The impact of office chair features on lumbar lordosis, intervertebral joint and sacral tilt angles: a radiographic assessment.

BACKGROUND: The purpose of this study was to determine which office chair feature is better at improving spine posture in sitting. METHOD: Participants (n = 28) were radiographed in standing, maximum flexion and seated in four chair conditions: control, lumbar support, seat pan tilt and backrest with scapular relief. Measures of lumbar lordosis, intervertebral joint angles and sacral tilt were compared between conditions and sex. RESULTS: Sitting consisted of approximately 70% of maximum range of spine flexion. No differences in lumbar flexion were found between the chair features or control. Significantly more anterior pelvic rotation was found with the lumbar support (p = 0.0028) and seat pan tilt (p < 0.0001). Males had significantly more anterior pelvic rotation and extended intervertebral joint angles through L1-L3 in all conditions (p < 0.0001). CONCLUSION: No one feature was statistically superior with respect to minimising spine flexion, however, seat pan tilt resulted in significantly improved pelvic posture. Practitioner Summary: Seat pan tilt, and to some extent lumbar supports, appear to improve seated postures. However, sitting, regardless of chair features used, still involves near end range flexion of the spine. This will increase stresses to the spine and could be a potential injury generator during prolonged seated exposures.

Multisegment Kinematics of the Spinal Column: Soft Tissue Artifacts Assessment.

A major challenge in the assessment of intersegmental spinal column angles during trunk motion is the inherent error in recording the movement of bony anatomical landmarks caused by soft tissue artifacts (STAs). This study aims to perform an uncertainty analysis and estimate the typical errors induced by STA into the intersegmental angles of a multisegment spinal column model during trunk bending in different directions by modeling the relative displacement between skin-mounted markers and actual bony landmarks during trunk bending. First, we modeled the maximum displacement of markers relative to the bony landmarks with a multivariate Gaussian distribution. In order to estimate the distribution parameters, we measured these relative displacements on five subjects at maximum trunk bending posture. Then, in order to model the error depending on trunk bending angle, we assumed that the error grows linearly as a function of the bending angle. Second, we applied our error model to the trunk motion measurement of 11 subjects to estimate the corrected trajectories of the bony landmarks and investigate the errors induced into the intersegmental angles of a multisegment spinal column model. For this purpose, the trunk was modeled as a seven-segment rigid-body system described using 23 reflective markers placed on various bony landmarks of the spinal column. Eleven seated subjects performed trunk bending in five directions and the three-dimensional (3D) intersegmental angles during trunk bending were calculated before and after error correction. While STA minimally affected the intersegmental angles in the sagittal plane (<16%), it considerably corrupted the intersegmental angles in the coronal (error ranged from 59% to 551%) and transverse (up to 161%) planes. Therefore, we recommend using the proposed error suppression technique for STA-induced error compensation as a tool to achieve more accurate spinal column kinematics measurements. Particularly, for intersegmental rotations in the coronal and transverse planes that have small range and are highly sensitive to measurement errors, the proposed technique makes the measurement more appropriate for use in clinical decision-making processes.

Quantitative ultrasound assessment of the facet joint in the lumbar spine: a feasibility study.

This study was designed to determine the feasibility and accuracy of a sonographic approach to assessment of facet joints of the lumbar spine in healthy populations. Five facet joints (L1-S1) on each side of 30 volunteers, for a total of 300 facet joints, were examined and evaluated by sonography and computed tomography. Parameters of the facet joints (height and width) were established to assess the facet joint in the parasagittal and transverse planes on all volunteers. Differences between means of continuous variables including age, height, weight, body surface area, body mass index and joint parameters were evaluated with Student's t-test. Stepwise multiple regression analysis was used to evaluate the associations between the mean values of facet joint parameters and age, height, body surface area and body mass index. In general, sonography revealed that facet joints had a clear and smooth border. There were no significant differences in width and height between the left and right facet joints at the same level by sonography. Stepwise multiple regression analysis revealed that body mass index and age (p < 0.05) were the only independent factors modulating height of the facet joint. Facet joint width was independently influenced by age (p < 0.01). There were no significant differences between ultrasound and computed tomography in mean measurements of height (1.23 ± 0.15 vs. 1.25 ± 0.07, p > 0.05) and width (0.17 ± 0.08 vs. 0.18 ± 0.07, p > 0.05) of the facet joint, respectively. In this article, we describe a feasible, accurate and simple technique for identification and depiction of facet joints of the lumbar spine in healthy populations.

The assessment of material handling strategies in dealing with sudden loading: influences of foot placement on trunk biomechanics.

Sudden unexpected loading has been identified as a risk factor of work-related low back pain (LBP). This study investigated the effects of different foot placements and load-releasing locations on trunk biomechanics under an unexpected sudden loading event. Fifteen subjects experienced sudden release of a 6.8-kg external load from symmetric or asymmetric directions while maintaining four different foot placements. The results showed that subjects experienced on average 4.1° less trunk flexion, 6.6 Nm less L5/S1 joint moment and 32.0 N less shear force with staggered stance with the right foot forward (the most preferred placement) compared with wide stance (the least preferred placement). Asymmetric load-releasing positions consistently resulted in smaller impacts on trunk biomechanics than symmetric positions. The findings suggest that staggered stance and asymmetric load-holding position can be used as a protective load-handling posture against LBP caused by sudden loading. PRACTITIONER SUMMARY: In a work environment, unexpected sudden loading may cause low back pain (LBP). In this study, we used empirical data to demonstrate how different foot placements and load-releasing locations can be used to mitigate the impact of sudden loading on the spine and to reduce the risk of LBP.

Comparative analysis of assessment of the craniocervical equilibrium through two methods: cephalometry of Rocabado and cervical range of motion.

UNLABELLED: There are several instruments of evaluation of the craniocervical equilibrium; the most reliable are the radiographies. This study used the cephalometric analysis of Rocabado to measure the sensibility and specificity of the Cervical Range of Motion (CROM), a goniometer designed to assess cervical movements in degrees, and measure the forward head position in centimeters. This instrument frequently used, has been tested as a reliable instrument to evaluate the cervical movements but not the forward head. The sample consisted of 30 volunteers, 18 females, 12 males, mean age of 24.63 years. All participants were evaluated with CROM and radiographies in the resting head position and in erect head position. The values considered by the cephalometry consisted in the angle made between the McGregor plane and the vertical line formed by the base of the odontoid process to its apex; the posterior space between C0-C1 and C1-C2 and the hyoid triangle. RESULTS: 30% of the subjects had forward head posture, according to de cephalometry of Rocabado (decreased space between C0-C1, C1-C2) and 43,3% according to CROM. 16,6% had decreased posterior-inferior angle, and 13% had the hyoid triangle facing up. ROC curve of identifying forward head posture yielded area under the curve of 0,778 (95% confidence interval 0,596-0,960). The sensibility of CROM was: 77%. The specificity 71%. CONCLUSION: This study suggests that CROM has a moderate sensibility and specificity, useful for clinic use, but not for research.

The influence of the axial, antero-posterior and lateral positions of the center of rotation of a ball-and-socket disc prosthesis on the cervical spine biomechanics.

BACKGROUND: Previous studies documented the importance of the positioning and the design parameters of the prosthesis in determining the biomechanics of the implanted spine. However, a comprehensive biomechanical evaluation of the significance of these parameters is still lacking. Therefore, the paper is aimed to the quantification of their influence on the flexibility of the implanted spine and the force transmitted through the facet joints. METHODS: A finite element model of the C5-C6 spine unit including a ball-and-socket disc prosthesis was built. Three probabilistic variables were considered: the axial, antero-posterior and lateral positions of the center of rotation. Randomized input parameters were generated with the Monte Carlo method. Pure moments of 1.6 Nm in flexion, extension, lateral bending and axial rotation were imposed to the upper endplate of C5; 100 simulations were conducted for the each of the considered loading conditions. FINDINGS: Axial position of the center of rotation influenced the spine flexibility in all loading conditions and the facet force in extension, lateral bending and axial rotation. The antero-posterior position was found to influence the spine flexibility in flexion and extension, and the facet force in lateral bending and axial rotation. The lateral position was not significant. INTERPRETATION: The effects of the positioning of a cervical disc prosthesis were estimated. A wide range of mechanical behaviors can be obtained by the manufacturers by appropriately manipulating the position of the center of rotation. A proper positioning of the artificial disc during the surgery, in particular in the antero-posterior direction, was found to be of critical importance.

Biomechanical assessment of minimally invasive decompression for lumbar spinal canal stenosis: a cadaver study.

STUDY DESIGN: A biomechanical study on the cadaveric human lumbar spine. OBJECTIVE: We focused on a biomechanical comparison of the changes wrought on motion segments after a minimally invasive decompression and after a conventional medial facetectomy. SUMMARY OF BACKGROUND DATA: Minimally invasive posterior decompression using a microscope or an endoscope is becoming popular for elderly patients with lumbar spinal canal stenosis. An advantage of the technique is that the cauda equina and nerve roots are in clear view and the facet joints, paravertebral muscles, and spinous process are well preserved. METHODS: Eight human lumbar motion segments were used in this study. Each specimen was tested according to the following loading protocol: axial compression, flexion, extension, lateral bending to the right and to the left, and axial rotation to the right and to the left. This loading protocol was applied to each motion segment after the following surgical interventions: (1) left fenestration, (2) bilateral decompression via unilateral approach, (3) medial facetectomy, and (4) total facetectomy. The relative stiffness of the motion segments was determined and compared with a normalized stiffness for the specimen when intact. RESULTS: Bilateral decompression via unilateral approach produces less biomechanical effect in terms of stiffness changes as compared with medial facetectomy. Bilateral decompression leaves the spine more than 80% as stiff as the intact spine. CONCLUSIONS: These results go toward supporting a minimally invasive bilateral decompression. Minimally invasive bilateral decompression, as opposed to a conventional medial facetectomy, preserves the facet joints as much as possible. Preserving the facet joints during the decompression should produce less postoperative instability.

Material sensitivity study on lumbar motion segment (L2-L3) under sagittal plane loadings using probabilistic method.

OBJECTIVE: In this study, the probabilistic responses of a three-dimensional finite element L2-L3 motion segment, with and without posterior elements, tested under sagittal plane loadings, are presented. Understanding the effect of biologic uncertainties and variations on the biomechanical response provides an insight into spinal behavior under normal and degenerated conditions. METHODS: The biologic variability of 19 spinal components (nucleus, annulus, ligament, cortical/cancellous bone, endplate, and ligaments) in the motion segment was incorporated using statistical distributions into the model. A total of 2000 runs were performed using Monte Carlo probabilistic algorithms to compute the probabilistic response. RESULTS: This study establishes the relative importance of the spinal components in resisting the loading modes. The results show that for an intact motion segment, posterior ligaments are more dominant than intervertebral disc in resisting flexion moment. In extension, the capsular ligaments were found to be the most influential parameter. The intervertebral disc (ie, nucleus and annulus) affects the angular response of the disc body segment more than the hard tissues (ie, cortical and cancellous bone). CONCLUSIONS: The application of the probabilistic analysis provides a new approach whereby the influences of inherent uncertainties and variations in biologic structures can be studied and the biomechanical response assessed.