Kinematic response of lumbar functional spinal units to axial torsion with and without superimposed compression and flexion/extension

Lumbar and pelvis movement comparison between cross-court and long-line topspin forehand in table tennis: based on musculoskeletal model

Introduction: Cross-court and the long-line topspin forehand is the common and basic stroke skill in table tennis. The purpose of this study was to investigate the differences in lumbar and pelvis movements between cross-court and long-line topspin forehand strokes in table tennis based on musculoskeletal demands using OpenSim. Materials and Methods: The eight-camera Vicon system and Kistler force platform were used to measure kinematics and kinetics in the lumbar and pelvis movement of sixteen participants (Weight: 69.89 ± 1.58 kg; Height: 1.73 ± 0.03 m; Age: 22.89 ± 2.03 years; BMI: 23.45 ± 0.69 kg/m²; Experience: 8.33 ± 0.71 years) during cross-court and long-line topspin forehand play. The data was imputed into OpenSim providing the establishment of the Giat2392 musculoskeletal model for simulation. One-dimensional statistical parametric mapping and independent samples t-test was performed in MATLAB and SPSS to analyze the kinematics and kinetics. Results: The results show that the range of motion, peak moment, and maximum angle of the lumbar and pelvis movement in cross-court play were significantly higher than in the long-line stroke play. The moment of long-line in the sagittal and frontal plane was significantly higher than cross-court play in the early stroke phase. Conclusion: The lumbar and pelvis embody greater weight transfer and greater energy production mechanisms when players performed cross-court compared to long-line topspin forehand. Beginners could enhance their motor control strategies in forehand topspin skills and master this skill more easily based on the results of this study.

Calibration and validation of a novel hybrid model of the lumbosacral spine in ArtiSynth-The passive structures

In computational biomechanics, two separate types of models have been used predominantly to enhance the understanding of the mechanisms of action of the lumbosacral spine (LSS): Finite element (FE) and musculoskeletal multibody (MB) models. To combine advantages of both models, hybrid FE-MB models are an increasingly used alternative. The aim of this paper is to develop, calibrate, and validate a novel passive hybrid FE-MB open-access simulation model of a ligamentous LSS using ArtiSynth. Based on anatomical data from the Male Visible Human Project, the LSS model is constructed from the L1-S1 rigid vertebrae interconnected with hyperelastic fiber-reinforced FE intervertebral discs, ligaments, and facet joints. A mesh convergence study, sensitivity analyses, and systematic calibration were conducted with the hybrid functional spinal unit (FSU) L4/5. The predicted mechanical responses of the FSU L4/5, the lumbar spine (L1-L5), and the LSS were validated against literature data from in vivo and in vitro measurements and in silico models. Spinal mechanical responses considered when loaded with pure moments and combined loading modes were total and intervertebral range of motions, instantaneous axes and centers of rotation, facet joint contact forces, intradiscal pressures, disc bulges, and stiffnesses. Undesirable correlations with the FE mesh were minimized, the number of crisscrossed collagen fiber rings was reduced to five, and the individual influences of specific anatomical structures were adjusted to in vitro range of motions. Including intervertebral motion couplings for axial rotation and nonlinear stiffening under increasing axial compression, the predicted kinematic and structural mechanics responses were consistent with the comparative data. The results demonstrate that the hybrid simulation model is robust and efficient in reproducing valid mechanical responses to provide a starting point for upcoming optimizations and extensions, such as with active skeletal muscles.

Spine biomechanical testing methodologies: The controversy of consensus vs scientific evidence

Biomechanical testing methodologies for the spine have developed over the past 50 years. During that time, there have been several paradigm shifts with respect to techniques. These techniques evolved by incorporating state-of-the-art engineering principles, in vivo measurements, anatomical structure-function relationships, and the scientific method. Multiple parametric studies have focused on the effects that the experimental technique has on outcomes. As a result, testing methodologies have evolved, but there are no standard testing protocols, which makes the comparison of findings between experiments difficult and conclusions about in vivo performance challenging. In 2019, the international spine research community was surveyed to determine the consensus on spine biomechanical testing and if the consensus opinion was consistent with the scientific evidence. More than 80 responses to the survey were received. The findings of this survey confirmed that while some methods have been commonly adopted, not all are consistent with the scientific evidence. This review summarizes the scientific literature, the current consensus, and the authors' recommendations on best practices based on the compendium of available evidence.

Lumbar axial rotation kinematics in men with non-specific chronic low back pain

BACKGROUND

Lumbar flexion, coupled with rotation, is a dominant factor in the etiology and exacerbation of low back pain. Yet, no study has examined its kinematics in patients with non-specific chronic low back pain (NSCLBP). The aim of the study was to evaluate the lumbar rotation kinematics in neutral standing and with full flexion in men with NSCLBP.

METHODS

ROM, average velocity, maximum velocity and maximal acceleration of lumbar rotation in neutral standing and with full flexion were measured using an industrial lumbar motion monitor in 50 men (25 with NSCLBP and 25 controls). VAS and Rolland Morris questionnaire were also included.

FINDINGS

All examined kinematical parameters were significantly lower in men with NSCLBP compared with controls (↓ROM = 29%-45%; ↓AV = 40%-68%; ↓MV = 25%-50%; ↓MA = 20%-37%). Left rotation manifested smaller kinematic values (except for MA) than right rotation (Δ ROM = 35%; Δ AV = 66%; Δ MV = 19%) in NSCLBP. Most kinematical parameters significantly decreased from neutral standing to standing with flexion (right rotation: ↓ROM = 43%-45%, ↓AV = 38%-45%, ↓MV = 24%-27%, ↓MA for the NSCLBP group = 21%; left rotation: ↓ROM = 25%-38%, ↓AV in the control group: =34%, ↓MV in the control group: =23%, ↓MA in the control group = 25%). No correlations were found between all measured kinematical parameters, VAS and RMQ total score in the NSCLBP group.

INTERPRETATION

The kinematic parameters of lumbar rotation were reduced in men with NSCLBP compared with controls both in neutral standing and with fully forward bending. Most lumbar rotation kinematics decreased from neutral standing to standing with flexion.

Effect of collagen fibre orientation on intervertebral disc torsion mechanics

The intervertebral disc is a complex fibro-cartilaginous material, consisting of a pressurized nucleus pulposus surrounded by the annulus fibrosus, which has an angle-ply structure. Disc injury and degeneration are noted by significant changes in tissue structure and function, which significantly alters stress distribution and disc joint stiffness. Differences in fibre orientation are thought to contribute to changes in disc torsion mechanics. Therefore, the objective of this study was to evaluate the effect of collagen fibre orientation on internal disc mechanics under compression combined with axial rotation. We developed and validated a finite element model (FEM) to delineate changes in disc mechanics due to fibre orientation from differences in material properties. FEM simulations were performed with fibres oriented at [Formula: see text] throughout the disc (uniform by region and fibre layer). The initial model was validated by published experimental results for two load conditions, including [Formula: see text] axial compression and [Formula: see text] axial rotation. Once validated, fibre orientation was rotated by [Formula: see text] or [Formula: see text] towards the horizontal plane, resulting in a decrease in disc joint torsional stiffness. Furthermore, we observed that axial rotation caused a sinusoidal change in disc height and radial bulge, which may be beneficial for nutrient transport. In conclusion, including anatomically relevant fibre angles in disc joint FEMs is important for understanding stress distribution throughout the disc and will be important for understanding potential causes for disc injury. Future models will include regional differences in fibre orientation to better represent the fibre architecture of the native disc.

Axial rotation mechanics in a cadaveric lumbar spine model: a biomechanical analysis

BACKGROUND CONTEXT

Postoperative patient motions are difficult to directly control. Very slow quasistatic motions are intuitively believed to be safer for patients, compared with fast dynamic motions, because the torque on the spine is reduced. Therefore, the outcomes of varying axial rotation (AR) angular loading rate during in vitro testing could expand the understanding of the dynamic behavior and spine response.

PURPOSE

To observe the effects of the loading rate in AR mechanics of lumbar cadaveric spines via in vitro biomechanical testing.

STUDY DESIGN

An in vitro biomechanical study in lumbar cadaveric spines.

METHODS

Fifteen lumbar cadaveric segments (L1-S1) were tested with varying loading frequencies of AR. Five different frequencies were normalized with the base line frequency (0.125 Hz n=15) in this analysis: 0.05 Hz (n=6), 0.166 Hz (n=6), 0.2 Hz (n=10), 0.25 Hz (n=10), and 0.4 Hz (n=8).

RESULTS

The lowest frequency (0.05 Hz) revealed significant differences (p<.05) for all parameters (torque, passive angular velocity, axial velocity [AV], axial reaction force [RF], and energy loss [EL]) with respect to all other frequencies. Significant differences (p<.05) were observed in the following: torque (0.4 Hz with respect to 0.2 Hz and 0.25 Hz), passive sagittal angular velocity (SAV) (0.4 Hz with respect to all other frequencies; 0.166 Hz with respect to 0.25 Hz), axial linear velocity (0.4 Hz with respect to all other frequencies), and RF (0.4 Hz with respect to 0.2 Hz and 0.25 Hz). Strong correlations (R2>0.75, p<.05) were observed between RF with intradiscal pressure (IDP) and AR angular displacement with IDP. Intradiscal pressure (p<.05) was significantly larger in 0.2 Hz in comparison with 0.125 Hz.

CONCLUSIONS

Evidences suggest that measurements at very small frequencies (0.05 Hz) of torque, SAV, AV, RF, and EL are significantly reduced when compared with higher frequencies (0.166 Hz, 0.2 Hz, 0.25 Hz, and 0.4 Hz). Higher frequencies increase torque, RF, passive SAV, and AV. Higher frequencies induce a greater IDP in comparison with lower frequencies.

Lumbar loading in the elite adolescent tennis serve: link to low back pain

PURPOSE

This study aimed to quantify and compare lumbar region kinetics in kick and flat serves performed by elite, adolescent male players with and without a history of low back pain (LBP). Lumbar region kinematics, as well as racquet velocity and the position of the ball at impact, was described to facilitate kinetic data interpretation.

METHODS

Twenty Tennis Australia adolescent male players participated; 7 had a history of disabling LBP and confirmed L4/L5 injury and 13 were age-, height-, mass-, and performance-matched controls. The VICON motion analysis system was used to record racquet, upper and lower limb, trunk, and lumbar movement during three "flat" and three "kick" serves. A customized mathematical model calculated lumbar region kinetics/kinematics, racquet velocity, and ball position at impact, and these are reported as if all players were right-handed. A series of 2 × 2 mixed-model ANOVA were used to compare between pain/no pain and kick/flat serves.

RESULTS

There was no significant difference in racquet velocity or ball position at impact between pain groups or serve types. The players with LBP reported significantly greater (mean difference = 1.5 N · kg(-1)) peak left lateral force than the control group. The flat serve was associated with significantly greater flexion moments (mean difference = 2.7 N · kg(-1)) than the kick serve.

CONCLUSIONS

The lumbar region undergoes substantial loading during both the kick and the flat tennis serves, including lateral flexion forces approximately eight times those experienced during running. Given that these left lateral flexion forces are significantly greater in players with a history of disabling LBP and occur simultaneous with peak vertical force and extension and right lateral rotations, this may be an important LBP mechanism in this population.

Nucleus pulposus deformation in response to rotation at L1-2 and L4-5

BACKGROUND

Spinal rotation couples with lateral flexion as a composite movement. Few data report the in vivo mechanical deformation of the nucleus pulposus following sustained rotation. MRI provides a non-invasive method of examining nucleus pulposus deformation by mapping the hydration signal distribution within the intervertebral disc.

METHODS

T1 weighted coronal and sagittal lumbar images and T2 weighted axial images at L1-2 and L4-5 were obtained from 10 asymptomatic subjects (mean age 29, range: 24-34 years) in sustained flexed and extended positions plus combined positions of left rotation with flexion and extension. Nucleus pulposus deformation was tracked by mapping the change in hydration profiles from coronal and sagittal pixel measurements.

FINDINGS

An average sagittal change in position of 44° (SD 14.5°) from flexion to extension was recorded between L1 and S1 (range: 18°- 60°) resulting in a mean anterior nucleus pulposus deformation of 16% of disc hydration profile (range: 3.5%-19%) in 19/20 discs. When rotation was combined with either flexion or extension, mean coronal deformation was 4.8% (SD-5.1%; range: 0.4%-15%). Lateral nucleus pulposus deformation direction varied in rotation (44% deformed left and 56% deformed right). Intersegmental lateral flexion direction more strongly predicted nucleus pulposus deformation direction with 75% deforming contralaterally.

INTERPRETATION

Nucleus pulposus deformation direction in young subjects was more predictable following sagittal position change than in rotation combined with flexion or extension. Deformation magnitude was reduced in rotated positions. Intersegmental lateral flexion was a stronger predictor of nucleus pulposus deformation direction.

Does total disc arthroplasty in C3/C4-segments change the kinematic features of axial rotation?

We analyze how kinematic properties of C3/C4-segments are modified after total disc arthroplasty (TDA) with PRESTIGE(®) and BRYAN(®) Cervical Discs. The measurements were focused on small ranges of axial rotation (<0.8°) in order to investigate physiologic rotations, which frequently occur in vivo. Eight human segments were stimulated by triangularly varying, axially directed torque. By using a 6D-measuring device with high resolution the response of segmental motion was characterised by the instantaneous helical axis (IHA). Position, direction, and migration rate of the IHA were measured before and after TDA. External parameters: constant axially directed pre-load, constant flexional/extensional and lateral-flexional pre-torque. The applied axial torque and IHA-direction did not run parallel. The IHA-direction was found to be rotated backwards and largely independent of the rotational angle, amount of axial pre-load, size of pre-torque, and TDA. In the intact segments pre-flexion/extension hardly influenced IHA-positions. After TDA, IHA-position was shifted backwards significantly (BRYAN-TDA: ≈8mm; PRESTIGE-TDA: ≈6mm) and in some segments laterally as well. Furthermore it was significantly shifted ventrally by pre-flexion and dorsally by pre-extension. The rate of lateral IHA-migration increased significantly after BRYAN-TDA during rightward or leftward rotations. In conclusion after the TDA the IHA-positions shifted backwards with significant increase in variability of the IHA-positions after the BRYAN-TDA more than in PRESTIGE-TDA. The TDA-procedure altered the segment kinematics considerably. TDA causes additional translations of the vertebrae, which superimpose the kinematics of the adjacent levels. The occurrence of adjacent level disease (ALD) is not excluded after the TDA for kinematical reasons.

Low back pain development response to sustained trunk axial twisting

PURPOSE

To investigate if there is an effect of sustained trunk axial twisting on the development of low back pain.

METHODS

Sixteen male pain-free university students volunteered for this study. The trunk axial twisting was created by a torsion moment of 50 Nm for 10-min duration. The axial rotational creep was estimated by the transverse camera view directly on the top of the head. The visual analog scale in low back area was examined both in the initial and at the end of twisting. Each performed three trials of lumbar flexion-extension with the cycle of 5 s flexion and 5 s extension in standing before and after twisting. Surface electromyography from bilateral erector spinae muscles as well as trunk flexion performance was recorded synchronously in video camera. A one-way ANOVA with repeated measures was used to evaluate the effect of twist.

RESULTS

The results showed that there was a significant (p < 0.001) twist creep with rotational angle 10.5° as well as VAS increase with a mean value 45 mm. The erector spinae was active in a larger angle during flexion as well as extension after trunk axial twisting.

CONCLUSIONS

Sustained trunk axial twisting elicits significant trunk rotational creep. It causes the visual analog scale to have a significant increase, and causes erector spinae muscles to become active longer during anterior flexion as well as extension, which may be linked to the decrease of the tension ability of passive tissues in low back area, indicating a higher risk in developing low back pain.

Clinical and statistical correlation of various lumbar pathological conditions

Current clinical evaluations often rely on static anatomic imaging modalities for diagnosis of mechanical low back pain, which provide anatomic snapshots and a surrogate analysis of a functional disease. Three dimensional in vivo motion is available with the use of digital fluoroscopy, which was used to capture kinematic data of the lumbar spine in order to identify coefficients of motion that may assist the physician in differentiating patient pathology. Forty patients distributed among 4 classes of lumbar degeneration, from healthy to degenerative, underwent CT, MRI, and digital x-ray fluoroscopy. Each patient underwent diagnosis by a neurosurgeon. Fluoroscopy was taken as the patient performed lateral bending (LB), axial rotation (AR) and flexion-extension (FE). Patient specific models were registered with the fluoroscopy images to obtain in vivo kinematic data. Motion coefficients, C(LB), C(AR), C(FE), were calculated as the ratio of in-plane motion to total out-of-plane motion. Range of motion (ROM) was calculated about the axis of motion for each exercise. Inter- and Intra- group statistics were examined for each coefficient and a flexible Bayesian classifier was used to differentiate patients with degeneration. The motion coefficients C(LB) and C(FE) were significantly different (p<0.05) in 4 of 6 group comparisons. In plane motion, ROM(LB), was significantly different in only 1 of 6 group comparisons. The classifier achieved 95% sensitivity and specificity using (C(FE), C(LB), ROM(LB)) as input features, and 40% specificity and 80% sensitivity using ROM variables. The new coefficients were better correlated with patient pathology than ROM measures. The coefficients suggest a relationship between pathology and measured motion which has not been reported previously.

Kinematic evaluation of one- and two-level Maverick lumbar total disc replacement caudal to a long thoracolumbar spinal fusion

PURPOSE

Adjacent level degeneration that occurs above and/or below long fusion constructs is a documented clinical problem that is widely believed to be associated with the considerable change in stiffness caused by the fusion. Some researchers have suggested that early degeneration at spinal joints adjacent to a fusion could be treated by implanting total disc replacements at these levels. It is thought that further degeneration could be prevented through the disc replacement's design aims to reproduce normal disc heights, kinematics and tissue loading. For this reason, there is a clinical need to evaluate if a total disc replacement can maintain both the quantity of motion (i.e. range) and the quality of motion (i.e. center of rotation and coupling) at segments adjacent to a long spinal fusion. The purpose of this study was to experimentally evaluate range of motion (ROM-the intervertebral motion measured) and helical axis of motion (HAM) changes due to one- and two-level Maverick total disc replacement (TDR) adjacent to a long spinal fusion.

METHODS

Seven spine specimens (T8-S1) were used in this study (66 ± 19 years old, 3F/4 M). A continuous pure moment of ±5.0 Nm was applied to the specimen in flexion-extension (FE), lateral bending (LB) and axial rotation (AR), with a compressive follower preload of 400 N. The 5.0 Nm data were analyzed to evaluate the operated segment biomechanics at the level of the disc replacements. The data were also analyzed at lower moments using a modified version of Panjabi's proposed "hybrid" method to evaluate adjacent segment kinematics (intervertebral motion at the segments adjacent to the fusion) under identical overall (T8-S1) specimen rotations. The motion of each vertebra was monitored with an optoelectronic camera system. The biomechanical test was completed for (1) the intact condition and repeated after each surgical technique was applied to the specimen, (2) capsulotomy at L4-L5 and L5-S1, (3) T8-L4 fusion and capsulotomy at L4-L5 and L5-S1, (4) Maverick at L4-L5, and (5) Maverick at L5-S1. The capsulotomy was performed to allow measurement of facet joint loads in a companion study. Paired t tests were used to determine if differences in the kinematic parameters measured were significant. Holm-Sidak corrections for multiple comparisons were applied where appropriate.

RESULTS

Under the 5.0 Nm loads, L4-L5 ROMs tended to decrease in all directions following L4-L5 Maverick replacement (mean = 22 %, compared to the fused condition). Two-level Maverick implantation also tended to reduce L4-S1 ROM (mean 18, 7 and 31 % in FE, LB and AR, respectively, compared to the fused condition without TDR). Following TDR replacement, the HAM location tended to shift posteriorly in FE (at L5-S1), anteriorly in AR, and inferiorly in LB. However, although the above-mentioned trends were observed, neither one- nor two-level TDR replacement showed statistically significant ROM or HAM change in any of the three directions. At the identical T8-S1 posture identified by the modified hybrid analysis, the L4-L5 and L5-S1 levels underwent significant larger motions, relative to the overall specimen rotation, after fusion. In the hybrid analysis, there were no significant differences between the ROM after fusion with intact natural discs at L4-L5 and L5-S1 and the motions at those levels with one or two TDRs implanted.

CONCLUSIONS

The present results demonstrated that one or two Maverick discs implanted subjacent to a long thoracolumbar fusion preserved considerable and intact-like ranges of motion and maintained motion patterns similar to the intact specimen, in this ex vivo study with applied pure moments and compressive follower preload. The hybrid analysis demonstrated that, after fusion, the TDR-implanted levels are required to undergo large rotations, relative to those necessary before fusion, in order to achieve the same motion between T8 and S1. Additional clinical and biomechanical research is necessary to determine if such a kinematic demand would be made on these levels clinically and the biomechanical performance of these implants if it were.

Biomechanical evaluation of the Total Facet Arthroplasty System® (TFAS®): loading as compared to a rigid posterior instrumentation system

PURPOSE

To gain insight into a new technology, a novel facet arthroplasty device (TFAS) was compared to a rigid posterior fixation system (UCR). The axial and bending loads through the implants and at the bone-implant interfaces were evaluated using an ex vivo biomechanical study and matched finite element analysis. Kinematic behaviour has been reported for TFAS, but implant loads have not. Implant loads are important indicators of an implant's performance and safety. The rigid posterior fixation system is used for comparison due to the extensive information available about these systems.

METHODS

Unconstrained pure moments were applied to 13 L3-S1 cadaveric spine segments. Specimens were tested intact, following decompression, UCR fixation and TFAS implantation at L4-L5. UCR fixation was via standard pedicle screws and TFAS implantation was via PMMA-cemented transpedicular stems. Three-dimensional 10 Nm moments and a 600 N follower load were applied; L4-L5 disc pressures and implant loads were measured using a pressure sensor and strain gauges, respectively. A finite element model was used to calculate TFAS bone-implant interface loads.

RESULTS

UCR experienced greater implant loads in extension (p < 0.004) and lateral bending (p < 0.02). Under flexion, TFAS was subject to greater implant moments (p < 0.04). At the bone-implant interface, flexion resulted in the smallest TFAS (average = 0.20 Nm) but greatest UCR (1.18 Nm) moment and axial rotation resulted in the greatest TFAS (3.10 Nm) and smallest UCR (0.40 Nm) moments. Disc pressures were similar to intact for TFAS but not for UCR (p < 0.04).

CONCLUSIONS

These results are most applicable to the immediate post-operative period prior to remodelling of the bone-implant interface since the UCR and TFAS implants are intended for different service lives (UCR--until fusion, TFAS--indefinitely). TFAS reproduced intact-like anterior column load-sharing--as measured by disc pressure. The highest bone-implant moment of 3.1 Nm was measured in TFAS and for the same loading condition the UCR interface moment was considerably lower (0.4 Nm). For other loading conditions, the differences between TFAS and UCR were smaller, with the UCR sometimes having larger values and for others the TFAS was larger. The long-term physiological meaning of these findings is unknown and demonstrates the need for a better understanding of the relationship between spinal arthroplasty devices and the host tissue as development of next generation motion-preserving posterior devices that hope to more accurately replicate the natural functions of the native tissue continues.

The effects of spinal posture and pelvic fixation on trunk rotation range of motion

BACKGROUND

Axial rotation of the trunk is important to many vocational tasks and activities of daily living, and may be associated with back injuries. The influence of spinal postures on trunk rotation appears conflicting. This study investigated the influence of forward trunk inclination, spinal posture and pelvic fixation on maximum trunk rotation.

METHODS

Twenty male participants were assessed using an optoelectronic motion-analysis system to track trunk movement during maximal trunk rotations in different spinal positions within the sagittal plane. A repeated-measures multivariate analysis of variance investigated the effects of forward trunk inclination, spinal posture and pelvic fixation on trunk and pelvic rotation. Test-retest reliability was determined using interclass correlation coefficients and standard error of measurement.

FINDINGS

Forward trunk inclination at 45° yielded a 19% (6.2°; P<0.001) increase in trunk rotation and a 40% (25.5°; P<0.001) decrease in pelvic rotation when compared to standing. When flexing and extending the spine at a forward trunk inclination of 45° there was a 5% (1.9°; P<0.01) and a 4% (1.6°; P<0.05) decrease in trunk rotation. Fixing the pelvis increased the trunk rotation by up to 9% (3.3°; P<0.001).

INTERPRETATION

Inclining the trunk forward and maintaining a neutral spine maximised trunk rotation range of motion (RoM). This has implications for educational programmes intended to maximise sporting performance. Within the clinical setting, unrestricted observation of trunk rotations is considered more appropriate as it may benefit the clinician in determining possible detrimental relative flexibilities that may exist within the body.

The epiphyseal ring: a long forgotten anatomical structure with significant physiological function

STUDY DESIGN

A descriptive study of the epiphyseal ring's structural design along the thoracolumbar spine.

OBJECTIVE

To characterize and analyze the shape and size of the epiphyseal ring, to better understand its function.

SUMMARY OF BACKGROUND DATA

The literature is lacking in metrical data pertaining to the epiphyseal ring that is usually described as a narrow bony labrum on which the external fibers of the anulus fibrosus are anchored. Most researchers express doubts as to whether the term epiphysis is justified in this case.

METHODS

The sample studied included 240 human skeletons (vertebrae T4-L5) from a normal adult population (divided by sex, ethnicity, and age). Measurements of the vertebral body and epiphyseal ring were taken using a digital caliper at four different locations: anterior, posterior, right, left. In addition, each vertebral surface was photographed and the epiphyseal ring area measured (using image analyzer software Image J).

RESULTS

We found that relative to vertebral body size throughout the thoracolumbar spine, the anterior section of the ring was the widest and the posterior section the narrowest. The lateral parts presented intermediate values. Relative to the discal area, the epiphyseal ring area gradually decreased from T7 to T12 and increased from T12 to L4. The area of the inferior ring was always larger than the superior ring (significant only for lumbar vertebrae), regardless of sex, ethnicity, and age.

CONCLUSION

The epiphyseal ring varies largely in size and shape along the thoracolumbar spine. Much of its metrical properties are dictated by the applied mechanical stress regime during various movements, and/or the general anatomic structure of the spine.

Development of a model based method for investigating facet articulation

Reported investigations of facet articulation in the human spine have often been conducted through the insertion of pressure sensitive film into the joint space, which requires incision of the facet capsule and may alter the characteristics of interaction between the facet surfaces. Load transmission through the facet has also been measured using strain gauges bonded to the articular processes. While this method allows for preservation of the facet capsule, it requires extensive instrumentation of the spine, as well as strain-gauge calibration, and is highly sensitive to placement and location of the strain gauges. The inherently invasive nature of these techniques makes it difficult to translate them into medical practice. A method has been developed to investigate facet articulation through the application of test kinematics to a specimen-specific rigid-body model of each vertebra within a lumbar spine segment. Rigid-body models of each vertebral body were developed from CT scans of each specimen. The distances between nearest-neighboring points on each facet surface were calculated for specific time frames of each specimen's flexion/extension test. A metric describing the proportion of each facet surface within a distance (2 mm) from the neighboring surface, the contact area ratio (CAR), was calculated at each of these time frames. A statistically significant difference (p<0.037) was found in the CAR between the time frames corresponding to full flexion and full extension in every level of the lumbar spine (L1-L5) using the data obtained from the seven specimens evaluated in this study. The finding that the contact area of the facet is greater in extension than flexion corresponds to other findings in the literature, as well as the generally accepted role of the facets in extension. Thus, a biomechanical method with a sufficiently sensitive metric is presented as a means to evaluate differences in facet articulation between intact and treated or between healthy and pathologic spines.

Sitting postures and trunk muscle activity in adolescents with and without nonspecific chronic low back pain: an analysis based on subclassification

STUDY DESIGN

A preliminary cross-sectional comparative study of adolescents with nonspecific chronic low back pain (NSCLBP) and healthy controls.

OBJECTIVE

To investigate whether differences in spinal kinematic and trunk muscle activity exist in both usual and slump sitting in adolescents with NSCLBP.

SUMMARY OF BACKGROUND

Evidence suggests that low back pain commonly develops in adolescence and increases the risk for low back pain in adulthood. Sitting is an important consideration in adolescents with NSCLBP: currently there are no reports investigating their motor control strategies in sitting.

METHODS

Twenty-eight adolescents (14 female) with NSCLBP and 28 matched pain-free controls were recruited from a large cohort study. Pain subjects were subclassified based on O'Sullivan's classification system. Three-dimensional lumbo-pelvic kinematic data and the activation of 3 back and 2 abdominal muscles were recorded during usual and slump sitting. The flexion-relaxation phenomenon in sitting was also investigated.

RESULTS

Spinal posture in usual and slump sitting were similar for adolescents with and without NSCLBP. However, differences were identified in both sitting conditions when those with NSCLPB were subclassified and compared with controls. Muscle activation differences were not consistently identified, with only lower levels of internal oblique activation in usual sitting in NSCLBP compared with pain-free controls showing significance. Flexion relaxation was observed in both iliocostalis and thoracic erector spinae in the NSCLBP group but not controls.

CONCLUSION

This study provides preliminary results. Differences with sitting posture are only seen when adolescents with NSCLBP are classified. Trunk muscle activation is not a sensitive marker for discriminating subgroups of NSCLBP during adolescence.

How do spinal segments move?

PURPOSE

To study and clarify the kinematics of spinal segments following cyclic torques causing axial rotation (T(z) (t)), lateral-flexion (T(x) (t)), flexion/extension (T(y) (t)).

METHODS

A 6D--Measurement of location, alignment, and migration of the instantaneous helical axis (IHA) as a function of rotational angle in cervical, thoracic, and lumbar segments subjected to axially directed preloads.

RESULTS

IHA retained an almost constant alignment, but migrated along distinct centrodes. THORACIC SEGMENTS: IHA was almost parallel to T(z) (t), T(x) (t), or T(y) (t), stationary for T(x) (t) or T(y) (t), and migrating for T(z) (t) along dorsally opened bows. IHA locations hardly depended on the position or size of axial preload. LUMBAR SEGMENTS: IHA was also almost parallel to T(z) (t), T(x) (t), or T(y) (t). In axial rotation IHA-migration along wide, ventrally or dorsally bent bows depending on segmental flexional/extensional status. Distances covered: 20-60mm. In lateral-flexion: IHA-migration to the left/right joint and vice versa. In flexion/extension IHA-migration from the facets to the centre of the disc. CERVICAL SEGMENTS: In flexion/flexion IHA was almost stationary for and parallel to T(y) (t). In axial rotation or lateral-flexion IHA intersected T(z) (t)/T(x) (t) under approximately -30 degrees /+30 degrees.

CONCLUSIONS

Generally joints alternate in guidance. Lumbar segments: in axial rotation and lateral-flexion parametrical control of IHA-position and IHA-migration by axial preload position. Cervical segments: kinematical coupling between axial rotation and lateral-flexion. The IHA-migration guided by the joints should be taken into account in the design of non-fusion implants. FE-calculations of spinal mechanics and kinematics should be based on detailed data of curvature morphology of the articulating surfaces of the joint facets.

PATHOANATOMIC BASIS FOR STRETCH-INDUCED LUMBAR NERVE ROOT INJURY WITH A REVIEW OF THE LITERATURE

OBJECTIVE

Persistent pain originating from a dysfunctional lumbar motion segment poses significant challenges in the clinical arena. Although the predominance of the existing spine literature has addressed nerve root compression as the principal cause of pain, it is equally likely that a stretch mechanism may be responsible for all or part of the pathology.

METHODS

The literature supporting the role of stretch damage as a primary cause of nerve root injury and pain was systematically reviewed. Pathoanatomic considerations between nerve roots and juxtaposed environment are described and correlated with the available literature. Potential anatomic relationships that may lead to stretch-induced injury are delineated.

RESULTS

A dynamic lumbar functional spinal unit that encloses a tethered nerve root can create significant stretch and/or compression. This phenomenon may be present in a variety of pathological conditions. These include anterior, posterior, and rotatory olisthesis as well as degenerative conditions such as the loss of disc interspace height and frank multisegment spinal deformity. Although numerous studies have demonstrated that stretch can result in nerve damage, the pathophysiology that may associate nerve stretch with chronic pain has yet to be determined.

CONCLUSION

The current literature concerning stretch-related injury to nerve roots is reviewed, and a conceptual framework for its diagnosis and treatment is proposed and graphically illustrated using cadaveric specimens. The dynamic biomechanical and functional interrelationships between neural structures and adjacent connective tissue elements are particularly important in the face of spinal deformity.

A comparison of the torsional stiffness of the lumbar spine in flexion and extension

OBJECTIVE

The main mechanism of injury to the spine is torsion especially when coupled with compression. In this study, the in vitro torsional stiffness of the lumbar spine segments is compared in flexion and extension positions by cyclic and failure testing.

METHODS

Fifteen lumbar spines were sectioned from fresh cadavers into 15 L2/3 and 15 L45 motion segments. Each vertebral segment was then potted superiorly and inferiorly in polymethylmethacrylate, effectively creating a bone-disk-bone construct. The potted spinal segments were mounted in a mechanical testing system, preloaded in compression to 300 N, and axially rotated to 3 degrees in both directions at a load rate of 1 degrees /s. This was done over 3 cycles for each motion segment in the flexion and extension positions. Each specimen was then tested to torsional failure in either flexion or extension. Stiffness, torque, and energy were determined from cyclic and failure testing.

RESULTS

The results showed that in all cases of cyclic testing, the higher segment extension resulted in higher torsional stiffness. In relative extension, the lumbar specimens were stiffer, generated higher torque values, and generally absorbed more energy than the relative flexion condition. There were no differences found in loading direction or failure testing.

CONCLUSIONS

Increasing the effective torsional stiffness of the lumbar spine in extension could provide a protective mechanism against interverbral disk injury. Restoration of segmental extension through increasing the lumbar lordosis may decrease the strain and reinjury of the joints, which can help reduce the extent of pain in the lumbar spine.

Influence of different artificial disc kinematics on spine biomechanics

BACKGROUND

There are several different artificial discs for the lumbar spine in clinical use. Though clinically established, little is known about the biomechanical advantages of different disc kinematics.

METHODS

A validated finite element model of the lumbosacral spine was used to compare the results of total disc arthroplasty at level L4/L5 performed by simulating the kinematics of three established artificial disc prostheses (Charité, ProDisc, Activ L). For flexion, extension, lateral bending, and axial torsion, the intervertebral rotations, the locations of the helical axes of rotation, the intradiscal pressures, and the facet joint forces were evaluated at the operated and adjacent levels.

FINDINGS

After insertion of an artificial disc, intervertebral rotation is reduced for flexion and increased for extension, lateral bending, and axial torsion for all studied discs at implant level. The positions of the helical axes are altered especially for lateral bending and axial torsion. Increased facet joint contact forces are predicted for the Charité disc during extension-- influenced by the existence of anterior scar tissue--and for the ProDisc and the Activ L during lateral bending and axial torsion. The studied artificial discs have only a minor effect on the adjacent levels.

INTERPRETATIONS

For some load cases, total disc arthroplasty leads to considerably altered kinematics and increased facet joint contact forces at implant level. The spinal kinematic alterations due to an artificial disc exceed by far the inter-implant differences, while facet joint contact force alterations are strongly implant and load case dependent. The importance of implant kinematics is often overestimated.

Determination of torque-limits for human and cat lumbar spine specimens during displacement-controlled physiological motions

BACKGROUND CONTEXT

Quadruped animal models have been validated and used as biomechanical models for the lumbar spine. The biomechanics of the cat lumbar spine has not been well characterized, even though it is a common model used in neuromechanical studies.

PURPOSE

Compare the physiological ranges of motion and determine torque-limits for cat and human lumbar spine specimens during physiological motions.

STUDY DESIGN/SETTING

Biomechanics study.

PATIENT SAMPLE

Cat and human lumbar spine specimens.

OUTCOME MEASURES

Intervertebral angle (IVA), joint moment, yield point, torque-limit, and correlation coefficients.

METHODS

Cat (L2-sacrum) and human (T12-sacrum) lumbar spine specimens were mechanically tested to failure during displacement-controlled extension (E), lateral bending (LB), and axial rotation (AR). Single trials consisted of 10 cycles (10mm/s or 5 degrees /s) to a target displacement where the magnitude of the target displacement was increased for subsequent trials until failure occurred. Whole-lumbar stiffness, torque at yield point, and joint stiffness were determined. Scaling relationships were established using equations analogous to those that describe the load response of elliptically shaped beams.

RESULTS

IVA magnitudes for cat and human lumbar spines were similar during physiological motions. Human whole-lumbar and joint stiffness magnitudes were significantly greater than those for cat spine specimens (p<.05). Torque-limits were also greater for humans compared with cats. Scaling relationships with high correlation (R(2) greater than 0.77) were established during later LB and AR.

CONCLUSIONS

The current study defined "physiological ranges of movement" for human and cat lumbar spine specimens during displacement-controlled testing, and should be observed in future biomechanical studies conducted under displacement control.

The influence of posture and loading on interfacet spacing: an investigation using magnetic resonance imaging on porcine spinal units

STUDY DESIGN

Basic scientific investigation using porcine spine segments and magnetic resonance imaging.

OBJECTIVE

To quantify the effects of flexion-extension postures and loading history on the distance between the facet articular surfaces.

SUMMARY OF BACKGROUND DATA

Increased axial twist motion is used clinically to indicate instability and has been implicated as a potential cause of low back pain. Recently, it has been demonstrated that larger twist angles can be achieved when coupled with forward flexion in vivo. These findings suggest a postural mechanism may be responsible for modulating how the facet joints articulate, thereby affecting the moment resisting capability of the facets and altering the load distribution between the facet joints and the disc.

METHODS

Four porcine cervical spine motion segments (C3-C4) were exposed to a compressive preload. Two of these specimens were also exposed to 5000 repeats of flexion-extension motions. The interfacet spacing was measured from magnetic resonance images of 6 postures: neutral, maximum flexed, maximum extended, neutral-twisted, maximum flexed-twisted, and maximum extended-twisted. The range of axial twist angle was quantified in the neutral, flexed, and extended postures.

RESULTS

Flexion-extension postures and loading history caused a difference in the interfacet spacing and twist angle measured. Repetitive loading and flexed postures independently increased the spacing and twist angle, whereas the preload condition and extended postures independently decreased the measures. The 2 specimens that underwent the preload only condition suffered no damage to the disc or vertebrae. Of the repetitively loaded specimens, 1 had a vertebral fracture with initiation of herniation, and the second had a complete herniation.

CONCLUSION

The findings support a posture-dependent injury mechanism and may account for the previously reported in vivo posture-dependent passive rotational differences quantified for combined postures. The changes in spine mechanics and resulting load distribution due to coupled postures may be a key to understanding the formation of low back injuries and eventually clinical spine instability.

Do flexion/extension postures affect the in vivo passive lumbar spine response to applied axial twist moments?

BACKGROUND

The injury potential and mechanical effects of combining axial rotation with non-neutral flexion/extension postures in vivo remains poorly understood, despite being identified as a risk factor in epidemiological and in vitro studies. The purpose of this experiment was to quantify the passive axial twist motion of the lumbar spine in various postures, and to assess whether non-neutral flexion/extension postures cause a detectable change in the range of twist motion and/or spine rotational stiffness.

METHODS

Ten healthy male participants were passively rotated three times from a neutral and six flexed/extended starting postures (maximum-, mid-, mild-), while the moment-angle relationships were measured. The upper body was fixed to an adjustable rigid harness and the lower body was fixed to a cradle that rested on a frictionless table, thereby isolating the lumbar spine.

FINDINGS

The lumbar spine stiffness and rotational range of motion were modulated by the different flexion/extension postures. The average maximum rotational stiffness values were smallest in maximum-flexion (81.0%, SD 16.6), and largest in maximum-/mid-extension postures at 125.4% (SD 24.4, P<0.0001) of the neutral stiffness magnitude. The axial twist angle was significantly different for each posture (P<0.0001), with 13.8% (SD 8.9) greater rotation in the maximum-flexion and 23.8% (SD 7.8) less rotation in the maximum-extension posture. The lateral bend coupled motion with axial twist was significantly different (P<0.0001) between the maximum-flexion (11.4 degrees , SD 6.3), mid-flexion/maximum-extension/mid-extension (6.5 degrees , SD 4.5), and mid-extension/mild-flexion/mild-extension postures (4.4 degrees , SD 3.8).

INTERPRETATION

The lumbar spine stiffness and rotational range were modified by flexed-extended postures. The postural mechanism observed may be due to a change in the initial distance separating the facets prior to rotation. This information will be useful in determining spine rotational injury mechanisms through comparison with in vitro literature and for patient positioning during diagnostic tests.

The effect of dynamic posterior stabilization on facet joint contact forces: an in vitro investigation

STUDY DESIGN

Facet contact forces in the lumbar spine were measured during flexibility tests using thin film electroresistive sensors in intact cadaveric spine specimens and in injured specimens stabilized with a dynamic posterior system.

OBJECTIVE

The purpose of this study was to investigate the effect of the Dynesys system on the loading in the facet joints.

SUMMARY OF BACKGROUND DATA

The Dynesys, a posterior nonfusion device, aims to preserve intersegmental kinematics and reduce facet loads. Recent biomechanical evidence showed that overall motion is less with the Dynesys than in the intact spine, but no studies have shown its effect on facet loads.

METHODS

Ten human cadaveric lumbar spine specimens (L2-L5) were tested by applying a pure moment of +/-7.5 N m in 3 directions of loading with and without a follower preload of 600 N. Test conditions included an intact specimen and an injured specimen stabilized with 3 Dynesys spacer lengths. Bilateral facet contact forces were measured during flexibility tests using thin film electroresistive sensors (Tekscan 6900).

RESULTS

Implanting the Dynesys significantly increased peak facet contact forces in flexion (from 3 N to 22 N per side) and lateral bending (from 14 N to 24 N per side), but had no significant effect on the magnitude of the peak forces in extension and axial rotation. Peak facet loads were significantly lower with the long spacer compared with the short spacer in flexion and lateral bending.

CONCLUSION

Implantation of the Dynesys did not affect peak facet contact forces in extension or axial rotation compared with an intact specimen, but did alter these loads in flexion and lateral bending. The spacer length affected the compression of the posterior elements, with a shorter spacer typically producing greater facets loads than a longer one.

Strength of the cervical spine in compression and bending

STUDY DESIGN

Cadaveric motion segment experiment.

OBJECTIVES

To compare the strength in bending and compression of the human cervical spine and to investigate which structures resist bending the most.

SUMMARY OF BACKGROUND DATA

The strength of the cervical spine when subjected to physiologically reasonable complex loading is unknown, as is the role of individual structures in resisting bending.

METHODS

A total of 22 human cervical motion segments, 64 to 89 years of age, were subjected to complex loading in bending and compression. Resistance to flexion and to extension was measured in consecutive tests. Sagittal-plane movements were recorded at 50 Hz using an optical two-dimensional "MacReflex" system. Experiments were repeated 1) after surgical removal of the spinous process, 2) after removal of both apophyseal joints, and 3) after the disc-vertebral body unit had been compressed to failure. Results were analyzed using t tests, analysis of variance, and linear regression. Results were compared with published data for the lumbar spine.

RESULTS

The elastic limit in flexion was reached at 8.5 degrees (SD, 1.7 degrees ) with a bending moment of 6.7 Nm (SD, 1.7 Nm). In extension, values were 9.5 degrees (SD, 1.6 degrees ) and 8.4 Nm (3.5 Nm), respectively. Spinous processes (and associated ligaments) provided 48% (SD, 17%) of the resistance to flexion. Apophyseal joints provided 47% (SD, 16%) of the resistance to extension. In compression, the disc-vertebral body units reached the elastic limit at 1.23 kN (SD, 0.46 Nm) and their ultimate compressive strength was 2.40 kN (SD, 0.96 kN). Strength was greater in male specimens, depended on spinal level and tended to decrease with age.

CONCLUSIONS

The cervical spine has approximately 20% of the bending strength of the lumbar spine but 45% of its compressive strength. This suggests that the neck is relatively vulnerable in bending.

Lower lumbar spine axial rotation is reduced in end-range sagittal postures when compared to a neutral spine posture

Sports such as rowing, gymnastics, cycling and fast bowling in cricket that combine rotation with spine flexion and extension are known to carry greater risk of low back pain (LBP). Few studies have investigated the capacity of the lumbar spine to rotate in various sagittal positions, and further, these studies have generated disparate conclusions. The purpose of this study was to determine whether the range of lower lumbar axial rotation (L3-S2) is decreased in end-range flexion and extension postures when compared to the neutral spine posture. Eighteen adolescent female rowers (mean age=14.9 years) with no history of LBP were recruited for this study. Lower lumbar axial rotation was measured by an electromagnetic tracking system (3-Space Fastrak) in end-range flexion, extension and neutral postures, in sitting and standing positions. There was a reduction in the range of lower lumbar axial rotation in both end-range extension and flexion (p<0.001) postures when compared to neutral. Further, the range of lower lumbar axial rotation measurements in flexion when sitting was reduced when compared to standing (p=0.013). These findings are likely due to the anatomical limitations of the passive structures in end-range sagittal postures.

Biomechanical evaluation of the Total Facet Arthroplasty System: 3-dimensional kinematics

STUDY DESIGN

An in vitro biomechanical study to quantify 3-dimensional kinematics of the lumbar spine following facet arthroplasty.

OBJECTIVES

To compare the multidirectional flexibility properties and helical axis of motion of the Total Facet Arthroplasty System (TFAS) (Archus Orthopedics, Redmond, WA) to the intact condition and to posterior pedicle screw fixation.

SUMMARY OF BACKGROUND DATA

Facet arthroplasty in the lumbar spine is a new concept in the field of spinal surgery. The kinematic behavior of any complete facet arthroplasty device in the lumbar spine has not been reported previously.

METHODS

Flexibility tests were conducted on 13 cadaveric specimens in an intact and injury model, and after stabilization with the TFAS and posterior pedicle screw fixation at the L4-L5 level. A pure moment of +/-10 Nm with a compressive follower preload of 600 N was applied to the specimen in flexion-extension, axial rotation, and lateral bending. Range of motion (ROM), neutral zone, and helical axis of motion were calculated for the L4-L5 segment.

RESULTS

ROM with the TFAS was 81% of intact in flexion (P = 0.035), 68% in extension (P = 0.079), 88% in lateral bending (P = 0.042), and 128% in axial rotation (P = 0.013). The only significant change in neutral zone with TFAS compared to the intact was an increase in axial rotation (P = 0.011). The only significant difference in helical axis of motion location or orientation between the TFAS and intact condition was an anterior shift of the helical axis of motion in axial rotation (P = 0.013).

CONCLUSIONS

The TFAS allowed considerable motion in all directions tested, with ROM being less than the intact in flexion and lateral bending, and greater than the intact in axial rotation. The helical axis of motion with the TFAS was not different from intact in flexion-extension and lateral bending, but it was shifted anteriorly in axial rotation. The kinematics of the TFAS were more similar to the intact spine than were the kinematics of the posterior fixation when applied to a destabilized lumbar spine.

Novel model to analyze the effect of a large compressive follower pre-load on range of motions in a lumbar spine

A 3-D finite element model (FEM) of the lumbar spine (L1-S1) was used to determine the effect of a large compressive follower pre-load on range of motions (ROM) in all three planes. The follower load modeled in the FEM produced minimal vertebral rotations in all the three planes. The model was validated by comparing the disc compression at all levels in the lumbar spine with the corresponding results obtained by compressing 10 cadevaric lumbar spines (L1-S1) using the follower load technique described by Patwardhan et al. [1999. A follower load increases the load-carrying capacity of the lumbar spine in compression. Spine 24(10), 1003-1009]. Further validation of the model was performed by comparing the lateral bending and torsion response without pre-load and the flexion-extension response without pre-load and with an 800 N follower pre-load with those obtained using cadaver lumbar spines. Following validation, the FEM was subjected to bending moments in all three planes with and without compressive follower pre-loads of up to 1200 N. Disc compression values and the flexion-extension range of motion under 800 N follower pre-load predicted by the FEM compared well with in vitro results. The current model showed that compressive follower pre-load decreased total as well as segmental ROM in flexion-extension by up to 18%, lateral bending by up to 42%, and torsion by up to 26%.

Mri-Based Morphological Predictorsof Spect Positive Facet Arthropathyin Patients With Axial Back Pain

OBJECTIVE

A major barrier to understanding facetogenic low back pain has been the lack of radiographic diagnostic criteria. This study investigates the correlation between radiographic findings on magnetic resonance imaging (MRI) scans and single photon emission computed tomographic (SPECT) scans in patients clinically found to have facetogenic axial back pain.

METHODS

Thirty-one patients with severe axial back pain underwent lumbar MRI and SPECT scans. Two hundred thirty facets were identified and were graded from 1 to 4 using synovial area, size, cartilaginous discontiguity, osteophytic overgrowth, and joint space obliteration. Twenty-nine "hot" joints were identified on SPECT scans. MRI features of 230 lumbar facets were correlated with SPECT results.

RESULTS

Four basic morphological patterns were identified on the basis of synovial appearance on MRI scans, light, mottled, narrowed, and obliterated, and formed the basis for the grading 1 to 4, respectively (sensitivity for "hot facet", 0.93). The mottled group had 0.90 specificity (P = 0.0001). Osteophytic overgrowth demonstrated 0.94 specificity (P = 0.0004). Facet hypertrophy was not associated with increased tracer uptake.

CONCLUSION

We identify four types of synovial architecture on T2-weighted MRI scans with overall high sensitivity for predicting SPECT positivity. These four grades likely represent a continuum of facet degeneration, from a normal to obliterated joint. One particular subtype, Grade 2, demonstrated a high specificity for SPECT and synovial fluid increase suggestive of inflammation. Facet hypertrophy was not predictive of bone scan positivity, perhaps suggesting the protective nature of a hypertrophied facet. Synovial abnormalities correlate with SPECT findings and a grading scale is proposed delineating the degeneration of a lumbar facet over time. A subtype of SPECT(+) inflamed joint is proposed. Further studies will be needed to improve our understanding of the natural history of the lumbar facet.

High loading rate during spinal manipulation produces unique facet joint capsule strain patterns compared with axial rotations

PURPOSE

Lumbar spinal manipulation (SM) is a popular, effective treatment for low back pain but the physiological mechanisms remain elusive. During SM, mechanoreceptors innervating the facet joint capsule (FJC) may receive a novel stimulus, contributing to the neurophysiological benefits of SM. The biomechanics of SM and physiological axial rotations were compared to determine whether speed or loading site affected FJC strain magnitudes or patterns.

METHODS

Human lumbar spine specimens were tested during physiological rotations and simulated SM while measuring applied torque, vertebral motion, and FJC strain. During physiological rotations, specimens were actuated at T12 to 20 degrees left and right axial rotation at 2 degrees to 125 degrees per second. During SM simulations, a 7-mm impulse displacement was applied to L3, L4, or L5 at 5 to 50 mm per second.

RESULTS

Physiological rotations. Increasing displacement rate resulted in significantly larger torque magnitudes (P < .001), whereas vertebral kinematics and FJC strain magnitudes were unchanged (P > .05). Physiological rotations vs SM. Applied torque and vertebral rotation magnitudes were similar across speed and vertebral level. Total vertebral translations were slightly larger during physiological rotations vs SM at a given loading rate (P < .05). Patterns of vertebral motions and FJC strain during SM and physiological rotations varied significantly with loading rate (P < .05) but not with actuation site (P > .15).

CONCLUSIONS

The similar patterns observed in vertebral motion and FJC strain across actuation sites during SM and physiological rotations suggest that site specificity of SM may have minimal clinical relevance. High loading rates during lumbar SM resulted in unique patterns in FJC strain, which may result in unique patterns of FJC mechanoreceptor response.

The influence of static axial torque in combined loading on intervertebral joint failure mechanics using a porcine model

BACKGROUND

The spine is routinely subjected to repetitive combined loading, including axial torque. Repetitive flexion-extension motions with low magnitude compressive forces have been shown to be an effective mechanism for causing disc herniations. The addition of axial torque to the efficacy of failure mechanisms, such as disc herniation, need to be quantified. The purpose of this study was to determine the role of static axial torque on the failure mechanics of the intervertebral joint under repetitive combined loading.

METHODS

Repetitive flexion-extension motions combined with 1472 N of compression were applied to two groups of nine porcine motion segments. Five Nm of axial torque was applied to one group. Load-displacement behaviour was quantified, and planar radiography was used to document tracking of the nucleus pulposus and to identify fractures.

FINDINGS

The occurrence of facet fractures was found to be higher (P=0.028) in the axial torque group (7/9), compared to the no axial torque group (2/9). More hysteresis energy was lost up to 3000 cycles of loading in the axial torque group (P<0.014). The flexion-extension cycle stiffness was not different between the two groups until 4000 cycles of loading, after which the axial torque group stiffness increased (P=0.016). The percentage of specimens that herniated after 3000 cycles of loading was significantly larger (P=0.049) for the axial torque group (71%) compared to the no axial torque group (29%).

INTERPRETATION

Small magnitudes of static axial torque alter the failure mechanics of the intervertebral disc and vertebrae in combined loading situations. Axial torque appears to accelerate the susceptibility for injury to the intervertebral joint complex. This suggests tasks involving axial torque with other types of loading, apart from axial twist motion, should be monitored to assess exposure and injury risk.

[The enthesis. Physiological morphology, molecular composition and pathoanatomical alterations]

The composition of the extracellular matrix in tendons and ligaments is directly related to the mechanical environment. Local compression triggers functional adaptation that leads to cartilage-specific transformation of the tissue. The molecular composition of the extracellular matrix at the enthesis is related to the amount of stress and to the geometry of the insertion. Comparison of physiologically and non-physiologically loaded entheses shows that only certain molecules occur under relatively high amounts of local compressive stress. The occurrence of certain cartilage specific molecules is clinically relevant, because some of these molecules have been identified as autoantigens during the autoimmune response in patients with rheumatoid arthritis. These molecules constitute potential targets for the manifestation of rheumatoid arthritis at fibrocartilaginous entheses.