Spinal Stiffness Research Articles

Lumbar Spinal Stiffness Overshadows Polyethylene Wear: A Modern Explanation for Late Dislocation in Total Hip Arthroplasty

Instability or dislocation after total hip arthroplasty (THA) is a dreaded complication, occurring with rates ranging from 0.3% to 10% [1-4], and is the most common reason for revision surgery [5]. Risk factors for instability following THA include patient-specific factors such as non-compliance, neuromuscular or cognitive disorders, as well as surgical considerations including approach [6], soft tissue tension, component size; positioning, implant choice and polyethylene wear [7]. Traditionally, it is thought that the THA dislocation occurs in a bimodal distribution, based on timing after surgery (early and late). Early dislocations, which occur within the first two years following THA, are more common than late dislocations, and are more commonly attributed to component malposition [8], patient non-compliance (drug abuse or dementia) or neurocognitive disability (Parkinson Disease), or conditions affecting soft tissue quality and tension including soft tissue repair, rheumatoid arthritis and a vascular necrosis [9-11]. Late THA dislocations, which usually occur many years after THA, have been largely attributed to (based on our classic adult reconstruction teaching dogma) eccentric polyethylene wear [12].

Viscoelasticity of spinal cord and meningeal tissues

Compared to the outer dura mater, the mechanical behavior of spinal pia and arachnoid meningeal layers has received very little attention in the literature. This is despite experimental evidence of their importance with respect to the overall spinal cord stiffness and recovery following compression. Accordingly, inclusion of the mechanical contribution of the pia and arachnoid maters would improve the predictive accuracy of finite element models of the spine, especially in the distribution of stresses and strain through the cord’s cross-section. However, to-date, only linearly elastic moduli for what has been previously identified as spinal pia mater is available in the literature. This study is the first to quantitatively compare the viscoelastic behavior of isolated spinal pia-arachnoid-complex, neural tissue of the spinal cord parenchyma, and intact construct of the two. The results show that while it only makes up 5.5% of the overall cross-sectional area, the thin membranes of the innermost meninges significantly affect both the elastic and viscous response of the intact construct. Without the contribution of the pia and arachnoid maters, the spinal cord has very little inherent stiffness and experiences significant relaxation when strained. The ability of the fitted non-linear viscoelastic material models of each condition to predict independent data within experimental variability supports their implementation into future finite element computational studies of the spine. Statement of SignificanceThe neural tissue of the spinal cord is surrounded by three fibrous layers called meninges which are important in the behavior of the overall spinal-cord-meningeal construct. While the mechanical properties of the outermost layer have been reported, the pia mater and arachnoid mater have received considerably less attention. This study is the first to directly compare the behavior of the isolated neural tissue of the cord, the isolated pia-arachnoid complex, and the construct of these individual components. The results show that, despite being very thin, the inner meninges significantly affect the elastic and time-dependent response of the spinal cord, which may have important implications for studies of spinal cord injury.

The rib cage stiffens the thoracic spine in a cadaveric model with body weight load under dynamic moments.

The thoracic spine presents a challenge for biomechanical testing. With more segments than the lumbar and cervical regions and the integration with the rib cage, experimental approaches to evaluate the mechanical behavior of cadaveric thoracic spines have varied widely. Some researchers are now including the rib cage intact during testing, and some are incorporating follower load techniques in the thoracic spine. Both of these approaches aim to more closely model physiological conditions. To date, no studies have examined the impact of the rib cage on thoracic spine motion and stiffness in conjunction with follower loads. The purpose of this research was to quantify the mechanical effect of the rib cage on cadaveric thoracic spine motion and stiffness with a follower load under dynamic moments. It was hypothesized that the rib cage would increase stiffness and decrease motion of the thoracic spine with a follower load. Eight fresh-frozen human cadaveric thoracic spines with rib cages (T1-T12) were loaded with a 400 N compressive follower load. Dynamic moments of ± 5 N m were applied in lateral bending, flexion/extension, and axial rotation, and the motion and stiffness of the specimens with the rib cage intact have been previously reported. This study evaluated the motion and stiffness of the specimens after rib cage removal, and compared the data to the rib cage intact condition. Range-of-motion and stiffness were calculated for the upper, middle, and lower segments of the thoracic spine. Range-of-motion significantly increased with the removal of the rib cage in lateral bending, flexion/extension, and axial rotation by 63.5%, 63.0%, and 58.8%, respectively (p < 0.05). Neutral and elastic zones increased in flexion/extension and axial rotation, and neutral zone stiffness decreased in axial rotation with rib cage removal. Overall, the removal of the rib cage increases the range-of-motion and decreases the stiffness of cadaveric thoracic spines under compressive follower loads in vitro. This study suggests that the rib cage should be included when testing a cadaveric thoracic spine with a follower load to optimize clinical relevance.

Anesthetic management of two patients with alkaptonuric ochronosis for total knee arthroplasty

The current case report describes two cases of alkaptonuric ochronosis for anesthetic management. Alkaptonuria is a rare genetic orphan disease of tyrosine metabolism characterized by an accumulation of homogentisic acid in cartilage and connective tissues. Patients present most commonly for orthopedic joint surgery due to progressive arthropathy that can be misdiagnosed many a times. However respiratory, airway, cardiovascular and genitourinary systems complications can occur with age progressing. Restricted range of motion of cervical spine may lead to difficulty with airway management. In addition, degenerative changes and stiffness of lumbar spine due to ochronosis would make neuraxial blockade challenging. Although this inherited condition is extremely rare, anesthesiologists should be aware of its existence and prepare for management of potential challenging problems. This report highlights special care and precautions that need to be taken during anesthetic management.

Head and Neck : Interest of Botulinum Toxin against Pain and Inflammation

To describe the treatment by Botulinum Toxin (BoNTA) for seven painful pathologies of head and neck : cervical neuralgia, trigeminal neuralgia, migraine headache, articular pain, hypertrophic scars pain and inflammation, post-operative muscular pain of the cervical spine and muscle pain due to stiffness of the cervical spine following hypertonia and hyperactivity of the manducatory muscles. BoNTA has been used for forty years by its action on muscle. During the last decade new indications have been added, following the proof of the effect of the BT on numerous neurotransmitters. Technically, we inject into the muscles to relax them, into the keloid scars or immediately around to stop the inflammation, to relieve pain, we simply follow it, by topping of the skin, the scalp or the oral mucosa, depending on the pathology and the painful zone. For the temporo-mandibular joint, the injection is directly placed in the articulation. The toxin is very efficient on paroxysmal pain and for all these indications, we note a real decrease of the VAS score. For some indications, the dosage can be high, but there are no side effects or very limited. Except migraine headache, the other indications are new and there are not so many teams doing it.

Magnetic resonance elastography of the lumbar back muscles: A preliminary study.

Back pain is associated with increased lumbar paraspinal muscle (LPM) stiffness identified by manual palpation and strain elastography. Recently, magnetic resonance elastography (MRE) has allowed the stiffness of muscle to be characterized noninvasively in vivo, providing quantitative 3D stiffness maps (elastograms). The aim of this study was to characterize the stiffness (shear modulus, SM) of the LPM (multifidus and erector spinae) using MRE. MRE of the lumbar region was performed on seven adults in supine position. MRE was acquired in three muscular states: relaxed with outstretched legs, stretched with passive pelvis flexion, and contracted with outstretched legs and tightened trunk muscles. The mean SM was measured within a region of interest manually defined in the multifidus, erector spinae, and the entire paraspinal compartment. The intermuscular difference and the effects of stretching and contraction were assessed by ANOVA and t-tests. At rest, the mean SM of the paraspinal compartment was 1.6 ± 0.2 kPa. It increased significantly with stretching to 1.65 ± 0.3 kPa, and with contraction to 2.0 ± 0.7 kPa. Irrespective of muscular state, the erector spinae was significantly stiffer than the multifidus. The multifidus underwent proportionally higher stiffness changes from rest to contraction and stretching. MRE can be used to measure the stiffness of the LPM in different muscular states. We hypothesize that, irrespective of posture, the erector spinae behaves as semi-rigid beam, and ensures permanent stiffness of the spine. The multifidus behaves as an adaptable muscle that provides segmental flexibility to the spine and tunes the spine stiffness. Clin. Anat. 31:514-520, 2018. © 2018 Wiley Periodicals, Inc.

Bone mineral density changes over time in diffuse idiopathic skeletal hyperostosis of the thoracic spine.

Diffuse idiopathic skeletal hyperostosis (DISH) is an increasingly prevalent ankylosing condition. Patients with DISH have an increased risk of spinal fractures, hypothetically the result of biomechanical changes in the spine. The aim of this study was to analyze the occurrence of biomechanical stress shielding in patients with DISH. To do this, bone mineral density (BMD) was measured longitudinally in the vertebral bodies of subjects with and without DISH and in the newly formed bone of subjects with DISH. The presence of DISH was evaluated using Resnick criteria on two chest computed tomography (CT) scans taken at least 2.5 years apart from subjects over 50 years of age. Three groups were identified: pre-DISH (individuals who developed DISH after the first CT scan), definite DISH (individuals who had DISH on both CT scans), and controls (individuals with no DISH). Hounsfield units (HU) were measured in the newly formed bone and in predefined anterior and posterior portions of the involved vertebral bodies. Mean BMD of the newly formed bone increased significantly (mean ΔHU 137.5; p < 0.01) during a mean interval of 5 years in the cranial, middle, and caudally involved vertebral segments of both DISH groups. Mean BMD of the vertebral bodies in the ankylotic segments in the DISH groups did not significantly differ from that of the non-ankylotic vertebral bodies of the same subject. In contrast to our hypothesis, the HU value of the vertebral body decreased more in the control group than in the DISH groups; however, statistical significance was only reached at the cranial level in the anterior part of the vertebral body (p = 0.048). Our data suggest that 1) vertebral BMD is not influenced by the presence of DISH and 2) increased spinal stiffness may play a more important role than vertebral BMD in the increased fracture risk of and the typical fracture patterns observed in individuals with DISH.

The associtation between self-reported spinal morning stiffness and radiographic lumbar disc degeneration

The associtation between self-reported spinal morning stiffness and radiographic lumbar disc degeneration

Finite Element Study to Evaluate the Biomechanical Performance of the Spine After Augmenting Percutaneous Pedicle Screw Fixation With Kyphoplasty in the Treatment of Burst Fractures.

Percutaneous pedicle screw fixation (PPSF) is a well-known minimally invasive surgery (MIS) employed in the treatment of thoracolumbar burst fractures (TBF). However, hardware failure and loss of angular correction are common limitations caused by the poor support of the anterior column of the spine. Balloon kyphoplasty (KP) is another MIS that was successfully used in the treatment of compression fractures by augmenting the injured vertebral body with cement. To overcome the limitations of stand-alone PPSF, it was suggested to augment PPSF with KP as a surgical treatment of TBF. Yet, little is known about the biomechanical alteration occurred to the spine after performing such procedure. The objective of this study was to evaluate and compare the immediate post-operative biomechanical performance of stand-alone PPSF, stand-alone-KP, and KP-augmented PPSF procedures. Novel three-dimensional (3D) finite element (FE) models of the thoracolumbar junction that describes the fractured spine and the three investigated procedures were developed and tested under mechanical loading conditions. The spinal stiffness, stresses at the implanted hardware, and the intradiscal pressure at the upper and lower segments were measured and compared. The results showed no major differences in the measured parameters between stand-alone PPSF and KP-augmented PPSF procedures, and demonstrated that the stand-alone KP may restore the stiffness of the intact spine. Accordingly, there was no immediate post-operative biomechanical advantage in augmenting PPSF with KP when compared to stand-alone PPSF, and fatigue testing may be required to evaluate the long-term biomechanical performance of such procedures.

The effect of static neck flexion on mechanical and neuromuscular behaviors of the cervical spine

Occupations that involve sustained or repetitive neck flexion are associated with a higher incidence of neck pain. Little in vivo information is available on the impact of static neck flexion on cervical spinal tissue. The aim of this study was to assess changes in mechanical and neuromuscular behaviors to sustained neck flexion in healthy adults. Sixty healthy subjects aged 20–35 years participated in this study. The participants were exposed to static neck flexion at a fixed angle of full flexion for 10 min. Mechanical and neuromuscular responses of the cervical spine to sudden perturbations were measured pre- and post-exposure. Magnitude of load-relaxation during flexion exposure, stiffness, peak head angular velocity, and reflexive activities of cervical muscles were recorded. Effective neck stiffness decreased significantly, especially in female participants (P = 0.0001). The reflexive response of the cervical erector spinae muscles to head perturbation delayed significantly (P = 0.0001). Peak head angular velocity was significantly increased after exposure to neck flexion for 10 min, especially in female participants (P = 0.001). In the present study, static flexion resulted in changes in mechanical and neuromuscular behavior of the cervical spine, potentially leading to decreased stiffness of the cervical spine. The results confirm the importance of maintaining a correct head and neck position during work and improving the work environment to reduce the cervical spinal load and work-related neck pain.

Assessment of cervical stiffness in axial rotation among chronic neck pain patients: A trial in the framework of a non-manipulative osteopathic management

BackgroundCervical stiffness is a clinical feature commonly appraised during the functional examination of cervical spine. Measurements of cervical stiffness in axial rotation have not been reported for patients with neck pain. The purpose of this study was to investigate cervical spine stiffness in axial rotation among neck pain patients and asymptomatic subjects, and to analyze the impact of osteopathic management. MethodsThirty-five individuals (17 patients) were enrolled. Measurements were carried out for left-right axial rotation using a torque meter device, prior and after intervention. Passive range of motion, stiffness, and elastic-and neutral zone magnitudes were analyzed. Pain intensity was also collected for patients. The intervention consisted in one single session of non-manipulative osteopathic treatment performed in both groups. FindingsA significant main effect of intervention was found for total range of motion and neutral zone. Also, treatment by group interaction was demonstrated for neutral-, elastic zone, stiffness in right axial rotation, and for total neutral zone. Significant changes were observed in the clinical group after intervention, indicating elastic zone decrease and neutral zone increase. In contrast, no significant alteration was detected for the control group. InterpretationsStiffness characteristics of the cervical spine in axial rotation are prone to be altered in patients with neck pain, but seem to be relieved after a session of non-manipulative manual therapeutic techniques. Further investigations, including randomized clinical trials with various clinical populations and therapeutic modalities, are needed to confirm these preliminary findings.

Case of Unusual Abscess Localization in Lumbar Pott’s Disease

In Pott’s disease, cold abscesses usually sit and spread along the psoas muscle. This case concerned a 60 years old man who came to us with bilateral lomboradicular pain and a swelling of inguinal area and the anterior part of the left thigh. We found a 2 years long lasting story of low back pain complaint. Physical examination showed good general health status, stiffness of lumber spine, a left psoitis and no neurological deficit. CT scan going downward from the lumbar spine to the pelvic region and femoral limb with coronal reconstruction demonstrated a huge disco-vertebral destruction of L2-L3 with translation, and bilateral paramedian psoas abscess migrating subfascially toward Scarpa triangle and cleaving anteriorly mainly muscles of the left thigh. After 12 months medical treatment, the evolution has been favorable with clinical cure. The localization of the cold abscess in the left thigh anterior muscles compatment is uncommon. It is why we report this case.

Investigation of the passive mechanical properties of spine muscles following disruption of the thoracolumbar fascia and erector spinae aponeurosis, as well as facet injury in a rat

Background ContextMuscle tissue is known to remodel in response to changes to its mechanical environment. Alterations in passive mechanical properties of muscles can influence spine stiffness and stability. PurposeThis study aimed to determine whether passive muscle elastic moduli and passive muscle stresses increased 28 days following mechanical disruption of the thoracolumbar fascia and erector spinae aponeurosis, and injury induced by facet joint compression. Study DesignMale Sprague Dawley rats were randomly assigned to three groups (Incision n=8; Injury n=8; and Control n=6). MethodsThe thoracolumbar fascia and erector spinae aponeurosis were incised in the Incision and Injury groups to expose the left L5–L6 facet joint. In the Injury group, this facet was additionally compressed for three minutes to induce facet injury and cartilage degeneration. Twenty-eight days after surgery, rats were sacrificed and muscle samples were harvested from lumbar and thoracic erector spinae and multifidus for mechanical testing. ResultsHistologic staining revealed mild cartilage degeneration and boney remodeling in the Injury group. However, the hypotheses that either (1) disruption of the thoracolumbar fascia and erector spinae aponeurosis (Incision group) or (2) the addition of facet compression (Injury group) would increase the passive elastic modulus and stress of surrounding muscles were rejected. There was no effect of surgery (Incision or Injury) on the passive elastic modulus (p=.6597). Passive muscle stresses were also not different at any sarcomere length between surgical groups (p>.7043). ConclusionDisruption of the thoracolumbar fascia and erector spinae aponeurosis and mild facet damage do not lead to measurable changes in passive muscle mechanical properties within 28 days. These findings contribute to our understanding of how spine muscles are affected by injury and fundamental aspects of the initial stages of spine surgery.

Effect of Flexible Spine Motion on Energy Efficiency in Quadruped Running

AbstractEnergy efficiency is important in the performance of quadruped robots and mammals. Flexible spine motion generally exists in quadruped mammals. This paper mainly explores the effect of flexible spinal motion on energy efficiency. Firstly, a planar simplified model of the quadruped robot with flexible spine motion is introduced and two simulation experiments are carried out. The results of simulation experiments demonstrate that both spine motion and spinal flexibility can indeed increase energy efficiency, and the curve of energy efficiency change along with spinal stiffness is acquired. So, in order to obtain higher energy efficiency, quadruped robots should have flexible spine motion. In a certain speed, there is an optimal spinal stiffness which can make energy efficiency to be the best. Secondly, a planar quadruped robot with flexible spine motion is designed and the conclusions drawn in the two simulation experiments are verified. Lastly, the third simulation experiment is carried out to explore the relationship between the optimal spinal stiffness, speed and total mass. The optimal spinal stiffness increases with both speed and total mass, which has important guiding significance for adjusting the spinal stiffness of quadruped robots to make them reach the best energy efficiency.

Paraspinal Muscle Passive Stiffness Remodels in Direct Response to Spine Stiffness: A Study Using the ENT1-Deficient Mouse.

Basic science study of the relationship between the structural properties of the spine and its surrounding musculature. To determine whether an increase in spine stiffness causes an inverse compensatory change in the passive stiffness of the adjacent paraspinal muscles. Intervertebral disc degeneration causes an increase in multifidus passive stiffness; this was hypothesized to compensate for a decrease in spine stiffness associated with disc degeneration. Mice lacking equilibrative nucleoside transporter 1 (ENT1) develop progressive ectopic calcification of the fibrous connective tissues of the spine, which affects the lumbar spine by 6 months of age and likely creates a mechanically stiffer spine. Experiments were conducted on four groups of mice (n = 8 mice/group): wild-type (WT) and ENT1 knockout (KO) at 2 or 8 months of age. Lumbar spines were removed and tested in cyclic axial compression to determine neutral zone length and stiffness. Single muscle fibers and bundles of fibers were isolated from lumbar multifidus and erector spinae, as well as tibialis anterior (a non-spine-related control) and tested to determine elastic modulus (passive stiffness). At 2 months of age, neither spine nor muscle stiffness was different between KO and WT. At 8 months of age, compared with WT the lumbar spines of ENT1 KO mice had a stiffer and shorter neutral zone, and the paraspinal muscle fibers were less stiff; however, fiber bundles were not different. In addition, tibialis anterior was not different between KO and WT. This work has confirmed that calcification of spinal connective tissues in the ENT1 KO mouse results in a stiffened spine, whereas the concurrent decrease in muscle fiber elastic modulus in the adjacent paraspinal muscles suggests a direct compensatory relationship between the stiffness of the spine and the muscles that are attached to it. N/A.

Impact of spinal rod stiffness on porcine lumbar biomechanics: Finite element model validation and parametric study.

A three-dimensional finite element model of the porcine lumbar spine (L1-L6) was used to assess the effect of spinal rod stiffness on lumbar biomechanics. The model was validated through a comparison with in vitro measurements performed on six porcine spine specimens. The validation metrics employed included intervertebral rotations and the nucleus pressure in the first instrumented intervertebral disc. The numerical results obtained suggest that rod stiffness values as low as 0.1 GPa are required to reduce the mobility gradient between the adjacent and instrumented segments and the nucleus pressures across the porcine lumbar spine significantly. Stiffness variations above this threshold value have no significant effect on spine biomechanics. For such low-stiffness rods, intervertebral rotations in the instrumented zone must be monitored closely in order to guarantee solid fusion. Looking ahead, the proposed model will serve to examine the transverse process hooks and variable stiffness rods in order to further smooth the transition between the adjacent and instrumented segments, while preserving the stability of the instrumented zone, which is needed for fusion.

The comfort and safety of a novel rolling mechanical indentation device for the measurement of lumbar trunk stiffness in young adults

BackgroundThe measurement of Posterior-Anterior (P-A) spinal stiffness is a common component of the physical examination of patients presenting with spinal disorders. The aim of this assessment is to provoke pain and/or to determine the degree of resistance or compliance of these structures and the associated soft-tissues to loading. This information, combined with other patient-specific history and examination findings, is integrated into the clinical reasoning process and is used to guide treatment decisions. Unfortunately, there are inter-rater reliability and standardisation issues associated with the manual performance of this type of assessment. In an attempt to remedy these issues researchers have developed mechanical devices for the measurement of spinal stiffness. The aim of this research is to investigate the comfort and safety of a novel device for measuring P-A trunk stiffness in a sample of young adults.MethodsA sample of young adults from a general population was recruited in May 2016 from Sydney, Australia. Demographic, anthropometric and clinical variables were collected prior to participants undergoing a lumbar P-A trunk stiffness assessment involving a mechanical indentation device called the VerteTrack. The primary outcomes for the study were key feasibility items; overall assessment time, perceived comfort measured both during and after the procedure, and adverse events. Univariate ordinal logistic regression was used to identify key variables associated with a participant’s subjective report of comfort both during and after the VerteTrack assessment.ResultsEighty four participants (35% female) with a median age of 23 years (IQR = 3) took part in the research. The mean assessment time for the Vertetrack assessment was 11.6 min (SD = 2.1). Increasing load (p < 0.001) and increasing number of days with lower back pain (p = 0.009) were associated with decreased comfort ratings during the procedure. The vast majority 63/84 (75%) of participants rated the overall assessment experience as comfortable. There were two minor, short-lived adverse events recorded leading to an adverse event rate of 2.4% (2/84).ConclusionsThe results of this study suggest that the VerteTrack device is well-tolerated and can be used safely and efficiently when measuring P-A stiffness of the lumbar trunk in young adults.Trial registrationNot applicable.

Design and modeling of linearly-constrained compliant spines for human-scale locomotion on rocky surfaces

We present a new spine solution for the locomotion of human-scale robots on steep, rocky surfaces, known as linearly-constrained spines. The spine stiffness is low in the normal direction but high with respect to lateral and bending loads. The solution differs from previous spine arrays used for small robots in having a much higher spine density and less spine scraping over asperities. We present theoretical and empirical results to demonstrate that this solution is capable of shear stresses of over 200kPa, enabling human-scale robots to apply forces parallel to steep rock surfaces for climbing, bracing, etc. The analysis includes the effects of spine geometry, stiffness, backlash and three-dimensional loading angle to predict the overall forces possible in three dimensions of both single and opposed configurations of spine arrays. Demonstrated applications include a gripper for a “smart staff” aimed at helping humanoid robots to negotiate steep terrain and a palm that provides over 700N in shear for the RoboSimian quadruped.

Influence of spinal disc translational stiffness on the lumbar spinal loads, ligament forces and trunk muscle forces during upper body inclination

Inverse dynamic musculoskeletal human body models are commonly used to predict the spinal loads and trunk muscle forces. These models include rigid body segments, mechanical joints, active and passive structural components such as muscles, tendons and ligaments. Several studies used simple definition of lumbar spinal discs idealized as spherical joints with infinite translational stiffness. The aim of the current sensitivity study was to investigate the influence of disc translational stiffness (shear and compressive stiffness) on the joint kinematics and forces in intervertebral discs (L1−L5), trunk muscles and ligaments for an intermediately flexed position (55°).Based on in vitro data, a range of disc shear stiffness (100−200N/mm) and compressive stiffness (1900−2700N/mm) was considered in the model using the technique of force dependent kinematics (FDK). Range of variation in spinal loads, trunk muscle forces and ligaments forces were calculated (with & without load in hands) and compared with the results of reference model (RM) having infinite translational stiffness. The discs’ centers of rotation (CoR) were computed for L3−L4 and L4−L5 motion segments.Between RM and FDK models, maximum differences in compressive forces were 7% (L1−L2 & L2−L3), 8% (L3−L4) and 6% (L4−L5) whereas in shear forces 35% (L1−L2), 47% (L2−L3), 45% (L3−L4) and more than 100% in L4−L5. Maximum differences in the sum of global and local muscle forces were approximately 10%, whereas in ligament forces were 27% (supraspinous), 40% (interspinous), 56% (intertransverse), 58% (lig. flavum) and 100% (lig. posterior). The CoRs were predicted posteriorly, below (L3−L4) and in the disc (L4−L5).FDK model predicted lower spinal loads, ligament forces and varied distribution of global and local muscle forces. Consideration of translational stiffnesses influenced the model results and showed increased differences with lower stiffness values.

Association of lumbar spine stiffness and flexion-relaxation phenomenon with patient-reported outcomes in adults with chronic low back pain \u2013 a single-arm clinical trial investigating the effects of thrust spinal manipulation

BackgroundSpinal manipulation (SM) is used commonly for treating low back pain (LBP). Spinal stiffness is routinely assessed by clinicians performing SM. Flexion-relaxation ratio (FRR) was shown to distinguish between LBP and healthy populations. The primary objective of this study was to examine the association of these two physiological variables with patient-reported pain intensity and disability in adults with chronic LBP (>12 weeks) receiving SM.MethodsA single-arm trial provided 12 sessions of side-lying thrust SM in the lumbosacral region over 6 weeks. Inclusion criteria included 21–65 years old, Roland-Morris Disability Questionnaire (RMDQ) score ≥ 6 and numerical pain rating score ≥ 2. Spinal stiffness and FRR were assessed pre-treatment at baseline, after 2 weeks and after 6 weeks of treatment. Lumbar spine global stiffness (GS) were calculated from the force-displacement curves obtained using i) hand palpation, ii) a hand-held device, and iii) an automated indenter device. Lumbar FRR was assessed during trunk flexion-extension using surface electromyography. The primary outcomes were RMDQ and pain intensity measured by visual analog scale (VAS). Mixed-effects regression models were used to analyze the data.ResultsThe mean age of the 82 participants was 45 years; 48% were female; and 84% reported LBP >1 year. The mean (standard deviation) baseline pain intensity and RMDQ were 46.1 (18.1) and 9.5 (4.3), respectively. The mean reduction (95% confidence interval) after 6 weeks in pain intensity and RMDQ were 20.1 mm (14.1 to 26.1) and 4.8 (3.7 to 5.8). There was a small change over time in the palpatory GS but not in the hand-held or automated GS, nor in FRR. The addition of each physiologic variable did not affect the model-estimated changes in VAS or RMDQ over time. There was no association seen between physiological variables and LBP intensity. Higher levels of hand-held GS at L3 and automated GS were significantly associated with higher levels of RMDQ (p = 0.02 and 0.03, respectively) and lower levels of flexion and extension FRR were significantly associated with higher levels of RMDQ (p = 0.02 and 0.008, respectively) across the 3 assessment time points.ConclusionsImprovement in pain and disability observed in study participants with chronic LBP was not associated with the measured GS or FRR.Trial registrationNCT01670292 on clinicaltrials.gov, August 2, 2012