A rigid body model of the dynamic posteroanterior motion response of the human lumbar spine

BACKGROUND: Clinicians apply posteroanterior (PA) forces to the spine for both mobility assessment and certain spinal mobilization and manipulation treatments. Commonly applied forces include low-frequency sinusoidal oscillations (<2 Hz) as used in mobilization, single haversine thrusts (<0.5 seconds) as imparted in high-velocity, low-amplitude (HVLA) manipulation, or very rapid impulsive thrusts (<5 ms) such as those delivered in mechanical-force, manually-assisted (MFMA) manipulation. Little is known about the mechanics of these procedures. Reliable methods are sought to obtain an adequate understanding of the force-induced displacement response of the lumbar spine to PA forces. OBJECTIVE: The objective of this study was to investigate the kinematic response of the lumbar spine to static and dynamic PA forces. DESIGN: A 2-dimensional modal analysis was performed to predict the dynamic motion response of the lumbar spine. METHODS: A 5-degree-of-freedom, lumped equivalent model was developed to predict the PA motion of the lumbar spine. Lumbar vertebrae were modeled as masses, massless-spring, and dampers, and the resulting equations of motion were solved by using a modal analysis approach. The sensitivity of the model to variations in the spring stiffness and damping coefficients was examined, and the model validity was determined by comparing the results to oscillatory and impulsive force measurements of vertebral motion associated with spine mobilization and 2 forms of spinal manipulation. RESULTS: Model predictions, based on a damping ratio of 0.15 (moderate damping) and PA spring stiffness coefficient ranging from 25 to 60 kN/m, showed good agreement with in vivo human studies. Quasi-static and low-frequency (<2.0 Hz) forces at L3 produced L3 segmental and L3-L4 intersegmental displacements up to 8.1 mm and 3.0 mm, respectively. PA oscillatory motions were over 2.5-fold greater for oscillatory forces applied at the natural frequency. Impulsive forces produced much lower segmental displacements in comparison to static and oscillatory forces. Differences in intersegmental displacements resulting from impulsive, static, and oscillatory forces were much less remarkable. The latter suggests that intersegmental motions produced by spinal manipulation may play a prominent role in eliciting therapeutic responses. CONCLUSIONS: The simple analytical model presented in this study can be used to predict the static, cyclic, and impulsive force PA displacement response of the lumbar spine. The model provides data on lumbar segmental and intersegmental motion patterns that are otherwise difficult to obtain experimentally. Modeling of the PA motion response of the lumbar spine to PA forces assists in the understanding the biomechanics of therapeutic PA forces applied to the lumbar spine and may ultimately be used to validate chiropractic technique procedures and minimize risk to patients receiving spinal manipulative therapy.     

Spinal manipulation force and duration affect vertebral movement and neuromuscular responses

BACKGROUND: Previous study in human subjects has documented biomechanical and neurophysiological responses to impulsive spinal manipulative thrusts, but very little is known about the neuromechanical effects of varying thrust force-time profiles. METHODS: Ten adolescent Merino sheep were anesthetized and posteroanterior mechanical thrusts were applied to the L3 spinous process using a computer-controlled, mechanical testing apparatus. Three variable pulse durations (10, 100, 200 ms, force = 80 N) and three variable force amplitudes (20, 40, 60 N, pulse duration = 100 ms) were examined for their effect on lumbar motion response (L3 displacement, L1, L2 acceleration) and normalized multifidus electromyographic response (L3, L4) using a repeated measures analysis of variance. FINDINGS: Increasing L3 posteroanterior force amplitude resulted in a fourfold linear increase in L3 posteroanterior vertebral displacement (p < 0.001) and adjacent segment (L1, L2) posteroanterior acceleration response (p < 0.001). L3 displacement was linearly correlated (p < 0.001) to the acceleration response over the 20-80 N force range (100 ms). At constant force, 10 ms thrusts resulted in nearly fivefold lower L3 displacements and significantly increased segmental (L2) acceleration responses compared to the 100 ms (19%, p = 0.005) and 200 ms (16%, p = 0.023) thrusts. Normalized electromyographic responses increased linearly with increasing force amplitude at higher amplitudes and were appreciably affected by mechanical excitation pulse duration. INTERPRETATION: Changes in the biomechanical and neuromuscular response of the ovine lumbar spine were observed in response to changes in the force-time characteristics of the spinal manipulative thrusts and may be an underlying mechanism in related clinical outcomes.     

Neuromechanical characterization of in vivo lumbar spinal manipulation. Part I. Vertebral motion

OBJECTIVE: To quantify in vivo spinal motions and coupling patterns occurring in human subjects in response to mechanical force, manually assisted, short-lever spinal manipulative thrusts (SMTs) applied to varying vertebral contact points and utilizing various excursion (force) settings. METHODS: Triaxial accelerometers were attached to intraosseous pins rigidly fixed to the L1, L3, or L4 lumbar spinous process of 4 patients (2 male, 2 female) undergoing lumbar decompressive surgery. Lumbar spine acceleration responses were recorded during the application of 14 externally applied posteroanterior (PA) impulsive SMTs (4 force settings and 3 contact points) in each of the 4 subjects. Displacement time responses in the PA, axial (AX), and medial-lateral (ML) axes were obtained, as were intervertebral (L3-4) motion responses in 1 subject. Statistical analysis of the effects of facet joint (FJ) contact point and force magnitude on peak-to-peak displacements was performed. Motion coupling between the 3 coordinate axes of the vertebrae was examined using a least squares linear regression. RESULTS: SMT forces ranged from 30 N (lowest setting) to 150 N (maximum setting). Peak-to-peak ML, PA, and AX vertebral displacements increased significantly with increasing applied force. For thrusts delivered over the FJs, pronounced coupling was observed between all axes (AX-ML, AX-PA, PA-ML) (linear regression, R(2) = 0.35-0.52, P <.001), whereas only the AX and PA axes showed a significant degree of coupling for thrusts delivered to the spinous processes (SPs) (linear regression, R(2) = 0.82, P <.001). The ML and PA motion responses were significantly (P <.05) greater than the AX response for all SMT force settings. PA vertebral displacements decreased significantly (P <.05) when the FJ contact point was caudal to the pin compared with FJ contact cranial to the pin. FJ contact at the level of the pin produced significantly greater ML vertebral displacements in comparison with contact above and below the pin. SMTs over the spinous processes produced significantly (P <.05) greater PA and AX displacements in comparison with ML displacements. The combined ML, PA, and AX peak-to-peak displacements for the 4 force settings and 2 contact points ranged from 0.15 to 0.66 mm, 0.15 to 0.81 mm, and 0.07 to 0.45 mm, respectively. Intervertebral motions were of similar amplitude as the vertebral motions. CONCLUSIONS: In vivo kinematic measurements of the lumbar spine during the application of SMTs over the FJs and SPs corroborate previous spinous process measurements in human subjects. Our findings demonstrate that PA, ML, and AX spinal motions are coupled and dependent on applied force and contact point.     

Validation of an Ultrasound Protocol to Measure Intervertebral Axial Twist during Functional Twisting Movements in Isolated Functional Spinal Units

Ultrasound has potential for use in evaluation of bone and joint movement during axial twist of the lumbar spine both in vivo and in vitro. Such segmental rotations could then be measured under controlled external thoracic axial twist conditions and in response to mechanical loading. The purpose of this study was to measure vertebral segmental rotations in a porcine model of the human lumbar spine using an ultrasound imaging protocol and to validate use of this imaging technique with an optical motion capture system. In part 1, ultrasound transducer angle was confirmed to have no effect on sonogram point digitization. In part 2, 12 porcine functional spinal units were fixed to a mechanical testing system, and compression (15% of compressive tolerance), flexion–extension and axial twist (0°, 2°, 4° or 6°) were applied. Axial twist motion was tracked using an optical motion capture system and posterior surface ultrasound. Correlation between the two measurement systems was >0.903, and absolute system error was 0.01° across all flexion–extension postures. These findings indicate that ultrasound can be used to track axial twist motion in an in vitro spine motion segment and has the potential for use in vivo to evaluate absolute intervertebral axial twist motion.     

Precision measurement of segmental motion from flexion-extension radiographs of the lumbar spine

OBJECTIVE: To measure sagittal plane motion of lumbar vertebrae from lateral radiographic views. Previously identified factors of imprecision such as distortion in central projection, off-centre position, axial rotation, and lateral tilt of the spine were compensated. STUDY DESIGN: This study presents a new protocol to measure sagittal plane rotational and translational motion from lateral flexion-extension radiographs of the lumbar spine. BACKGROUND: Conventional methods to determine sagittal plane rotation and translation are prone to error from the distortional effects of the divergence of the radiographic beam and the measurement error inherent in constructing tangents to the contours of the vertebral body. High precision is attained by roentgen-stereophotogrammetric methods, but because of their invasive nature they can be applied only in exceptional cases. Agreement has been reached only in that measurement of sagittal plane motion from lumbar spine flexion-extension radiographs is inaccurate. Normal patterns of sagittal plane motion and the definition of what is an abnormal flexion-extension radiograph have not been settled. METHOD: Starting from an analysis of vertebral contours in the lateral view, geometric measures are identified which are virtually independent of distortion, axial rotation or lateral tilt. Applying a new protocol based on those geometric measures, the pattern of translational and rotational motion was determined from flexion-extension radiographs of 61 symptom-free, adult subjects. Measurement errors were quantified in a specimen experiment; a reproducibility study quantified inter- and intraobserver errors. RESULTS: Magnitude and sign of 'translation per degree of rotation' determined from a cohort of 61 adult subjects were very uniform for all levels of the lumbar spine. An auxiliary study evaluating a cohort of 10 healthy subjects where flexion-extension radiographs had been taken standing and side-lying showed no dependence of the rotation/translation pattern on posture. The error study demonstrated errors in angle ranging between 0.7 and 1.6 degrees and errors in displacement ranging between 1.2% and 2.4% of vertebral depth (the largest errors occurring at the L(5)/S(1) segment). Intra- and interobserver tests showed no or only negligibly small bias and an SD virtually equal to the measurement error multiplied by radical2. The relation of displacement to angle observed in the normal cohort can be used in individual cases to predict translational motion depending on the rotation actually performed. A comparison of the predicted translation (determined from normal controls) and the value actually measured allows translational hypo-, normal, or hypermobility to be quantified. Examples illustrate application of the new method in cases of normal, hypo-, and hypermobility and in the case of an instrumented spine. CONCLUSIONS: The results of this study show that precision of the measurement of rotational and translational motion can be considerably enhanced by making allowance for radiographic distortional effects and by minimizing subjective influence in the measurement procedure.     

The middle layer of lumbar fascia can transmit tensile forces capable of fracturing the lumbar transverse processes: An experimental study

Background

Transversus abdominis and its aponeurotic attachment to the lumbar transverse processes via the middle layer of lumbar fascia are of proposed clinical and biomechanical importance. Moderate traction on these structures (simulating submaximal contraction of transversus abdominis) is reported to influence segmental motion, but their tensile capacity is unknown and the effects of sudden, maximal traction on these attachments and the transverse processes are uncertain.

Methods

In 15 embalmed cadaver abdomens, the middle layer of lumbar fascia was isolated, gripped and rapid tension applied in either a lateral or posteroanterior direction (simulating forces that may produce avulsion and traumatic fractures). Peak forces prior to tissue failure were recorded and the gross effects of traction documented.

Findings

Lumbar transverse process fractures were produced in all specimens; by transverse traction in 50% of tests and posteroanterior force in 80%. In the remainder the middle layer of lumbar fascia was torn. Mean transverse and posteroanterior peak forces reached in the middle layer of lumbar fascia prior to failure were 82 N (range 20–190 N) and 47 N (range 25–70 N), respectively.

Interpretation

The middle layer of lumbar fascia can transmit substantial tensile forces to lumbar vertebrae, capable of transverse process fracture under experimental conditions. Tensile capacity is likely to be even greater in-vivo. This suggests tranversus abdominis and the middle layer of lumbar fascia can strongly influence vertebral motion, should be incorporated in biomechanical models of the spine and considered as potential contributors to transverse process fractures by avulsion.     

Active trunk extensor contributions to dynamic posteroanterior lumbar spinal stiffness

BACKGROUND: Assessments of posteroanterior (PA) spinal stiffness using mobilization apparatuses have demonstrated an increase in PA spine stiffness during voluntary contraction of the lumbar extensor muscles; yet, little work has been done to this degree in symptomatic subjects. OBJECTIVE: To use a previously validated dynamic mechanical impedance procedure to quantify changes in PA dynamic spinal stiffness at rest and during lumbar isotonic extension tasks in patients with low back pain (LBP). METHODS: Thirteen patients with LBP underwent a dynamic spinal stiffness assessment in the prone-resting position and again during lumbar extensor efforts. Stiffness assessments were obtained using a handheld impulsive mechanical device equipped with an impedance head (load cell and accelerometer). PA manipulative thrusts (approximately 150 N, <5 milliseconds) were delivered to skin overlying the L3 left and right transverse processes (TPs) and to the L3 spinous process (SP) in a predefined order (left TP, SP, right TP) while patients were at rest and again during prone-lying lumbar isotonic extension tasks. Dynamic spinal stiffness characteristics were determined from force and acceleration measurements using the apparent mass (peak force/peak acceleration, kg). Apparent mass measurements for the resting and active lumbar isotonic task trials of each patient were compared using a 2-tailed, paired t test. RESULTS: A significant increase in the PA dynamic spinal stiffness was noted for thrusts over the SP (apparent mass [17.0%], P=.0004) during isotonic trunk extension tasks compared with prone resting, but no statistically significant changes in apparent mass were noted for the same measures over the TPs. CONCLUSIONS: These findings add support to the significance of the trunk musculature and spinal posture in providing increased spinal stability.     

No effects of cervical spine motion on cranial dura mater strain

OBJECTIVE: The aim of this study was to analyze the effects of cervical spine motion on cranial dura mater length variations in anatomical specimens using high-resolution linear displacement transducers. We hypothesized that transducer resolution was sufficient to measure dura mater length changes if they occurred during cervical spine motion. DESIGN: Cranial dura mater strain was measured using differential variable reluctance transducers during cervical spine motion in 11 formaldehyde-fixed whole-body anatomical specimens (mean age: 82 years). BACKGROUND: Several theories hypothesize that functional maneuvers carried out on the spine have an effect on intra-cranial structures due to the supposed continuity of spinal and cranial dura mater. The displacements of the spinal dura mater are supposed to be transmitted to the cranial dura mater. METHODS: Eleven anatomical specimens were used. Each specimen (positioned supine) was provided with three openings in the skull (frontal and parietal regions), leaving the dura mater intact. A differential variable reluctance transducer was inserted in frontal or sagittal orientation in the dura mater exposed in each opening. Strain was recorded during cyclic motions of cervical spine flexion-extension, lateral bending and axial rotation. RESULTS: Average length changes ranged from 0.01 to 0.13% (SD 0.01-0.21%) of initial length for all motions and locations studied, which in all cases was less than the accuracy of the transducers. CONCLUSION: It can thus be concluded that cervical spine motion does not induce significant strain of the cerebral dura mater. RELEVANCE: The present study does not support theories that are based on the transmission of strains from spinal to cranial dura mater.     

下段颈椎脊椎功能单位活动度与椎管狭窄程度间相关性分析

目的：探讨退变性下段颈椎的脊椎功能单位（FSU）活动度与相应节段椎管狭窄程度间相关性。资料与方法：随机选取拟行手术治疗的脊髓型颈椎病病人62例。全部拍摄MRI及动力位（过伸-过屈位）颈椎侧位CR片。测量参数包括C2~C7过伸/过屈位Cobb角和,反映颈椎整体活动度;选取C3~C4、C4~C5、C5~C6三个水平的颈椎FSU过伸/过屈位Cobb角和表示FSU的节段性活动度。依据椎管狭窄等级（Ⅰ、Ⅱ、Ⅲ级）,分别对该3个FSU活动度行统计学分析。结果：Ⅰ级椎管狭窄病人的C4~C5、C5~C6椎间活动度大于C3~C4水平,其中C4~C5、与C3~C4水平间显示统计学差异。C4~C5、椎间活动度在Ⅲ级椎管狭窄时显著降低,与Ⅰ级、Ⅱ级有统计学意义。8例未显示Ⅲ级椎管狭窄病人与54例Ⅲ级椎管狭窄病人的椎体整体活动度间差异无统计学意义。结论：颈椎FSU作为维持颈椎稳定性的基本单元,随着椎管狭窄程度的增加稳定性增加,但却以牺牲椎管空间为代价,出现椎管狭窄,联合应用动力位CR侧位片及MR检查在判定颈椎活动度与椎管狭窄程度间关系显示重要价值。     

Lumbar intradiscal pressure after posterolateral fusion and pedicle screw fixation.

In vitro biomechanical testing was performed in single-functional spinal units of fresh calf lumbar spines, using pressure needle transducers to investigate the effect of posterolateral fusion (PLF) and pedicle screw constructs (PS) on intradiscal pressure (IDP), in order to elucidate the mechanical factors concerned with residual low back pain after PLF. IDP of 6 calf lumbar spines consisting of L4 and L5 vertebrae and an intervening disc was measured under axial compression, flexion-extension and lateral bending in the intact spine, PS, PLF and the destabilized spine. Relative to the intact spines, the destabilized spines showed increased IDP in all of lordings and moments. IDP under PS and PLF were significantly decreased in axial compression, extension and lateral bending loads (p<0.05). In flexion, IDP under PS and PLF increased linearly proportional to the magnitude of flexion moment and reached as high as IDP of the intact spines. These results demonstrated that despite an increase in the stiffness of motion segments after PLF and PS, significant high disc pressure is still generated in flexion. Flexibility of PS and PLF may cause increased axial load sharing of the disc in flexion and increased IDP. This high IDP may explain patients' persisting pain following PS and PLF.     

Functional radiography of the lumbar spine

Functional methods utilising the effects of gravity on the upright lordotic spine were developed for both static and dynamic radiography. Static standing orthoradiography of the lumbar spine and weight-bearing joints of the lower extremities shows constitutional and functional abnormalities not visible in conventional recumbent radiography, e.g., postural scoliosis, hypo- or hyperlordosis, "kissing spine"-syndrome and signs of segmental instability. In dynamic traction-compression radiography segmental instability is provoked by axial traction and compression of the spine. With this method translatory instability of 5 to 15 mm was found in about half of the patients with lytic spondylolisthesis of L5 for which flexion-extension radiography had consistently failed to produce any abnormal movement. The amount of anterior spondylolisthetic and posterior retro-olisthetic instability correlated significantly with the severity of back pain symptoms, the degree of maximal static slip, however, being without significance. Functional radiography showed positive findings in most patients suffering from chronic low back pain of otherwise unknown aetiology.     

The role of spinal tissues in resisting posteroanterior forces applied to the lumbar spine

OBJECTIVE: To determine the effects of the dissection of spinal tissues on the mechanical behavior of motion segments under the application of posteroanterior forces. DESIGN: A cadaveric motion segment study. SETTING: A tissue mechanics research laboratory. PROCEDURE: Anterior shear and extension moment were applied to 10 motion segments to simulate the clinical situation when posteroanterior forces were applied to the spine. The movements of the specimens in the sagittal plane were studied by a camera. Spinal tissues were dissected sequentially, and the mechanical testing was repeated after the dissection of each tissue. RESULTS: The most significant movements produced were extension and superior translation of the anteroinferior corner of the superior vertebral body. Translational movements in the other directions were small. The dissection of the posterior ligaments and zygapophyseal joints did not lead to significant changes in the movements. CONCLUSIONS: Injuries of the posterior ligaments are unlikely to alter the mechanical response of the spine to posteroanterior forces. However, these posterior tissues are pain sensitive and may be subjected to large strains and elicit symptoms.     

Manual fixation versus locking during upper cervical segmental mobilization. Part 2: an in vitro three-dimensional arthrokinematic analysis of manual axial rotation and lateral bending mobilization of the atlanto-axial joint

BackgroundThree-dimensional kinematic aspects of coupled motion during manual cervical mobilization have not previously been studied. Using an in vitro 3D-motion analysis method, the kinematic effects of two different segmental techniques for axial rotation and lateral bending mobilization of the upper cervical spine were investigated as a second part of the study (in part one, kinematic effects of flexion-extension mobilization have been investigated).MethodsAxial rotation and lateral bending mobilization of the atlanto-occipital and atlanto-axial segments were analysed in vitro using an electromagnetic tracking device. Local reference frames were defined based on bony reference points that were registered using a 3D-digitizing stylus.Five embalmed and one fresh specimen were analysed. Segmental motion was registered simultaneously in the atlanto-occipital and the atlanto-axial joints during manual mobilization through the full range of axial rotation and lateral bending mobility. The 3D-kinematic aspects during regional mobilization were compared with those during segmental mobilization with manual fixation and during segmental mobilization using a locking technique.ResultsDuring both segmental axial rotation techniques of the atlanto-axial joint, a significant reduction of the coupled lateral bending and flexion-extension motion was observed. The locking technique also induced an increase in the main axial rotation component. During lateral bending mobilization of the atlanto-axial joint, the manual fixation technique reduced the effect on the coupled flexion-extension component significantly.InterpretationsThese results suggest that for manual segmental axial rotation and lateral bending mobilization of the upper cervical spine segmental manual fixation or locking may be preferred in different situations depending on the desired effects. This study brings additional information to the data provided by part 1 of this study on the 3D-arthrokinematic effects of flexion-extension mobilization.     

In vivo transient vibration assessment of the normal human thoracolumbar spine

OBJECTIVE: The objective of this study was to quantify the mobility characteristics (dynamic stiffness and mechanical impedance) of the normal human thoracolumbar spine with a transient vibration analysis technique. DESIGN: This study is a prospective clinical investigation to obtain normative biomechanical data from the human male and female spine in vivo. SETTING: Musculoskeletal research laboratory, university setting. SUBJECTS: Twenty asymptomatic subjects (age range, 20-60 years) with no recent history of musculoskeletal complaints. MAIN OUTCOME MEASURES: Mechanical impedance, effective stiffness, and resonant frequency analyses were used to quantify the dynamic stiffness of the thoracolumbar spine in this subject population. Data were obtained from posteroanterior mechanical thrusts delivered with an activator adjusting instrument equipped with a load cell and accelerometer by means of a portable computer. RESULTS: In response to the activator adjusting instrument thrusts, the thoracolumbar spine typically exhibited an impedance minimum at frequencies ranging between 30 and 50 Hz. The maximum posteroanterior impedance and corresponding maximum effective stiffness of the thoracolumbar spine and sacrum was roughly 2 to 8 times greater than the magnitude of the impedance minimum. Statistically significant differences in mobility between male and female subjects were noted, particularly for frequencies corresponding to the maximum mobility (40 Hz) and minimum mobility (10-20 Hz, 70-80 Hz). For most subjects (both male and female), the lumbar region exhibited a higher impedance and stiffness (less mobility) when compared with the thoracic region. CONCLUSIONS: The posteroanterior mechanical behavior of the human thoracolumbar spine was found to be sensitive to mechanical stimulus frequency and showed significant region-specific and gender differences. In the frequency range of 30 to 50 Hz, the lumbar spine of this subject population is the least stiff and therefore has the greatest mobility. From a biomechanical point-of-view, the results of this study indicate that dynamic spinal manipulative therapy procedures will produce more spinal motion for a given force, particularly when the posteroanterior manipulative thrust is delivered in frequency ranges at or near the resonant frequency. In this regard, spinal manipulative therapy procedures designed to target the resonant frequency of the spine require less force application. Both magnitude and frequency content of manual and mechanical thrusting manipulations may be critical elements for therapeutic outcome.     

The effect of spinal instrumentation on lumbar intradiscal pressure.

The purpose of this study was to investigate the effect of spinal instrumentation on the intradiscal pressure (IDP) within the fixed motion segment. In vitro biomechanical testing was performed in six single functional spinal units of fresh calf lumbar spines using a pressure needle transducer. Various loads were applied by a materials testing system device. In addition to intact spine (control), anterior spinal instrumentation (ASI) and pedicle screw fixation (PS) constructs, as well as destabilized spine were tested. Relative to the control, the destabilized spine tended to have an increased IDP; by 15% in axial compression and by 9-36% in flexion-extension. Compared to the control, PS decreased the IDP by 23% in axial loading and 51% in extension loading and increased it by 60% in flexion for each loading. ASI decreased the IDP by 32% in flexion and 1% in extension. Lateral bending produced symmetrical changes of IDP in the control and destabilized spine, but no change in the PS construct. The IDP of the ASI construct was decreased by 77% in ipsilateral bending and increased by 22% in contralateral bending. These results demonstrated that eccentric loading from the spinal instruments increased IDP and significant disc pressure may still exist despite an increase in motion segment stiffness after lumbar stabilization.     

Anatomical relationships between selected segmental muscles of the lumbar spine in the context of multi-planar segmental motion: a preliminary investigation

In the last decade, concepts regarding spinal stability have been redefined. Whereas traditional stability models considered only the integrity of the intervertebral disc and spinal ligaments, mechanisms contributing to spinal stability are now thought to include neural and muscular elements. Lumbar muscles capable of generating intersegmental stiffness are considered necessary for the control of multi-planar segmental spinal motion. The transversus abdominis, psoas, quadratus lumborum and multifidus have each been described functionally as contributing to segmental motion control in the lumbar spine. However, the fundamental anatomy of these muscles has not been fully established nor have their architectural characteristics as a functional group been explored. A dissection of the lumbar spine was undertaken to document the attachments of the deep vertebral muscles and illustrate their group architectural characteristics in the context of multi-planar segmental motion. The transversus abdominis, psoas, quadratus lumborum and multifidus were each noted to have segmental attachment patterns in the lumbar spine. As a group, they surround the lumbar motion segments from the anterolateral aspect of a vertebral body to the spinous process. A hypothetical role for this muscle group in maintaining lumbar spine stability is discussed as are suggestions for future research.     

Motion characteristics of the lower lumbar spine in individuals with different pelvic incidence: An in vivo biomechanical study

BackgroundPelvic incidence is the quantification of the pelvis anatomical shape which has significant effect on the occurrence of various lumbar degenerative diseases. The aim of this study was to measure the in vivo dynamic motion characteristics of the lower lumbar spine in people with different pelvic incidence.MethodsA total of 55 volunteers were included in the study. The participants were devided into 3 groups (A: pelvic incidence≤40°, B: 40° < pelvic incidence <60° and C: pelvic incidence ≥60°). The L3–S1 vertebrae of each subject was MRI scanned to construct 3D models. The lumbar spine was then imaged using a dual fluoroscopic imaging system as the subject performed physiological position. The 3D vertebral models and the fluoroscopic images were used to reproduce the in vivo vertebral positions along the motion path. The relative translations and rotations of each motion segment were analyzed.FindingsAt the L5-S1 segment, the primary ranges of motion for left-right axial rotation and flexion-extension of the patients with large pelvic incidence (3.28° ± 0.79°, 7.56° ± 1.81°) were significantly larger than normal pelvic incidence (2.61° ± 1.01°, 6.57° ± 2.18°) and small pelvic incidence (2.00° ± 0.60°, 5.83° ± 1.67°).InterpretationThe anatomic variable pelvic incidence is associated with the ranges of motion in lower lumbar vertebrae, especially in the L4–5 and L5-S1 segments.     

Low back three-dimensional joint forces, kinematics, and kinetics during walking

OBJECTIVE: The purpose of this study was to examine the three-dimensional low back loads, spinal motions, and trunk muscular activity during gait. Specific objectives involved assessment of the effects of walking speed, and arm swing on spinal loads, lumbar spine motion, and muscular activation. DESIGN: An in vivo modeling experiment using five male participants. Thirty walking trials were performed by each participant yielding five repeats of each condition (3 walking cadences x 2 arm swing conditions). BACKGROUND: Walking is often prescribed as a rehabilitation task for individuals with low back injuries. However, there are few studies which have examined the joint loading, spinal motions, and muscular activity present when walking. Additionally, the majority of studies examining spine loading during gait have used an inverse dynamics model, commencing at the cranial aspect of the body, approach which does not include the impulsive phases of gait (i.e. heel strikes and toe offs). METHODS: Low back joint forces (bone on bone) and moments were determined using an anatomically complex three-dimensional model (detailing 54 muscles and the passive structures acting at the low back) during three walking cadences and with free arm swing or restricted arm swing. In order to assess the influence of the transient factors such as heel contact on the joint forces a bottom up (from the feet to the lumbar spine) rigid link segment analyses approach was used as one input to the three-dimensional anatomic model. Lumbar spine motion and trunk muscle activation levels were also recorded to assist in partitioning forces amongst the active and passive tissues of the low back. RESULTS: Net joint anterior-posterior shear loading was the only variable significantly affected by walking cadence (fast versus slow P < 0.0003). No variable was significantly affected by the arm swing condition. Trends demonstrated an increase in all variables with increased walking cadence. Similarly, most variables, with the exception of axial twist and lateral bend lumbar spine motion and lateral joint shear, demonstrated increasing trends caused by the restriction of normal arm swing. CONCLUSIONS: Tissue loading during walking appears to be below levels caused by many specific rehabilitation tasks, suggesting that walking is a wise choice for general back exercise and rehabilitation programs. Slow walking with restricted arm swing produced more 'static' lumbar spine loading and motion patterns, which could be detrimental for certain injuries and tissues. Fast walking produced a more cyclic loading pattern.