Kinematics of the lumbar spine in trunk rotation: in vivo three-dimensional analysis using magnetic resonance imaging

Hip joint kinematic assessment in chronic non-specific low back pain patients. A Delphi study

BACKGROUND

Chronic nonspecific low back pain (CNSLBP) has been associated with movement impairment (MI) of the hip joint. However, evidence supporting this is inconsistent. Agreement from experts may provide rationale and recommendations for the assessment of the hip joint in the management of CNSLBP patients.

OBJECTIVE

Gain expert consensus on whether hip MIs are related to CNSLBP, whether they should be assessed and which movement types and directions they recommend.

METHODS

Through a three-round e-Delphi process, international experts in the field rated levels of agreement for generated themes pertaining to assessing proposed hip joint MI in individuals with CNSLBP and underlying rationales. Consensus was defined a priori as ≥75% ratings on Likert scales with an IQR≤ 1.

RESULTS

International expert panel consisted of a mix of researchers and clinicians with the majority involved in both. Response for round I was 27, round 2 was 21 and round III was 26 individuals. Consensus was achieved for the association of active and passive hip joint MI in CNSLBP and their assessment. 100% agreement was achieved for the rationale regarding compensatory movement of the lumbar spine, and the assessment of passive hip movements, in particular extension. Consensus was also achieved for assessing hip passive flexion, extension, rotations, and abduction, active flexion, extension, and abduction. No agreement was attained regarding passive accessory movement.

CONCLUSION

The assessment of active and passive hip joint MI is regarded by experts as appropriate and informative in the management of and research pertaining to CNSLBP.

A multibody simulation of the spine for objectification of biomechanical quantities after VBT: a proof of concept and description of baseline data

PURPOSE

Vertebral Body Tethering (VBT), an alternative treatment for adolescent idiopathic scoliosis, shows satisfactory post-operative results. However, the biomechanical quantities and consequences after VBT surgery remain largely unknown. Therefore, the aim of this study is to analyze the spinal biomechanics during different motions using a multibody simulation approach.

METHODS

The tether and intervertebral compression forces were simulated in a validated spine model during different physiological movements at different pre-tensions and screw positions, while considering the anatomical muscle and ligament properties.

RESULTS

The simulations showed that an augmentation of the pre-tension and an alteration of the screw position have both significant impact on the intervertebral compression and tether forces. The forces also vary depending on the movement performed, with the highest tether forces measured during lateral bending. In the upright position, with a pre-tension of 200 N, the maximum compression force increases by up to 157% compared to the untethered maximum compression force. The screw position can lead to large differences in the distribution of forces in the spine.

CONCLUSION

The biomechanical data provide a first impression of the forces that occur along the spine during various physiological movements and are consistent with published clinical data. Forces are not evenly distributed along the spine, with higher lumbar forces. The tether forces reach values during lateral bending that can potentially destroy the tether´s integrity and thus may explain the common post-operative complication, namely tether breakage. The results of the model can therefore have an impact on future directions for improved surgical VBT treatment.

Physiological rotation patterns of the thoracolumbar spine across different ages: A detailed analysis using upright CT

BACKGROUND

The rotational motion of the spine plays a crucial role in daily activities. Understanding the mechanisms of spinal rotation is essential for evaluating normal spinal function, especially in standing positions due to the influence of gravity. However, previous studies on spinal rotation have been limited.

RESEARCH QUESTION

What are the differences in thoracolumbar rotation during trunk rotation in a standing position among different age and gender groups?

METHODS

This cross-sectional study involved 49 healthy volunteers without back pain, including 24 younger participants (13 males, 11 females) and 25 elderly participants (12 males, 13 females). Upright and trunk-rotated CT (right-rotated standing positions) scans were taken. Vertebral rotation was measured using the femoral head center as an axis.

RESULTS

Analysis of spinal alignment in the standing position revealed mild rotation from the lumbar to thoracic vertebrae. The lumbar spine exhibited left rotation at apex of L3 (L3: -1.3±3.8°, p=0.01), while the lower thoracic spine showed right rotation at apex of T8 (T8: 1.9±2.4°, p<0.001) and the upper thoracic spine showed left rotation at apex of T3 (T3: -2.6±2.9°, p<0.001). The lumbar spine showed minimal rotation during maximum trunk rotation, with significant rotation noted above T10 (16 % vs 84 %). The total thoracolumbar spinal rotation at T1 showed significant differences by gender and age (male vs. female: 23.9±° vs. 30.3±°, p=0.001; young vs. elderly: 29.2±° vs. 25.0±°, p=0.028; elderly male vs. elderly female: 19.2±° vs. 30.4±°, p<0.001). Younger participants did not show significant gender differences, while elderly females retained more rotation compared to males.

SIGNIFICANCE

This pioneering study provides the first detailed report on the range of spinal rotation in a physiological standing situation, highlighting significant differences by gender and age. These findings offer new insights into the natural patterns of spinal rotation and their potential implications for diagnosing and treating spinal disorders.

Initial evaluation of the relationship between maximal axial vertebra rotation and the rotation deformity in adolescent idiopathic scoliosis

PURPOSE

This study evaluated the relationship between maximal axial vertebra rotation (maxAVR) and other clinical and radiological indexes, compared to apical vertebra rotation (AVR) in idiopathic adolescent scoliosis (AIS).

METHODS

Forty consecutive patients of AIS with Cobb angle of major curve > 40° were included. They were scanned by an EOS imaging system and had trunk rotational angle (TRA) measured by scoliometer. The correlation between variables was assessed using Pearson's correlation coefficient and loaded onto a meta-analysis model.

RESULTS

There were (34 girls and 6 boys) with an average age of 13.8 ± 1.6 years. AVR was maxAVR in only 47.5% (19/40) cases of the major curves and 42.3% (11/26) cases of the minor curves. The correlation between maxAVR and TRA was significantly higher than the correlation between AVR and TRA for the MT curves (p = 0.0001) and TL/L curves (p = 0.0001). On multivariate regression analysis, the magnitude of maxAVR showed a significant correlation with TRA (p = 0.0002), Cobb angle (p = 0.001), and coronal deformity angular ratio (C-DAR) (p = 0.027).

CONCLUSIONS

The apical vertebra was not the most rotated in most cases. The correlation between maxAVR and TRA was significantly higher than the correlation between AVR and TRA. Moreover, the maxAVR was multivariately related to TRA, Cobb angle, and C-DAR.

LEVEL OF EVIDENCE

Level II, diagnostic.

Biomechanical analysis of complications following T10-Pelvis spinal fusion: A population based computational study

Proximal junctional kyphosis (PJK) and proximal junctional failure (PJF) are challenging complications of long fusion constructs for the treatment of adult spinal deformity. The objective of this study is to understand the biomechanical stresses proximal to the upper instrumentation of a T10-pelvis fusion in a large patient cohort. The pre-fusion models were subject-specific thoracolumbar spine models that incorporate the height, weight, spine curvature, and muscle morphology of 250 individuals from the Framingham Heart Study Multidetector CT Study. To create post-fusion models, the subject-specific models were further modified to eliminate motion between the intervertebral joints from T10 to the pelvis. OpenSim analysis tools were used to calculate the medial lateral shear force, anterior posterior shear force, and compressive force on the T9 vertebra during the static postures. Differences between pre-fusion and post-fusion T9 biomechanics were consistent between increased segmental mobility and unchanged segmental mobility conditions. For all static postures, compression decreased (p < 0. 0005). Anterior-posterior shear force significantly increased (p < 0. 0005) during axial twist and significantly increased (p < 0. 0005) during trunk flexion. Medial lateral shear force significantly increased (p < 0. 0005) during axial twist. This computational study provided the first use of subject-specific models to investigate the biomechanics of long spinal fusions. Patients undergoing T10-Pelvis fusion were predicted to have increased shear forces and decreased compressive force at the T9 vertebra, independent of change in segmental mobility. The computational model shows potential for the investigation of spinal fusion biomechanics to reduce the risk of PJK or PJF.

An Enhanced Spine Model Validated for Simulating Dynamic Lifting Tasks in OpenSim

A fully articulated thoracolumbar spine model had been previously developed in OpenSim and had been extensively validated against experimental data during various static tasks. In the present study, we enhanced this detailed musculoskeletal model by adding the role of passive structures and adding kinematic constraints to make it suitable for dynamic tasks. We validated the spinal forces estimated by this enhanced model during nine dynamic lifting/lowering tasks. Moreover, we recently developed and evaluated five approaches in OpenSim to model the external loads applied to the hands during lifting/lowering tasks, and in the present study, we assessed which approach results in more accurate spinal forces. Regardless of the external load modeling approach, the maximum forces predicted by our enhanced spine model across all tasks, as well as the pattern of estimated spinal forces within each task, showed strong correlations (r-values and cross-correlation coefficients > 0.9) with experimental data. Given the biofidelity of our enhanced model, its accessibility via the open-source OpenSim software, and the extent to which this model has been validated, we recommend it for applications requiring estimation of spinal forces during lifting/lowering tasks using multibody-based models and inverse dynamic analyses.

Differences in spinal axial rotation angles during the lumbar-locked rotation test between hyper and normal thoracic rotation groups: A cross-sectional study

BACKGROUND

Trunk rotation is important in many sporting activities The thoracic spine has reciprocal relationships with the lumbar and pelvic spines, such that reduced flexibility in the lumbar or thoracic spine can lead to abnormal patterns of trunk movement and pain. However, few studies have investigated the relative trunk rotation mobilities of the thorax, lumbar, and pelvis.

OBJECTIVE

To compare thoracic, lumbar, and pelvic rotation angles during the lumbar-locked rotation test between hyper and normal thoracic rotation groups.

METHODS

Thirty-two young, active participants were enrolled in this study. After the attachment of inertial measurement units at the T1, T7, T12, L3, and S2 levels, the participants were required to stand in a comfortable upright posture for 5 s to allow postural measurements before performing the lumbar-locked rotation test. The participants were then divided into hyper thoracic rotation and normal thoracic rotation groups based on T1 angle measurements obtained during the lumbar-locked rotation test.

RESULTS

The hyper thoracic rotation group had significantly higher thoracic rotation angles on both the right (p< 0.05) and left (p< 0.05) sides compared with the normal thoracic rotation group. Furthermore, we observed flat lumbar lordosis in the hyper thoracic rotation group compared with the normal thoracic rotation group, particularly in the lower lumbar region in standing posture.

CONCLUSION

Our data suggest that evaluations of thoracic mobility should consider relative thoracic, lumbar, and pelvic motions, rather than the T1 angle alone. This study provides a basis for health professionals to evaluate movement dysfunctions associated with thoracic hypermobility.

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.

Range of rotation of thoracolumbar vertebrae in Japanese macaques

In humans, the range of thoracic vertebral rotation is known to be greater than that of the lumbar vertebrae due to their zygapophyseal orientation and soft tissue structure. However, little is known regarding vertebral movements in non-human primate species, which are primarily quadrupedal walkers. To understand the evolutionary background of human vertebral movements, this study estimated the range of axial rotation of the thoracolumbar spine in macaque monkeys. First, computed tomography (CT) was performed while passively rotating the trunk of whole-body cadavers of Japanese macaques, after which the motion of each thoracolumbar vertebra was estimated. Second, to evaluate the influence of the shoulder girdle and surrounding soft tissues, specimens with only bones and ligaments were prepared, after which the rotation of each vertebra was estimated using an optical motion tracking system. In both conditions, the three-dimensional coordinates of each vertebra were digitized, and the axial rotational angles between adjacent vertebrae were calculated. In the whole-body condition, the lower thoracic vertebrae had a greater range of rotation than did the other regions, similar to that observed in humans. In addition, absolute values for the range of rotation were similar between humans and macaques. However, in the bone-ligament preparation condition, the upper thoracic vertebrae had a range of rotation similar to that of the lower thoracic vertebrae. Contrary to previous speculations, our results showed that the mechanical restrictions by the ribs were not as significant; rather, the shoulder girdle largely restricted the rotation of the upper thoracic vertebrae, at least, in macaques.

Dynamic segmental kinematics of the lumbar spine during diagnostic movements

Background: In vivo measurements of segmental-level kinematics are a promising avenue for better understanding the relationship between pain and its underlying, multi-factorial basis. To date, the bulk of the reported segmental-level motion has been restricted to single plane motions. Methods: The present work implemented a novel marker set used with an optical motion capture system to non-invasively measure dynamic, 3D in vivo segmental kinematics of the lower spine in a laboratory setting. Lumbar spinal kinematics were measured for 28 subjects during 17 diagnostic movements. Results: Overall regional range of motion data and lumbar angular velocity measurement were consistent with previously published studies. Key findings from the work included measurement of differences in ascending versus descending segmental velocities during functional movements and observations of motion coupling paradigms in the lumbar spinal segments. Conclusion: The work contributes to the task of establishing a baseline of segmental lumbar movement patterns in an asymptomatic cohort, which serves as a necessary pre-requisite for identifying pathological and symptomatic deviations from the baseline.

Effects of Thoracic Spine Self-mobilization on Patients with Low Back Pain and Lumbar Hypermobility: A Randomized Controlled Trial

Objectives

This study used magnetic resonance imaging (MRI) to investigate the effects of thoracic spine self-mobilization on patients with low back pain (LBP) and lumbar hypermobility.

Methods

Twenty-four patients (15 men, 9 women) with LBP were randomly allocated to a thoracic spine self-mobilization group or sham group. The thoracic spine self-mobilization group performed thoracic spine active flexion and extension activities using two tennis balls fixed with athletic tape. Outcome measures were collected pre-intervention and after 4 weeks and included the Visual Analog Scale (VAS) for pain, the Oswestry Disability Index, lumbar rotation angle measured using MRI taken in the lateral position with 45° of trunk rotation, thoracolumbar rotation range of motion (ROM) in the sitting position, and stiffness of the erector spinae muscles. The effects of the intervention were analyzed using two-way repeated-measures analysis of variance (ANOVA), followed by multiple comparisons. The significance level was set at 5%.

Results

The results of the two-way repeated measures ANOVA indicated that the main effect of the group was significant (P<0.05) for VAS, the sum of the lumbar rotation angle, and the thoracolumbar rotation ROM. A significant group-by-time interaction was found for the sum of lumbar rotation angles. The results of the multiple comparison tests for VAS, sum of the lumbar rotation angle from L1 to S1, and thoracolumbar rotation ROM were significantly different after 4 weeks.

Conclusions

This study revealed a decrease in lumbar segmentation after thoracic spine mobilization. Thoracic spine mobilization may be effective in patients with LBP and hypermobility.

A neuromuscular human body model for lumbar injury risk analysis in a vibration loading environment

BACKGROUND AND OBJECTIVE

Long-term intensive exposure to whole-body vibration substantially increases the risk of low back pain and degenerative diseases in special occupational groups, like motor vehicle drivers, military vehicle occupants, aircraft pilots, etc. This study aims to establish and validate a neuromuscular human body model focusing on improvement of the detailed description of anatomic structures and neural reflex control, for lumbar injury analysis in vibration loading environments.

METHODS

A whole-body musculoskeletal in Opensim codes was first improved by including a detailed anatomic description of spinal ligaments, non-linear intervertebral disc, and lumbar facet joints, and coupling a proprioceptive feedback closed-loop control strategy with GTOs and muscle spindles modeling in Python codes. Then, the established neuromuscular model was multi-levelly validated from sub-segments to the whole model, from regular movements to dynamic responses to vibration loadings. Finally, the neuromuscular model was combined with a dynamic model of an armored vehicle to analyze occupant lumbar injury risk in vibration loadings due to different road conditions and traveling velocities.

RESULT

Based on a series of biomechanical indexes, including lumbar joint rotation angles, the lumbar intervertebral pressures, the displacement of the lumbar segments, and the lumbar muscle activities, the validation results show that the present neuromuscular model is available and feasible in predicting lumbar biomechanical responses in normal daily movement and vibration loading environments. Furthermore, the combined analysis with the armored vehicle model predicted similar lumbar injury risk to the experimental or epidemiologic studies. The preliminary analysis results also showed that road types and travelling velocities have substantial combined effects on lumbar muscle activities, and indicated that intervertebral joint pressure and muscle activity indexes can need to be jointly considered for lumbar injury risk evaluation.

CONCLUSION

In conclusion, the established neuromuscular model is an effective tool to evaluate vibration loading effects on injury risk of the human body and assist vehicle design vibration comfort by directly concerning the human body injury itself.

Biomechanical Comparison of Different Numbers and Configurations of Cross-Links in Long-Segment Spinal Fixation-An Experimental Study in a Porcine Model

STUDY DESIGN

Biomechanical study.

OBJECTIVE

Cross-links are a type of common clinical spinal instrumentation. However, the effects of the position and number of cross-links have never been investigated in long-segment spinal fixation, and the variables have not been optimized. We conducted an in vitro biomechanical study by using a porcine long-segment spinal model with 5 different crosslink configurations to determine the optimal construct for clinical practice.

METHODS

Five modalities with paired segmental screws from T15-L5 were tested in 20 porcine spines. The spines without cross-links composed the control group, Group A; those with a single cross-link from L2-3 composed Group B; those with 2 cross-links from L1-2 and L3-4 composed Group C; those with 2 cross-links from T15-L1 and L4-5 composed Group D; and those with 3 cross-links from T15-L1, L2-3 and L4-5 composed Group E. Spinal stiffnesses in flexion, extension, lateral bending, and axial rotation were compared among 5 different cross-link configurations in 5-level porcine spinal units.

RESULTS

Flexional, extensional and lateral bending stiffnesses did not significantly change with an increasing number of cross-links or positions in the construct. Axial stiffness was significantly increased with 2 cross-links compared to one (P < 0.05) and with placement more distant from the center of the long spinal fixation construct (P < 0.05).

CONCLUSIONS

Two cross-links individually placed proximal and distal from the center of a construct is an optimal and efficient configuration to achieve biomechanical stability in non-rigid lumbar spines undergoing long-level fixation.

The Effects of Adolescent Idiopathic Scoliosis on Axial Rotation of the Spine: A Study of Twisting Using Surface Topography

Axial twisting of the spine has been previously shown to be affected by scoliosis with decreased motion and asymmetric twisting. Existing methods for evaluating twisting may be cumbersome, unreliable, or require radiation exposure. In this study, we present an automated surface topographic measurement tool to evaluate global axial rotation of the spine, along with two measurements: twisting range of motion (TROM) and twisting asymmetry index (TASI). The aim of this study is to evaluate the impact of scoliosis on axial range of motion. Adolescent idiopathic scoliosis (AIS) patients and asymptomatic controls were scanned in a topographic scanner while twisting maximally to the left and right. TROM was significantly lower for AIS patients compared to control patients (69.1° vs. 78.5°, p = 0.020). TASI was significantly higher for AIS patients compared to control patients (29.6 vs. 19.8, p = 0.023). After stratifying by scoliosis severity, both TROM and TASI were significantly different only between control and severe scoliosis patients (Cobb angle > 40°). AIS patients were then divided by their major curve region (thoracic, thoracolumbar, or lumbar). ANOVA and post hoc tests showed that only TROM is significantly different between thoracic AIS patients and control patients. Thus, we demonstrate that surface topographic scanning can be used to evaluate twisting in AIS patients.

Investigation of geometric deformations of the lumbar disc during axial body rotations

Background

Quantitative data on in vivo vertebral disc deformations are critical for enhancing our understanding of spinal pathology and improving the design of surgical materials. This study investigated in vivo lumbar intervertebral disc deformations during axial rotations under different load-bearing conditions.

Methods

Twelve healthy subjects (7 males and 5 females) between the ages of 25 and 39 were recruited. Using a combination of a dual fluoroscopic imaging system (DFIS) and CT, the images of L3–5 segments scanned by CT were transformed into three-dimensional models, which matched the instantaneous images of the lumbar spine taken by a double fluorescent X-ray system during axial rotations to reproduce motions. Then, the kinematic data of the compression and shear deformations of the lumbar disc and the coupled bending of the vertebral body were obtained.

Results

Relative to the supine position, the average compression deformation caused by rotation is between + 10% and − 40%, and the shear deformation is between 17 and 50%. Under physiological weightbearing loads, different levels of lumbar discs exhibit similar deformation patterns, and the deformation patterns of left and right rotations are approximately symmetrical. The deformation patterns change significantly under a 10 kg load, with the exception of the L3–4 disc during the right rotation.

Conclusion

The deformation of the lumbar disc was direction-specific and level-specific during axial rotations and was affected by extra weight. These data can provide new insights into the biomechanics of the lumbar spine and optimize the parameters of artificial lumbar spine devices.

The Influence of Kinematic Constraints on Model Performance During Inverse Kinematics Analysis of the Thoracolumbar Spine

Motion analysis is increasingly applied to spine musculoskeletal models using kinematic constraints to estimate individual intervertebral joint movements, which cannot be directly measured from the skin surface markers. Traditionally, kinematic constraints have allowed a single spinal degree of freedom (DOF) in each direction, and there has been little examination of how different kinematic constraints affect evaluations of spine motion. Thus, the objective of this study was to evaluate the performance of different kinematic constraints for inverse kinematics analysis. We collected motion analysis marker data in seven healthy participants (4F, 3M, aged 27–67) during flexion–extension, lateral bending, and axial rotation tasks. Inverse kinematics analyses were performed on subject-specific models with 17 thoracolumbar joints allowing 51 rotational DOF (51DOF) and corresponding models including seven sets of kinematic constraints that limited spine motion from 3 to 9DOF. Outcomes included: (1) root mean square (RMS) error of spine markers (measured vs. model); (2) lag-one autocorrelation coefficients to assess smoothness of angular motions; (3) maximum range of motion (ROM) of intervertebral joints in three directions of motion (FE, LB, AR) to assess whether they are physiologically reasonable; and (4) segmental spine angles in static ROM trials. We found that RMS error of spine markers was higher with constraints than without (p < 0.0001) but did not notably improve kinematic constraints above 6DOF. Compared to segmental angles calculated directly from spine markers, models with kinematic constraints had moderate to good intraclass correlation coefficients (ICCs) for flexion–extension and lateral bending, though weak to moderate ICCs for axial rotation. Adding more DOF to kinematic constraints did not improve performance in matching segmental angles. Kinematic constraints with 4–6DOF produced similar levels of smoothness across all tasks and generally improved smoothness compared to 9DOF or unconstrained (51DOF) models. Our results also revealed that the maximum joint ROMs predicted using 4–6DOF constraints were largely within physiologically acceptable ranges throughout the spine and in all directions of motions. We conclude that a kinematic constraint with 5DOF can produce smooth spine motions with physiologically reasonable joint ROMs and relatively low marker error.

The relationship between external thoracopelvic angle and lumbar segmental axial twist angle using an ultrasound imaging technique

The relationship between externally measured and internal spine axial twist motion (rotation about a vertical axis) is not well understood. Ultrasound is a validated technique for measurement of vertebral axial twist motion and has the potential for measuring segmental vertebral axial twist in vivo. The objective of this study was to evaluate lumbar segmental axial twist in relation to external thoracopelvic twist from optical motion capture using an ultrasound imaging technique. Sixteen participants were tested in a custom-built axial twist jig, which isolated motion to the lumbar spine. Participants were moved from neutral to 75% of maximum axial twist range of motion in an upright kneeling posture. Thoracopelvic motion was recorded with a motion capture system and L1 to S1 vertebral axial twist was recorded using ultrasound. From motion capture, maximum thoracopelvic axial twist motion was 41.1 degrees. From ultrasound, the majority of axial twist motion occurred at the L2-L3 (46.8% of lumbar axial twist motion) and L5-S1 (33.5%) intervertebral joints. Linear regression linking axial twist at each vertebral level to thoracopelvic axial twist ranged from 0.43 to 0.79. These findings demonstrate a mathematical relationship between internal and external axial twist motion and the distribution of motion across the lumbar spine suggests that classic use of L4-L5 to represent lumbar spine motion may not be appropriate for axial twist modelling approaches.

In-vitro 3D Analysis of Sacroiliac Joint Kinematics: Primary and Coupled Motions

STUDY DESIGN

An in-vitro biomechanical study of human cadaver sacroiliac joints.

OBJECTIVE

Our study aimed to develop a more comprehensive understanding of the native motion of the SIJ within the context of spinal kinematics and spinal implant evaluation.

SUMMARY OF BACKGROUND DATA

Increasing attention has been given to the sacroiliac joint (SIJ) as a source of low back pain, despite its limited range of motion. We sought to characterize the rotational and translational motion in each axis utilizing standard pure moment flexion-extension (FE), lateral bending (LB), and axial rotation (AR) testing.

METHODS

Sixteen sacroiliac joints were evaluated from eight lumbosacral cadaver specimens (six females, two males) from subjects aged 28 to 57 years (mean age 46.8) with body mass index (BMI) 22 to 36 (mean BMI 30). Single leg stance was modeled by clamping the blocks on one ischium in a vise and letting the contralateral ischium hang freely. Pure moment loading was applied in FE, right/left AR, and right/left LB. Relative motions were collected with infrared markers.

RESULTS

The on-axis ratio was significantly lower in LB than in FE (P = 0.012) and in AR (P = 0.017). The rotation deviation angle measured 13.9 ± 9.1° in FE, 17.1 ± 8.7° in AR, and 35.7 ± 25.7° in LB. In LB the rotational deviation angle is significantly higher than both FE and AR (P = 0.003 and P = 0.011, respectively). In-plane translation was significantly higher (P = 0.005) in FE loading than in LB loading.

CONCLUSION

A nontrivial amount of rotation and translation occurred out of the expected axis of motion. The largest amount of off-axis rotation was observed in lateral bending. Relative to resultant translation, in-plane translation was lowest in lateral bending. Our results indicate that rotation of the SIJ is not fully described with the in-plane metrics which are normally reported in evaluation of fusion devices. Future studies of the SIJ may need to consider including off-axis rotation measurements when describing SIJ kinematics.Level of Evidence: 5.

An open-source musculoskeletal model of the lumbar spine and lower limbs: a validation for movements of the lumbar spine

Musculoskeletal models of the lumbar spine have been developed with varying levels of detail for a wide range of clinical applications. Providing consistency is ensured throughout the modelling approach, these models can be combined with other computational models and be used in predictive modelling studies to investigate bone health deterioration and the associated fracture risk. To provide precise physiological loading conditions for such predictive modelling studies, a new full-body musculoskeletal model including a detailed and consistent representation of the lower limbs and the lumbar spine was developed. The model was assessed against in vivo measurements from the literature for a range of spine movements representative of daily living activities. Comparison between model estimations and electromyography recordings was also made for a range of lifting tasks. This new musculoskeletal model will provide a comprehensive physiological mechanical environment for future predictive finite element modelling studies on bone structural adaptation. It is freely available on https://simtk.org/projects/llsm/.

Development of a multiscale model of the human lumbar spine for investigation of tissue loads in people with and without a transtibial amputation during sit-to-stand

Quantification of lumbar spine load transfer is important for understanding low back pain, especially among persons with a lower limb amputation. Computational modeling provides a helpful solution for obtaining estimates of in vivo loads. A multiscale model was constructed by combining musculoskeletal and finite element (FE) models of the lumbar spine to determine tissue loading during daily activities. Three-dimensional kinematic and ground reaction force data were collected from participants with ([Formula: see text]) and without ([Formula: see text]) a unilateral transtibial amputation (TTA) during 5 sit-to-stand trials. We estimated tissue-level load transfer from the multiscale model by controlling the FE model with intervertebral kinematics and muscle forces predicted by the musculoskeletal model. Annulus fibrosis stress, intradiscal pressure (IDP), and facet contact forces were calculated using the FE model. Differences in whole-body kinematics, muscle forces, and tissue-level loads were found between participant groups. Notably, participants with TTA had greater axial rotation toward their intact limb ([Formula: see text]), greater abdominal muscle activity ([Formula: see text]), and greater overall tissue loading throughout sit-to-stand ([Formula: see text]) compared to able-bodied participants. Both normalized (to upright standing) and absolute estimates of L4-L5 IDP were close to in vivo values reported in the literature. The multiscale model can be used to estimate the distribution of loads within different lumbar spine tissue structures and can be adapted for use with different activities, populations, and spinal geometries.

Identification of the most relevant intervertebral effort indicators during gait of adolescents with idiopathic scoliosis

The intervertebral efforts, i.e., forces and torques, during gait have been recognized as influencing the progression of scoliosis, due to the mechanical modulations according to the Hueter-Volkmann Law. Therefore, these efforts are key variables for posture correction and to control the progression of scoliosis. Using the intervertebral efforts during gait for the clinical follow-ups has never been performed. For this, it would be necessary to identify amongst all these efforts the most relevant ones, which is the objective of this study. A previously developed dynamical model of the human body was used to compute the 3 D intervertebral efforts during the gait of 15 participants with adolescent idiopathic scoliosis (AIS) and 12 typically developed adolescents (TDA). Kolmogorov-Smirnov and Two-sample t-test were applied on the calculated intervertebral efforts and the graphs of intervertebral efforts were studied. Antero-posterior (AP) forces and torques and medio-lateral (ML) forces are the most relevant intervertebral efforts amongst the other efforts in adolescents with AIS during gait. Discussion: Gait analysis in adolescents with AIS based on the relevant intervertebral efforts could be an effective means to follow-up and evaluate the progression of scoliosis during their treatment period. This study highlights the most relevant intervertebral efforts of individuals with AIS during gait. As future work, the identified intervertebral efforts could be implemented in a quantified and visual feedback tool for therapeutic and performance evaluation or interactive sessions in physiotherapy, e.g., via video games for dynamic posture self-correction.

Clinical reasoning framework for thoracic spine exercise prescription in sport: a systematic review and narrative synthesis

BACKGROUND

The thoracic spine is critical for athletic kinetic chain functioning yet widely overlooked in terms of specific evidenced-based exercise prescription. Thoracic mobility, motor control and strength are required to optimise performance in sport and minimise excessive load/stress on other components of the kinetic chain.

OBJECTIVE

To identify and evaluate mobility, motor control, work capacity and strength thoracic exercises for use in athletes.

DESIGN

Systematic review involving expert reviewers at key stages: searches and screening (n=1), eligibility, evaluation, data extraction and evaluation (n=3). Key databases and social media sources were searched to 16 August 2019. Eligible exercises were thoracic exercises to promote mobility, motor control, work capacity and strength. A narrative synthesis enabled an outcome-based classification of exercises, with level of evidence of individual sources informing overall level of evidence for each outcome (Oxford Centre for Evidence-based Medicine).

RESULTS

From 2348 sources (social media, database searches and other sources), 38 exercises were included. Sources included images, video clips and written descriptions of exercises. Exercises targeting all planes of motion were evaluated and classified according to outcome. Exercises comprised functional and non-functional exercises for mobility (n=9), work capacity (n=15), motor control (n=7) and strength (n=7). Overall level of evidence for each outcome was level 5.

CONCLUSION

This synthesis and evaluation of exercises has captured the scope of thoracic exercises used in 'practice'. Evaluation against an expert-derived outcome-based classification provides practitioners with a framework to facilitate exercise prescription. Evaluation of validity and effectiveness of exercises on outcomes is now required.

Assessment of Hip Translation In Vivo in Patients With Femoracetabular Impingement Syndrome Using 3-Dimensional Computed Tomography

Purpose

To determine the 3-dimensional (3D) in vivo hip translation in patients with symptomatic femoroacetabular impingement syndrome (FAIS) using 3D computed tomography (CT) models with the hip in neutral and FABER (flexion, abduction, and the external rotation) positions and to identify patient predictors associated with the degree of hip translation.

Methods

Seventy-eight patients with FAIS and cam lesions underwent CT scans in neutral and FABER positions. Demographics including age, sex, and body mass index (BMI) were recorded for each patient. The cam deformity was characterized both in plain x-ray film and 3D. Translation between both positions was calculated using a validated high-precision 3D-3D registration technique. Univariate and multivariate regression analyses sought factors correlated with translation.

Results

The mean age of the patients included in the analysis was 36.3 ± 9.2 years, with 51% of the study group being female. The mean 3D femoral head center translation was 0.84 ± 0.37 mm, decomposed into vectors on standard anatomical directions as 0.13 ± 0.58 mm medial, 0.10 ± 0.54 mm posterior, and 0.08 ± 0.46 mm inferior. Multivariate analysis demonstrated that total translation was associated with larger alpha angles (β = 0.014; 95% confidence interval [CI] 0.003-0.024; P = .013), and greater BMI (β = 0.033; 95% CI 0.001-0.065; P = .042). Furthermore, posterior–inferior translation was associated with BMI (β = 0.032; 95% CI 0.003-0.061; P = .031), whereas medial–lateral translation is associated with the female sex (β = 0.388; 95% CI 0.124-0.634; P = .002), and smaller head radius (β = –0.068; 95% CI –0.128 to –0.007; P = .029).

Conclusions

As a provocative maneuver, FABER positioning in patients with FAIS resulted in an average measurable translation of the femoral head center in the posterior, medial, and inferior direction. Factors including sex, BMI, and alpha angle predicted the degree of translation.

Clinical Relevance

The current study demonstrates that there is measurable hip translation between the neutral and FABER positions in patients with symptomatic FAIS, which may cause hip microinstability. Furthermore, the study found an association between hip translation and both modifiable and nonmodifiable factors. This may indicate the need for more comprehensive preoperative surgical planning, intraoperative dynamic examination of the hip, and consideration of capsular plication in certain patients.

Lumbar spine angles and intervertebral disc characteristics with end-range positions in three planes of motion in healthy people using upright MRI

Understanding changes in lumbar spine (LS) angles and intervertebral disc (IVD) behavior in end-range positions in healthy subjects can provide a basis for developing more specific LS models and comparing people with spine pathology. The purposes of this study are to quantify 3D LS angles and changes in IVD characteristics with end-range positions in 3 planes of motion using upright MRI in healthy people, and to determine which intervertebral segments contribute most in each plane of movement. Thirteen people (average age = 24.4 years, range 18-51 years; 9 females; BMI = 22.4 ± 1.8 kg/m²) with no history of low back pain were scanned in an upright MRI in standing, sitting flexion, sitting axial rotation (left, right), prone on elbows, prone extension, and standing lateral bending (left, right). Global and local intervertebral LS angles were measured. Anterior-posterior length of the IVD and location of the nucleus pulposus was measured. For the sagittal plane, lower LS segments contribute most to change in position, and the location of the nucleus pulposus migrated from a more posterior position in sitting flexion to a more anterior position in end-range extension. For lateral bending, the upper LS contributes most to end-range positions. Small degrees of intervertebral rotation (1-2°) across all levels were observed for axial plane positions. There were no systematic changes in IVD characteristics for axial or coronal plane positions.

Twente Spine Model: A thorough investigation of the spinal loads in a complete and coherent musculoskeletal model of the human spine

Although in vivospinal loads have been previously measured, existing data are limited to certain lumbar and thoracic levels. A detailed investigation of spinal loads would assist with injury prevention and implant design but is unavailable. In this study, we developed a complete and coherent musculoskeletal model of the entire human spine and studied the intervertebral disc compression forces for physiological movements on three anatomical planes. This model incorporates the individual vertebrae at the cervical, thoracic, and lumbar regions, a flexible ribcage, and complete muscle anatomy. Intradiscal pressures were estimated from predicted compressive forces, and these were generally in close agreement with previously measured data. We found that compressive forces at the trunk discs increased during trunk lateral bending and axial rotation of the trunk. During flexion, compressive forces increased in the thoracolumbar and lumbar regions and slightly decreased at the middle thoracic discs. In extension, the forces generally decreased at the thoracolumbar and lumbar discs whereas they slightly increased at the upper and middle thoracic discs. Furthermore, similar to a previous biomechanical model of the cervical spine, our model predicted increased compression forces in neck flexion, lateral bending, and axial rotation, and decreased forces in neck extension.

Kinematics of the Spine During Sit-to-Stand Movement Using Motion Analysis Systems: A Systematic Review of Literature

CONTEXT

Clinical evaluation of the spine is commonplace in musculoskeletal therapies, such as physiotherapy, physical medicine/rehabilitation, osteopathic, and chiropractic clinics. Sit-to-stand (STS) is one of the most mechanically demanding daily activities and crucial to independence. Difficulty or inability to perform STS is common in individuals with a variety of motor disabilities, such as low back pain (LBP).

OBJECTIVE

The purpose of this systematic review was to evaluate available evidence in literature to determine 2-dimensional and 3-dimensional kinematics of the spine during STS in patients with LBP and healthy young adult participants using motion analysis systems (electromagnetic and marker based).

METHODS

Electronic databases (PubMed/MEDLINE [National Library of Medicine], Scopus, ScienceDirect, and Google Scholar) were searched between January 2002 and February 2017. Additionally, the reference lists of the articles that met the inclusion criteria were also searched. Prospective studies published in peer-reviewed journals, with full text available in English, investigating the kinematics of the spine during STS in healthy subjects (mean age between 18 and 50 y) or in patients with LBP using motion analysis systems, were included. Sixteen studies fulfilled the eligibility criteria. All information relating to methodology and kinematic modeling of the spine segments along with the outcome measures was extracted from the studies identified for synthesis.

RESULTS

The results indicated that the kinematics of the spine are greatly changed in patients with LBP. In order to develop a better understanding of spine kinematics, studies recommended that the trunk should be analyzed as a multisegment. It has been shown that there is no difference between the kinematics of patients with LBP and healthy population when the spine is analyzed as a single segment. Furthermore, between-gender differences are present during STS movement.

CONCLUSION

This review provided a valuable summary of the research to date examining the kinematics of the spine during STS.

What is the effect of prolonged sitting and physical activity on thoracic spine mobility? An observational study of young adults in a UK university setting

OBJECTIVE

Sedentary behaviour has long been associated with neck and low back pain, although relatively little is known about the thoracic spine. Contributing around 33% of functional neck movement, understanding the effect of sedentary behaviour and physical activity on thoracic spinal mobility may guide clinical practice and inform research of novel interventions.

DESIGN

An assessor-blinded prospective observational study designed and reported in accordance with Strengthening the Reporting of Observational Studies in Epidemiology.

SETTING

UK university (June-September 2016).

PARTICIPANTS

A convenience sample (18-30 years) was recruited and based on self-report behaviours, the participants were assigned to one of three groups: group 1, sitters-sitting >7 hours/day+physical activity<150 min/week; group 2, physically active-moderate exercise >150 min/week+sitting <4 hours/day and group 3, low activity-sitting 2-7 hours/day+physical activity <150 min/week.

OUTCOME MEASURES

Thoracic spine mobility was assessed in the heel-sit position using Acumar digital goniometer; a validated measure. Descriptive and inferential analyses included analysis of variance and analysis of covariance for between group differences and Spearman's rank correlation for post hoc analysis of associations.

RESULTS

The sample (n=92) comprised: sitters n=30, physically active n=32 and low activity n=30. Groups were comparable with respect to age and body mass index.Thoracic spine mobility (mean (SD)) was: group 1 sitters 64.75 (1.20), group 2 physically active 74.96 (1.18) and group 3 low activity 68.44 (1.22). Significant differences were detected between (1) sitters and low activity, (2) sitters and physically active (p<0.001). There was an overall effect size of 0.31. Correlations between thoracic rotation and exercise duration (r=0.67, p<0.001), sitting duration (r=-0.29, p<0.001) and days exercised (r=0.45, p<0.001) were observed.

CONCLUSIONS

Findings evidence reduced thoracic mobility in individuals who spend >7 hours/day sitting and <150 min/week of physical activity. Further research is required to explore possible causal relationships between activity behaviours and spinal musculoskeletal health.

A model-based approach for estimation of changes in lumbar segmental kinematics associated with alterations in trunk muscle forces

The kinematics information from imaging, if combined with optimization-based biomechanical models, may provide a unique platform for personalized assessment of trunk muscle forces (TMFs). Such a method, however, is feasible only if differences in lumbar spine kinematics due to differences in TMFs can be captured by the current imaging techniques. A finite element model of the spine within an optimization procedure was used to estimate segmental kinematics of lumbar spine associated with five different sets of TMFs. Each set of TMFs was associated with a hypothetical trunk neuromuscular strategy that optimized one aspect of lower back biomechanics. For each set of TMFs, the segmental kinematics of lumbar spine was estimated for a single static trunk flexed posture involving, respectively, 40° and 10° of thoracic and pelvic rotations. Minimum changes in the angular and translational deformations of a motion segment with alterations in TMFs ranged from 0° to 0.7° and 0 mm to 0.04 mm, respectively. Maximum changes in the angular and translational deformations of a motion segment with alterations in TMFs ranged from 2.4° to 7.6° and 0.11 mm to 0.39 mm, respectively. The differences in kinematics of lumbar segments between each combination of two sets of TMFs in 97% of cases for angular deformation and 55% of cases for translational deformation were within the reported accuracy of current imaging techniques. Therefore, it might be possible to use image-based kinematics of lumbar segments along with computational modeling for personalized assessment of TMFs.

Validity of the Digital Inclinometer and iPhone When Measuring Thoracic Spine Rotation

CONTEXT

  Spinal axial rotation is required for many functional and sporting activities. Eighty percent of axial rotation occurs in the thoracic spine. Existing measures of thoracic spine rotation commonly involve laboratory equipment, use a seated position, and include lumbar motion. A simple performance-based outcome measure would allow clinicians to evaluate isolated thoracic spine rotation. Currently, no valid measure exists.

OBJECTIVE

  To explore the criterion and concurrent validity of a digital inclinometer (DI) and iPhone Clinometer app (iPhone) for measuring thoracic spine rotation using the heel-sit position.

DESIGN

  Controlled laboratory study.

SETTING

  University laboratory.

PATIENTS OR OTHER PARTICIPANTS

  A total of 23 asymptomatic healthy participants (14 men, 9 women; age = 25.82 ± 4.28 years, height = 170.26 ± 8.01 cm, mass = 67.50 ± 9.46 kg, body mass index = 23.26 ± 2.79) were recruited from a student population.

MAIN OUTCOME MEASURE(S)

  We took DI and iPhone measurements of thoracic spine rotation in the heel-sit position concurrently with dual-motion analysis (laboratory measure) and ultrasound imaging of the underlying bony tissue motion (reference standard). To determine the criterion and concurrent validity, we used the Pearson product moment correlation coefficient (r, 2 tailed) and Bland-Altman plots.

RESULTS

  The DI (r = 0.88, P < .001) and iPhone (r = 0.88, P < .001) demonstrated strong criterion validity. Both also had strong concurrent validity (r = 0.98, P < .001). Bland-Altman plots illustrated mean differences of 5.82° (95% confidence interval [CI] = 20.37°, -8.73°) and 4.94° (95% CI = 19.23°, -9.35°) between the DI and iPhone, respectively, and the reference standard and 0.87° (95% CI = 6.79°, -5.05°) between the DI and iPhone.

CONCLUSIONS

  The DI and iPhone provided valid measures of thoracic spine rotation in the heel-sit position. Both can be used in clinical practice to assess thoracic spine rotation, which may be valuable when evaluating thoracic dysfunction.

Adjacent Segment Disease in the Cervical and Lumbar Spine

Adjacent segment disease (ASD) is disappointing long-term outcome for both the patient and clinician. In contrast to adjacent segment degeneration, which is a common radiographic finding, ASD is less common. The incidence of ASD in both the cervical and lumbar spine is between 2% and 4% per year, and ASD is a significant contributor to reoperation rates after spinal arthrodesis. The etiology of ASD is multifactorial, stemming from existing spondylosis at adjacent levels, predisposed risk to degenerative changes, and altered biomechanical forces near a previous fusion site. Numerous studies have sought to identify both patient and surgical risk factors for ASD, but a consistent, sole predictor has yet to be found. Spinal arthroplasty techniques seek to preserve physiological biomechanics, thereby minimizing the risk of ASD, and long-term clinical outcome studies will help quantify its efficacy. Treatment strategies for ASD are initially nonoperative, provided a progressive neurological deficit is not present. The spine surgeon is afforded many surgical strategies once operative treatment is elected. The goal of this manuscript is to consider the etiologies of ASD, review its manifestations, and offer an approach to treatment.

Incorporating Six Degree-of-Freedom Intervertebral Joint Stiffness in a Lumbar Spine Musculoskeletal Model-Method and Performance in Flexed Postures

Intervertebral translations and rotations are likely dependent on intervertebral stiffness properties. The objective of this study was to incorporate realistic intervertebral stiffnesses in a musculoskeletal model of the lumbar spine using a novel force-dependent kinematics approach, and examine the effects on vertebral compressive loading and intervertebral motions. Predicted vertebral loading and intervertebral motions were compared to previously reported in vivo measurements. Intervertebral joint reaction forces and motions were strongly affected by flexion stiffness, as well as force-motion coupling of the intervertebral stiffness. Better understanding of intervertebral stiffness and force-motion coupling could improve musculoskeletal modeling, implant design, and surgical planning.

Intraoperative CT as a registration benchmark for intervertebral motion compensation in image-guided open spinal surgery

PURPOSE

An accurate and reliable benchmark of registration accuracy and intervertebral motion compensation is important for spinal image guidance. In this study, we evaluated the utility of intraoperative CT (iCT) in place of bone-implanted screws as the ground-truth registration and illustrated its use to benchmark the performance of intraoperative stereovision (iSV).

METHODS

A template-based, multi-body registration scheme was developed to individually segment and pair corresponding vertebrae between preoperative CT and iCT of the spine. Intervertebral motion was determined from the resulting vertebral pair-wise registrations. The accuracy of the image-driven registration was evaluated using surface-to-surface distance error (SDE) based on segmented bony features and was independently verified using point-to-point target registration error (TRE) computed from bone-implanted mini-screws. Both SDE and TRE were used to assess the compensation accuracy using iSV.

RESULTS

The iCT-based technique was evaluated on four explanted porcine spines (20 vertebral pairs) with artificially induced motion. We report a registration accuracy of 0.57 [Formula: see text] 0.32 mm (range 0.34-1.14 mm) and 0.29 [Formula: see text] 0.15 mm (range 0.14-0.78 mm) in SDE and TRE, respectively, for all vertebrae pooled, with an average intervertebral rotation of [Formula: see text] (range 1.5[Formula: see text]-7.9[Formula: see text]). The iSV-based compensation accuracy for one sample (four vertebrae) was 1.32 [Formula: see text] 0.19 mm and 1.72 [Formula: see text] 0.55 mm in SDE and TRE, respectively, exceeding the recommended accuracy of 2 mm.

CONCLUSION

This study demonstrates the effectiveness of iCT in place of invasive fiducials as a registration ground truth. These findings are important for future development of on-demand spinal image guidance using radiation-free images such as stereovision and ultrasound on human subjects.

Lumbar spine kinematics during walking in people with and people without low back pain

Low back pain (LBP) is a problem that can contribute to functional limitations and disability. Understanding kinematics during walking can provide a basis for examination and treatment in people with LBP. Prior research related to kinematics during walking is conflicting. However, investigators have not considered regional differences in lumbar spine kinematics or movement-based LBP subgroups. In the current study, three-dimensional kinematics of the upper and lower lumbar regions were examined in people with and without LBP. A clinical examination then was conducted to assign people with LBP to a movement-based subgroup and differences in kinematics among subgroups were examined. All subjects displayed significantly more upper than lower lumbar movement in the axial and coronal planes (P<.01). People with LBP displayed significantly less overall lumbar rotation than controls (P<.05). There were no significant group differences in sagittal plane kinematics (P>.05). Walking was limited by or provocative of pain in <25% of subjects with LBP. There were predictable differences in kinematics among some movement-based LBP subgroups that approached statistical significance (P=.09-.11). Walking was provocative of LBP in few subjects, and differences between people with and without LBP and among LBP subgroups were minimal. Limitations include that attempts to standardize gait speed may have minimized observed effects, and there was limited power to detect movement-based LBP subgroup differences.

Sacroiliac joint motion in patients with degenerative lumbar spine disorders

OBJECT

Usually additional anchors into the ilium are necessary in long fusion to the sacrum for degenerative lumbar spine disorders (DLSDs), especially for adult spine deformity. Although the use of anchors is becoming quite common, surgeons must always keep in mind that the sacroiliac (SI) joint is mobile and they should be aware of the kinematic properties of the SI joint in patients with DLSDs, including adult spinal deformity. No previous study has clarified in vivo kinematic changes in the SI joint with respect to patient age, sex, or parturition status or the presence of DLSDs. The authors conducted a study to clarify the mobility and kinematic characteristics of the SI joint in patients with DLSDs in comparison with healthy volunteers by using in vivo 3D motion analysis with voxel-based registration, a highly accurate, noninvasive method.

METHODS

Thirteen healthy volunteers (the control group) and 20 patients with DLSDs (the DLSD group) underwent low-dose 3D CT of the lumbar spine and pelvis in 3 positions (neutral, maximal trunk flexion, and maximal trunk extension). SI joint motion was calculated by computer processing of the CT images (voxel-based registration). 3D motion of the SI joint was expressed as both 6 df by Euler angles and translations on the coordinate system and a helical axis of rotation. The correlation between joint motion and the cross-sectional area of the trunk muscles was also investigated.

RESULTS

SI joint motion during trunk flexion-extension was minute in healthy volunteers. The mean rotation angles during trunk flexion were 0.07° around the x axis, −0.02° around the y axis, and 0.16° around the z axis. The mean rotation angles during trunk extension were 0.38° around the x axis, −0.08° around the y axis, and 0.08° around the z axis. During trunk flexion-extension, the largest amount of motion occurred around the x axis. In patients with DLSDs, the mean rotation angles during trunk flexion were 0.57° around the x axis, 0.01° around the y axis, and 0.19° around the z axis. The mean rotation angles during trunk extension were 0.68° around the x axis, −0.11° around the y axis, and 0.05° around the z axis. Joint motion in patients with DLSDs was significantly greater, with greater individual difference, than in healthy volunteers. Among patients with DLSDs, women had significantly more motion than men did during trunk extension. SI joint motion was significantly negatively correlated with the cross-sectional area of the trunk muscles during both flexion and extension of the trunk.

CONCLUSIONS

The authors elucidated the mobility and kinematic characteristics of the SI joint in patients with DLSDs compared with healthy volunteers for the first time. This information is useful for spine surgeons because of the recent increase in spinopelvic fusion for the treatment of DLSDs.

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).

Kinematics of the thoracic spine in trunk lateral bending: in vivo three-dimensional analysis

BACKGROUND CONTEXT

In vivo three-dimensional kinematics of the thoracic spine in trunk lateral bending with an intact rib cage and soft tissues has not been well documented. There is no quantitative data in the literature for lateral bending in consecutive thoracic spinal segments, and there has not been consensus on the patterns of coupled motion with lateral bending.

PURPOSE

To demonstrate segmental ranges of motion (ROMs) in lateral bending and coupled motions of the thoracic spine.

STUDY DESIGN

In vivo three-dimensional biomechanics study of the thoracic spine.

PATIENT SAMPLE

Fifteen healthy male volunteers.

OUTCOME MEASURES

Computed analysis by using voxel-based registration.

METHODS

Participants underwent computed tomography of the thoracic spine in three supine positions: neutral, right maximum lateral bending, and left maximum lateral bending. The relative motions of vertebrae were calculated by automatically superimposing an image of vertebrae in a neutral position over images in bending positions, using voxel-based registration. Mean values of lateral bending were compared among the upper (T1-T2 to T3-T4), the middle-upper (T4-T5 to T6-T7), the middle-lower (T7-T8 to T9-T10), and the lower (T10-T11 to T12-L1) parts of the spine.

RESULTS

At lateral bending, the mean ROM (±standard deviation) of T1 with respect to L1 was 15.6°±6.3° for lateral bending and 6.2°±4.8° for coupled axial rotation in the same direction as lateral bending. The mean lateral bending of each spinal segment with respect to the inferior adjacent vertebra was 1.4°±1.3° at T1-T2, 1.3°±1.2° at T2-T3, 1.4°±1.3° at T3-T4, 0.9°±0.9° at T4-T5, 0.8°±1.0° at T5-T6, 1.1°±1.1° at T6-T7, 1.7°±1.2° at T7-T8, 1.3°±1.2° at T8-T9, 1.6°±0.7° at T9-T10, 1.8°±0.8° at T10-T11, 2.3°±1.0° at T11-T12, and 2.2°±0.8° at T12-L1. The smallest and the largest amounts of lateral bending were observed in the middle-upper and the lower parts, respectively. There was no significant difference in lateral bending between the upper and the middle-lower parts. Coupled axial rotation of each segment was generally observed in the same direction as lateral bending. However, high variability was found at the T2-T3 to T5-T6 segments. Coupled flexion was observed at the upper and middle parts, and coupled extension was observed at the lower part.

CONCLUSIONS

This study revealed in vivo three-dimensional motions of consecutive thoracic spinal segments in trunk lateral bending. The thoracolumbar segments significantly contributed to lateral bending. Coupled axial rotation generally occurred in the same direction with lateral bending. However, more variability was observed in the direction of coupled axial rotation at T2-T3 to T5-T6 segments in the supine position. These results are useful for understanding normal kinematics of the thoracic spine.

Finite element investigation of the effect of a bifid arch on loading of the vertebral isthmus

BACKGROUND

The biomechanical effect of a bifid arch as seen in spina bifida occulta and following a midline laminectomy is poorly understood.

PURPOSE

To test the hypothesis that fatigue failure limits will be exceeded in the case of a bifid arch, but not in the intact case, when the segment is subjected to complex loading corresponding to normal sporting activities.

STUDY DESIGN

Finite element analysis.

METHODS

Finite element model of an intact L4-S1 human lumbar motion segment including ligaments was used. A section of the L5 vertebral arch and spinous process was removed to create the model with a midline defect. The models were loaded axially to 1 kN and then combined with axial rotation of 3°. Bilateral stresses, alternating stresses, and shear fatigue failure on both models were assessed and compared.

RESULTS

Under 1 kN axial load, the von Mises stresses observed in midline defect case and in the intact case were very similar (differences <5 MPa) having a maximum at the ventral end of the isthmus that decreases monotonically to the dorsal end. However, under 1 kN axial load and rotation, the maximum von Mises stresses observed in the ipsilateral L5 isthmus in the midline defect case (31 MPa) was much higher than the intact case (24.2 MPa), indicating a lack of load sharing across the vertebral arch in the midline defect case. When assessing the equivalent alternating shear stress amplitude, this was found to be 22.6 MPa for the midline defect case and 13.6 MPa for the intact case. From this, it is estimated that shear fatigue failure will occur in less than 70,000 cycles, under repetitive axial load and rotation conditions in the midline defect case, whereas for the intact case, fatigue failure will occur only after more than 10 million cycles.

CONCLUSIONS

A bifid arch predisposes the isthmus to early fatigue fracture by generating increased stresses across the inferior isthmus of the inferior articular process, specifically in combined axial rotation and anteroposterior shear.

A fast, accurate, and reliable reconstruction method of the lumbar spine vertebrae using positional MRI

In vivo measurement of lumbar spine configuration is useful for constructing quantitative biomechanical models. Positional magnetic resonance imaging (MRI) accommodates a larger range of movement in most joints than conventional MRI and does not require a supine position. However, this is achieved at the expense of image resolution and contrast. As a result, quantitative research using positional MRI has required long reconstruction times and is sensitive to incorrectly identifying the vertebral boundary due to low contrast between bone and surrounding tissue in the images. We present a semi-automated method used to obtain digitized reconstructions of lumbar vertebrae in any posture of interest. This method combines a high-resolution reference scan with a low-resolution postural scan to provide a detailed and accurate representation of the vertebrae in the posture of interest. Compared to a criterion standard, translational reconstruction error ranged from 0.7 to 1.6 mm and rotational reconstruction error ranged from 0.3 to 2.6°. Intraclass correlation coefficients indicated high interrater reliability for measurements within the imaging plane (ICC 0.97-0.99). Computational efficiency indicates that this method may be used to compile data sets large enough to account for population variance, and potentially expand the use of positional MRI as a quantitative biomechanics research tool.

Capturing Three-Dimensional In Vivo Lumbar Intervertebral Joint Kinematics Using Dynamic Stereo-X-Ray Imaging

Availability of accurate three-dimensional (3D) kinematics of lumbar vertebrae is necessary to understand normal and pathological biomechanics of the lumbar spine. Due to the technical challenges of imaging the lumbar spine motion in vivo, it has been difficult to obtain comprehensive, 3D lumbar kinematics during dynamic functional tasks. The present study demonstrates a recently developed technique to acquire true 3D lumbar vertebral kinematics, in vivo, during a functional load-lifting task. The technique uses a high-speed dynamic stereo-radiography (DSX) system coupled with a volumetric model-based bone tracking procedure. Eight asymptomatic male participants performed weight-lifting tasks, while dynamic X-ray images of their lumbar spines were acquired at 30 fps. A custom-designed radiation attenuator reduced the radiation white-out effect and enhanced the image quality. High resolution CT scans of participants' lumbar spines were obtained to create 3D bone models, which were used to track the X-ray images via a volumetric bone tracking procedure. Continuous 3D intervertebral kinematics from the second lumbar vertebra (L2) to the sacrum (S1) were derived. Results revealed motions occurring simultaneously in all the segments. Differences in contributions to overall lumbar motion from individual segments, particularly L2–L3, L3–L4, and L4–L5, were not statistically significant. However, a reduced contribution from the L5–S1 segment was observed. Segmental extension was nominally linear in the middle range (20%–80%) of motion during the lifting task, but exhibited nonlinear behavior at the beginning and end of the motion. L5–S1 extension exhibited the greatest nonlinearity and variability across participants. Substantial AP translations occurred in all segments (5.0 ± 0.3 mm) and exhibited more scatter and deviation from a nominally linear path compared to segmental extension. Maximum out-of-plane rotations (<1.91 deg) and translations (<0.94 mm) were small compared to the dominant motion in the sagittal plane. The demonstrated success in capturing continuous 3D in vivo lumbar intervertebral kinematics during functional tasks affords the possibility to create a baseline data set for evaluating the lumbar spinal function. The technique can be used to address the gaps in knowledge of lumbar kinematics, to improve the accuracy of the kinematic input into biomechanical models, and to support development of new disk replacement designs more closely replicating the natural lumbar biomechanics.