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Biomedical subjects

N Yoganandan

Publications and source records attributed to N Yoganandan.

At least 19 recordsLinked to original sources
PubMed1999

Evaluation of cervical laminectomy and laminoplasty. A longitudinal study in the goat model.

STUDY DESIGN: An evaluation of the longitudinal radiologic changes up to 6 months induced by multilevel laminectomy and laminoplasty and the biomechanical responses in the goat model, complemented by biomechanical studies of intact specimens. OBJECTIVES: To determine the long-term radiographic differences and biomechanical responses of laminectomy and laminoplasty in an in vivo animal model. SUMMARY OF BACKGROUND DATA: Previous clinical and laboratory studies have indicated that multilevel laminectomy can cause increased flexibility in the cervical spinal column. Although the potential for laminoplasty to resolve these changes has been suggested, other evaluations have not supported this contention. Clarification of this controversy with long-term in vivo studies has not been performed. METHODS: Ten adult goats were divided into two groups, one undergoing C3-C5 laminectomy and the other open-door laminoplasty. Lateral cervical spine radiographs were obtained at 4-week intervals for a 6-month period. After the goats were killed, biomechanical testing was performed using pure moment loading on the surgically treated specimens and on three intact (without surgery) cervical spinal columns. RESULTS: In the laminectomy preparations, the cervical curvature index was noted to decrease by 59% at 16 weeks (P < 0.028) and by 70% at 24 weeks (P < 0.002), whereas the decrease in laminoplasty was not significantly different. Biomechanical testing indicated a significantly increased sagittal-plane slack motion in the laminectomy group (55 degrees) compared with that in intact specimens (39 degrees), but no significant difference between the laminoplasty and intact groups with respect to this motion. Laminectomy was found to be significantly stiffer (36%) in flexion than in extension, whereas the contrary was true for laminoplasty (37%). CONCLUSIONS: Radiographic and biomechanical results in the goat model suggest that laminoplasty is superior to laminectomy in maintaining cervical alignment and preventing postoperative spinal deformities.

Animals↗
PubMed1999

Biomechanical effect of anterior cervical spine fusion on adjacent segments.

The biomechanical effects of superior (C4-C5) and inferior (C5-C6) level fusions with different graft materials on the adjacent unaltered components were quantified using an anatomically accurate and experimentally validated C4-C5-C6 finite element model. Smith-Robinson and Bailey-Badgley fusion procedures were analyzed with five different types of inter-body fusion materials with varying stiffnesses. Intact and surgically altered finite element models were subjected to physiologic compression, flexion, extension and lateral bending. The external axial and angular stiffness, and the internal unaltered intervertebral disc (C5-C6 for the superior and C4-C5 for inferior fusion) and C5 vertebral body stresses were determined. The superior level fusion resulted in the highest increase in external response in lateral bending for all implant materials in both surgical procedures. In contrast, the inferior level fusion produced a higher increase in the C4-C5 disc and C5 vertebral body stresses in compression than the superior level fusion in both surgical procedures. The increased internal stress responses reflecting the changes in the load-sharing following inferior level fusion may explain clinical observations such as enhanced degeneration subsequent to surgery. Because of the inclusion of three levels in the present multi-segment finite element model, it was possible to determine these responses in the unaltered adjacent components of the cervical spine.

Biocompatible Materials↗
PubMed1998

Effect of age and loading rate on human cervical spine injury threshold.

STUDY DESIGN: Statistical analysis of human cadaver cervical spine compression experiments. OBJECTIVES: To quantify the cervical spine compressive injury threshold as a function of the person's age, gender, and external loading rate. SUMMARY OF BACKGROUND DATA: Results of epidemiologic studies have indicated that most survivors of cervical spinal cord injury have spinal column fractures and dislocations that result from a compression or compression-flexion force vector. Cervical spinal column injury thresholds are dependent on many factors. Delineation of the injury thresholds according to age, gender, and loading rate is necessary to improve clinical assessments and prevention strategies. METHODS: Twenty-five human cadaver head-neck compression tests were included in the analysis. Two statistical models were used to quantify the effects of age, gender, and loading rate on the force required to induce failure in the cervical spine. A multiple linear regression model provided a direct equation that quantified the effects of the variables, and a proportional hazards model was used to quantify probability of injury with each factor. RESULTS: The regression model had a correlation coefficient of 0.87. There was an interactive effect between age and loading rate: Increasing age reduced the effect of loading rate and at approximately 82 years, loading rate had no effect. Men were consistently 600 N stronger than women. The 50% probability of failure for a 50-year-old man at a 4.5-m/sec loading rate was approximately 3.9 kN. Differences in probability curves followed the same trends as seen in the regression model. CONCLUSIONS: The effects of age on cervical spine injury threshold are coupled with the rate of loading experienced through the external force vector that causes the trauma. Assessment of injury mechanisms and thresholds should be based on the person's age, gender, and loading rate to determine treatment and prevent injuries.

Adult↗
PubMed1998

Finite element modeling approaches of human cervical spine facet joint capsule.

The human cervical spine facet joint capsule was modeled using four nonlinear finite element approaches: slideline, contact surface, hyperelastic, and fluid models. Slideline elements and contact surface definitions were used in the first two models to simulate the synovial fluid between the articulating cartilages. Incompressible solid elements approximated the synovial fluid in the hyperelastic model. Hydrostatic fluid elements idealized the synovial fluid in the fluid model. The finite element analysis incorporated geometric, material and contact nonlinearities. All models were subjected to compression, flexion, extension, and lateral bending. The fluid model idealization better approximates the actual facet joint anatomy and its behavior than the gap assumption in the slideline and contact surface models, and the solid element simulation in the hyperelastic model.

Biomechanical Phenomena↗
PubMed1998

Cervical spine vertebral and facet joint kinematics under whiplash.

Whiplash injuries sustained during a rear-end automobile collision have significant societal impact. The scientific literature on whiplash loading is both diverse and confusing. Definitive studies are lacking to describe the local mechanisms of injury that induce either acute or chronic pain symptoms. A methodology has been presented to quantify the kinematics of the cervical spine components by inducing controlled whiplash-type forces to intact human head-neck complexes. The localized facet joint kinematics and the overall segmental motions of the cervical spine are presented. It is anticipated that the use of this methodology will assist in a better delineation of the localized mechanisms of injury leading to whiplash pain.

Acceleration↗
PubMed1998

Biomechanics of human thoracic ribs.

Considerable advances have been made to determine the failure biomechanical properties of the human thoracic spinal column and its components. Except for a few fundamental studies, there is a paucity of such data for the costovertebral elements. The present study was designed to determine the biomechanics of the human thoracic spine ribs from a large population. Seventh and eighth ribs bilaterally were tested from 30 human cadavers using the principles of three-point bending techniques to failure. Biomechanical test parameters included the cross-sectional area (core, marrow, and total), moment of inertia, failure load, deflection, and the Young's elastic modulus. The strength-related results indicated no specific bias with respect to anatomical level and hemisphere (right or left), although the geometry-related variables demonstrated statistically significant differences (p < 0.05) between the seventh and the eighth ribs. This study offers basic biomechanical information on the ultimate failure and geometric characteristics of the human thoracic spine ribs.

Adult↗
PubMed1998

Static and dynamic bending responses of the human cervical spine.

The quasi-static and dynamic bending responses of the human mid-lower cervical spine were determined using cadaver intervertebral joints fixed at the base to a six-axis load cell. Flexion bending moment was applied to the superior end of the specimen using an electrohydraulic piston. Each specimen was tested under three cycles of quasi-static load-unload and one high-speed dynamic load. A total of five specimens were included in this study. The maximum intervertebral rotation ranged from 11.0 to 15.4 deg for quasi-static tests and from 22.9 to 34.4 deg for dynamic tests. The resulting peak moments at the center of the intervertebral joint ranged from 3.8 to 6.9 Nm for quasi-static tests and from 14.0 to 31.8 Nm for dynamic tests. The quasi-static stiffness ranged from 0.80 to 1.35 Nm/deg with a mean of 1.03 Nm/deg (+/- 0.11 Nm/deg). The dynamic stiffness ranged from 1.08 to 2.00 Nm/deg with a mean of 1.50 Nm/deg (+/- 0.17 Nm/deg). The differences between the two stiffnesses were statistically significant (p < 0.01). Exponential functions were derived to describe the quasi-static and dynamic moment-rotation responses. These results provide input data for lumped-parameter models and validation data for finite element models to better investigate the biomechanics of the human cervical spine.

Aged↗
PubMed1997

Finite element analysis of cervical facetectomy.

STUDY DESIGN: Moment-rotation responses and disc anulus stresses of intact and facetectomized C4-C6 cervical spinal units were analyzed using detailed, three-dimensional, finite element models. OBJECTIVES: To evaluate biomechanical effects of progressive unilateral and bilateral facet resections on cervical spine segmental mobility (external response) and disc anulus stress (internal response). SUMMARY OF BACKGROUND DATA: Experimental studies have demonstrated that facetectomy significantly increases segmental mobility of the cervical spine. The biomechanical effects of facetectomy on the internal response, however, have not been investigated. METHODS: Moment-rotation responses of C4 with respect to C6 and von Mises stress in the disc anulus were examined using finite element models of a 0% (intact), 25%, 50%, 75%, and 100% unilaterally and bilaterally facetectomized cervical spinal unit. The model simulations were conducted under the pure-moment loading of 1.8 Nm in flexion, extension, lateral bending, and axial torsion. The intact model also was validated experimentally under the same conditions. RESULTS: The moment-rotation responses of the intact unit were within the ranges of experimental data. Cervical rotations increased with the increased degree of facet resection. The greatest change occurred between 50% and 75% facet resections in bilateral facetectomy. Similar patterns were found for disc anulus stresses, but to a greater extent. The maximum increase in rotation (11%) and in anulus stress (30%) occurred in lateral bending. Torsion was the least affected loading mode. The effects of unilateral facetectomy were considerably less than those of 75% bilateral facetectomy. CONCLUSIONS: Facetectomy has a greater effect on anulus stress than on intervertebral joint stiffness. Significant increase in anulus stresses and segmental mobility may occur when bilateral facet resection exceeds 50%.

Adult↗
PubMed1997

Wire fixation techniques of the cervical facets.

STUDY DESIGN: The changes in the biomechanical responses of the cervical spine altered by multilevel laminectomy to various facet wiring techniques were evaluated. OBJECTIVE: To determine the effectiveness of various proposed techniques of cervical facet wiring used to offer rigid internal fixation after multilevel laminectomy. METHODS: Eight human cadaveric spine segments from C2-11 underwent combined flexion-compression loading. After testing intact and three-level laminectomy (C4-C6) preparations, two techniques of facet wiring fixation were evaluated in an identical manner. Force, displacement, and kinematics data at every level of the column were obtained. RESULTS: The mean stiffness of the intact column was significantly greater than the mean stiffness for laminectomized specimens. Individual facet wiring to the bone graft and through the spinous process below the laminectomy failed to restore stiffness to the laminectomized preparations, whereas the Luque rectangle method restored the stiffness to that found in the intact column. The increases in segmental and overall sagittal rotations resulting from multilevel laminectomy were not decreased significantly by the individual facet wiring technique, but the Luque rectangle technique demonstrated a reduction of sagittal rotations compared with laminectomy without fixation. CONCLUSIONS: The significant increases in total column flexibility and segmental flexural rotations after multilevel laminectomy were not corrected by techniques that depend on individual facet wires secured to an overlying strut, including wiring to the inferior intact segment. Crosslinking of the facet wire fixation above and below the laminectomized segments, as exemplified by the Luque rectangle technique, restored column stiffness and reduced segmental sagittal rotations.

Biomechanical Phenomena↗
PubMed1997

Dynamic analysis of penetrating trauma.

BACKGROUND: Whereas considerable literature exists on the wounding mechanics of high velocity projectiles in the military domain, there is a paucity of such data from projectiles routinely encountered in the civilian population in the United States. This study was undertaken to develop a methodology and to determine the dynamics of penetrating trauma secondary to low velocity projectiles (200-300 m/sec). To demonstrate the feasibility of the methodology and the experimental protocol, two markedly different projectiles were chosen in the study. METHODS: Two projectiles were discharged into a human tissue simulant; one projectile was smooth and the other was of the expansion type. High-speed video photographic analysis and synchronized trigger techniques were used to describe the path of the projectile during its travel within the simulant. The temporal transient and residual profiles demonstrating the "wound involvement" were computed. RESULTS: Results indicated a stark contrast between the two cases. There was a ratio of approximately three-to-one in the maximum wound involvement due to penetration. Transient wave oscillations during penetration and perforation of the projectile from the tissue simulant demonstrated significant differences in amplitudes and time durations. In addition, the residual wound involvement profiles indicated differences in the injury potential. CONCLUSIONS: This study has provided an experimental methodology to delineate the temporal dynamic behavior of penetrating projectiles. To fully quantify and differentiate the dynamic differences in the temporal behaviors of the numerous available projectiles (with various combinations in design, type of equipment, and discharge), further research in this area is clearly necessary. The present protocol lends itself to be used to systematically analyze all these behaviors. Quantified data may assist clinical personnel in the management of penetrating trauma.

Biomechanical Phenomena↗
PubMed1997

Finite element model of the human lower cervical spine: parametric analysis of the C4-C6 unit.

In this study, a three-dimensional finite element model of the human lower cervical spine (C4-C6) was constructed. The mathematical model was based on close-up CT scans from a young human cadaver. Cortical shell, cancellous core, endplates, and posterior elements including the lateral masses, pedicle, lamina, and transverse and spinous processes, and the intervertebral disks, were simulated. Using the material properties from literature, the 10,371-element model was exercised under an axial compressive mode of loading. The finite element model response agreed with literature. As a logical step, a parametric study was conducted by evaluating the biomechanical response secondary to changes in the elastic moduli of the intervertebral disk and the endplates. In the stress analysis, the minimum principal compressive stress was used for the cancellous core of the vertebral body and von Mises stress was used for the endplate component. The model output indicated that an increase in the elastic modulii of the disk resulted in an increase in the endplate stresses at all the three spinal levels. In addition, the inferior endplate of the middle vertebral body responded with the highest mean compressive stress followed by its superior counterpart. Furthermore, the middle vertebral body produced the highest compressive stresses compared to its counterparts. These findings appear to correlate with experimental results as well as common clinical experience wherein cervical fractures are induced due to external compressive forces. As a first step, this model will lead to more advanced simulations as additional data become available.

Aging↗
PubMed1997

Inertial loading of the human cervical spine.

While the majority of experimental cervical spine biomechanics research has been conducted using slowly applied forces and/or moments, or dynamically applied forces with contact, little research has been performed to delineate the biomechanics of the human neck under inertial "noncontact" type forces. This study was designed to develop a comprehensive methodology to induce these loads. A minisled pendulum experimental setup was designed to test specimens (such as human cadaver neck) at subfailure or failure levels under different loading modalities including flexion, extension, and lateral bending. The system allows acceleration/deceleration input with varying wave form shapes. The test setup dynamically records the input and output strength information such as forces, accelerations, moments, and angular velocities; it also has the flexibility to obtain the temporal overall and local kinematic data of the cervical spine components at every vertebral level. These data will permit a complete biomechanical structural analysis. In this paper, the feasibility of the methodology is demonstrated by subjecting a human cadaver head-neck complex with intact musculature and skin under inertial flexion and extension whiplash loading at two velocities.

Cadaver↗
PubMed1997

Axial impact biomechanics of the human foot-ankle complex.

Recent epidemiological, clinical, and biomechanical studies have implicated axial impact to the plantar surface of the foot to be a cause of lower extremity trauma in vehicular crashes. The present study was conducted to evaluate the biomechanics of the human foot-ankle complex under axial impact. Nine tests were conducted on human cadaver below knee-foot-ankle complexes. All specimens were oriented in a consistent anatomical position on a mini-sled and the impact load was delivered using a pendulum. Specimens underwent radiography and gross dissection following the test. The pathology included intra-articular fractures of the calcaneus and/or the distal tibia complex with extensions into the anatomic joints. Impactor load cell forces consistently exceeded the tibial loads for all tests. The mean dynamic forces at the plantar surface of the foot were 7.7 kN (SD = 4.3) and 15.1 kN (SD = 2.7) for the nonfracture and fracture tests, respectively. In contrast, the mean dynamic forces at the proximal tibial end of the preparation were 5.2 kN (SD = 3.1) in the nonfracture group, and 10.2 kN (SD = 1.5) in the fracture group. The foot and tibial end forces were statistically significantly different between these two groups (p < 0.01). The present investigation provides fundamental data to the understanding of the biomechanics of human foot-ankle trauma. Quantifying the effects of other factors such as gender and bone quality on the injury thresholds is necessary to understand foot-ankle tolerance fully.

Accidents, Traffic↗
PubMed1997

Biomechanics of penetrating trauma.

It is well known that injuries and deaths due to penetrating projectiles have become a national and an international epidemic in Western society. The application of biomedical engineering to solve day-to-day problems has produced considerable advances in safety and mitigation/prevention of trauma. The study of penetrating trauma has been largely in the military domain where war-time specific applications were advanced with the use of high-velocity weapons. With the velocity and weapon caliber in the civilian population at half or less compared with the military counterpart, wound ballistics is a largely different problem in today's trauma centers. The principal goal of the study of penetrating injuries in the civilian population is secondary prevention and optimized emergency care after occurrence. A thorough understanding of the dynamic biomechanics of penetrating injuries quantifies missile type, caliber, and velocity to hard and soft tissue damage. Such information leads to a comprehensive assessment of the acute and long-term treatment of patients with penetrating injuries. A review of the relevant military research applied to the civilian domain and presentation of new technology in the biomechanical study of these injuries offer foundation to this field. Relevant issues addressed in this review article include introduction of the military literature, the need for secondary prevention, environmental factors including projectile velocity and design, experimental studies with biological tissues and physical models, and mathematical simulations and analyses. Areas of advancement are identified that enables the pursuit of biomechanics research in order to arrive at better secondary prevention strategies.

Animals↗
PubMed1997

Finite element modeling of cervical laminectomy with graded facetectomy.

In this study, an anatomically accurate three-dimensional finite element model of the human lower cervical spine (C4-C6) was used to study the biomechanical effects of cervical laminectomy with and without graded facetectomy. The intact finite element model was validated under flexion, extension, lateral bending, and axial torsion load vectors of 1.8 Nm magnitude. The moment rotation response of the finite element model matched well with experimental data. The gross external (angular motion) and the internal (superior and inferior intervertebral disc stress) responses were delineated under the four physiological loading modes for these iatrogenic changes. Results indicated that laminectomy markedly altered the cervical angular motion and the disc stress under flexion compared with all other loading modes. Facetectomy increased the angular motion and the inferior disc stress notably under flexion but did not affect the adjacent superior disc stress. Facet resection of > 50% caused pronounced increases in angular rotation and intervertebral disc stresses. These findings suggest that the resection of more than one-half of this structure may require additional procedures to restore the strength of the cervical column. Although gross external motion response can be obtained by experimental studies, the internal stress response can only be determined using mathematical models such as the finite element model used in the present study. The accentuated changes in the disc stress compared with the changes in the external rotation may be clinically relevant because increased internal load/stress can result in disc degeneration. The present three-dimensional finite element model offers additional information to better understand the extrinsic and intrinsic responses of the iatrogenically altered cervical spine.

Biomechanical Phenomena↗
PubMed1997

Finite element analysis of anterior cervical spine interbody fusion.

The present study investigated the external and the internal biomechanical responses of anterior cervical discectomy coupled with fusion. Five different types of interbody fusion materials were used: titanium core, titanium cage, tricortical iliac crest, tantalum core, and tantalum cage. Two different types of surgical procedures were analyzed: Smith-Robinson and Bailey-Badgley. A validated three-dimensional anatomically accurate finite element model of the human cervical spine was used in the study. The finite element model was exercised in compression, flexion, extension, and lateral bending for the intact case and for the two surgical procedures with five implant materials. The external response in terms of the stiffness and angular rotation, and the internal response in terms of the disc and the vertebral stresses were determined. The Smith-Robinson technique resulted in the highest increase in external response under all modes of loading for all implant materials. In contrast, the Bailey-Badgley technique produced a higher increase in the disc and the vertebral body stresses than the Smith-Robinson technique. As experimental human cadaver tests can only determine the external response of the non-fused spine simulating immediate post-operative structure, the present finite element studies assist in the understanding of biomechanics of interbody fusion by delineating the changes in the extrinsic and intrinsic characteristics of the cervical spine components due to surgery.

Biomechanical Phenomena↗
PubMed1997

Modular data acquisition system updated using LabWindows/CVI Graphical User Interface.

The Biomechanics Laboratory of the Neuroscience Department of the Medical College of Wisconsin is currently engaged in research involving trauma biomechanics. For some experiments, 24 channels of analog data must be sampled at 10,000 Hertz. The Modular Data Acquisition System (MDAS) is able to acquire up to 60 channels of analog data at sampling intervals as low as 6 microseconds. This excellent hardware system has only menu-driven utility software that is no longer supported and required updating to a Graphical User Interface (GUI). Using National Instruments LabWindows/CVI software a GUI was developed. The GUI consists of 9 Graphical User Interface panels controlled by a 3000 line C program "MDAS3SAM". "MDAS3SAM" controls a driver program "MDAS_SAM" which communicates with the MDAS unit via a National Instruments GPIB interface. The 9 GUI panels allow the user to configure the MDAS system (selecting channels, sampling interval, triggering levels etc.), start sampling the data, writing the data to hard disk, graphing the data and printing the graphs. The new system allows the user to quickly reconfigure the MDAS unit and obtain accurate results.

Biomechanical Phenomena↗