Motion In Axial Rotation Research Articles

Biomechanical Comparison of Occiput-C1–C2 Fixation Techniques

In vitro human cadaveric biomechanical study. The objective was to evaluate and compare the construct stability of occiput-C1-C2 fixation provided by C0-C1 transarticular screws or occipital condyle screws. The placement of an occipital plate is commonly recommended in occipitocervical fixation surgery. However, there are unique clinical situations in which the placement of the occipital plate may not be possible or may have already failed. For these situations, 2 novel techniques that use the occipital condyle have been recently introduced: (1) C0-C1 transarticular screws fixation and (2) direct occipital condyle screws and C1 lateral mass screws fixation. However, there is a lack of thorough biomechanics studies of these techniques. Nondestructive kinematic tests and destructive tests were conducted in 16 fresh frozen cadaveric spines. As a nondestructive kinematic test, a pure moment of up to 2.0 N·m was applied in smooth continuous flexion/extension, lateral bending, and axial rotation motions. In addition to an intact-state case, a total of 5 different constructs (standard occipital plate, C0-C1 transarticular screws with/without occipital plate, and occipital condyle screws with/without occipital plate) were tested after destabilization of C0-C1 and C1-C2. All constructs had C2 pedicle screws fixation, and occipital condyle screws were incorporated with C1 lateral screws. All fixation techniques significantly reduced ranges of motion compared with the intact state. In comparison with the standard occipital plate construct, the 2 novel techniques showed higher stability in axial rotation and lower stability in lateral bending. In both nondestructive and destructive tests, there were no statistical differences between C0-C1 transarticular screw construct and occipital condyle screw construct. The C0-C1 transarticular screw technique and direct occipital condyle screw with C1 lateral mass screw technique can be salvage fixation methods when occipital plate fixation is not feasible.

Effect of Graded Facetectomy on Biomechanics of Dynesys Dynamic Stabilization System

Finite element (FE) method was used to compare the biomechanics of L3-S1 lumbar spine with graded facetectomy before and after placement of Dynesys. To evaluate the biomechanics of Dynesys as a function of graded bilateral facetectomies. Spinal fusion or posterior dynamic stabilization systems are used to restore stability after facetectomies. The intact FE spine was modified to simulate decompression at L4-L5 with 50% and 75% and total facetectomy with/without dynamic stabilization with Dynesys. Biomechanics of the implanted level was investigated under different physiological loadings. Total facetectomy increased the motion in extension (8.7° vs. 2.7° for intact) and axial rotation (8.4° vs. 2.4° for intact). However the decrease in motion in the Dynesys model ranged from 65% in axial rotation to 80% in flexion for all facetectomies, except in the total facetectomy axial rotation case (motion higher than intact). The center of rotation of dynamic stabilized segment moved inferior/posterior in partial facetectomy and superior/posterior in total facetectomy with respect to the intact and destabilized cases. The Dynesys screws observed peak stresses up to 28% higher than those of a rigid fixation system in certain loadings, such as lateral bending and extension. The critical loosening torque applied to the screws in total facetectomy case was 6 times the partial facetectomy case in axial rotation. Partial facetectomy had a minimal effect on range of motion on the Dynesys-implanted segment. However, in the case of total facetectomy the motion increased by almost 40% in flexion and by 200% in axial rotation. The higher stresses applied to the screws in Dynesys in specific loadings may lead to higher risk of screw failure in Dynesys than in a generic rigid fixation construct.

Numerical simulation for heat transfer and velocity field characteristics of two-phase flow systems in axially rotating horizontal cans

Volume of fluid (VOF) element method coupled with a finite volume (FV) discretization technique was used to simulate two-dimensional, transient, two-phase flow patterns (air–water and air–food material) in an axially rotating horizontal can for rotational speeds of 10–160rpm. Rotational Reynolds number ranged from 1700 to 27200 and 0.88 to 14.1 for water and food phases, respectively. FV solution was performed on a moving mesh system representing the can motion in on-axis axial rotation with respect to an inertial-fixed frame. Since the two-phase flow pattern prediction was an important aspect of modeling fluid mixing and improved heat transfer in canning process, reliable time- and spatially-dependent flow pattern maps were given to identify the rotational effects on two-phase flow characteristics and to determine flow patterns prevailing at different rotational speeds. Single-phase and food-phase flow computations with the corresponding flow patterns were also provided for a direct comparison with air–water results to further determine the physical limitations of the rotational effects. Numerical results demonstrated that two-phase flow patterns were significantly influenced by increasing rotational speeds leading to distinguishable flow patterns in terms of air–liquid (water/food material) interface characteristics and associated headspace air bubble movement through the liquid phase.

Does an Advanced Generation Artificial Cervical Disc Provide Normal Postoperative Kinematics?

The M6®-C artificial cervical disc (Spinal Kinetics, Sunnyvale, CA) is an advanced generation artificial disc designed to replicate the anatomic structure of a natural disc by incorporating an artificial nucleus and annulus. The compressible polymer nucleus of the M6-C is designed to simulate the function of the native nucleus and the surrounding multi-layer high tensile strength fiber annulus is intended to provide controlled range of motion. This unique design allows the M6-C to have all 6 degrees of freedom including angular motion in flexion-extension, lateral bending and axial rotation while allowing independent translations along the 3 anatomic planes (AP, side-to-side and axial compression). The study hypothesis is that the novel design of the M6-C will provide normal post-operative kinematics.

Relationship between the mobility of phosphocholine headgroups of liposomes and the hydrophobicity at the membrane interface: A characterization with spectrophotometric measurements

In this study, we investigated the dynamics of a membrane interface of liposomes prepared by eight zwitterionic phosphatidylcholines in terms of their headgroup mobility, with spectroscopic methods such as dielectric dispersion analysis (DDA), fluorescence spectroscopy. The DDA measurement is based on the response of the permanent dipole moment to a driving electric field and could give the information on the axial rotational Brownian motion of a headgroup with the permanent dipole moment. This motion depended on kinds of phospholipids, the diameter of the liposomes, and the temperature. The activation energy required to overcome the intermolecular force between headgroups of phospholipids depended on the strength of the interaction between headgroups such as hydrogen bonds and/or dipole-dipole interaction. Hydration at the phosphorous group of phospholipid and the molecular order of lipid membrane impaired the interaction between headgroups. Furthermore, the hydrophobicity of membrane surface increased parallel to the increase in headgroup mobility. It is, therefore, concluded that hydration of headgroup promoted its mobility to make the membrane surface hydrophobic. The lipid membrane in liquid crystalline phase or the lipid membrane with the larger curvature was more hydrophobic.

Multi-segment trunk kinematics during locomotion and elementary exercises

Background Motion of human trunk segments in healthy subjects during activities of daily living has been described either with oversimplified models or with cumbersome techniques of isolated anatomical complex. This study describes multi-segmental trunk motion based on a new technique which is a compromise between technical limitations, implied with the experiments, and clinical relevance. Methods The thorax segment was tracked by the optimal spatial matching of four thoracic markers. The separate bi-dimensional shoulder line rotations and translations with respect to the thorax were calculated by markers on the two acromions. Spine motion was characterised by a 5-link-segment model from additional four skin markers, in the anatomical reference frame based on four pelvic spine markers. These 14 markers were tracked in 10 healthy subjects and one clinical case during static upright posture, chair rising–sitting, step up-and-down and level walking, and also during elementary flexion and extension, lateral bending, and axial rotation movements of the entire trunk. Findings Intra-subject repeatability over ten repetitions was found to be high for most of the measurements, with average standard deviations of less than 1.8° for all planar rotations at the spine, and less smaller than 1 mm for shoulder translations. Large motion, albeit with different patterns, was found in all subjects, also revealing interesting couplings over the three anatomical planes. Interpretation Considerable subject-specific motion occurs at each of these different trunk segments in all three anatomical planes, in simple exercises and in motor tasks of daily living. Measurements taken with the present new trunk model in pathological subjects shall reveal corresponding patterns and ranges of motion in abnormal conditions.

Validation of a Noninvasive Technique to Precisely Measure In Vivo Three-Dimensional Cervical Spine Movement

In vivo validation during functional loading. To determine the accuracy and repeatability of a model-based tracking technique that combines subject-specific computed tomographic (CT) models and high-speed biplane x-ray images to measure three-dimensional (3D) in vivo cervical spine motion. Accurate 3D spine motion is difficult to obtain in vivo during physiological loading because of the inability to directly attach measurement equipment to individual vertebrae. Previous measurement systems were limited by two-dimensional (2D) results and/or their need for manual identification of anatomical landmarks, precipitating unreliable and inaccurate results. All previous techniques lack the ability to capture true 3D motion during dynamic functional loading. Three subjects had 1.0-mm-diameter tantalum beads implanted into their fused and adjacent vertebrae during anterior cervical discectomy and fusion surgery. High-resolution CT scans were obtained after surgery and used to create subject-specific 3D models of each cervical vertebra. Biplane x-ray images were collected at 30 frames per second while the subjects performed flexion/extension and axial rotation movements 6 months after surgery. Individual bone motion, intervertebral kinematics, and arthrokinematics derived from dynamic radiostereophotogrammetric analysis served as a gold standard to evaluate the accuracy of the model-based tracking technique. Individual bones were tracked with an average precision of 0.19 and 0.33 mm in nonfused and fused bones, respectively. Precision in measuring 3D joint kinematics in fused and adjacent segments averaged 0.4 mm for translations and 1.1° for rotations, while anterior and posterior disc height above and below the fusion were measured with a precision ranging between 0.2 and 0.4 mm. The variability in 3D joint kinematics associated with tracking the same trial repeatedly was 0.02 mm in translation and 0.06° in rotation. The 3D cervical spine motion can be precisely measured in vivo with submillimeter accuracy during functional loading without the need for bead implantation. Fusion instrumentation did not diminish the accuracy of kinematic and arthrokinematic results. The semiautomated model-based tracking technique has excellent repeatability.

Is the ‘Crunch Factor’ an Important Consideration in the Aetiology of Lumbar Spine Pathology in Cricket Fast Bowlers?

The 'crunch factor' is defined as the instantaneous product of lateral flexion and axial rotational velocity of the lumbar spine. It was originally implicated in the development of lumbar spine pathology and lower back pain in golfers and, although empirical evidence supporting or refuting the crunch factor is inconclusive, it remains an intuitively appealing concept that requires further investigation, not only in golf, but also in other sports involving hitting and throwing motions. This article considers whether the crunch factor might be instrumental in the aetiology of contralateral lumbar spine injuries sustained by cricket fast bowlers. Based on recent empirical research, it is argued that the crunch factor could be important in cricket fast bowling especially considering that peak crunch factor appears to occur just after front foot impact when ground reaction forces are known to be at their highest. The crunch factor may also occupy an integral role in lower back injuries sustained in other sports involving unilateral overhead throwing (e.g. javelin throwing) and hitting (e.g. tennis serving) actions where the spatial orientation of the arm at release or impact is largely determined by lateral flexion of the trunk and where the transfer of energy and momentum along the kinetic chain is initiated by a rapid rotation of the pelvis. Further research is required to empirically verify the role of the crunch factor in the development of lower back injuries in cricket fast bowling and sports that involve similar lower trunk mechanics. This research programme should ideally be supported by modelling work examining the stresses imposed on bony, disc and joint structures by lateral flexion and axial rotation motions so that their respective contribution to injury can be identified.

Spinal Kinematics and Facet Load Transmission After Total Disc Replacement

In vitro human cadaveric biomechanical study. The objectives were to determine the effect of total disc replacement (TDR) on kinematics, especially range of motion (ROM), helical axis of motion (HAM), and facet joint contact force. Ball-and-socket type artificial discs are designed to mimic normal motion, but the biomechanical effect on kinematics has not been thoroughly clarified. Fourteen human cadaveric L4-L5 units were tested before and after TDR. In 7 specimens, facet contact forces were directly measured with thin-film piezoresistive load transducers inserted in the facet joints. In the other 7 specimens, the facet joint capsules were kept intact. Moments (±7.5 Nm) were applied in flexion/extension, lateral bending, and axial rotation motion, with and without an axial compressive preload of 400 N. Three-dimensional motion was recorded, and each angular ROM and HAM were calculated. Without axial compressive preload, the TDR did not produce significant differences in ROMs in all cases. However, under compressive preload, the TDR produced significantly larger ROMs for flexion (4.0° and 8.7°) and lateral bending (2.4° and 5.6°) (intact state and TDR, respectively). The TDR did not alter the HAM significantly except the location in lateral bending without compressive preload and the orientation in flexion/extension against horizontal plane. The location of HAM was slightly shifted caudally by the compressive preload in intact and TDR states. Despite the increased ROMs, the facet contact forces were not significantly altered by the TDR either with or without compressive preload (26 N and 27 N in extension, 41 N and 41 N in lateral bending, 117 N and 126 N in axial rotation). TDR using a ball-and-socket type artificial disc significantly increased ROM under axial load and maintained the HAM with similar facet contact forces to the intact state.

Primary and coupled motions after cervical total disc replacement using a compressible six-degree-of-freedom prosthesis

This study tested the hypotheses that (1) cervical total disc replacement with a compressible, six-degree-of-freedom prosthesis would allow restoration of physiologic range and quality of motion, and (2) the kinematic response would not be adversely affected by variability in prosthesis position in the sagittal plane. Twelve human cadaveric cervical spines were tested. Prostheses were implanted at C5-C6. Range of motion (ROM) was measured in flexion-extension, lateral bending, and axial rotation under ± 1.5 Nm moments. Motion coupling between axial rotation and lateral bending was calculated. Stiffness in the high flexibility zone was evaluated in all three testing modes, while the center of rotation (COR) was calculated using digital video fluoroscopic images in flexion-extension. Implantation in the middle position increased ROM in flexion-extension from 13.5 ± 2.3 to 15.7 ± 3.0° (p < 0.05), decreased axial rotation from 9.9 ± 1.7 to 8.3 ± 1.6° (p < 0.05), and decreased lateral bending from 8.0 ± 2.1 to 4.5 ± 1.1° (p < 0.05). Coupled lateral bending decreased from 0.62 ± 0.16 to 0.39 ± 0.15° for each degree of axial rotation (p < 0.05). Flexion-extension stiffness of the reconstructed segment with the prosthesis in the middle position did not deviate significantly from intact controls, whereas the lateral bending and axial rotation stiffness values were significantly larger than intact. Implanting the prosthesis in the posterior position as compared to the middle position did not significantly affect the ROM, motion coupling, or stiffness of the reconstructed segment; however, the COR location better approximated intact controls with the prosthesis midline located within ± 1 mm of the disc-space midline. Overall, the kinematic response after reconstruction with the compressible, six-degree-of-freedom prosthesis within ± 1 mm of the disc-space midline approximated the intact response in flexion-extension. Clinical studies are needed to understand and interpret the effects of limited restoration of lateral bending and axial rotation motions and motion coupling on clinical outcome.

Three-dimensional dynamic in vivo motion of the cervical spine: assessment of measurement accuracy and preliminary findings

Background context Previous research has quantified cervical spine motion with conventional measurement techniques (eg, cadaveric studies, motion capture systems, and fluoroscopy), but these techniques were not designed to accurately measure three-dimensional (3D) dynamic cervical spine motion under in vivo conditions. Purpose The purposes of this study were to characterize the accuracy of model-based tracking for measuring 3D dynamic cervical spine kinematics and to demonstrate its in vivo application. Study design Through accuracy assessment and application of technique, in vivo cervical spine motion was measured. Methods The accuracy of model-based tracking for measuring cervical spine motion was determined in an in vitro experiment. Tantalum beads were implanted into the vertebrae of an ovine specimen, and biplane X-ray images were acquired as the specimen's neck was manually moved through neck extension and axial neck rotation. The 3D position and orientation of each cervical vertebra were determined from the biplane X-ray images using model-based tracking. For comparison, the position and orientation of each vertebra were also determined by tracking the position of the implanted beads with dynamic radiostereometric analysis. To demonstrate in vivo application of this technique, biplane X-ray images were acquired as a human subject performed two motion tasks: neck extension and axial neck rotation. The positions and orientations of each cervical vertebra were determined with model-based tracking. Cervical spine motion was reported with standard kinematic descriptions of translation and rotation. Results The in vitro validation demonstrated that model-based tracking is accurate to within ±0.6 mm and ±0.6° for measuring cervical spine motion. For the in vivo application, there were significant rotations about all three anatomical axes for both the neck extension and axial neck rotation motion tasks. Conclusions Model-based tracking is an accurate technique for measuring in vivo, 3D, dynamic cervical spine motion. Preliminary data acquired using this technique are in agreement with previous studies. It is anticipated that this experimental approach will enhance our understanding of cervical spine motion under normal and pathologic conditions.

Biomechanical Evaluation of Short-Segment Posterior Instrumentation With and Without Crosslinks in a Human Cadaveric Unstable Thoracolumbar Burst Fracture Model

This study evaluates the biomechanical characteristics of spinal instrumentation constructs in a human unstable thoracolumbar burst fracture model simulated by corpectomy. To compare the biomechanical characteristics of short-segment posterior instrumentation, with and without crosslinks, in a human unstable burst fracture model simulated by corpectomy. Unstable thoracolumbar burst fractures are serious injuries, and their management remains controversial. Some authors advocate the use of short-segment posterior instrumentation for certain burst fractures. Whether crosslinks contribute additional stability has not been determined. Six fresh frozen human spines (T10-L2) were potted to isolate the T11-L1 segments, and biomechanically tested in axial rotation, lateral bending, flexion, and extension. A custom spine testing system was used that allows motion with 6 degrees of freedom. After testing was completed on intact specimens, a corpectomy was performed at T12 to simulate an unstable burst fracture with loss of anterior and middle column support. Short-segment transpedicular instrumentation was then performed from T11 to L1. Each specimen was retested with 1, 2, or no crosslinks. Construct stiffness and motion data were analyzed with each intact specimen serving as its own internal control. Torsional stiffness in axial rotation was significantly increased (P < 0.05) in short-segment fixation constructs with 1 and 2 crosslinks, but none was restored to the preinjury baseline level. Significant reductions in standardized motion were also achieved with 1 and 2 crosslinks compared to no crosslinks (P < 0.05), but they remained greater than baseline. Crosslinks significantly increased stiffness and decreased motion in lateral bending, beyond the baseline level (P < 0.05). In flexion, all constructs had significantly decreased stiffness and increased motion compared to the intact specimen (P < 0.05), with crosslinks providing no additional benefit. Conversely, none of the constructs demonstrated a significant change in extension compared to baseline (P > 0.05). When attempting to load the constructs to failure, screw pullout was seen in all specimens. Crosslinks, when added to short-segment posterior fixation, improve stiffness and decrease motion in axial rotation, but do not restore baseline stability in this corpectomy model. Short-segment posterior fixation is also inadequate in restoring stability in flexion with injuries of this severity. Short-segment posterior instrumentation alone can achieve baseline stability in lateral bending, and crosslinks provide even greater stiffness.

Assessment of Two Measurement Techniques of Cervical Spine and C1–C2 Rotation in the Outcome Research of Axis Fractures

In vivo study on cervical spine motion. To estimate the accuracy of clinical measurements, using a handheld goniometer for the assessment of total cervical neck rotation in outcome research of patients with C2 fractures and particularly odontoid fractures. Investigation on whether functional computed tomography (CT)-scanning is decisive in the investigation of functional outcome after C2 fractures. Pertinent literature exists concerning indications, techniques, complications of treatment, and risk factors for nonunion in C2 fractures; however, there are scarce data regarding the functional outcome in C2 fractures. Only a few studies assess functional outcome in terms of clinical outcome vehicles and clinical investigation of axial neck rotation, using a handheld goniometer. Measurements of axial neck rotation using a handheld goniometer are assumed not sufficient to compare the results of treatment strategies for C2-fractures or elucidate the ability for posttreatment rotation of C1-C2. The authors selected a homogenous group of 35 patients treated for C2 fractures using nonsurgical and surgical techniques. 69% of patients had odontoid fractures. Mean age of patients was 52 years. Patients were subjected to clinical assessment of axial cervical range of motion for rotation, using a handheld goniometer. Patients were also subjected to functional CT-scanning and measurements of total neck and atlantoaxial rotation were performed according to an established protocol. With clinical measurements mean range of motion for left and right axial neck rotation was both 56 degrees. According to the functional CT scans, the mean left-sided and right-sided axial neck rotation was 48.6 degrees and 52.0 degrees. The mean for left- and right-sided atlantoaxial rotation was 20.2 degrees and 20.6 degrees. Total axial atlantoaxial rotation on CT scans was 40.3 degrees and total axial neck rotation was 103.3 degrees. In comparison to age and gender matched normal individuals total cervical neck rotation was reduced to a mean of 69.5%. The differences between total axial neck rotation assessed using a handheld goniometer and with functional CT-scanning were strongly significant (P < 0.0001). In addition, there was no statistically significant correlation between the clinically assessed total neck rotation to either the left or the right side and the ipsilateral percentage atlantoaxial rotation of total head neck rotation. The current study demonstrated that for the comparison of functional outcome after different therapies of C2 fractures clinical measurements do not serve for reliable data on total neck rotation and particularly atlantoaxial rotation and the percentage of C1-C2 rotation of total neck rotation. The use of dynamic CT-scans in the analysis of functional outcome after C2 fractures is strongly recommended.

Dynamics of Retinal Studied by 2H NMR Relaxation Underlie Multiscale Conformational Changes in Rhodopsin Activation

The activation mechanism of the G protein-coupled receptor rhodopsin has been investigated through solid-state 2H NMR relaxation studies. Rhodopsin was regenerated with retinal 2H-labeled at the C5-, C9-, and C13-methyl groups and was recombined into POPC (dark state and Meta I) or POPC:DOPE (Meta II) [1-4]. The 2H NMR relaxation rates of Zeeman order (R1Z) or quadrupolar order (R1Q) were measured from −30 to −150°C in the dark, Meta I, and Meta II states. Relaxation data were interpreted in terms of axial rotation and off-axial motion of the methyl groups and revealed interactions between the retinal cofactor and the rhodopsin binding pocket. Relaxation rates show considerable mobility of the retinal ligand in the dark state despite the complete absence of basal activity. 2H NMR data indicate that the retinal C9-methyl group does not change its orientation upon photoisomerization. Rather it acts as a hinge for light-induced rotation of the C13-methyl toward the second extracellular loop E2. The C13-methyl rotation leads to a displacement of the E2 loop that is observed already in the Meta I state. Short T1Z relaxation times for the C5-methyl indicate that the β-ionone ring adopts a twisted 6-s-cis conformation, and remains in its hydrophobic binding pocket up to the Meta II state. An activation mechanism is proposed whereby the photonic energy is channeled by 11-cis to trans isomerization of retinal against the E2 loop by the C9- and C13-methyl groups, and toward helices H5 and H3 by the β-ionone ring and C5-methyl group.[1] G.F.J. Salgado et al. (2004) Biochemistry43, 12819. [2] G.F.J. Salgado et al. (2006) JACS128, 11067. [3] A.V. Struts et al. (2007) JMB372, 50. [4] M.F. Brown et al. (2009) Photochem. Photobiol.85, 442.

In Situ Contact Analysis of the Prosthesis Components of Prodisc-L in Lumbar Spine Following Total Disc Replacement

A three-dimensional, nonlinear finite element analysis was performed to predict the in situ contact interaction of prosthesis components of the Prodisc-L in a multisegmental lumbar model following total disc replacement (TDR). Efforts were made to investigate how the TDR implant contact characteristics could affect the 3-dimensional kinematics, facet loads of the lumbar spine following TDR. Although spinal motion analyses of human lumbar cadaveric models after Prodisc TDR have been widely studied, the interaction of the disc prosthesis, particularly its in situ contact mechanics, is never known. A validated intact multisegmental lumbar finite element model L2-L4 was altered to accommodate the TDR prosthesis through anterior approach. At L3-L4 disc space, the Prodisc-L of 6 degrees lordosis angle was implanted centrally. The model was subjected to compressive preload and pure moments to create flexion, extension, lateral bending, and axial rotation motion in physiologic range. The contact interaction between the superior component of Prodisc-L and the UHMWPE inlay were assessed in terms of contact region (CR), contact area (CA), and contact pressure (CP). Parameters of range of motion (ROM) and facet loading transfer were simultaneously analyzed and compared with those of the intact model. The predicted contact area was 3.5 times larger in flexion than that observed in extension, whereas the maximum contact pressure in the disc articulation was very similar with 15.1 MPa for flexion and 14.5 MPa for extension. Joint surface incongruence was developed in extension motion. The implanted model exhibited a 91.4% increase in ROM accompanied by a 150.6% rising in facet force during extension, while the flexion motion showed the least effects of TDR. In lateral bending and axial rotation, the abnormal joint "lift off" was not seen. The in situ function of the TDR prosthesis was highly dependent on how well the device could incorporate itself into the mechanical environment in the disc space, which has been determined by the rest of the spinal structures, including the retained disc anulus, articular facets, ligaments, vertebrae, and muscular stabilizers. The different contact interaction of the artificial disc components revealed here could be attributed to the violation of this mechanical environment which, in turn, may bring adverse effects to those spinal elements.

Non-fusion instrumentation of the lumbar spine with a hinged pedicle screw rod system: an in vitro experiment

In advanced stages of degenerative disease of the lumbar spine instrumented spondylodesis is still the golden standard treatment. However, in recent years dynamic stabilisation devices are being implanted to treat the segmental instability due to iatrogenic decompression or segmental degeneration. The purpose of the present study was to investigate the stabilising effect of a classical pedicle screw/rod combination, with a moveable hinge joint connection between the screw and rod allowing one degree of freedom (cosmicMIA). Six human lumbar spines (L2-5) were loaded in a spine tester with pure moments of +/-7.5 Nm in lateral bending, flexion/extension and axial rotation. The range of motion (ROM) and the neutral zone were determined for the following states: (1) intact, (2) monosegmental dynamic instrumentation (L4-5), (3) bisegmental dynamic instrumentation (L3-5), (4) bisegmental decompression (L3-5), (5) bisegmental dynamic instrumentation (L3-5) and (6) bisegmental rigid instrumentation (L3-5). Compared to the intact, with monosegmental instrumentation (2) the ROM of the treated segment was reduced to 47, 40 and 77% in lateral bending, flexion/extension and axial rotation, respectively. Bisegmental dynamic instrumentation (3) further reduced the ROM in L4-5 compared to monosegmental instrumentation to 25% (lateral bending), 28% (flexion/extension) and 57% (axial rotation). Bisegmental surgical decompression (4) caused an increase in ROM in both segments (L3-4 and L4-5) to approximately 125% and approximately 135% and 187-234% in lateral bending, flexion/extension and axial rotation, respectively. Compared to the intact state, bisegmental dynamic instrumentation after surgical decompression reduced the ROM of the two-bridged segments to 29-35% in lateral bending and 33-38% in flexion/extension. In axial rotation, the ROM was in the range of the intact specimen (87-117%). A rigid instrumentation (6) further reduced the ROM of the two-bridged segments to 20-30, 23-27 and 50-68% in lateral bending, flexion/extension and axial rotation, respectively. The results of the present study showed that compared to the intact specimen the investigated hinged dynamic stabilisation device reduced the ROM after bisegmental decompression in lateral bending and flexion/extension. Following bisegmental decompression and the thereby caused large rotational instability the device is capable of restoring the motion in axial rotation back to values in the range of the intact motion segments.

Comparison of the Flat Torso Versus the Elevated Torso Shoulder Pad Removal Techniques in a Cadaveric Cervical Spine Instability Model

Controlled laboratory study in a cadaveric model. To determine if removing shoulder pads using the elevated torso technique generated less spinal segment motion than using the flat torso method. Guidelines for care of the injured football player with a suspected spinal injury recommend initial immobilization with shoulder pads and helmet in place. There is a need to develop a safe protocol, for shoulder pad removal that maintains optimum cervical stability. Five lightly embalmed cadavers were studied before and after a globally unstable segment was created at C5-C6. A trained group of medical staff conducted repeated measures trials for 2 pad removal protocols. The elevated torso technique, outlined by the NATA Inter-Association Task Force, is the same as the flat torso except an additional assistant is employed to lift the patient's shoulders 30 degrees to 40 degrees off the ground while the head holder maintains spinal alignment as the pads are removed. An electromagnetic tracking device captured angular and linear motions in 3 planes between the C5-C6 segments. The elevated torso technique generated significantly less C5-C6 motion in flexion/extension (P = 0.015) and lateral bending (P = 0.001), with a trend toward decreased cervical motion in axial rotation (P = 0.052). When moving the spine-injured cadavers, linear translation was also slightly, but not significantly less when the elevated torso technique was used. In the intact spine, significantly less motion was seen in 5 of 6 measures when the elevated torso technique was used. However, the differences were not large enough to be clinically significant in an intact spine. These findings support use of the elevated torso method to minimize cervical spine motion during shoulder pad removal when neither thoracic nor lumbar spinal injury is a concern.

Lumbar Fusion Leads to Increases in Angular Motion and Stress Across Sacroiliac Joint

The assessment of sacrum angular motions and stress across sacroiliac joint (SIJ) articular surfaces using finite element lumbar spine-pelvis model and simulated posterior fusion surgical procedures. To quantify the increase in sacrum angular motions and stress across SIJ as a function of fused lumbar spine using finite element lumbar spine-pelvis model. A review of the literature suggests that for 20% to 30% of spine surgery patients, failed back surgery syndrome as a possible complication. The SIJ might be a contributing factor in failed back surgery syndrome in 29% to 40% of cases. The exact pathomechanism which leads to SIJ pain generation is not well understood. We hypothesized that lumbar spine fusion leads to increased motion or stresses at the SIJ; this alone could be a trigger of the pain syndrome. A finite element model of the lumbar spine-pelvis was used to simulate the posterior fusion at L4-L5, L4-S1, and L5-S1 levels. The magnitude of the sacrum angular motion and average of stresses across SIJ articular surfaces were compared with intact model in flexion, extension, lateral bending, and axial rotation motions. The computed sacrum angular motions in intact spine, after L4-L5, L5-S1, and L4-S1 fusion gradually increased with maximum value in L4-S1 fusion model. Also, the average stress on SIJ articular surfaces progressively increased from minimum in L4-L5 to maximum in L4-S1 fusion models. The fusion at the lumbar spine level increased motion and stresses at the SIJ. This could be a probable reason for low back pain in patients after lumbar spine fusion procedures.

Dynamics of Retinal Studied by 2H NMR Relaxation Sheds New Light on Rhodopsin Activation

The dynamics of retinal 2H-labeled at the C5-, C9-, and C13-methyl groups have been studied by solid-state deuterium NMR relaxation in the dark, meta I, and meta II states of the G protein-coupled receptor rhodopsin. Relaxation rates and quadrupolar splittings were interpreted in terms of axial rotation and off-axial motion of the methyl groups and revealed interactions between the retinal cofactor and the rhodopsin binding pocket. Surprisingly, in the dark state the crucial C9-methyl group is the most mobile despite its role in stabilizing the polyene chain. The C5-methyl group is slowest which is most likely due to interactions with Glu122 on helix 3. Dynamics of the ligand change significantly after light absorption. However, most of the changes occur between the dark and meta I states, and can be attributed to variations in intra-retinal interactions due to isomerization. Only small changes are observed upon transition from the meta I to meta II state where activation takes place. Overall, the dynamics of the C9- and C13-methyl groups in the meta I and meta II states indicate the absence of significant steric clashes of these groups with the surrounding amino acids. Even more surprising, there is little change in mobility of the β-ionone ring upon light activation. An activation mechanism based on the relaxation data is suggested which assumes that retinal is maintained in a similar environment, and does not experience significant reorientation or displacement upon transition from the pre-activated meta I to the active meta II state.[1] G. F. J. Salgado et al. (2004) Biochemistry 43, 12819.[2] G. F. J. Salgado et al. (2006) JACS 128, 11067.[3] A. V. Struts et al. (2007) J. Mol. Biol. 372, 50.

Effect of Uncovertebral Joint Excision on the Motion Response of the Cervical Spine After Total Disc Replacement

In vitro biomechanical study. To quantify the effects of uncinatectomy on cervical motion after total disc replacement (TDR). The effect of uncinatectomy on TDR motion is unknown. Partial uncinatectomy may be required to decompress the foramen; however, the residual uncinates can potentially limit TDR motion and serve as a source of progressive spondylosis. Complete resection of the uncinates may decrease this risk yet endanger destabilizing the segment. Seven human cervical spines (C3-C7) (age, 63.4 +/- 6.9 years) were tested first intact and then after implantation of a metal-on-polyethylene ball-and-socket semiconstrained prosthesis at C5-C6. Following this, gradually increased uncinatectomy was performed in the following order: 1) right partial-posteromedial (two thirds), 2) right complete, and 3) bilateral complete resection. Specimens were tested in flexion-extension, lateral bending, and axial rotation (+/-1.5 Nm). Flexion-extension was tested under 150 N follower preload. TDR without uncinatectomy increased C5-C6 flexion-extension range of motion from 8.4 degrees +/- 3.5 degrees to 11.6 degrees +/- 3.4 degrees, but statistical significance was not reached (P > 0.05). Lateral bending decreased from 6.2 degrees +/- 2.2 degrees to 3.1 degrees +/- 1.4 degrees, with a trend for statistical significance (P = 0.07). Axial rotation decreased from 5.5 degrees +/- 2.4 degrees to 4.3 degrees +/- 1.4 degrees after the implantation (P > 0.05). Both right partial and right complete uncinatectomy resulted in nearly symmetrical restoration of lateral bending to intact values and significantly increased flexion-extension compared with intact (P < or = 0.05); however, axial rotation still did not differ from intact (P > 0.05). Complete bilateral resection also restored lateral bending to intact values (7.3 degrees +/- 2.7 degrees, P > 0.05); however, it resulted in significant increase in range of motion in flexion-extension (14.1 degrees +/- 3.0 degrees, P < or = 0.05) and axial rotation (8.7 degrees +/- 2.4 degrees, P < or = 0.05). Unilateral complete or even partial uncinatectomy can normalize lateral bending after TDR. Bilateral complete uncinatectomy is not necessary to restore lateral bending and may result in significantly increased range of motion in flexion-extension and axial rotation compared with intact values.