Baseline electrocardiographic changes as determinants in the prognosis of cerebrovascular accidents.
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Electrocardiography↗
Biomedical subjects
V K Goel
Publications and source records attributed to V K Goel.
Biomechanical comparison of lumbar spine with or without spina bifida occulta. A finite element analysis.
STUDY DESIGN: Biomechanical study using finite element model (FEM) of lumbar spine. OBJECTIVES: Very high coincidence of spina bifida occulta (SBO) has been reported more than in 60% of lumbar spondylolysis. The altered biomechanics due to SBO is one considerable factor for this coincidence. Thus, in this study, the biomechanical changes in the lumbar spine due to the presence of SBO were evaluated. SETTING: United States of America (USA). METHODS: An experimentally validated three-dimensional nonlinear FEM of the intact ligamentous L3-S1 segment was used and modified to simulate two kinds of SBO at L5. One model had SBO with no change in the length of the spinous process and the other had a small dysplastic spinous process. Von Mises stresses at pars interarticularis were analyzed in the six degrees of lumbar motion with 400 N axial compression, which simulates the standing position. The range of motion at L4/5 and L5/S1 were also calculated. RESULTS: It was observed that the stresses in all the models were similar, and there was no change in the highest stress value when compared to the intact model. The range of motion was also similar in all the models. The lumbar kinematics of SBO was thus shown to be similar to the intact model. CONCLUSION: SBO does not alter lumbar biomechanics with respect to stress and range of motion. The high coincidence of spondylolysis in spines with SBO may not be due to the mechanical factors.
Biomechanical Phenomena↗
Biomechanical rationale of endoscopic decompression for lumbar spondylolysis as an effective minimally invasive procedure - a study based on the finite element analysis.
We evaluated the biomechanical behavior of the endoscopic decompression for lumbar spondylolysis using the finite element technique. An experimentally validated, 3-dimensional, non-linear finite element model of the intact L3 - 5 segment was modified to create the L4 bilateral spondylolysis and left-sided endoscopic decompression. The model of Gill's laminectomy (conventional decompression surgery of the spondylolysis) was also created. The stress distributions in the disc and endplate regions were analyzed in response to 400 N compression and 10.6 Nm moment in clinically relevant modes. The results were compared among three models. During the flexion motion, the pressure in the L4/5 nucleus pulposus was 0.09, 0.09 and 0.16 (MPa) for spondylolysis, endoscopic decompression and Gill's procedure, respectively. The corresponding stresses in the annulus fibrosus were 0.65, 0.65 and 1.25 (MPa), respectively. The stress at the adjoining endplates showed an about 2-fold increase in the Gill's procedure compared to the other two models. The stress values for the endoscopic and spondylolysis models were of similar magnitudes. In the other motions, i. e., extension, lateral bending, or axial rotation, the results were similar among all of the models. These results indicate that the Gill's procedure may lead to an increase in intradiscal pressure (IDP) and other biomechanical parameters after the surgery during flexion, whereas the endoscopic decompression did not change the segment mechanics after the surgery, as compared to the spondylolysis alone case. In conclusion, endoscopic decompression of the spondylolysis, as a minimally invasive surgery, does not alert mechanical stability by itself.
Biomechanical Phenomena↗
Effects of branched beta-carbon dehydro-residues on peptide conformations: syntheses, crystal structures and molecular conformations of two tetrapeptides: (a) N-(benzyloxycarbonyl)-DeltaVal-Leu-DeltaPhe-Leu-OCH3 and (b) N-(benzyloxycarbonyl)-DeltaIle-Ala-DeltaPhe-Ala-OCH3.
The roles of branched beta-carbon dehydro-residues in the design of peptide conformations have not been systematically explored so far. In order to determine the effects of branched beta-carbon dehydro-residues on the peptide conformations, two N-protected tetrapeptides containing new combinations of DeltaVal and DeltaPhe in (a) N-(benzyloxycarbonyl)-DeltaVal-Leu-DeltaPhe-Leu-OCH(3) and DeltaIle and DeltaPhe in (b) N-(benzyloxycarbonyl)-DeltaIle-Ala-DeltaPhe-Ala-OCH(3) were synthesized by solution procedure. The crystal structures of these peptides were determined by X-ray diffraction methods. Single crystals of both peptides were grown by slow evaporation method from their solutions in acetone-water mixtures (80 : 20) at 25 degrees C. The crystals of these peptides belong to the orthorhombic space group P2(1)2(1)2(1) with cell dimensions of a = 12.342(1) A, b = 15.659(1) A, c = 18.970(1) A for peptide (a) and a = 8.093(1) A, b = 15.791(1) A, c = 23.816(1) A for peptide (b) having Z = 4 in the unit cells of both peptides. The structures were refined by full-matrix least-squares procedure to R-factors of 0.076 and 0.052 respectively. Both peptides adopt the right-handed 3(10)-helical conformations stabilized by two intramolecular (i + 3-->i) hydrogen bonds between the CO of N-terminal benzyloxycarbonyl (Cbz) group and the NH of residue at position 3, and between the CO of residue at position 1 and NH of the residue at position 4. The two consecutive 10-membered rings formed by the hydrogen bonds have dihedral angles corresponding to the standard values for type III beta-turns. DeltaVal and DeltaIle in peptides (a) and (b) respectively are located at the (i + 1) position of the first beta-turn while DeltaPhe is located at the (i + 2) position of the second beta-turn. In the crystals, the molecules are linked head to tail by intermolecular hydrogen bonds to form long helical chains. The axes of helices are parallel to the b-axes while the neighbouring helices run in the opposite directions. The crystal packings are further stabilized by van der Waals forces between the columns of molecular packings.
Amino Acid Sequence↗
Role of mechanical factors in the evaluation of pedicle screw type spinal fixation devices.
Prior to implantation, spinal implants are subjected to rigorous testing to ensure safety and efficacy. A full battery of tests for the devices may include many steps ranging from biocompatibility tests to in vivo animal studies. This paper describes some of the essential tests from a mechanical engineering perspective (e.g., motion, load sharing, bench type tests, and finite element model analyses). These protocols reflect the research experience of the past decade or so.
Animals↗
A finite element investigation of upper cervical instrumentation.
STUDY DESIGN: The finite element technique was used to predict changes in biomechanics that accompany the application of a novel instrumentation system designed for use in the upper cervical spine. OBJECTIVE: To determine alterations in joint loading, kinematics, and instrumentation stresses in the craniovertebral junction after application of a novel instrumentation system. Specifically, this design was used to assess the changes in these parameters brought about by two different cervical anchor types: C2 pedicle versus C2-C1 transarticular screws, and unilateral versus bilateral instrumentation. SUMMARY OF BACKGROUND DATA: Arthrodesis procedures can be difficult to obtain in the highly mobile craniovertebral junction. Solid fusion is most likely achieved when motion is eliminated. Biomechanical studies have shown that C1-C2 transarticular screws provide good stability in craniovertebral constructs; however, implantation of these screws is accompanied by risk of vertebral artery injury. A novel instrumentation system that can be used with transarticular screws or with C2 pedicle screws has been developed. This design also allows for unilateral or bilateral implantation. However, the authors are unaware of any reports to date on the changes in joint loading or instrumentation stresses that are associated with the choice of C2 anchor or unilateral/bilateral use. METHODS: A ligamentous, nonlinear, sliding contact, three-dimensional finite element model of the C0-C1-C2 complex and a novel instrumentation system was developed. Validation of the model has been previously reported. Finite element models representing combinations of cervical anchor type (C1-C2 transarticular screws vs. C2 pedicle screws) and unilateral versus bilateral instrumentation were evaluated. All models were subjected to compression with pure moments in either flexion, extension, or lateral bending. Kinematic reductions with respect to the intact (uninjured and without instrumentation) case caused by instrumentation use were reported. Changes in loading profiles through the right and left C0-C1 and C1-C2 facets, transverse ligament-dens, and dens-anterior ring of C1 articulations were calculated by the finite element model. Maximum von Mises stresses within the instrumentation were predicted for each model variant and loading scenario. RESULTS: Bilateral instrumentation provided greater motion reductions than the unilateral instrumentation. When used bilaterally, C2 pedicle screws approximate the kinematic reductions and instrumentation stresses (except in lateral bending) that are seen with C1-C2 transarticular screws. The finite element model predicted that the maximum stress was always in the region in which the plate transformed into the rod. CONCLUSIONS: To the best of the authors' knowledge, this is the first report of predicting changes in loading in the upper cervical spine caused by instrumentation. The most significant conclusion that can be drawn from the finite element model predictions is that C2 pedicle screw fixation provides the same relative stability and instrumentation stresses as C1-C2 transarticular screw use. C2 pedicle screws can be a good alternative to C2-C1 transarticular screws when bilateral instrumentation is applied.
Biomechanical Phenomena↗
Slippage mechanism of pediatric spondylolysis: biomechanical study using immature calf spines.
STUDY DESIGN: This study analyzed the skeletal-age-dependent strength of the lumbar growth plate to resist anterior shearing forces using the MTS system in the immature calf spine with pars defects. OBJECTIVE: To clarify the pathomechanism of the skeletal-age-dependent incidence of slippage in pediatric patients with pars defects by comparing the strength of the lumbar growth plate among three skeletal age groups. SUMMARY OF BACKGROUND DATA: Isthmic spondylolisthesis occurs and progresses more frequently during the growth period, whereas it is rare afterward. However, little evidence has been demonstrated to elucidate the etiology. METHODS: For this study, 15 lumbar functional spine units were divided into three groups according to their skeletal ages. Five were from neonates (Group 1), five from calves approximately 2 months old (Group 2), and five from calves about 24 months old (Group 3). An anterior shearing force was applied to each specimen until failure, after bilateral pars defects were created. Failure load (newtons) and displacement at failure (millimeters) were calculated from the load-displacement curve. The site of failure was confirmed by plain radiograph. RESULTS: All 15 functional spine units failed at the growth plate. The failure load was 242.79 +/- 46.05 N in Group 1, 986.40 +/- 124.16 N in Group 2, and 2024.54 +/- 245.53 N in Group 3. Statistically significant differences were found among the three groups (P < 0.05). The displacement at failure was 7.52 +/- 1.84 mm in Group 1, 11.10 +/- 2.30 mm in Group 2, and 8.15 +/- 2.66 mm in Group 3. There were no significant differences among the groups. CONCLUSIONS: The results indicate that the strength of the growth plate, the weakest link in this model, against anterior shearing forces depends on the skeletal maturity, and that the biomechanical weakness of the growth plate plays an important role in the slippage mechanism.
Aging↗
Monoclonal antibodies against the iron regulated outer membrane Proteins of Acinetobacter baumannii are bactericidal.
BACKGROUND: Iron is an important nutrient required by all forms of life.In the case of human hosts,the free iron availability is 10(-18) M,which is far less than what is needed for the survival of the invading bacterial pathogen. To survive in such conditions, bacteria express new proteins in their outer membrane and also secrete iron chelators called siderophores. RESULTS/ DISCUSSION: Acinetobacter baumannii ATCC 19606, a nosocomial pathogen which grows under iron restricted conditions, expresses four new outer membrane proteins,with molecular weight ranging from 77 kDa to 88 kDa, that are called Iron Regulated Outer Membrane Proteins (IROMPs). We studied the functional and immunological properties of IROMPs expressed by A.baumanii ATCC 19606. The bands corresponding to IROMPs were eluted from SDS-PAGE and were used to immunize BALB/c mice for the production of monoclonal antibodies. Hybridomas secreting specific antibodies against these IROMPs were selected after screening by ELISA and their reactivity was confirmed by Western Blot. The antibodies then generated belonged to IgM isotype and showed bactericidical and opsonising activities against A.baumanii in vitro. These antibodies also blocked siderophore mediated iron uptake via IROMPs in bacteria. CONCLUSION: This proves that iron uptake via IROMPs,which is mediated through siderophores,may have an important role in the survival of A.baumanii inside the host,and helps establishing the infection.
Acinetobacter↗
A biomechanical comparison between anterior and transverse interbody fusion cages.
STUDY DESIGN: Human cadaveric lumbar spines underwent placement of threaded fusion cages (TFCs) in either an anterior or transverse orientation. Spines underwent load testing and angular rotation measurement in the intact state, after diskectomy, after cage placement, and after fatiguing. Angular rotations were compared between cage orientations and interventions. OBJECTIVE: To determine which cage orientation resulted in greater immediate stability. SUMMARY OF BACKGROUND DATA: There has been extensive biomechanical study of interbody fusion cages. The lateral orientation has been increasingly used for intervertebral fusion, but a direct biomechanical comparison between cages implanted either anteriorly or transversely in human cadaveric spines has not been performed. METHODS: Fourteen spines were randomized into the anterior group (anterior diskectomy and dual anterior cage placement) and the lateral group (lateral diskectomy and single transverse cage placement). Pure bending moments of 1.5, 3.0, 4.5, and 6.0 Nm were applied in flexion, extension, lateral bending, and axial rotation. Load testing was performed while intact, after diskectomy, after cage placement, and after fatiguing. Angular rotation was compared between anterior and lateral groups and, within each group, among the different interventions. RESULTS: Segmental ranges of motion were similar between spines undergoing either anterior or lateral cage implantation. CONCLUSIONS: These results demonstrate few differences between angular rotation after either anterior or lateral TFC implantation. These findings add to data that find few differences between orientation of implanted TFCs. Combined with a decreased risk of adjacent structure injury through a lateral approach, these data support a lateral approach for lumbar interbody fusion.
Cadaver↗
Load-sharing between anterior and posterior elements in a lumbar motion segment implanted with an artificial disc.
STUDY DESIGN: A nonlinear three-dimensional finite element model of the osteoligamentous L3-L4 motion segment was used to predict changes in posterior element loads as a function of disc implantation and associated surgical procedures. OBJECTIVES: To evaluate the effects of disc implantation on the biomechanics of the posterior spinal elements (including the facet joints, pedicles, and lamina) and on the vertebral bodies. SUMMARY OF BACKGROUND DATA: Although several artificial disc designs have been used clinically, biomechanical data-particularly the change in loads in the posterior elements after disc implantation-are sparse. METHODS: A previously validated intact finite element model was implanted with a ball-and-cup-type artificial disc model via an anterior approach. The implanted model predictions were compared with in vitro data. To study surgical variables, small and large windows were cut into the anulus, and the implant was placed anteriorly and posteriorly within the disc space. The anterior longitudinal ligament was also restored. Models were subjected to either 800 N axial compression force alone or to a combination of 10 N-m flexion-extension moment and 400 N axial preload. Implanted model predictions were compared with those of the intact model. RESULTS: Facet loads were more sensitive to the anteroposterior location of the artificial disc than to the amount of anulus removed. Under 800 N axial compression, implanted models with an anteriorly placed artificial disc exhibited facet loads 2.5 times greater than loads observed with the intact model, whereas posteriorly implanted models predicted no facet loads in compression. Implanted models with a posteriorly placed disc exhibited greater flexibility than the intact and implanted models with anteriorly placed discs. Restoration of the anterior longitudinal ligament reduced pedicle stresses, facet loads, and extension rotation to nearly intact levels. CONCLUSIONS: The models suggest that, by altering placement of the artificial disc in the anteroposterior direction, a surgeon can modulate motion-segment flexuralstiffness and posterior load-sharing, even though the specific disc replacement design has no inherent rotational stiffness.
Finite Element Analysis↗
The pathomechanism of spondylolytic spondylolisthesis in immature primate lumbar spines in vitro and finite element assessments.
STUDY DESIGN: Immature Chacma baboon (Papio ursinus) spine specimens were used to determine load-displacement behavior as related to disc injury. This was accomplished through the application of A-P shear force until failure of FSUs with pars defects. Several finite element models (FEMs) of the FSU were developed to study the mechanism of slippage in immature baboon lumbar spines. OBJECTIVES: The purpose was to show that spondylolisthesis (olisthesis) always occurs through the growth plate using a model similar to immature human lumbar spines. Using FEMs, the roles of facet orientation, pars interarticularis thickness, and a weak growth-plate in producing slippage were examined. SUMMARY OF BACKGROUND DATA: Progression from spondylolysis (lysis) to olisthesis occurs, most often, during the adolescent growth spurt. The biomechanical literature dealing with the slippage mechanism in the immature lumbar spine does not provide a clear understanding and is sparse. METHODS: Several groups of FSUs were subjected to A-P shear force until failure. The results provided displacement at failure as a function of disc injury and flexion-extension fatigue. A bilateral pars defect was created in each specimen prior to application of A-P shear force using an MTS machine. Failure sites were assessed radiographically and histologically. A nonlinear 3-D FEM of the intact L4-L5 was created from CT scans. The model was modified to predict the effects of a pars fracture, a thin pars, a weak growth plate, and facet orientation on the shear load through the growth plate and stresses in the pars. RESULTS: Experimentally, failures always occurred through the growth-plate in the disc intact and disc-incised groups. In the intact FEM, the growth plate carried21% of the applied A-P shear force. The load increased when the facets were more sagittally oriented. The effect of thin pars and/or weaker growth plate was an increase in stresses in the pars. Changes in the load through the growth plate were minimal. CONCLUSIONS: The weakest link in immature baboon lumbar functional spinal units (FSUs) with lysis during an A-P shear load was the growth plate, between the cartilaginous and osseous end plates. Surgeons may assess this lesion on MRI views, thereby predicting the possible development and preventing progression of olisthesis. Finite element model results predict that more sagittally orientated facets and/or a pars fracture are prerequisites for olisthesis to occur.
Age Factors↗
Contribution of disc degeneration to osteophyte formation in the cervical spine: a biomechanical investigation.
Cervical spine disorders such as spondylotic radiculopathy and myelopathy are often related to osteophyte formation. Bone remodeling experimental-analytical studies have correlated biomechanical responses such as stress and strain energy density to the formation of bony outgrowth. Using these responses of the spinal components, the present study was conducted to investigate the basis for the occurrence of disc-related pathological conditions. An anatomically accurate and validated intact finite element model of the C4-C5-C6 cervical spine was used to simulate progressive disc degeneration at the C5-C6 level. Slight degeneration included an alteration of material properties of the nucleus pulposus representing the dehydration process. Moderate degeneration included an alteration of fiber content and material properties of the anulus fibrosus representing the disintegrated nature of the anulus in addition to dehydrated nucleus. Severe degeneration included decrease in the intervertebral disc height with dehydrated nucleus and disintegrated anulus. The intact and three degenerated models were exercised under compression, and the overall force-displacement response, local segmental stiffness, anulus fiber strain, disc bulge, anulus stress, load shared by the disc and facet joints, pressure in the disc, facet and uncovertebral joints, and strain energy density and stress in the vertebral cortex were determined. The overall stiffness (C4-C6) increased with the severity of degeneration. The segmental stiffness at the degenerated level (C5-C6) increased with the severity of degeneration. Intervertebral disc bulge and anulus stress and strain decreased at the degenerated level. The strain energy density and stress in vertebral cortex increased adjacent to the degenerated disc. Specifically, the anterior region of the cortex responded with a higher increase in these responses. The increased strain energy density and stress in the vertebral cortex over time may induce the remodeling process according to Wolff's law, leading to the formation of osteophytes.
Biomechanical Phenomena↗
Experimental validation of a finite element model of the temporomandibular joint.
PURPOSE: A 2-dimensional finite model of the temporomandibular joint (TMJ) was previously developed to provide a way of studying the specific roles of individual components as well as the overall dynamics of joint motion. This study was undertaken to show that the previously reported finite element model provides results that are consistent with the experimentally obtained results. MATERIALS AND METHODS: The upper compartment of a TMJ of a fresh cadaver specimen was exposed to allow the insertion of a small strip of pressure-sensitive film. Measured loads were applied to the chin and angle of the mandible, pressing the condyle into the glenoid fossa. The resulting stresses in the joint stained the film, providing a way to determine their magnitude. Similar loads were applied to the finite element model and the stresses in the TMJ were mathematically calculated. RESULTS: Experimental results were successfully obtained in 4 separate attempts, recording maximum stresses of 5.6, 8.6, 6.4, and 9.9 MPa (megapascals), respectively. The corresponding finite element model predictions were 7.3, 6.9, 6.4, and 8.2 MPa, respectively. CONCLUSIONS: This study indicates that the results of the previously reported finite element model of the TMJ provide a reasonable approximation of the actual physical situation.
Aged↗
Pathomechanisms of failures of the odontoid.
STUDY DESIGN: A finite element investigation to determine the causal mechanisms that lead to odontoid fracture. OBJECTIVES: To elucidate which loading scenarios, including rotational moments, compression-tension, and lateral and anteroposterior shear, can result in Type I, Type II, and Type III odontoid failures. SUMMARY OF BACKGROUND DATA: There is considerable controversy about the major loading path that causes odontoid fractures. A review of the clinical and laboratory research literature did not provide a consensus on this issue. METHODS: A three-dimensional, nonlinear finite element model of the occipito-atlantoaxial (C0-C1-C2) complex was generated from human cadaveric data. Force loads were applied at the posterior margin of the occiput and were applied as lone entities or after the model was prepositioned in flexion, extension, or lateral-bending moments through applied rotation moments. Intraosseous stresses were reported to characterize the probability of fracture due to the applied loadings. RESULTS: The data indicate that hyperextension can lead to failure of the odontoid at its superior tip (Type I). Finite element model predictions also demonstrated the propensity of loads that induce axial rotation to create relatively high maximum von Mises stress in the Type II fracture region. Flexion prepositioning reduced the stress response of the odontoid. CONCLUSIONS: Force loading that puts the head in extension coupled with lateral shear or compression leads to Type I fractures, whereas axial rotation and lateral shear can produce Type II fractures. The model failed to elucidate causal mechanisms for Type III fractures. Flexion seems to provide a protective mechanism against force application that would otherwise cause a higher risk of odontoid failure.
Atlanto-Occipital Joint↗
Impact response of the intervertebral disc in a finite-element model.
STUDY DESIGN: A three-dimensional nonlinear poroelastic finite-element model of a vertebra disc was used to analyze the biomechanical effects of impact loading on the spinal segment. OBJECTIVES: To predict changes in biomechanical parameters such as intradiscal pressure, dynamic stiffness, stresses in the endplate region, and the shock-absorbing mechanism of the spine under different impact duration/loading rates, and to investigate the relation between the rate of loading and the fracture potential of the vertebral body. SUMMARY OF BACKGROUND DATA: It is not practical to discern the role of impact duration using experimental protocols. Analytical studies are better suited to this purpose. However, previous poroelastic finite-element models of the motion segments have dealt mostly with creep phenomena. METHODS: A three-dimensional, L3-L4 motion-segment, finite-element model was modified to incorporate the poroelastic properties of the disc, endplate, and cancellous core, and thus simulate the shock-absorbing phenomena. The results were analyzed under variable impact durations for a constant maximum compressive impact load of 3 kN. RESULTS: For a shorter impact duration and a given F(max), relatively high cancellous core pressure was generated as compared with a case of long impact duration, although the amount of impulse was increased. In contrast, relatively constant pore pressures were generated in the nucleus regardless of the impact duration. The changes in spinal segment stiffness as a function of impact duration indicated that for a shorter duration of impact, high dynamic stiffness increases the stability of the spinal segment against the impact load. However, the corresponding increase in stresses within the vertebral body and endplate may produce fractures. CONCLUSIONS: The finite-element technique was used to address the role of impact duration in producing trauma to the spinal motion segment. Within the limitations of the model, the results suggest that fractures are likely to occur under shorter impact duration conditions. Depending on the strength of the region, a fracture may be initiated in the endplate region or the posterior wall of the cortical shell. The nucleus pressure is independent of the impact duration and depends only on the magnitude of the impact force.
Computer Simulation↗
Biomechanical rationale for the pathology of rheumatoid arthritis in the craniovertebral junction.
STUDY DESIGN: A finite-element model of the craniovertebral junction was developed and used to determine whether a biomechanical mechanism, in addition to inflammatory synovitis, is involved in the progression of rheumatoid arthritis in this region of the spine. OBJECTIVES: To determine specific structure involvement during the progression of rheumatoid arthritis and to evaluate these structures in terms of their effect on clinically observed erosive changes associated with the disease by assessing changes in loading patterns and degree of anterior atlantoaxial subluxation. SUMMARY OF BACKGROUND DATA: Rheumatoid arthritis involvement of the occipito-atlantoaxial (C0-C1-C2) complex is commonly seen. However, the biomechanical contribution to the development and progression of the disease is neither well understood nor quantified. Although previous cadaver studies have elucidated information on kinematic motion and fusion techniques, the modeling of progressive disease states is not easily accomplished using these methods. The finite-element method is well suited for studying progressive disease states caused by the gradual changes in material properties that can be modeled. METHODS: A ligamentous, nonlinear, sliding-contact, three-dimensional finite-element model of the C0-C1-C2 complex was generated from 0.5 mm thick serial computed tomography scans. Validation of the model was accomplished by comparing baseline kinematic predictions with experimental data. Transverse, alar, and capsular ligament stiffness were reduced sequentially by 50%, 75%, and 100% (removal) of their intact values. All models were subjected to flexion moments replicating the clinical diagnosis of rheumatoid arthritis using full flexion lateral plane radiographs. Stress profiles at the transverse ligament-odontoid process junction were monitored. Changes in loading profiles through the C0-C1 and C1-C2 lateral articulations and their associated capsular ligaments were calculated. Anterior and posterior atlantodental interval values were calculated to correlate ligamentous destruction with advancement of atlantoaxial subluxation. RESULTS: Model predictions (at 0.3 Nm) fell within one standard deviation of experimental means, and range of motion data agreed with published in vitro and in vivo values. The model predicted that stresses at the posterior base of the odontoid process were greatly reduced with transverse ligament compromise beyond 75%. Decreases through the lateral C0-C1 and C1-C2 articulations were compensated by their capsular ligaments. Anterior and posterior atlantodental interval values indicate that the transverse ligament stiffness decreases beyond 75% had the greatest effect on atlantoaxial subluxation during the early stages of the disease (no alar and capsular ligament damage). Subsequent involvement of the alar and capsular ligaments produced advanced atlantoaxial subluxation, for which surgical intervention may be warranted. CONCLUSIONS: To the best of the authors' knowledge, this is the first report of a validated, three-dimensional model of the C0-C1-C2 complex with application to rheumatoid arthritis. The data indicate that there may be a mechanical component (in addition to enzymatic degradation) associated with the osseous resorption observed during rheumatoid arthritis. Specifically, erosion of the odontoid base may involve Wolff's law of unloading considerations. Changes through the lateral aspects of the atlas suggest that this same mechanism may be partially responsible for the erosive changes seen during progressive rheumatoid arthritis. Anterior and posterior atlantodental interval values indicate that complete destruction of the transverse ligament coupled with alar and/or capsular ligament compromise is requisite if advanced levels of atlantoaxial subluxation are present.
Arthritis, Rheumatoid↗
Biomechanical studies of a dynamized anterior thoracolumbar implant.
STUDY DESIGN: An in vitro investigation into the biomechanical properties of a dynamized anterolateral compression implant that allows controlled subsidence. OBJECTIVES: To determine the extent to which both modes of the anterolateral compression implant (controlled collapsing and rigid) are able to reestablish the stability of the lumbar spine after L4 corpectomy. SUMMARY OF BACKGROUND DATA: Over time, anterior and posterior spinal implants have been associated with progressive angulation, and occasionally implant failure and breakage. To circumvent this occurrence and provide better graft loading, dynamized or collapsing devices for clinical use have been developed. METHODS: Eight fresh calf spines (L1-L6) were placed in a biomechanical testing frame. Pure moments of 6 Nm were loaded onto the intact spine in six directions: flexion, extension, right and left lateral bending, and right and left axial rotation. A total L4 corpectomy then was performed, and the defect grafted with a wooden dowel. Loading was repeated after the specimens were stabilized using the two modes of the anterolateral compression implant in succession. RESULTS: The results showed that both modes of the implant (the rigid mode in particular) restore the stiffness of the unstable spine to normal levels of flexion, extension, and right and left lateral bending, even to levels exceeding normal. These devices, however, fall short of achieving normal stability in right and left axial rotation. CONCLUSION: In the cadaveric calf spine after L4 corpectomy, restoration of stability with a dynamized anterior spinal implant is possible in flexion, extension, and right and left lateral bending, but not in axial rotation.
Animals↗
Evaluation of low back muscle surface EMG signals using wavelets.
OBJECTIVE: To compare the ability of observers to correctly detect the reaction time of erector spinae response to unexpected load by inspecting nonprocessed electromyographic signals versus inspection of wavelet transformed electromyographic signals and versus automatic detection on the same wavelet transformed signals. BACKGROUND: Traditionally, electromyographic signal analysis is performed using Fourier transform based methods. However, muscle response to transients such as unexpected load, have limitations when using these methods of electromyographic processing. DESIGN: A comparison was made of the three methods using the same signals attained during sudden loading of the trunk. METHODS: 11 chronic low back pain patients and eleven normal subjects were investigated in sudden loading. Surface electromyographic signals were obtained from the erector spine muscle at L3. The ability of observers to detect reaction time of erector spinae muscle responses of nonprocessed electromyographic signals versus inspection of wavelet transformed electromyographic signals versus an automatic peak detection program was determined. RESULTS: The results have shown that the spine muscle reaction time was easier and more accurately determined in the wavelet domain rather than in its original signal representation. CONCLUSION: Wavelet transform methods improved the analysis of electromyographic signals in the time domain by facilitating the determination of the time of muscle activity. RELEVANCE: Wavelet transform could be a valuable tool for electromyographic analysis in resolving the psychophysical problem of perception involved in the analysis of nonprocessed signals. In clinical environments, where the speed and the accuracy of the analysis of electromyographic signal is critical, the wavelet based signal processing could be very important.
Adult↗