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Biomedical subjects

N Yoganandan

Publications and source records attributed to N Yoganandan.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1996

Finite element applications in human cervical spine modeling.

The authors present a comprehensive state-of-the-art and critical review of the finite element models of the human cervical spine. They also focused on the developments in model construction (geometry generation), constitutive law (material property) identification, loading and boundary condition details, and validation, the most important phase. A data base of available experimental sources is also provided, which can be used by the modeler for validating the finite element model. The potential developments in finite element modeling of the human cervical spine are discussed.

Biomechanical Phenomena↗
PubMed1996

Biomechanical analysis of thoracolumbar interbody constructs. How important is the endplate?

STUDY DESIGN: A biomechanical study of human cadaveric thoracic vertebral bodies was conducted using several anterior fusion options subjected to axial loads. This study emphasized the contribution of the endplate to resistance of graft subsidence. OBJECTIVES: To determine the importance of the vertebral endplate in resisting subsidence of various constructs into the vertebral body; the relative efficacy of potential alternative graft constructs such as iliac crest, ribs, humerus, and titanium mesh cage; and the importance of bone mineral content, vertebral level, and cross-sectional graft area on construct subsidence. SUMMARY OF BACKGROUND DATA: As the fixation length of anterior and posterior spinal constructs is reduced, load sharing of the anterior column has become more important to reduce failure of the shorter devices. Several alternative graft constructs and surgical techniques have been used for reconstruction of the anterior column. There exist little comparative data as to whether any of these constructs are superior and whether the vertebral endplate contributes significantly to the integrity of the construct. METHODS: Sixty-three isolated human cadaveric vertebral bodies from T3 to T12 were used to test seven different constructs in direct axial load onto prepared endplates with an electrohydraulic testing device. These constructs were: 1) titanium mesh cage (17 x 22 mm) on intact endplate, 2) C-shaped humerus on intact endplate, 3) tricorticated iliac graft in "tee configuration" on intact endplate, 4) tricorticated iliac graft in cancellous trough, 5) triple rib strut graft, 6) single rib on endplate, and 7) single rib on cancellous body. Dual X-ray absorptiometry assessment of bone mineral content was performed. A uniaxial load was applied with force and displacement data collected to determine maximal load to "failure" of the vertebral body. RESULTS: Preservation of vertebral endplate did not significantly increase the resistance to graft subsidence. The titanium cage construct provided the greatest resistance to axial load. CONCLUSIONS: Preservation of the vertebral endplate may not offer a significant biomechanical advantage in reconstructing the anterior column. Several alternative constructs are mechanically equivalent.

Adult↗
PubMed1996

Finite-element models of the human head.

A review is presented of the existing finite-element (FE) models for the biomechanics of human head injury. Finite element analysis can be an important tool in describing the injury biomechanics of the human head. Complex geometric and material properties pose challenges to FE modelling. Various assumptions and simplifications are made in model development that require experimental validation. More recent models incorporate anatomic details with higher precision. The cervical vertebral column and spinal cord are included. Model results have been more qualitative than quantitative owing to the lack of adequate experimental validation. Advances include transient stress distribution in the brain tissue, frequency responses, effects of boundary conditions, pressure release mechanism of the foramen magnum and the spinal cord, verification of rotation and cavitation theories of brain injury, and protective effects of helmets. These theoretical results provide a basic understanding of the internal biomechanical responses of the head under various dynamic loading conditions. Basic experimental research is still needed to be determine more accurate material properties and injury tolerance criteria, so that FE models can fully exercise their analytical and predictive power for the study and prevention of human head injury.

Biomechanical Phenomena↗
PubMed1996

Human head-neck biomechanics under axial tension.

A significant majority of cervical spine biomechanics studies has applied the external loading in the form of compressive force vectors. In contrast, there is a paucity of data on the tensile loading of the neck structure. These data are important as the human neck not only resists compression but also has to withstand distraction due to factors such as the anatomical characteristics and loading asymmetry. Furthermore, evidence exists implicating tensile stresses to be a mechanism of cervical spinal cord injury. Recent advancements in vehicular restraint systems such as air bags may induce tension to the neck in adverse circumstances. Consequently, this study was designed to develop experimental methodologies to determine the biomechanics of the human cervical spinal structures under distractive forces. A part-to-whole approach was used in the study. Four experimental models from 15 unembalmed human cadavers were used to demonstrate the feasibility of the methodology. Structures included isolated cervical spinal cords, intervertebral disc units, skull to T3 preparations, and intact unembalmed human cadavers. Axial tensile forces were applied, and the failure load and distraction were recorded. Stiffness and energy absorbing characteristics were computed. Maximum forces for the spinal cord specimens were the lowest (278 N +/- 90). The forces increased for the intervertebral disc (569 N +/- 54). skull to T3 (1555 N +/- 459), and intact human cadaver (3373 N +/- 464) preparations, indicating the load-carrying capacities when additional components are included to the experimental model. The experimental methodologies outlined in the present study provide a basis for further investigation into the mechanism of injury and the clinical applicability of biomechanical parameters.

Adult↗
PubMed1996

Finite element modeling of the C4-C6 cervical spine unit.

This study was conducted to develop a detailed, three-dimensional, anatomically accurate finite element model of the human cervical spine structure using close-up computed tomography scans and to validate against experimental data. The finite element model of the three vertebra segment C4-C6 unit consisted of 9178 solid elements and 1193 thin shell elements. The force-displacement response under axial compression correlated well with experimental data. Because of the inclusion of three levels in the spinal structure, it was possible to determine the internal mechanics of the various components at each level. The applicability of the model was illustrated by adopting appropriate material properties from literature. Results indicated that, the stresses in the anterior column were higher compared to the posterior column at the inferior level, while the opposite was found to be true at the superior level. The superior and inferior endplate stresses were higher in the middle vertebral body compared to the adjacent vertebrae. In addition, the stresses in the cancellous core of the middle, unconstrained vertebral body were higher. The present three-dimensional finite element model offers an additional facet to a better understanding of the biomechanics of the human cervical spine.

Adult↗
PubMed1996

Biomechanics of the intact and surgically repaired proximal interphalangeal joint collateral ligaments.

Collateral ligament injuries to the proximal interphalangeal joint are common. When the collateral ligament is completely ruptured, surgical repair may be required. The strength of the lateral collateral ligaments of the proximal interphalangeal joint was examined using axial distraction on an electrohydraulic testing apparatus. Eighty-five fresh human adult cadaver fingers were assessed; 38 intact ligaments were first examined. The strength of the native ligament was 162.5 N. Forty-seven ligament repair preparations were tested: suture repair (27.8 N), pull-out wire repair (35.9 N), and repair using a Mitek suture anchor (38.4 N). The breaking strength of the intact ligaments was significantly greater than that of any repair. All repaired ligaments failed at the site of the repair. The ligaments repaired by the pull-out wire and Mitek anchor technique were significantly stronger than those repaired with the suture technique.

Adult↗
PubMed1996

Cervical spine injuries from high-velocity forces: a pathoanatomic and radiologic study.

The detailed analysis of the radiologic and pathoanatomic data from 10 human cadaver head-neck complexes defined the type and extent of expected cervical spine injuries after high-velocity flexion-compression loads to the cranium. All specimens demonstrated multiple injuries with both contiguous and noncontiguous patterns. Although all preparations showed evidence of axial compression, a multiplicity of other force vectors, including noncontiguous occurrences of flexion, extension, and shear, were documented. These findings indicate that the injury pattern is not a sequential process but a reaction to changes in the segmental interrelations of the various vertebral column components, including varying vector applications of injurious forces at the segmental level. The presence of moderate or severe spondylotic alterations restricted the distal transmission of injury forces with the principal injury patterns occurring at or proximal to the initial level of severe spondylotic involvement. These data emphasize the need for increased awareness of the presence of multiple cervical spine injuries, both contiguous and noncontiguous, and that separate levels of compromise may not share similar mechanisms of injury.

Aged↗
PubMed1996

Instrumented artificial spinal cord for human cervical pressure measurement.

Spinal cord injuries continue to generate large individual and societal costs. The study of spinal cord injury has been undertaken from the perspective of animal studies to understand cord functioning, and from the use of cadaver material to understand ligamentous column failure. The present study was conducted to develop a tool to link results from both these methods of research. An instrumented artificial spinal cord was designed, constructed, and evaluated under different testing scenarios. Properties of the in vivo animal cord were obtained using the dorsal impact method and reproduced in a collagen-encased gelatin physical model. The cord was instrumented in seven places using thin, non-invasive piezo-electric pressure sensors. The instrumented artificial cord was then evaluated in the canal of a human cadaver head-neck column under dynamic loading conditions. A C5 compression fracture correlated to high local pressure changes. These results demonstrate the feasibility of using this new tool to understand the mechanisms of spinal cord injury.

Animals↗
PubMed1995

Biomechanical alterations induced by multilevel cervical laminectomy.

STUDY DESIGN: The biomechanical responses of the cervical spine undergoing a combined loading vector within the physiologic range and after multilevel laminectomy were evaluated. The experimental conditions were designed to more closely replicate the typical clinical situation than accomplished by previous studies. OBJECTIVE: To determine the biomechanical alterations induced by multilevel cervical spine laminectomy using an in vitro model. SUMMARY OF BACKGROUND DATA: The few previous laboratory studies concerned with the effects of cervical laminectomy have generally indicated a lack of significant change in strength or flexibility induced by the procedure. These studies have been limited by a variety of factors, including the use of pure loads under low physiologic loading conditions, restriction of the laminectomy to one or two segments, and the evaluation of a small number of specimens. METHODS: Twelve fresh human cadaver cervical spine segments from C2-T1 were used. A custom-designed fixture was attached to the proximal end of the specimen to apply a flexion-compression load. Retroreflective targets were positioned in bony landmarks for localized temporal kinematics of the entire cervical column. Testing was performed before (intact) and after a three-level (C4-C6) laminectomy, and data regarding the force, displacement, and kinematics at every level of the column were obtained. RESULTS: The mean stiffness of the intact cervical column was significantly greater (P < 0.05) than the mean stiffness for the laminectomized specimen. Sagittal rotation angle had significant (P < 0.05) differences between intact (3.6 degrees) and laminectomy (8.0 degrees). Laminectomized specimens consistently responded with higher rotations compared with the intact specimen at every cervical spine level. CONCLUSION: Multilevel cervical laminectomy induces significant increases in total column flexibility associated with increased segmental flexural sagittal rotations. These motion changes were generalized with a tendency to show the greatest change at the lower level of laminectomy. Such biomechanical changes may constitute part of the underlying basis for failure of laminectomy to offer sustained good therapeutic results of the myelopathy associated with cervical stenosis and cervical spondyloarthropathy.

Adult↗
PubMed1995

Biomechanics of skull fracture.

This study was conducted to determine the biomechanics of the human head under quasistatic and dynamic loads. Twelve unembalmed intact human cadaver heads were tested to failure using an electrohydraulic testing device. Quasistatic loading was done at a rate of 2.5 mm/s. Impact loading tests were conducted at a rate of 7.1 to 8.0 m/s. Vertex, parietal, temporal, frontal, and occipital regions were selected as the loading sites. Pathological alterations were determined by pretest and posttest radiography, close-up computed tomography (CT) images, macroscopic evaluation, and defleshing techniques. Biomechanical force-deflection response, stiffness, and energy-absorbing characteristics were obtained. Results indicated the skull to have nonlinear structural response. The failure loads, deflections, stiffness, and energies ranged from 4.5 to 14.1 kN, 3.4 to 16.6 mm, 467 to 5867 N/mm, and 14.1 to 68.5 J, respectively. The overall mean values of these parameters for quasistatic and dynamic loads were 6.4 kN (+/- 1.1), 12.0 mm (+/- 1.6), 812 N/mm (+/- 139), 33.5 J (+/- 8.5), and 11.9 kN (+/-0.9), 5.8 mm (+/- 1.0), 4023 N/mm (+/- 541), 28.0 J (+/- 5.1), respectively. It should be emphasized that these values do not account for the individual variations in the anatomical locations on the cranium of the specimens. While the X-rays and CT scans identified the fracture, the precise direction and location of the impact on the skull were not apparent in these images. Fracture widths were consistently wider at sites remote from the loading region. Consequently, based on retrospective images, it may not be appropriate to extrapolate the anatomical region that sustained the impact forces. The quantified biomechanical response parameters will assist in the development and validation of finite element models of head injury.

Aged↗
PubMed1995

Thoracic deformation and velocity analysis in frontal impact.

The objective of the present study was to measure dynamic chest deformations and compute chest velocity and viscous criterion during real world frontal impacts conducted on a horizontal sled. Four unembalmed human cadavers were restrained using a three-point belt restraint in the driver seat of a sled buck. Two chest bands (each with a 24 gauge capability) were placed on the thorax to record the temporal deformation patterns during impact. All tests were conducted at a velocity of approximately 50 kph. Biomechanical data were gathered digitally at a sampling rate of 12,500 Hz. Multiple rib fractures were identified in all specimens at autopsy. Analysis of approximately 800 temporal deformation contours of the thorax demonstrated regional differences. The overall mean maximum normalized chest deflections, maximum chest compression velocities, and peak viscous response variables ranged from 0.15 to 0.51, 1.79 to 4.87 m/s, and 0.15 to 1.95 m/s, respectively. These findings clearly illustrate the potential use of the chest band output to correlate injury with biomechanical variables and establish thoracic impact tolerance.

Accidents, Traffic↗