Search PubMed⌕ Search

Biomedical subjects

Narayan Yoganandan

Publications and source records attributed to Narayan Yoganandan.

At least 55 records · Page 3Linked to original sources
PubMed2004

Gender- and region-dependent local facet joint kinematics in rear impact: implications in whiplash injury.

STUDY DESIGN: Localized facet joint kinematics resulting from whiplash acceleration were analyzed in the dynamic domain during the time of cervical S-curvature using intact head and neck specimens and a pendulum mini-sled loading apparatus. OBJECTIVES: To determine the effects of gender, impact severity, cervical level, and anatomic joint region on shear and distraction motion of lower cervical facet joints. SUMMARY OF BACKGROUND DATA: Clinical and experimental studies identify cervical facet joints to be a likely location of whiplash injury. Epidemiologic studies report that female occupants sustain a greater percentage of whiplash injuries. Previous experimental studies have not analyzed facet joint motion as a function of variables such as gender. METHODS: Intact head and neck complexes were subjected to whiplash acceleration using a pendulum mini-sled apparatus at four impact severities. Facet joint kinematics were analyzed using digital high-resolution video at 1000 frames per second during the time of maximum cervical S-curvature. Shear and distraction motions were analyzed in the ventral and dorsal joint regions from C4-C5 to C6-C7 levels. Analysis of variance techniques were used to analyze biomechanical data. RESULTS: Intact head and neck complexes sustained cervical S-curvature during whiplash loading. Lower cervical facet joints demonstrated dorsally directed shear motion with distraction in the ventral and compression in the dorsal regions of the joint. Magnitudes of distraction and compression were significantly lower than shear motion (P < 0.05). Facet joint shear and distraction motion increased with impact severity. Lower cervical facet joint shear and distraction motions in female specimens were greater than in male specimens. This difference reached statistical significance at C4-C5 (P < 0.05). CONCLUSIONS: Secondary to whiplash loading, lower cervical facet joints responded with a shear plus distraction mechanism in the anatomic ventral and shear plus compression mechanisms in the dorsal region. Injury to the ventral region stems from tensile failure of the joint capsule. Injury to the dorsal region stems from pinching of the joint capsule or synovial fold and contact between subchondral bone of superior and inferior facet processes. Because excess spinal motion is biomechanically related to abnormalities and because lower cervical facet joints sustain greater motion in female specimens, this population is more likely to be injured under whiplash loading. Potential contributors for the susceptibility of females to injury, including genotypic (apolipoprotein APOE-epsilon4), hormonal, structural, and tolerance factors, are discussed.

Biomechanical Phenomena↗
PubMed2004

Biomechanics of temporo-parietal skull fracture.

UNLABELLED: This paper presents an analysis of research on the biomechanics of head injury with an emphasis on the tolerance of the skull to lateral impacts. The anatomy of this region of the skull is briefly described from a biomechanical perspective. Human cadaver investigations using unembalmed and embalmed and intact and isolated specimens subjected to static and various types of dynamic loading (e.g., drop, impactor) are described. Fracture tolerances in the form of biomechanical variables such as peak force, peak acceleration, and head injury criteria are used in the presentation. Lateral impact data are compared, where possible, with other regions of the cranial vault (e.g., frontal and occipital bones) to provide a perspective on relative variations between different anatomic regions of the human skull. The importance of using appropriate instrumentation to derive injury metrics is underscored to guide future experiments. RELEVANCE: A unique advantage of human cadaver tests is the ability to obtain fundamental data for delineating the biomechanics of the structure and establishing tolerance limits. Force-deflection curves and acceleration time histories are used to derive secondary variables such as head injury criteria. These parameters have direct application in safety engineering, for example, in designing vehicular interiors for occupant protection. Differences in regional biomechanical tolerances of the human head have implications in clinical and biomechanical applications.

Acceleration↗
PubMed2004

Rear impact responses of different sized adult Hybrid III dummies.

Rear impact sled tests were conducted using 5th, 50th, and 95th percentile Hybrid III dummies to evaluate proposed injury criteria. Different head restraint height (750, 800 mm) and backset (0, 50, 100 mm) positions were used to determine axial and shear forces, bending moments, and injury criteria (NIC, N(ij), and N(km)). The time sequence to attain each parameter was also determined. Three events were identified in the response. Event I was coincident with the maximum rearward motion of the torso, Event II occurred at the time of the peak upper neck flexion moment, and Event III occurred at the time of maximum rearward motion of the head. Parameters such as backset, head restraint height, seat-head restraint interaction, and anthropometry affected impact responses. Head rotations increased with increasing backset and increasing head restraint height. However, N(ij) and N(km) did not exhibit such clear trends. The 50th percentile dummy responded with consistent injury criteria values (e.g., the magnitude of the injury criteria increased with backset increase or head restraint height decrease). However, the 5th and 95th percentile dummies did not demonstrate such trends. These findings underscore the need to include subject anthropometry in addition to seat and head restraint characteristics for better assessment of rear impact responses.

Acceleration↗
PubMed2004

Force and acceleration corridors from lateral head impact.

This study was conducted to provide force and acceleration corridors at different velocities describing the dynamic biomechanics of the lateral region of the human head. Temporo-parietal impact tests were conducted using specimens from ten unembalmed post-mortem human subjects. The specimens were isolated at the occipital condyle level, and pre-test x-ray and computed tomography images were obtained. They were prepared with multiple triaxial accelerometers and subjected to increasing velocities (up to 7.7 m/s) using free-fall techniques by impacting onto a force plate from which forces were recorded. A 40-durometer padding (50-mm thickness) material covering the force plate served as the impacting boundary condition. Computed tomography images obtained following the final impact test were used to identify pathology. Four specimens sustained skull fractures. Peak force, displacement, acceleration, energy, and head injury criterion variables were used to describe the dynamic biomechanics. Force and acceleration responses obtained from this experimental study along with other data will be of value in validating finite element models. The study underscored the need to enhance the sample size to derive probability-based human tolerance to side impacts.

Abbreviated Injury Scale↗
PubMed2004

Influence of muscle contraction on whiplash kinematics.

It is unclear whether reflexive muscle contraction in unaware occupants can alter spinal kinematics to mitigate injury in the unaware occupant subjected to whiplash loading. Whiplash injury likely occurs during the non-physiologic S-curvature phase of spinal kinematics, present during the first 100 msec after the initiation of T1 acceleration. Experimental investigations using human volunteers have reported 45 to 60 msec delays prior to electrical activity of the sternocleidomastoid. The effects of reflexive contraction of the neck muscles were investigated using a validated head-neck computational model consisting of head, cervical spine, and first thoracic vertebra. Intervertebral discs. spinal ligaments, and facet joints were modeled using discrete elements. Passive and active musculature were incorporated using the Hill-type muscle model. The computational model was subjected to 2.6 m/sec rear impact velocity, applied to T1. Reflexive muscle contraction in the unaware occupant model was incorporated using a 54-msec muscle delay, 13-msec electromechanical delay, and an 81-msec muscle rise time. Results of the unaware occupant model were compared to the model exercised without muscle contraction. Reflexive muscle contraction altered segmental angulations by less than 10% and facet joint capsular ligament distractions by less than 16% during the time of maximum S-curvature. At the C5-C6 and C6-C7 levels, muscle contraction increased capsular ligament distractions. Due to the nominal affect of reflexive muscle contraction on segmental angulations and facet joint capsular ligament distractions during S-curvature, it is unlikely that this contraction can alter the cervical kinematics responsible for whiplash injury.

Acceleration↗
PubMed2004

Response corridors of the human head-neck complex in rear impact.

In recent years, anatomically accurate dummies were developed to produce a more biofidelic response to rear impacts. The detailed dummy geometry permits more comprehensive kinematic validation, which is typically accomplished through response corridors developed using human volunteers and cadavers. In the present investigation, ten intact head-neck cadaver specimens were subjected to 1.8 and 2.6 m/s rear impacts. Response corridors were developed for overall head to T1 angulation, head retraction, and segmental angulations from C2-C3 through C6-C7 levels. The corridors were developed to emphasize the detailed validation of dummy response during initial stages of whiplash loading.

Accidents, Traffic↗
PubMed2004

A new biomechanically-based criterion for lateral skull fracture.

This work develops a skull fracture criterion for lateral impact-induced head injury using postmortem human subject tests, anatomical test device measurements, statistical analyses, and finite element modeling. It is shown that skull fracture correlates with the tensile strain in the compact tables of the cranial bone as calculated by the finite element model and that the Skull Fracture Correlate (SFC), the average acceleration over the HIC time interval, is the best predictor of skull fracture. For 15% or less probability of skull fracture the lateral skull fracture criterion is SFC < 120 g, which is the same as the frontal criterion derived earlier. The biomechanical basis of SFC is established by its correlation with strain.

Biomechanical Phenomena↗
PubMed2004

Injury biomechanics of C2 dens fractures.

The objective of this study is to analyze the biomechanics of dens fractures of the second cervical vertebra in the adult population due to motor vehicle crashes. Case-by-case records from the Crash Injury Research and Engineering Network (CIREN) and National Automotive Sampling System (NASS) databases were used. Variables such as change in velocity, impact direction and body habitus were extracted. Results indicated that similarities exist in the two databases despite differences in sampling methods between the two sources (e.g., CIREN is not population based). Trauma is predominantly associated with the frontal mode of impact. Majority of injuries occur with change in velocities below current federal guideline thresholds. No specific bias exists with respect to variables such as age, height, weight, and gender. Because similar conclusions can be drawn with regard to vehicle model years, design changes during these years may have had little effect on this injury. To ameliorate trauma, emphasis should be placed on the frontal impact mode and entire adult population. Because of clinical implications in the fracture type (II being most critical) and lack of specific coding, CIREN data demonstrates the need to improve injury coding in the AIS and application in the NASS to enhance occupant safety and treatment in the field of automotive medicine.

Adult↗
PubMed2003

Anatomic study of the morphology of human cervical facet joint.

STUDY DESIGN: Geometrical properties of the facet joint including cartilage thickness and gap were obtained using human cadaver cervical spinal columns and cryomicrotomy techniques. OBJECTIVES: To determine the existence of level or gender dependency on facet joint morphology in the human cervical spine. BACKGROUND DATA: Although measurements of the human cervical spine have been reported in literature, to the best of knowledge of the authors, geometrical data on the facet joint structures such as the cartilage are not available. These data are important to understand the anatomy of the cervical spine and the role of the cartilage in sharing the external load during physiologic and traumatic situations. Furthermore, the data will assist mathematical modelers to accurately simulate this component of the cervical facet joint in finite element analysis of the spine. MATERIALS AND METHODS: Six unembalmed human cadaver cervical spinal columns were used. A heavy-duty cryomicrotome was used to obtain the geometrical characteristics. The specimens were sectioned in the sagittal plane at 20- to 40-microm intervals. Geometric properties of the facet joint width, cartilage thickness, and cartilage gap (defined as the distance from the ventral-most or dorsal-most region of the facet joint to the location where the cartilage began to appear) were extracted from the anatomic sections that were midsagittal with respect to the facet joints from occiput to T1 levels. Multiple factorial analysis of variance techniques were used to determine the statistical significance of various geometrical parameters obtained from the anatomic sections. RESULTS: The cartilage gap in the upper cervical spine (UCS) (C1-C2, i.e., UCS, 5.4% +/- 0.8) was lower (P < 0.0001) than the gap in the lower cervical spine (LCS) (C3-C7, i.e., LCS, 16.4% +/- 0.8). The gap at the ventral and dorsal regions was lower in the UCS (ventral 3.8% +/- 0.6, dorsal 7.0% +/- 1.4) than in the LCS (ventral 18.5% +/- 0.9, dorsal 14.2% +/- 1.1) with p values of less than 0.0001 and equal to 0.0004, respectively. Further, the gap in the dorsal region for females (14.7% +/- 1.8) was greater (P = 0.0523) than the gap for males (10.8% +/- 1.1). The overall mean facet cartilage thickness was lower (P = 0.0111) in females (0.6 mm +/- 0.1) than males (0.9 mm +/- 0.2) in the UCS. It was also lower (P = 0.0077) in females (0.4 mm +/- 0.02) than males (0.5 mm +/- 0.03) in the LCS. The facet joint width demonstrated differences only between the UCS and LCS (P < 0.0001), with higher magnitudes in the upper (17.4 mm +/- 0.4) than in the lower (11.3 mm +/- 0.3) region. CONCLUSIONS: Facet joint morphology varies with the regions of the cervical spine (upper vs. lower), gender (male vs. female), and location (dorsal vs. ventral). Because of the lack of intervertebral discs in the UCS region, variations in these geometrical characteristics affect the biomechanical behaviors of the human spine secondary to external loads. Furthermore, the lack of adequate cartilage in females may expose the underlying adjacent subchondral bone to direct stresses during normal physiologic and traumatic loads.

Age Factors↗
PubMed2003

Gender dependent cervical spine segmental kinematics during whiplash.

Clinical and epidemiological studies have frequently reported that female occupants sustain whiplash injuries more often than males. The current study was based on the hypothesis that segmental level-by-level cervical intervertebral motions in females are greater than in males during rear impact. The hypothesis was tested by subjecting 10 intact human cadaver head-neck complexes (five males, five females) to rear impact loading. Intervertebral kinematics were analyzed as a function of spinal level at the time of maximum cervical S-curve, which occurred during the loading phase. Segmental angles were significantly greater (p<0.05) in female specimens at C2-C3, C4-C5, C5-C6, and C6-C7 levels. Because greater angulations are associated with stretch in the innervated components of the cervical spinal column, these findings may offer a biomechanical explanation for the higher incidence of whiplash-related complaints in female patients secondary to rear impact acceleration.

Adult↗
PubMed2003

Development of Side Impact Thoracic Injury Criteria and Their Application to the Modified ES-2 Dummy with Rib Extensions (ES-2re).

Forty-two side impact cadaver sled tests were conducted at 24 and 32 km/h impact speeds into rigid and padded walls. The post-mortem human subjects were instrumented with accelerometers on the ribs and spine and chest bands around the thorax and abdomen to characterize their mechanical response during the impact. Load cells at the wall measured the impact force at the level of the thorax, abdomen, pelvis, and lower extremities. The resulting injuries were determined through detailed autopsy and radiography. Rib fractures with or without associated hemo/pneumo thorax or flail chest were the most common injury with severity ranging from AIS=0 to 5. Full and half thorax deflections were computed from the chest band data. The cadaver test data was analyzed using ANOVA and logistic regression. The age of the subject at the time of death had influence on injury outcome while gender and mass of the subject had little or no influence on injury outcome. Existing side impact injury criteria were evaluated such as Thoracic Trauma Index (TTI), Average Spinal Acceleration (ASA), full and half thorax deflections, chest velocity and viscous criterion, and contact force. The analysis results indicate that maximum normalized average half thorax deflection was the best predictor of AIS>/=3 and AIS>/=4 thoracic injury. TTI and upper spine accelerations were also good predictors of thoracic injury. Sixteen side impact sled tests were also conducted with the modified ES-2 dummy with rib extensions (ES-2re) under similar impact conditions as the cadaver tests. The rib extensions were added to the original ES-2 dummy ribs to prevent the "seat grabbing" action of the back plate that was noticed in some side impact vehicle crash tests with the ES-2 dummy. A separate analysis was conducted using the injury response and subject characteristics from the cadaver tests and the physical parameters derived from measurements on the ES-2re dummy in sled tests under similar conditions as the cadaver tests. This analysis provided thoracic injury criteria that could be directly applied to the ES-2re dummy. This analysis indicated subject age to have significant influence on injury outcome. Maximum rib deflection and ASA of the ES-2re were the best predictors of thoracic injury. A 50% risk of AIS>/=3 thoracic injury for a 45 year old corresponds to 44 mm (standard error range: 32 to 54 mm) of ES-2re maximum rib deflection and ASA of 46 gs (standard error range: 34 -58 gs).

Journal Article↗
PubMed2003

Statistically and biomechanically based criterion for impact-induced skull fracture.

This work developed a skull fracture criterion for impact-induced head injury, using post mortem human subject tests, anatomical test device measurements, statistical analyses, and finite element modeling. It is shown that skull fracture correlates with the tensile strain in the outer table of the cranial bone, and an index termed the Skull Fracture Correlate (SFC) predicts injury. SFC offers several advantages as a protection criterion. It accounts for compliance of the impact site; it is extensible to varying head mass; and it is easily implemented using current software. For a 15% or less probability of skull fracture the criterion is SFC < 120 g, with a 95% confidence band of 88 < SFC < 135 g.

Acceleration↗
PubMed2002

Biomechanical analyses of whiplash injuries using an experimental model.

Neck pain and headaches are the two most common symptoms of whiplash. The working hypothesis is that pain originates from excessive motions in the upper and lower cervical segments. The research design used an intact human cadaver head-neck complex as an experimental model. The intact head-neck preparation was fixed at the thoracic end with the head unconstrained. Retroreflective targets were placed on the mastoid process, anterior regions of the vertebral bodies, and lateral masses at every spinal level. Whiplash loading was delivered using a mini-sled pendulum device. A six-axis load cell and an accelerometer were attached to the inferior fixation of the specimen. High-speed video cameras were used to obtain the kinematics. During the initial stages of loading, a transient decoupling of the head occurs with respect to the neck exhibiting a lag of the cranium. The upper cervical spine-head undergoes local flexion concomitant with a lag of the head while the lower column is in local extension. This establishes a reverse curvature to the head-neck complex. With continuing application of whiplash loading, the inertia of the head catches up with the neck. Later, the entire head-neck complex is under an extension mode with a single extension curvature. The lower cervical facet joint kinematics demonstrates varying local compression and sliding. While the anterior- and posterior-most regions of the facet joint slide, the posterior-most region of the joint compresses more than the anterior-most region. These varying kinematics at the two ends of the facet joint result in a pinching mechanism. Excessive flexion of the posterior upper cervical regions can be correlated to headaches. The pinching mechanism of the facet joints can be correlated to neck pain. The kinematics of the soft tissue-related structures explain the mechanism of these common whiplash associated disorders.

Aged↗
PubMed2002

Biomechanics of the cervical spine 4: major injuries.

This review presents considerations regarding major cervical spine injury, including some concepts that are presently undergoing evaluation and clarification. Correlation of certain biomechanical parameters and clinical factors associated with the causation and occurrence of traumatic cervical spine injuries assists in clarifying the pathogenesis and treatment of this diverse group of injuries. Instability of the cervical column based on clinical and mechanistic perspectives as well as the role of ligaments in determining instability is discussed. Patient variables such as pre-existing conditions (degenerative disease) and age that can influence the susceptibility or resistance to injury are reviewed. Radiological considerations of major injuries including dynamic films, CT and MRI are presented in the diagnosis and treatment of cervical trauma. Specific injury patterns of the cervical vertebral column are described including attention to the relative mechanisms of trauma. From a biomechanical perspective, quantification of injury tolerance is discussed in terms of external and human-related variables using laboratory-driven experimental models. This includes force vectors (type, magnitude, direction) responsible for injury causation, as well as potential influences of loading rate, gender, age, and type of injury.

Biomechanical Phenomena↗
PubMed2002

Seat belts are more effective than airbags in reducing thoracic aortic injury in frontal motor vehicle crashes.

BACKGROUND: Airbags reduce the probability of death in frontal collisions, but the effect is small compared with seat belts. Little is known about the influence of seat belts and airbags on the incidence of thoracic aortic injury (TAI). METHODS: The National Automotive Sampling System database was queried for the years 1993 to 1998 to determine the impact of seat belts and airbags on the incidence of TAI in survivors of frontal motor vehicle crashes. Proportions were compared using the two-sample Z test. RESULTS: Seat belts prevent TAI regardless of airbag deployment. The effect of airbags is limited to those wearing seat belts. In frontal collisions without seat belt use, airbag deployment does not alter TAI incidence. CONCLUSION: Seat belts are considerably more effective in preventing TAI than airbags after frontal motor vehicle crashes. Prevention efforts should continue to emphasize the use of active restraints. Restraint use should be considered a risk factor in evaluating patients for potential TAI.

Accidents, Traffic↗
PubMed2002

Biophysics of cochlear implant/MRI interactions emphasizing bone biomechanical properties.

OBJECTIVE/HYPOTHESIS: The forces exerted during a 1.5-Tesla MRI evaluation on the internal magnet of a cochlear implant (CI) raise concern about the safety for CI recipients. This study determines the magnitude of force required to fracture the floor of a CI receiver bed. METHOD: Recessed CI beds were drilled to maximum uniform thinness into formalin-fixed and fresh-frozen human calvaria specimens. A Med-El stainless steel CI template mounted to the piston of an electrohydraulic testing device was used to fracture the floor of the implant beds. Force and displacement were measured as a function of time using a digital data acquisition system. RESULTS: Mean force to first failure, displacement to first failure, and minimum thickness, respectively, were: group 1 (formalin-fixed, 0.3-0.4-mm thick [n = 22]), 34.08 N (8.21-59.64 N, standard deviation [SD] 15.41 N), 1.09 mm (0.40-2.16 mm, SD 0.51 mm), 0.36 mm (0.3-0.4 mm, SD 0.05 mm); group 2 (formalin-fixed, 0.5-0.9 mm thick [n = 21]), 52.82 N (20.28-135.53 N, SD 25.29 N), 1.08 mm (0.50-2.28 mm, SD 0.47 mm), 0.58 mm (0.5-0.9 mm, SD 0.12 mm); group 3 (fresh-frozen [n = 9]), 134.13 N (86.44-190.70 N, SD 34.92 N), 1.96 mm (1.47-2.46 mm, SD 0.35 mm), 0.42 mm (0.3-0.6 mm, SD 0.11 mm). CONCLUSIONS: The mean magnitude of force required to fracture the floor of a CI bed is significantly greater than those that are generated when a Med-El Combi 40+, CII Bionic Ear CI, or Nucleus Contour CI is placed into a 1.5-Tesla MRI unit.

Adult↗
PubMed2002

Preinjury cervical alignment affecting spinal trauma.

OBJECT: The authors tested the hypothesis that initial alignment of the head-neck complex affects cervical spine injury mechanism, trauma rating, injury classification based on stability, and fracture pattern. METHODS: Thirty intact human cadaveric head-neck complexes were prepared by fixing the thoracic end in polymethylmethacrylate. The cranium was unconstrained. The initial spinal alignment was described in terms of eccentricity, defined as the anteroposterior position of the occipital condyles with respect to the T-1 vertebral body. The specimens were subjected to impact loading delivered using an electrohydraulic testing device. Outcomes after injury were identified using radiography and computerized tomography. The mechanisms of injury were classified according to fracture pattern into compression-extension, compression-flexion, hyperflexion, and vertical compression. Trauma was graded according to the Abbreviated Injury Scale rating system. Based on clinical assessment, injuries were classified as stable or unstable. Injuries were also classified into bone fracture or nonfracture groups. Analysis of variance tests were used to determine the influence of eccentricity on spinal injury outcomes. Eccentricity significantly influenced the mechanism of injury (p < 0.0001), trauma rating (p < 0.005), and fracture (p < 0.0001) classification. Statistically significant differences, however, were not apparent when the classification of injury was based on stability considerations. CONCLUSIONS: Spinal alignment is a strong determinant of the biomechanics of impact-induced cervical spine injury.

Analysis of Variance↗