Biomedical subjects

Narayan Yoganandan

Publications and source records attributed to Narayan Yoganandan.

At least 37 records · Page 2Linked to original sources

PubMed2005

Reflex muscle contraction in the unaware occupant in whiplash injury.

STUDY DESIGN: Computer modeling and parametric analysis were used to determine the effect of reflex contraction of the neck muscles in the unaware occupant in whiplash. OBJECTIVE: To delineate effects of reflex contraction on spinal segmental kinematics during the retraction phase. SUMMARY OF BACKGROUND DATA: The ability of reflex neck muscle contraction to mitigate whiplash injury in the unaware occupant remains unclear. Analyzing relative timing between electromyographic and head-neck kinematics, previous investigators theorized that muscle contraction alters spinal kinematics, decreasing injury likelihood. Other investigators suggested that injury occurs during the initial (retraction) phase of head-neck kinematics, before significant muscle force generation. METHODS: Computer modeling was used to determine reflex contraction effects on segmental angulations, implementing parametric analysis techniques to vary reflex delay and impact severity. RESULTS: Shorter reflex delays had a greater effect on segmental angulations later in the event and at lower impact severities. However, the magnitude of this effect, particularly at higher impact severities and during maximum cervical S-curvature (factors implicated in the whiplash injury mechanism) was minimal, altering segmental angulations by a maximum of 19%. CONCLUSIONS: Because reflex contraction did not substantially alter spinal kinematics, muscle contraction likely does not initiate in sufficient time to mitigate whiplash injuries that may occur during the retraction phase.

Cervical Vertebrae↗

PubMed2005

Effect of head restraint backset on head-neck kinematics in whiplash.

Although head restraints were introduced in the 1960s as a countermeasure for whiplash, their limited effectiveness has been attributed to incorrect positioning. The effect of backset on cervical segmental angulations, which were previously correlated with spinal injury, has not been delineated. Therefore, the practical restraint position to minimize injury remains unclear. A parametric study of increasing head restraint backset between 0 and 140mm was conducted using a comprehensively validated computational model. Head retraction values increased with increasing backset, reaching a maximum value of 53.5mm for backsets greater than 60mm. Segmental angulation magnitudes, greatest at levels C5-C6 and C6-C7, reached maximum values during the retraction phase and increased with increasing backset. Results were compared to a previously published head restraint rating system, wherein lower cervical extension magnitudes from this study exceeded mean physiologic limits for restraint positions rated good, acceptable, marginal, and poor. As head restraint contact was the limiting factor in head retraction and segmental angulations, the present study indicates that minimizing whiplash injury may be accomplished by limiting head restraint backset to less than 60mm either passively or actively after impact.

Biomechanical Phenomena↗

PubMed2005

Anterior longitudinal ligament injuries in whiplash may lead to cervical instability.

Although whiplash injuries account for a significant annual cost to society, the exact mechanism of injury and affected tissues remain unknown. Previous investigations documented injuries to the cervical anterior longitudinal ligament in whiplash. The present investigation implemented a comprehensively validated computational model to quantify level-dependent distraction magnitudes of this structure in whiplash. Maximum ligament distractions approached failure levels, particularly in middle to lower cervical levels, and occurred during the initial phase of head-neck kinematics. In particular, the C5-C6 anterior longitudinal ligament sustained distraction magnitudes as high as 2.6mm during the retraction phase, corresponding to 56% of distraction necessary to result in ligament failure. Present results demonstrated that anterior structures in the lower cervical spine may be susceptible to injury through excess distraction during the retraction phase of whiplash, which likely occurs prior to head restraint contact. Susceptibility of these structures is likely due to non-physiologic loading placed on the cervical spinal column as the head translates posteriorly relative to the thorax. Injury to anterior spinal structures can result in clinical indications including cervical instability in extension, axial rotation, and lateral bending modes. Mitigation of whiplash injury may be achieved by minimizing head retraction during initial stages of whiplash.

Biomechanical Phenomena↗

PubMed2005

Influence of thoracic ramping on whiplash kinematics.

BACKGROUND: Some experimental whiplash investigations using human volunteers and full-body cadavers reported thoracic ramping, characterized by superior translation and extension rotation of the cervico-thoracic junction. The effect of this phenomenon on cervical spinal kinematics has not been quantitatively determined. METHODS: A comprehensively validated computational model exercised in 2.7 m/s rear impact was used to determine effects of superior translation and extension rotation of T1 on cervical segmental kinematics during the retraction phase. FINDINGS: In general, thoracic ramping had a minimal effect on cervical intervertebral kinematics during retraction. INTERPRETATION: Results of the present study demonstrated that magnitude of thoracic ramping plays a minimal role in the whiplash injury mechanism due to decreased effect on cervical segmental kinematics.

Acceleration↗

PubMed2005

Experimental flexion/extension data corridors for validation of finite element models of the young, normal cervical spine.

Finite element (FE) modeling is an important tool for studying the cervical spine in normal, injured and diseased conditions. To understand the role of mechanical changes on the spine as it goes from a normal to a diseased or injured state, experimental studies are needed to establish the external response of young, normal cervical spinal segments compared to injured or degenerated cervical spinal segments under physiologic loading. It is important to differentiate injured or degenerated specimens from young, normal specimens to provide accurate experimental results necessary for the validation of FE models. This study used seven young, normal fresh adult cadaver cervical spine segments C2-T1 ranging in age from 20 to 51 years. Prior to testing, the spines were graded in three ways: specimen quality, facet degeneration and disc degeneration. Spine segments were tested in flexion/extension, and the range of loads applied to the specimens was 0.33, 0.5, 1.0, 1.5 and 2.0 Nm. These loads resulted in rotations in the direction of loading as the primary response to loading. In general, results for young, normal specimens showed greater flexibility in flexion and less flexibility in extension than results previously reported in the literature. The flexion/extension curves are asymmetric with a greater magnitude in flexion than in extension. These experimental results will be used to validate FE models of young, normal cervical spines.

Adult↗

PubMed2005

Responses of side impact dummies in sled tests.

Sled tests were conducted at a velocity of 6.7 m/s using side impact dummies (SID, BioSID, ES-2, and WorldSIDp) and the resulting biomechanical responses were compared with responses from post mortem human subjects (PMHS). Initial impact conditions were with and without pelvic offset in combination with and without padding on the impacting wall. Impact forces, thoracic trauma index, chest compression, and viscous criteria were evaluated. The probability of injury was estimated and rates of deformation were computed for each body region. Dummy responses were not always similar in terms of trend and injury criteria when compared with PMHS tests under the same initial conditions. Response variations will be of value in improving the biofidelity characteristics of dummies for crashworthiness evaluations.

Accidents, Traffic↗

PubMed2005

Odontoid fracture in motor vehicle environments.

The National Automotive Sampling System (NASS) and Crash Injury Research and Engineering Network (CIREN) databases were used in an analysis of odontoid fracture in motor vehicle crashes. NASS data were evaluated for the years 1996-2002, and CIREN from 1996 to 2003. Out of 58 fractures, 38 were identified in the NASS and 20 in the CIREN databases. There were 3108 weighted cases in the NASS database. Frontal impacts (11:00 to 1:00 h) were most commonly associated with the injury in both databases. Although male and female occupants sustained the injury, females were shorter in stature, older in age, lighter in weight, and crashes were less severe (lower change in velocity) when female occupants were involved in trauma. In both databases, pure odontoid fracture and facet/lamina fracture accounted for approximately one-third of the cases, and a majority of impacts were associated with changes in velocity less than 56 km/h. Although vehicle model years ranged from 1976 to 2002, recent model years were more frequently associated with CIREN data. In the CIREN database, type II odontoid fracture was the most common, but no particular mechanism of injury dominated; such information was not available in the NASS database. To ameliorate odontoid fracture, focus should be on frontal impacts. Because different types of odontoid fracture are not included in the current Abbreviated Injury Scale, appropriate coding schemes should be developed to classify this injury. The CIREN database is unique because it provides important clinical information, i.e., fracture type, and the associated mechanism of injury. The mechanism component in any epidemiologically based injury analyses is valuable to advance improvements in vehicle crashworthiness.

Accidents, Traffic↗

PubMed2005

Effects of abnormal posture on capsular ligament elongations in a computational model subjected to whiplash loading.

Although considerable biomechanical investigations have been conducted to understand the response of the cervical spine under whiplash (rear impact-induced postero-anterior loading to the thorax), studies delineating the effects of initial spinal curvature are limited. This study advanced the hypothesis that abnormal curvatures (straight or kyphotic) of the cervical column affect spinal kinematics during whiplash loading. Specifically, compared to the normal lordotic curvature, abnormal curvatures altered facet joint ligament elongations. The quantifications of these elongations were accomplished using a validated mathematical model of the human head-neck complex that simulated three curvatures. The model was validated using companion experiments conducted in our laboratory that provided facet joint kinematics as a function of cervical spinal level. Regional facet joint ligament elongations were investigated as a function of whiplash loading in the four local anatomic regions of each joint. Under the normal posture, greatest elongations occurred in the dorsal anatomic region at the C2-C3 level and in the lateral anatomic region from C3-C4 to C6-C7 levels. Abnormal postures increased elongation magnitudes in these regions by up to 70%. Excessive ligament elongations induce laxity to the facet joint, particularly at the local regions of the anatomy in the abnormal kyphotic posture. Increased laxity may predispose the cervical spine to accelerated degenerative changes over time and lead to instability. Results from the present study, while providing quantified level- and region-specific kinematic data, concur with clinical findings that abnormal spinal curvatures enhance the likelihood of whiplash injury and may have long-term clinical and biomechanical implications.

Cervical Vertebrae↗

PubMed2005

Deflection, acceleration, and force corridors for small females in side impacts.

OBJECTIVE: This study was undertaken to develop biomechanical corridors applicable to the small-sized female in side impacts. METHODS: Sled tests were conducted using post mortem human subjects at a velocity of 6.7 m/s. Three chestbands were used to compute deflection-time histories at the axilla, xyphoid process, and tenth rib levels. Triaxial accelerometers were fixed to the upper and lower spine and sacrum to record acceleration-time histories. Specimens contacted the load wall with varying initial conditions (rigid and padded; flat wall and offset) from which impact forces to the thoracic, abdominal, and pelvic regions were obtained using load cell data. Adopting signal processing and mass-based scaling methods, corridors were derived for forces, accelerations, and chest deflections at three levels for all initial conditions. RESULTS: All time history corridors were expressed as mean plus/minus one standard deviation and provided in the article. CONCLUSIONS: Acceleration-, deflection-, and force-time corridors obtained for the chest and pelvic regions of the human body will assist in the assessment of anthropomorphic test devices used in crashworthiness evaluations.

Abdomen↗

PubMed2005

Temporal cavity and pressure distribution in a brain simulant following ballistic penetration.

To study ballistic brain injury biomechanics, two common civilian full metal jacket handgun projectiles (25-caliber and 9-mm) were discharged into a transparent brain simulant (Sylgard gel). Five pressure transducers were placed at the entry (two), exit (two) and center (one) of the simulant. High-speed digital video photography (20,000 frames/second) was used to capture the temporal cavity pulsation. Pressure histories and high-speed video images were synchronized with a common trigger. Pressure data were sampled at 308 kHz. The 25-caliber projectile had an entry velocity of 238 m/s and exit velocity of 170 m/s. The 9-mm projectile had an entry velocity of 379 m/s and exit velocity of 259 m/s. Kinetic energies lost during penetration were 45.2 J for the 25-caliber projectile and 283.7 J for the 9-mm. Size of temporary cavities and pressures were dependent on projectile size and velocity. The 9-mm projectile created temporary cavities 1.5 times larger in size and lasted 1.5 times longer than the 25-caliber projectile. The 9-mm projectile had pressures three times higher than the 25-caliber projectile. Pressure differences between the center location and surrounding regions were approximately 1.4 times higher and lasted about 1.6 times longer in the 9- mm projectile than the 25-caliber projectile. Collapsing of the temporary cavity drew the brain simulant toward the center of the temporary cavity and created negative pressures of approximately -0.5 atmospheric pressure in the surrounding region. Pressures reached approximately +2 atmospheric pressure when temporary cavities collapsed. These quantified data may assist in understanding injury biomechanics and management of penetration brain trauma.

Biomechanical Phenomena↗

PubMed2005

Risk of pediatric head injury after motor vehicle accidents.

OBJECT: Injury to the brain as a result of motor vehicle accidents (MVAs) represents a frequent cause of pediatric disability. The authors analyze the correlation between the relative risk of pediatric brain injury and the use of child safety seats (CSSs). METHODS: A national database of MVAs was examined to provide data for the analysis of four age categories (infant, toddler, young child, and adolescent) and four restraint categories (unrestrained, properly restrained, improperly restrained, and other). The Abbreviated Injury Scale (AIS) was used to assess the severity of head injury; children with no injuries and children with moderate-to-maximum head injuries were evaluated. The data confirm that proper use of a CSS substantially increases the likelihood of not sustaining head injury in an MVA. The data are most dramatic for infants (the likelihood of sustaining no head injury was 15.2% for unrestrained infants compared with 92.8% for properly restrained infants) but the protective effect is seen in all age categories, with the least difference observed in the adolescent category. For children who sustain a moderate-to-maximum head injury, proper use of a CSS reduces the incidence of injury, again most dramatically for the infant category (unrestrained infants had a 7% risk of moderate-to-maximum head injury compared with only 0.5% for properly restrained infants). CONCLUSIONS: Improvements in CSSs have reduced the risk of moderate-to-maximum head injuries in children of all age categories. Overall, a CSS is most protective for the infant and toddler categories. The improperly restrained child still has substantial protection, although the properly restrained child has more. Detailed parental education regarding appropriate restraint system installation and use should be required.

Accidents, Traffic↗

PubMed2005

Type II odontoid fracture from frontal impact: case report and biomechanical mechanism of injury.

The authors report a case of Type II odontoid fracture from a frontal impact sustained in the crash of a late-model motor vehicle. They discuss the biomechanical mechanisms of injury after considering patient demographic data, type and use of restraint systems including seatbelt and airbags, crash characteristics, and laboratory-based experimental studies. Multiple factors contributed to the Type II odontoid fracture: the patient's tall stature and intoxicated state; lack of manual three-point seat belt use; obliqueness of the frontal impact; and the most likely preflexed position of the head-neck complex at the time of impact, which led to contact of the parietal region with the A-pillar roof-rail area of the vehicle and resulted in the transfer of the dynamic compressive force associated with lateral bending. Odontoid fractures still occur in individuals involved in late-model motor vehicle frontal crashes, and because this injury occurs secondary to head impact, airbags may not play a major role in mitigating this type of trauma to an unrestrained occupant. It may be more important to use seat belts than to depend on the airbag alone for protection from injury.

Accidents, Traffic↗

PubMed2005

Localized cervical facet joint kinematics under physiological and whiplash loading.

OBJECT: Although facet joints have been implicated in the whiplash injury mechanism, no investigators have determined the degree to which joint motions in whiplash are nonphysiological. The purpose of this investigation was to quantify the correlation between facet joint and segmental motions under physiological and whiplash loading. METHODS: Human cadaveric cervical spine specimens were exercise tested under physiological extension loading, and intact human head-neck complexes were exercise tested under whiplash loading to correlate the localized component motions of the C4-5 facet joint with segmental extension. Facet joint shear and distraction kinematics demonstrated a linear correlation with segmental extension under both loading modes. Facet joints responded differently to whiplash and physiological loading, with significantly increased kinematics for the same-segmental angulation. The limitations of this study include removal of superficial musculature and the limited sample size for physiological testing. CONCLUSIONS: The presence of increased facet joint motions indicated that synovial joint soft-tissue components (that is, synovial membrane and capsular ligament) sustain increased distortion that may subject these tissues to a greater likelihood of injury. This finding is supported by clinical investigations in which lower cervical facet joint injury resulted in similar pain patterns due to the most commonly reported whiplash symptoms.

Biomechanical Phenomena↗

PubMed2005

Characterizing occipital condyle loads under high-speed head rotation.

Because of the need to evaluate anthropomorphic test device (ATD) biofidelity under high-head angular accelerations, the purpose of the present investigation was to develop appropriate instrumentation for intact post mortem human subject (PMHS) testing, validate the instrumentation, and obtain information to characterize the response of the head-neck complex under this loading scenario. A series of rigid-arm pendulum, inertially loaded ATD tests was conducted. Head and neck ATD hydraulic piston chin pull tests were conducted. Subsequently, a series of PMHS tests was conducted to derive the response of the human head-neck under high-rate chin loading. Finally, Hybrid III and THOR-NT ATD head-neck systems were evaluated under the same scenario as the PMHS. A parametric analysis for center of gravity (CG) location and accelerometer orientation determined that even small errors (+/- 3 mm or 2 degrees), produced errors in the force and moment calculations by as much as 17 %. If the moment of inertia (MOI) term was varied by 5 %, resulting moment calculations were affected by as much as 8 %. If the 5 % error in MOI was used to compute occipital condyle moments, and results compared to upper load cell derived moments, peaks differed by as much as 24 %. The head CG and mass MOI should be directly measured for each preparation to obtain accurate results. The injury run on each specimen resulted in predominantly C1-C2 separations or partial separations. The 50(th) percentile probability of AIS=2+ neck injury using tensile force was about 2400 N; for AIS=3+ neck injury the 50(th) percentile risk was about 3180 N. When inserting extension moment as the criteria, the 50(th) percentile probability of an AIS=2+ injury was 51 Nm. The AIS=3+ extension moment at the 50(th) percentile probability was 75 Nm. The new THOR-NT ATD head-neck produced more biofidelic responses with an alternate head-neck junction design compared to the Hybrid III ATD.

Journal Article↗

PubMed2005

New mechanism for inducing closed head injury in the rat.

Due to the frequency of closed head injuries and cost of treatment, there is great interest in the mechanical parameters involved in provoking the injury. A new device has been developed to produce closed head injury due to impact-induced angular acceleration in the rat. A 488-gram mass was propelled down a 2-meter drop tube by springs at a velocity of 21 mph (9.5 m/s), depending on strength and displacement of the springs. The projectile then impacts a lever arm protruding laterally from an aluminum helmet fixed at the anterior face with a ball-bearing pivot allowing only lateral rotation, which has been shown to cause severe brain injury. A sodium silicate elastomeric material with a thickness of 1 cm was placed at the impact interface to increase the contact time between the projectile and the lever arm. Biomechanical results from a lumped parameter mathematical model and testing indicated an angular acceleration of 300,000 +/- 20,000 rad/s2, angular velocity of 300 +/- 50 rad/s, and impact duration of 2.0 +/- 0.3 ms. When scaled to the human, the results indicated an angular acceleration of 4,100 rad/s2, angular velocity of 32 rad/s, and impact duration of 20 ms, consistent with values associated with classical concussion. Magnitudes and durations at these levels have not been produced in the rat by rotational loading caused by impact, and due to the flexibility of the design, these parameters can be further increased.

Animals↗

PubMed2005

Subcatastrophic failure characteristics of the porcine descending aorta.

Failure of internal arterial layers prior to overall catastrophic vessel failure has been clinically documented and has significant clinical implications. For example, intimal failure of the internal carotid artery was associated with extremely high rates of morbidity (40-80%) and mortality (up to 40%). However, failure of internal vessel layers prior to catastrophic vessel failure has been experimentally documented in a limited number of studies and the mechanical relationship between initial and ultimate vessel failure has not been systematically explored. In the present investigation, seven porcine descending aorta specimens were mechanically tested using a novel protocol to quantify failure of internal layers relative to overall vessel failure. The protocol consisted of opening the vessel at the mid-diameter level, mechanically distracting the vessel to failure under quasi-static loading, and imaging the event from intimal and adventitial sides using a high-speed, high-resolution digital imaging system. The internal layer failed prior to catastrophic vessel failure in all specimens. Adventitial (outer) layers remained intact until ultimate failure. Initial internal layer subfailures occurred at 88% of the strain to ultimate failure. The present results demonstrate internal layer susceptibility to subcatastrophic failure without overall failure of the vessel. Although the porcine descending aorta may not be particularly susceptible to distraction failure, this vessel may be a suitable model for human arterial tissue due to similarities in geometric size and vessel structure.

Animals↗

PubMed2005

Field data on head injuries in side airbag vehicles in lateral impact.

Field data on side airbag deployments in lateral crashes and head injuries have largely remained anecdotal. Consequently, the purpose of this research was to report head injuries in lateral motor vehicle impacts. Data from the National Automotive Sampling System files were extracted from side impacts associated with side airbag deployments. Matched pairs with similar vehicle characteristics but without side airbags were also extracted. All data were limited to the United States Federal Motor vehicle Safety Standards FMVSS 214 compliant vehicles so that the information may be more effectively used in the future. In this study, some fundamental analyses are presented regarding occupant- and vehicle-related parameters.

Accidents, Traffic↗

PubMed2004

Methodology to study intimal failure mechanics in human internal carotid arteries.

While the incidence of blunt carotid artery injuries is low, the mortality rate is extremely high (40%). Clinical evidence indicates that the intimal region of the artery often sustains failure, while maintaining the integrity of the outer layers. This condition may lead to delayed ischemic symptoms, commonly reported in clinical literature. To date, the mechanical properties of the intima relative to the outer vessel layers have not been quantified in the human carotid artery. The purpose of the present study was to develop a methodology to determine the longitudinal mechanical properties of the human internal carotid artery in tension, with an emphasis on intimal failure. This was accomplished by opening the vessel at the mid-diameter level, creating an 'I'-shaped testing specimen, subjecting the specimen to failure loading, documenting the stretch characteristics of the intimal and adventitial sides in the temporal domain, and correlating the synchronized videography with mechanical loading. Intimal failure data were quantified using stress and strain parameters in conjunction with digital videography of the intimal and adventitial sides. The present methodology can be used to determine the mechanical properties of the intima relative to ultimate carotid artery failure. These data will assist in the understanding of blunt carotid artery injuries, its diagnosis and treatment.

Biomechanical Phenomena↗