combining two existing musculoskeletal models. The model was further modified and heavily personalized to represent various aspects of the pelvic sarcoma patient, all of which contributed to the estimation of trunk muscle activations. This proposed method can facilitate the prediction of post-surgery walking function and pelvic prosthesis loading, as well as provide objective evaluations for surgical and prosthesis design decisions.

Morphometry of lumbar muscles in the seated posture with weight-bearing MR scans

Conventional imaging studies of human spine are done in a supine posture in which the axial loading of the spine is not considered. Upright images better reveal the interrelationships between the various internal structures of the spine. The objective of the current study is to determine the cross-sectional areas, radii, and angulations of the psoas, erector spinae, and multifidus muscles of the lumbar spine in the sitting posture. Ten young (mean age 31 ± 4.8 years) asymptomatic female subjects were enrolled. They were seated in an erect posture and weight-bearing T1 and T2 MRIs were obtained. Cross-sectional areas, radii, and angulations of the muscles were measured from L1-L5. Two observers repeated all the measurements for all parameters, and reliability was determined using the inter- and intra-class coefficients. The Pearson product moment correlation was used for association between levels, while level differences were used using a linear regression model. The cross-sectional areas of the psoas and multifidus muscles increased from L1 to L5 (1.9 ± 1.1 to 12.1 ± 2.5 cm2 and 1.8 ± 0.3 to 5.7 ± 1.4 cm2). The cross-sectional area of the erector spinae was greatest at the midlevel (13.9 ± 2.2 cm2) and it decreased in both directions. For the angle, the range for psoas muscles was 75-105°, erector spinae were 39-46° and multifidus was 11-19°. Correlations magnitudes were inconsistent between levels and muscle types. These quantitated data improve our understanding of the geometrical properties in the sitting posture. The weight-bearing MRI-quantified morphometrics of human lumbar spine muscles from this study can be used in biomechanical models for predicting loads on spinal joints under physiological and traumatic situations.

Evaluation of Load-To-Strength Ratios in Metastatic Vertebrae and Comparison With Age- and Sex-Matched Healthy Individuals

Vertebrae containing osteolytic and osteosclerotic bone metastases undergo pathologic vertebral fracture (PVF) when the lesioned vertebrae fail to carry daily loads. We hypothesize that task-specific spinal loading patterns amplify the risk of PVF, with a higher degree of risk in osteolytic than in osteosclerotic vertebrae. To test this hypothesis, we obtained clinical CT images of 11 cadaveric spines with bone metastases, estimated the individual vertebral strength from the CT data, and created spine-specific musculoskeletal models from the CT data. We established a musculoskeletal model for each spine to compute vertebral loading for natural standing, natural standing + weights, forward flexion + weights, and lateral bending + weights and derived the individual vertebral load-to-strength ratio (LSR). For each activity, we compared the metastatic spines' predicted LSRs with the normative LSRs generated from a population-based sample of 250 men and women of comparable ages. Bone metastases classification significantly affected the CT-estimated vertebral strength (Kruskal-Wallis, p < 0.0001). Post-test analysis showed that the estimated vertebral strength of osteosclerotic and mixed metastases vertebrae was significantly higher than that of osteolytic vertebrae (p = 0.0016 and p = 0.0003) or vertebrae without radiographic evidence of bone metastasis (p = 0.0010 and p = 0.0003). Compared with the median (50%) LSRs of the normative dataset, osteolytic vertebrae had higher median (50%) LSRs under natural standing (p = 0.0375), natural standing + weights (p = 0.0118), and lateral bending + weights (p = 0.0111). Surprisingly, vertebrae showing minimal radiographic evidence of bone metastasis presented significantly higher median (50%) LSRs under natural standing (p < 0.0001) and lateral bending + weights (p = 0.0009) than the normative dataset. Osteosclerotic vertebrae had lower median (50%) LSRs under natural standing (p < 0.0001), natural standing + weights (p = 0.0005), forward flexion + weights (p < 0.0001), and lateral bending + weights (p = 0.0002), a trend shared by vertebrae with mixed lesions. This study is the first to apply musculoskeletal modeling to estimate individual vertebral loading in pathologic spines and highlights the role of task-specific loading in augmenting PVF risk associated with specific bone metastatic types. Our finding of high LSRs in vertebrae without radiologically observed bone metastasis highlights that patients with metastatic spine disease could be at an increased risk of vertebral fractures even at levels where lesions have not been identified radiologically.

Evaluating stability of human spine in static tasks: a combined in vivo-computational study

Various interpretations and parameters have been proposed to assess spinal stability such as antagonist muscle coactivity, trunk stiffness and spinal buckling load; however, the correlation between these parameters remains unknown. We evaluated spinal stability during different tasks while changing the external moment and load height and investigated likely relationships between different EMG- and model-based parameters (e.g., EMG coactivity ratio, trunk stiffness, force coactivity ratio) and stability margins. EMG and kinematics of 40 young healthy subjects were recorded during various quasi-static tasks. Muscle forces, trunk stiffness and stability margins were calculated by a nonlinear subject-specific EMG-assisted-optimization musculoskeletal model of the trunk. The load elevation and external moment increased muscle activities and trunk stiffness while all stability margins (i.e., buckling loads) decreased. The force coactivity ratio was strongly correlated with the hand-load stability margin (i.e., additional weight in hands to initiate instability; R² = 0.54) demonstrating the stabilizing role of abdominal muscles. The total trunk stiffness (Pearson's r = 0.96) and the sum of EMGs of back muscles (Pearson's r = 0.65) contributed the most to the T1 stability margin (i.e., additional required load at T1 for instability/buckling). Force coactivity ratio and trunk stiffness can be used as alternative spinal stability metrics.

Sex-Dependent Estimation of Spinal Loads During Static Manual Material Handling Activities-Combined in vivo and in silico Analyses

Manual material handling (MMH) is considered as one of the main contributors to low back pain. While males traditionally perform MMH tasks, recently the number of females who undertake these physically-demanding activities is also increasing. To evaluate the risk of mechanical injuries, the majority of previous studies have estimated spinal forces using different modeling approaches that mostly focus on male individuals. Notable sex-dependent differences have, however, been reported in torso muscle strength and anatomy, segmental mass distribution, as well as lifting strategy during MMH. Therefore, this study aimed to use sex-specific models to estimate lumbar spinal and muscle forces during static MHH tasks in 10 healthy males and 10 females. Motion-capture, surface electromyographic from select trunk muscles, and ground reaction force data were simultaneously collected while subjects performed twelve symmetric and asymmetric static lifting (10 kg) tasks. AnyBody Modeling System was used to develop base-models (subject-specific segmental length, muscle architecture, and kinematics data) for both sexes. For females, female-specific models were also developed by taking into account for the female’s muscle physiological cross-sectional areas, segmental mass distributions, and body fat percentage. Males showed higher absolute L5-S1 compressive and shear loads as compared to both female base-models (25.3% compressive and 14% shear) and female-specific models (41% compressive and 23.6% shear). When the predicted spine loads were normalized to subjects’ body weight, however, female base-models showed larger loads (9% compressive and 16.2% shear on average), and female-specific models showed 2.4% smaller and 9.4% larger loads than males. Females showed larger forces in oblique abdominal muscles during both symmetric and asymmetric lifting tasks, while males had larger back extensor muscle forces during symmetric lifting tasks. A stronger correlation between measured and predicted muscle activities was found in females than males. Results indicate that female-specific characteristics affect the predicted spinal loads and must be considered in musculoskeletal models. Neglecting sex-specific parameters in these models could lead to the overestimation of spinal loads in females.

Subject-Specific Alignment and Mass Distribution in Musculoskeletal Models of the Lumbar Spine

Musculoskeletal modeling is a well-established method in spine biomechanics and generally employed for investigations concerning both the healthy and the pathological spine. It commonly involves inverse kinematics and optimization of muscle activity and provides detailed insight into joint loading. The aim of the present work was to develop and validate a procedure for the automatized generation of semi-subject-specific multi-rigid body models with an articulated lumbar spine. Individualization of the models was achieved with a novel approach incorporating information from annotated EOS images. The size and alignment of bony structures, as well as specific body weight distribution along the spine segments, were accurately reproduced in the 3D models. To ensure the pipeline’s robustness, models based on 145 EOS images of subjects with various weight distributions and spinopelvic parameters were generated. For validation, we performed kinematics-dependent and segment-dependent comparisons of the average joint loads obtained for our cohort with the outcome of various published in vivo and in situ studies. Overall, our results agreed well with literature data. The here described method is a promising tool for studying a variety of clinical questions, ranging from the evaluation of the effects of alignment variation on joint loading to the assessment of possible pathomechanisms involved in adjacent segment disease.

Estimation and assessment of sagittal spinal curvature and thoracic muscle morphometry in different postures

Spine models are typically developed from supine clinical imaging data, and hence clearly do not fully reflect postures that replicate subjects' clinical symptoms. Our objectives were to develop a method to: (i) estimate the subject-specific sagittal curvature of the whole spine in different postures from limited imaging data, (ii) obtain muscle lines-of-action in different postures and analyze the effect of posture on muscle fascicle length, and (iii) correct for cosine between the magnetic resonance imaging (MRI) scan plane and dominant fiber line-of-action for muscle parameters (cross-sectional area (CSA) and position). The thoracic spines of six healthy volunteers were scanned in four postures (supine, standing, flexion, and sitting) in an upright MRI. Geometry of the sagittal spine was approximated with a circular spline. A pipeline was developed to estimate spine geometry in different postures and was validated. The lines-of-action for two muscles, erector spinae (ES) and transversospinalis (TS) were obtained for every posture and hence muscle fascicle lengths were computed. A correction factor based on published literature was then computed and applied to the muscle parameters. The maximum registration error between the estimated spine geometry and MRI data was small (average RMSE∼1.2%). The muscle fascicle length increased (up to 20%) in flexion when compared to erect postures. The correction factor reduced muscle parameters (∼5% for ES and ∼25% for TS) when compared to raw MRI data. The proposed pipeline is a preliminary step in subject-specific modeling. Direction cosines of muscles could be used while improving the inputs of spine models.

Preliminary investigation of spinal level and postural effects on thoracic muscle morphology with upright open MRI

OBJECTIVE

Spinal-muscle morphological differences between weight-bearing and supine postures have potential diagnostic, prognostic, and therapeutic applications. While the focus to date has been on cervical and lumbar regions, recent findings have associated spinal deformity with smaller paraspinal musculature in the thoracic region. We aim to quantitatively investigate the morphology of trapezius (TZ), erector spinae (ES) and transversospinalis (TS) muscles in upright postures with open upright MRI and also determine the effect of level and posture on the morphological measures.

METHODS

Six healthy volunteers (age 26 ± 6 years) were imaged (0.5 T MROpen, Paramed, Genoa, Italy) in four postures (supine, standing, standing with 30° flexion, and sitting). Two regions of the thorax, middle (T4-T5), and lower (T8-T9), were scanned separately for each posture. 2D muscle parameters such as cross-sectional area (CSA) and position (radius and angle) with respect to the vertebral body centroid were measured for the three muscles. Effect of spinal level and posture on muscle parameters was examined using 2-way repeated measures ANOVA separately for T4-T5 and T8-T9 regions.

RESULTS

The TZ CSA was smaller (40%, P = .0027) at T9 than at T8. The ES CSA was larger at T5 than at T4 (12%, P = .0048) and at T9 than at T8 (10%, P = .0018). TS CSA showed opposite trends at the two spinal regions with it being smaller (16%, P = .0047) at T5 than at T4 and larger (11%, P = .0009) at T9 than at T8. At T4-T5, the TZ CSA increased (up to 23%), and the ES and TS CSA decreased (up to 10%) in upright postures compared to supine.

CONCLUSION

Geometrical parameters that describe muscle morphology in the thorax change with level and posture. The increase in TZ CSA in upright postures could result from greater activation while upright. The decrease in ES CSA in flexed positions likely represents passive stretching compared to neutral posture.

Age-related degeneration of the lumbar paravertebral muscles: Systematic review and three-level meta-regression

BACKGROUND

Morphological changes of the lumbar spine muscles are not well characterised with ageing. To further the understanding of age-related degeneration of the lumbar spine musculature, normative morphological changes that occur within the paravertebral muscles must first be established.

METHODS

A systematic review and meta-regressions were conducted adhering to PRISMA guidelines. Searches for published and unpublished data were completed in June 2019.

RESULTS

Searches returned 4781 articles. 34 articles were included in the quantitative analysis. Three-level meta-analyses showed age-related atrophy (r = -0.26; 95% CI: -0.33, -0.17) and fat infiltration (r = 0.39; 95% CI: 0.28, 0.50) in the lumbar paravertebral muscles. Degenerative changes were muscle-specific and men (r = -0.32; 95% CI: -0.61, 0.01) exhibited significantly greater muscle atrophy than women (r = -0.24; 95% CI: -0.47, 0.03). Imaging modality, specifically ultrasound, also influenced age-related muscle atrophy. Measurements taken across all lumbar levels revealed the greatest fat infiltration with ageing (r = 0.58, 95% CI: 0.35, 0.74). Moderators explained a large proportion of between-study variance in true effects for muscle atrophy (72.6%) and fat infiltration (79.8%) models.

CONCLUSIONS

Lumbar paravertebral muscles undergo age-related degeneration in healthy adults with muscle, lumbar level and sex-specific responses. Future studies should use high-resolution imaging modalities to quantify muscle atrophy and fat infiltration.

Regression models for the erector spinae muscle (ESM) cross-sectional area (CSA): Asymptomatic populations

Understanding low back morphology is critical to understanding spinal loading and the underlying injury mechanisms, which helps to characterize risk and, therefore, minimize low back pain injuries. Individualized erector spinae muscle (ESM) cross-sectional area (CSA) allows biomechanics practitioners to calculate individualized force-generating capacities and spinal loadings for given tasks. The objective is to perform morphological analyses and then provide regression models to estimate the ESM CSA of an individual with his/her subject characteristics. Thirty-five subjects (13 females and 22 males) without LBP history were included in this MRI study. Axial-oblique scans of the low back region were used to measure the ESM CSA. Subject demographics and anthropometrics were obtained and regressed over the ESM CSA. Best-subset regression analyses were performed. Lean body mass and the ankle, wrist, and head indexes were the most frequent predictive variables. Regression models with easy-to-measure variables showed smaller predictive power and increased estimation error compared to other regression models. Practitioners should consider this trade-off between model accuracy and complexity. An individual's ESM CSA could be estimated by his/her individual characteristics, which enables biomechanical practitioners to estimate individualized low back force capacity and spinal loading.

A comparison of lumbar spine and muscle loading between male and female workers during box transfers

There is a clear relationship between lumbar spine loading and back musculoskeletal disorders in manual materials handling. The incidence of back disorders is greater in women than men, and for similar work demands females are functioning closer to their physiological limit. It is crucial to study loading on the spine musculoskeletal system with actual handlers, including females, to better understand the risk of back disorders. Extrapolation from biomechanical studies conducted on unexperienced subjects (mainly males) might not be applicable to actual female workers. For male workers, expertise changes the lumbar spine flexion, passive spine resistance, and active/passive muscle forces. However, experienced females select similar postures to those of novices when spine loading is critical. This study proposes that the techniques adopted by male experts, male novices, and females (with considerable experience but not categorized as experts) impact their lumbar spine musculoskeletal systems differently. Spinal loads, muscle forces, and passive resistance (muscle and ligamentous spine) were predicted by a multi-joint EMG-assisted optimization musculoskeletal model of the lumbar spine. Expert males flexed their lumbar spine less (avg. 21.9° vs 30.3-31.7°) and showed decreased passive internal moments (muscle avg. 8.9% vs 15.9-16.0%; spine avg. 4.7% vs 7.1-7.8%) and increased active internal moments (avg. 72.9% vs 62.0-63.9%), thus producing a different impact on their lumbar spine musculoskeletal systems. Experienced females sustained the highest relative spine loads (compression avg. 7.3 N/BW vs 6.2-6.4 N/BW; shear avg. 2.3 N/BW vs 1.7-1.8 N/BW) in addition to passive muscle and ligamentous spine resistance similar to novices. Combined with smaller body size, less strength, and the sequential lifting technique used by females, this could potentially mean greater risk of back injury. Workers should be trained early to limit excessive and repetitive stretching of their lumbar spine passive tissues.

Population-based study of age- and sex-related differences in muscle density and size in thoracic and lumbar spine: the Framingham study

Relative age-related deficit in trunk muscle density was greater in women than men whereas the relative decrease in muscle mass with age was similar in both sexes. The greater muscle fat content and greater age-related fat accumulation among women may contribute to women suffering more functional disabilities than men.

INTRODUCTION

A better understanding of the effect of aging on trunk musculature will have implications for physical function, disability, pain, and risk of injury in older adults. Thus, we determined the age- and sex-related differences in muscle density and size of both thoracic and lumbar trunk muscles.

METHODS

In this cross-sectional study, muscle density and size were measured from quantitative computed tomography (QCT) scans for 10 trunk muscle groups at different vertebral levels in 250 community-based men and women aged 40 to 90 years from the Framingham Offspring and Third Generation cohorts.

RESULTS

Trunk muscles in men were 20-67% larger and had 5-68% higher density than in women. The relative age-related deficits in muscle size were similar in both sexes, and decreased on average by ~ 8% per decade in both sexes. In contrast, women had greater age-related decreases in muscle density than men (- 17% in women, and - 11% in men, p < 0.01). Age-related declines varied by specific muscle, tending to be greater for outer trunk muscles than for paraspinal muscles, but within a given muscle the age-related changes in muscle density and size were similar among spinal levels.

CONCLUSION

This comprehensive study of trunk muscle deficits with increasing age may have important implications for physical function, disability, pain, and risk of injury in older adults. The greater levels of mobility impairments with aging in women may in part be explained by greater proportion of intramuscular fat tissue and greater age-related fat accumulation in trunk muscles in women than in men.

Do Older Adults and Those Recovered from Low Back Injury Share Common Muscle Activation Adaptations?

Theoretical models suggest trunk muscle activation compensates for spinal systems impairments. The purpose of this study was to determine if two populations (older adults and those recovered from a lower back injury (rLBI)) with spinal system impairments have similar muscle activation patterns to each other, but differ from controls. Trunk electromyograms collected from 12 older adults, 16 rLBI, and 19 controls during two dynamic tasks showed that older adults and rLBI had higher activation amplitudes, sustained temporal and more synergistic activation relative to controls. However, differences found between older adults and rLBI suggest that spinal system impairments differed between groups or that recent pain (rLBI) uniquely influenced muscle activation. This sheds light on our understanding of the relationship between spinal system impairments and muscle activation.

Morphology of the lumbar multifidus muscle in lumbar disc herniation at different durations and at different ages

The aim of the present study was to evaluate the relative functional volume of bilateral lumbar multifidus (LM) muscles across different stages and ages of patients with lumbar disc herniation (LDH). The relative functional volumes of LM muscles in both non-affected and affected sides in the L4-L5 and L5-S1 segmental level were measured in a resting prone position, and visual analogue score (VAS) for pain and Japanese Orthopedic Association (JOA) scores were recorded. The correlation between changes in the relative net volume of LM muscles and times of onset, ages, VAS and JOA scores were analyzed. A total of 327 cases were selected. The affected sides of LM muscles could present a certain degree of atrophy in stages >3 weeks. During the duration of the course, all cases presented different degrees of LM muscle atrophy. In addition, the degree of LM muscle atrophy was positively correlated with its duration. Age could influence the degree of LM muscle atrophy. Patients with unilateral LDH had <10% asymmetry on relative functional volume in the youth group. At the L4-L5 segments, patients with unilateral LDH had >10% asymmetry within the course of 3 months in the elderly group. The reduced rate of the relative functional net LM muscle volume was positively correlated with VAS scores, age, duration and JOA scores. In conclusion, the reduced rate of relative functional net LM muscle volume was positively correlated with age, duration, VAS scores and JOA scores. Although these findings are unreliable markers of lumbar pathology in an individual level for use in clinical or research settings, there is a notable importance of early intervention in LM muscle atrophy.

Trunk musculoskeletal response in maximum voluntary exertions: A combined measurement-modeling investigation

Maximum voluntary exertion (MVE) tasks quantify trunk strength and maximal muscle electromyography (EMG) activities with both clinical and biomechanical implications. The aims here are to evaluate the performance of an existing trunk musculoskeletal model, estimate maximum muscle stresses and spinal forces, and explore likely differences between males and females in maximum voluntary exertions. We, therefore, measured trunk strength and EMG activities of 19 healthy right-handed subjects (9 females and 10 males) in flexion, extension, lateral and axial directions. MVEs for all subjects were then simulated in a subject-specific trunk musculoskeletal model, and estimated muscle activities were compared with EMGs. Analysis of variance was used to compare measured moments and estimated spinal loads at the L5-S1 level between females and males. MVE moments in both sexes were greatest in extension (means of 236 Nm in males and 190 Nm in females) and least in left axial torque (97 Nm in males and 64 Nm in females). Being much greater in lateral and axial MVEs, coupled moments reached ∼50% of primary moments in average. Females exerted less moments in all directions reaching significance except in flexion. Muscle activity estimations were strongly correlated with measurements in flexion and extension (Pearson's r = 0.69 and 0.76), but the correlations were very weak in lateral and axial MVEs (Pearson's r = 0.27 and 0.13). Maximum muscle stress was in average 0.80 ± 0.42 MPa but varied among muscles from 0.40 ± 0.22  MPa in rectus abdominis to 0.99 ± 0.29 MPa in external oblique. To estimate maximum muscle stresses and evaluate validity of a musculoskeletal model, MVEs in all directions with all coupled moments should be considered.

Incorporation of CT-based measurements of trunk anatomy into subject-specific musculoskeletal models of the spine influences vertebral loading predictions

We created subject-specific musculoskeletal models of the thoracolumbar spine by incorporating spine curvature and muscle morphology measurements from computed tomography (CT) scans to determine the degree to which vertebral compressive and shear loading estimates are sensitive to variations in trunk anatomy. We measured spine curvature and trunk muscle morphology using spine CT scans of 125 men, and then created four different thoracolumbar spine models for each person: (i) height and weight adjusted (Ht/Wt models); (ii) height, weight, and spine curvature adjusted (+C models); (iii) height, weight, and muscle morphology adjusted (+M models); and (iv) height, weight, spine curvature, and muscle morphology adjusted (+CM models). We determined vertebral compressive and shear loading at three regions of the spine (T8, T12, and L3) for four different activities. Vertebral compressive loads predicted by the subject-specific CT-based musculoskeletal models were between 54% lower to 45% higher from those estimated using musculoskeletal models adjusted only for subject height and weight. The impact of subject-specific information on vertebral loading estimates varied with the activity and spinal region. Vertebral loading estimates were more sensitive to incorporation of subject-specific spinal curvature than subject-specific muscle morphology. Our results indicate that individual variations in spine curvature and trunk muscle morphology can have a major impact on estimated vertebral compressive and shear loads, and thus should be accounted for when estimating subject-specific vertebral loading. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2164-2173, 2017.

Spinal Loading Patterns From Biomechanical Modeling Explain the High Incidence of Vertebral Fractures in the Thoracolumbar Region

Vertebral fractures occur most frequently in the mid-thoracic and thoracolumbar regions of the spine, yet the reasons for this site-specific occurrence are not known. Our working hypothesis is that the locations of vertebral fracture may be explained by the pattern of spine loading, such that during daily activities the mid-thoracic and thoracolumbar regions experience preferentially higher mechanical loading compared to other spine regions. To test this hypothesis, we used a female musculoskeletal model of the full thoracolumbar spine and rib cage to estimate the variation in vertebral compressive loads and associated factor-of-risk (load-to-strength ratio) throughout the spine for 119 activities of daily living, while also parametrically varying spine curvature (high, average, low, and zero thoracic kyphosis models). We found that nearly all activities produced loading peaks in the thoracolumbar and lower lumbar regions of the spine, but that the highest factor-of-risk values generally occurred in the thoracolumbar region of the spine because these vertebrae had lower compressive strength than vertebrae in the lumbar spine. The peaks in compressive loading and factor-of-risk in the thoracolumbar region were accentuated by increasing thoracic kyphosis. Activation of the multifidus muscle fascicles selectively in the thoracolumbar region appeared to be the main contributor to the relatively high vertebral compressive loading in the thoracolumbar spine. In summary, by using advanced musculoskeletal modeling to estimate vertebral loading throughout the spine, this study provides a biomechanical mechanism for the higher incidence of fractures in thoracolumbar vertebrae compared to other spinal regions. © 2017 American Society for Bone and Mineral Research.

Development of a new palpation method using alternative landmarks for the determination of thoracic transverse processes: An in vitro study

Palpation methods (PMs) have been proposed to guide clinicians in locating the thoracic transverse processes (TTPs). However, no studies have assessed the validity of TTPs palpation or the added value of musculoskeletal ultrasound (MSU). The objectives of the present study were (1) to explore the validity of TTPs location using palpation as commonly performed by clinicians, (2) to develop an accurate and valid PM, and (3) to assess the added value of MSU. A standardized procedure was used on six cadavers. It consisted in the insertion of markers through the T3, T5, T6 and T8 TTPs and spinous processes, which were identified using palpation and MSU. First, a fresh cadaver was used to explore the validity of the common palpation method. Since poor validity was observed, one intermediate and a final PMs were tested on a total of five Thiel-embalmed specimens. A descriptive analysis was performed and agreement between MSU and the final PM was determined. The final PM led to the proper determination of all TTPs on three specimens with a mean error of 4 ± 1.8 mm in relation to the TTPs center. The coefficient of variations and root mean square errors were ≤0.15 and 0.21 mm, respectively. Bland-Altman plot showed no differences between palpation and MSU. In conclusion, this study reports the validity of a new PM using multiple landmarks to guide TTPs determination and for which MSU does not seem to add value in accuracy. These results may have important clinical implications for clinicians using palpation.

Medidas angulares da coluna lombar em idosos: comparação entre duas estratégias de análise radiográfica

RESUMO A literatura sobre postura em idosos tem apresentado artigos que medem os ângulos da coluna por diferentes estratégias. Isso pode interferir no diagnóstico postural e impactar na resolução das comorbidades que afetam a coluna desses indivíduos. O objetivo deste estudo foi comparar dois métodos de medida da coluna lombar comumente utilizados em pesquisa. A associação dessas medidas com o ângulo da cifose foi utilizada como base para comparação. Participaram da pesquisa 160 idosos, submetidos a raio-X anteroposterior da coluna lombar. Foram realizadas duas medidas de Cobb para cada radiografia: uma com base em T12-S1 e outra em L1-L5. Somente a medida com base em L1-L5 apresentou associação significativa com o ângulo da cifose. Não houve associação da medida T12-S1 com o ângulo da curva torácica. Nossos achados indicam que o método de Cobb mais adequado para analisar radiografias de coluna lombar em idosos é o do traçado de linhas entre L1-L5.

A biologically-assisted curved muscle model of the lumbar spine: Model validation

BACKGROUND

Biomechanical models have been developed to predict spinal loads in vivo to assess potential risk of injury in workplaces. Most models represent trunk muscles with straight-lines. Even though straight-line muscles behave reasonably well in simple exertions, they could be less reliable during complex dynamic exertions. A curved muscle representation was developed to overcome this issue. However, most curved muscle models have not been validated during dynamic exertions. Thus, the objective of this study was to investigate the fidelity of a curved muscle model during complex dynamic lifting tasks, and to investigate the changes in spine tissue loads.

METHODS

Twelve subjects (7 males and 5 females) participated in this study. Subjects performed lifting tasks as a function of load weight, load origin, and load height to simulate complex exertions. Moment matching measures were recorded to evaluate how well the model predicted spinal moments compared to measured spinal moments from T12/L1 to L5/S1 levels.

FINDINGS

The biologically-assisted curved muscle model demonstrated better model performance than the straight-line muscle model between various experimental conditions. In general, the curved muscle model predicted at least 80% of the variability in spinal moments, and less than 15% of average absolute error across levels. The model predicted that the compression and anterior-posterior shear load significantly increased as trunk flexion increased, whereas the lateral shear load significantly increased as trunk twisted more asymmetric during lifting tasks.

INTERPRETATION

A curved muscle representation in a biologically-assisted model is an empirically reasonable approach to accurately predict spinal moments and spinal tissue loads of the lumbar spine.

Prediction of magnetic resonance imaging-derived trunk muscle geometry with application to spine biomechanical modeling

BACKGROUND

Accurate geometry of the trunk musculature is essential for reliably estimating spinal loads in biomechanical models. Currently, many models employ straight muscle path assumptions that yield far less accurate tissue loads, particularly in extreme postures. Precise muscle moment-arms and physiological cross-sectional areas are important when incorporating curved muscle geometry in biomechanical models. The objective of this study was to develop a predictive model of moment arms and physiological cross-sectional areas of trunk musculature at multiple levels in the thoracic/lumbar spine as a function of anthropometric measures.

METHODS

Based on magnetic resonance imaging data from thirty subjects (10 male and 20 female) reported in a previous study, a polynomial regression analysis was conducted to estimate the muscle moment-arms and physiological cross-sectional areas of trunk muscles through thoracic/lumbar spine as a function of vertebral level, gender, age, height, and body mass.

FINDINGS

Gender, body mass, and height were the best predictors of muscle moment-arms and physiological cross-sectional areas. The predictability of muscle parameters tended to be higher for erector spinae than other muscles. Most muscles showed a curved muscle path along the thoracic/lumbar spine.

INTERPRETATION

The polynomial regression model of the muscle geometry in this study generally showed good predictability compared to previous reports. The predictive model in this study will be useful to develop personalized biomechanical models that incorporate curved trunk muscle geometries.

The assessment of abdominal and multifidus muscles and their role in physical function in older adults: a systematic review

BACKGROUND

Age-related changes in the trunk (abdominal and lumbar multifidus) muscles and their impact on physical function of older adults are not clearly understood.

OBJECTIVES

To systematically summarise studies of these trunk muscles in older adults.

DATA SOURCES

Cochrane Library, Pubmed, EMBASE and CINAHL were searched using terms for abdominal and MF muscles and measurement methods.

STUDY SELECTION

Two reviewers independently assessed studies and included those reporting measurements of abdominal muscles and/or MF by ultrasound, computed tomography, magnetic resonance imaging or electromyography of adults aged ≥50 years.

DATA SYNTHESIS

A best evidence synthesis was performed.

RESULTS

Best evidence synthesis revealed limited evidence for detrimental effects of ageing or spinal conditions on trunk muscles, and conflicting evidence for decreased physical activity or stroke having detrimental effects on trunk muscles. Thicknesses of rectus abdominis, internal oblique and external oblique muscles were 36% to 48% smaller for older than younger adults. Muscle quality was poorer among people with moderate-extreme low back pain and predicted physical function outcomes.

LIMITATIONS

Study heterogeneity precluded meta-analysis.

CONCLUSION

Overall, the evidence base in older people has significant limitations, so the role of physiotherapy interventions aimed at these muscles remains unclear. The results point to areas in which further research could lead to clinically useful outcomes. These include determining the role of the trunk muscles in the physical function of older adults and disease; developing and testing rehabilitation programmes for older people with spinal conditions and lower back pain; and identifying modifiable factors that could mitigate age-related changes.

The Role of Trunk Musculature in Osteoporotic Vertebral Fractures: Implications for Prediction, Prevention, and Management

This review examines the current evidence for associations between vertebral fractures (VFx), the most common type of fracture in older adults, and trunk muscles, which are intimately tied to spinal loading and function. Individuals with prevalent VFxs have more fat infiltration in the trunk muscles, lower trunk extension strength, and altered muscle activation patterns. However, no longitudinal studies have examined whether assessment of trunk muscle can contribute to prediction of fracture risk. A few studies report that exercise interventions targeting the trunk muscles can reduce the risk of VFx, improve trunk strength and endurance in patients who have had a VFx, and reduce the risk of falling, a common cause of VFx, but the quality of evidence is low. Trunk muscles likely have an important role to play in prediction, prevention, and management of VFx, but additional longitudinal studies and randomized controlled trials are needed to clarify this role.

Vertebral Strength and Estimated Fracture Risk Across the BMI Spectrum in Women

Somewhat paradoxically, fracture risk, which depends on applied loads and bone strength, is elevated in both anorexia nervosa and obesity at certain skeletal sites. Factor-of-risk (Φ), the ratio of applied load to bone strength, is a biomechanically based method to estimate fracture risk; theoretically, higher Φ reflects increased fracture risk. We estimated vertebral strength (linear combination of integral volumetric bone mineral density [Int.vBMD] and cross-sectional area from quantitative computed tomography [QCT]), vertebral compressive loads, and Φ at L4 in 176 women (65 anorexia nervosa, 45 lean controls, and 66 obese). Using biomechanical models, applied loads were estimated for: 1) standing; 2) arms flexed 90°, holding 5 kg in each hand (holding); 3) 45° trunk flexion, 5 kg in each hand (lifting); 4) 20° trunk right lateral bend, 10 kg in right hand (bending). We also investigated associations of Int.vBMD and vertebral strength with lean mass (from dual-energy X-ray absorptiometry [DXA]) and visceral adipose tissue (VAT, from QCT). Women with anorexia nervosa had lower, whereas obese women had similar, Int.vBMD and estimated vertebral strength compared with controls. Vertebral loads were highest in obesity and lowest in anorexia nervosa for standing, holding, and lifting (p < 0.0001) but were highest in anorexia nervosa for bending (p < 0.02). Obese women had highest Φ for standing and lifting, whereas women with anorexia nervosa had highest Φ for bending (p < 0.0001). Obese and anorexia nervosa subjects had higher Φ for holding than controls (p < 0.03). Int.vBMD and estimated vertebral strength were associated positively with lean mass (R = 0.28 to 0.45, p ≤ 0.0001) in all groups combined and negatively with VAT (R = -[0.36 to 0.38], p < 0.003) within the obese group. Therefore, women with anorexia nervosa had higher estimated vertebral fracture risk (Φ) for holding and bending because of inferior vertebral strength. Despite similar vertebral strength as controls, obese women had higher vertebral fracture risk for standing, holding, and lifting because of higher applied loads from higher body weight. Examining the load-to-strength ratio helps explain increased fracture risk in both low-weight and obese women.

Associations of Computed Tomography-Based Trunk Muscle Size and Density With Balance and Falls in Older Adults

BACKGROUND

Deficits in balance and muscle function are important risk factors for falls in older adults. Aging is associated with significant declines in muscle size and density, but associations of trunk muscle size and density with balance and falls in older adults have not been previously examined.

METHODS

Trunk muscle size (cross-sectional area) and attenuation (a measure of tissue density) were measured in computed tomography scans (at the L2 lumbar level) in a cohort of older adults (mean ± SD age of 81.9±6.4) residing in independent living communities. Outcome measures were postural sway measured during quiet standing and Short Physical Performance Battery (SPPB) at baseline, and falls reported by participants for up to 3 years after baseline measurements.

RESULTS

Higher muscle density was associated with reduced postural sway, particularly sway velocities, in both men and women, and better Short Physical Performance Battery score in women, but was not associated with falls. Larger muscle size was associated with increased postural sway in men and women and with increased likelihood of falling in men.

CONCLUSIONS

The results suggest that balance depends more on muscle quality than on the size of the muscle. The unexpected finding that larger muscle size was associated with increased postural sway and increased fall risk requires further investigation, but highlights the importance of factors besides muscle size in muscle function in older adults.

Prediction Models for the Erector Spinae Muscle Cross-Sectional Area

Accurate and reliable “individualized” low back erector spinae muscle (ESM) data are of importance to estimate its force producing capacity. Knowing the force producing capacity, along with spinal loading, enhances the understanding of low back injury mechanisms. The objective of this study was to build regression models to estimate the ESM cross-sectional area (CSA). Measurements were taken from axial-oblique magnetic resonance imaging (MRI) scans of a large historical population [54 females and 53 males at L3/L4, 50 females and 44 males at L4/L5, and 41 females and 35 males at L5/S1 levels]. Results suggest that an individual's ESM CSA can be accurately estimated based on his/her gender, height, and weight. Results further show that there is no significant difference between the measured and estimated ESM CSAs, and expected absolute error is less than 15%.

Development and Validation of a Musculoskeletal Model of the Fully Articulated Thoracolumbar Spine and Rib Cage

We developed and validated a fully articulated model of the thoracolumbar spine in opensim that includes the individual vertebrae, ribs, and sternum. To ensure trunk muscles in the model accurately represent muscles in vivo, we used a novel approach to adjust muscle cross-sectional area (CSA) and position using computed tomography (CT) scans of the trunk sampled from a community-based cohort. Model predictions of vertebral compressive loading and trunk muscle tension were highly correlated to previous in vivo measures of intradiscal pressure (IDP), vertebral loading from telemeterized implants and trunk muscle myoelectric activity recorded by electromyography (EMG).

Age-related changes in trunk neuromuscular activation patterns during a controlled functional transfer task include amplitude and temporal synergies

While healthy aging is associated with physiological changes that can impair control of trunk motion, few studies examine how spinal muscle responses change with increasing age. This study examined whether older (over 65 years) compared to younger (20-45 years) adults had higher overall amplitude and altered temporal recruitment patterns of trunk musculature when performing a functional transfer task. Surface electromyograms from twelve bilateral trunk muscle (24) sites were analyzed using principal component analysis, extracting amplitude and temporal features (PCs) from electromyographic waveforms. Two PCs explained 96% of the waveform variance. Three factor ANOVA models tested main effects (group, muscle and reach) and interactions for PC scores. Significant (p<.0125) group interactions were found for all PC scores. Post hoc analysis revealed that relative to younger adults, older adults recruited higher agonist and antagonistic activity, demonstrated continuous activation levels in specific muscle sites despite changing external moments, and had altered temporal synergies within abdominal and back musculature. In summary both older and younger adults recruit highly organized activation patterns in response to changing external moments. Differences in temporal trunk musculature recruitment patterns suggest that older adults experience different dynamic spinal stiffness and loading compared to younger adults during a functional lifting task.

Age and side-related morphometric MRI evaluation of trunk muscles in people without back pain

This study evaluated lumbar spine muscle volume and Muscle Fatty Infiltrate (MFI) across two age groups of healthy adults. Twenty-four participants (young group - YG: age 18-25, n = 12; mature group - MG: age 45-60, n = 12) without low back pain underwent T1-weighted axial MRI. Muscle volume and MFI were obtained from the left and right lumbar erector spinae (ES), multifidus (M), rectus abdominis (RA) and psoas (PS) muscles. For MFI, mean pixel intensity (MPI) of muscles was reported as a percentage of subcutaneous fat MPI. Within-group comparison of left and right side muscle volume was not significantly different in the YG. In the MG, right RA and ES were significantly smaller than left (RA p = 0.049; ES p = 0.03). In both groups, left PS, M and ES MFI was significantly smaller compared to the right side and left RA MFI was significantly greater compared to right side (all p ≤ 0.001). For M volume, 81.7-84.6% of variance was explained by age, height and Body Mass Index (BMI). For ES volume, 81.6-82.8% of variance was explained by height and BMI. Age explained 18.1%-36.0% of variance in M and ES right MFI. Therefore, age and BMI are relevant factors for extensor muscle volume, but not for flexor muscle volume. Also, age significantly influences MFI for right-sided extensors only. The age effect is apparently independent of full subjective back functionality. For future spinal muscle research, the side-and muscle-specific effect of age on muscle morphology should be considered.

Vertebral size, bone density, and strength in men and women matched for age and areal spine BMD

To explore the possible mechanisms underlying sex-specific differences in skeletal fragility that may be obscured by two-dimensional areal bone mineral density (aBMD) measures, we compared quantitative computed tomography (QCT)-based vertebral bone measures among pairs of men and women from the Framingham Heart Study Multidetector Computed Tomography Study who were matched for age and spine aBMD. Measurements included vertebral body cross-sectional area (CSA, cm(2) ), trabecular volumetric BMD (Tb.vBMD, g/cm(3) ), integral volumetric BMD (Int.vBMD, g/cm(3) ), estimated vertebral compressive loading and strength (Newtons) at L3 , the factor-of-risk (load-to-strength ratio), and vertebral fracture prevalence. We identified 981 male-female pairs (1:1 matching) matched on age (± 1 year) and QCT-derived aBMD of L3 (± 1%), with an average age of 51 years (range 34 to 81 years). Matched for aBMD and age, men had 20% larger vertebral CSA, lower Int.vBMD (-8%) and Tb.vBMD (-9%), 10% greater vertebral compressive strength, 24% greater vertebral compressive loading, and 12% greater factor-of-risk than women (p < 0.0001 for all), as well as higher prevalence of vertebral fracture. After adjusting for height and weight, the differences in CSA and volumetric bone mineral density (vBMD) between men and women were attenuated but remained significant, whereas compressive strength was no longer different. In conclusion, vertebral size, morphology, and density differ significantly between men and women matched for age and spine aBMD, suggesting that men and women attain the same aBMD by different mechanisms. These results provide novel information regarding sex-specific differences in mechanisms that underlie vertebral fragility.

Foldover-free shape deformation for biomedicine

Shape deformation as a fundamental geometric operation underpins a wide range of applications, from geometric modelling, medical imaging to biomechanics. In medical imaging, for example, to quantify the difference between two corresponding images, 2D or 3D, one needs to find the deformation between both images. However, such deformations, particularly deforming complex volume datasets, are prone to the problem of foldover, i.e. during deformation, the required property of one-to-one mapping no longer holds for some points. Despite numerous research efforts, the construction of a mathematically robust foldover-free solution subject to positional constraints remains open. In this paper, we address this challenge by developing a radial basis function-based deformation method. In particular we formulate an effective iterative mechanism which ensures the foldover-free property is satisfied all the time. The experimental results suggest that the resulting deformations meet the internal positional constraints. In addition to radial basis functions, this iterative mechanism can also be incorporated into other deformation approaches, e.g. B-spline based FFDs, to develop different deformable approaches for various applications.