Biomedical subjects

Frank A Pintar

Publications and source records attributed to Frank A Pintar.

10 recordsLinked to original sources

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↗

PubMed2003

Exposure to pulsed magnetic fields enhances motor recovery in cats after spinal cord injury.

STUDY DESIGN: Animal model study of eight healthy commercial cats was conducted. OBJECTIVE: To determine whether pulsed electromagnetic field (PMF) stimulation results in improvement of function after contusive spinal cord injury in cats. SUMMARY OF BACKGROUND DATA: PMF stimulation has been shown to enhance nerve growth, regeneration, and functional recovery of peripheral nerves. Little research has been performed examining the effects of PMF stimulation on the central nervous system and no studies of PMF effects on in vivo spinal cord injury (SCI) models have been reported. MATERIALS AND METHODS: PMF stimulation was noninvasively applied for up to 12 weeks to the midthoracic spine of cats with acute contusive spinal cord injury. The injury was produced using a weight-drop apparatus. Motor functions were evaluated with the modified Tarlov assessment scale. Morphologic analyses of the injury sites and somatosensory-evoked potential measurements were conducted to compare results between PMF-stimulated and control groups. RESULTS: There was a significant difference in locomotor recovery between the PMF-stimulated and control groups. Although not statistically significant, PMF-stimulated spinal cords demonstrated greater sparing of peripheral white matter and smaller lesion volumes compared to controls. Somatosensory-evoked potential measurements indicated that the PMF-stimulated group had better recovery of preinjury waveforms than the control group; however, this observation also was not statistically significant because of the small sample size. CONCLUSIONS: This preliminary study indicates that pulsed magnetic fields may have beneficial effects on motor function recovery and lesion volume size after acute spinal cord injury.

Acute Disease↗

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

Kinetics of the head-neck complex in low-speed rear impact.

A comprehensive characterization of the biomechanics of the cervical spine in rear impact will lead to an understanding of the mechanisms of whiplash injury. Cervical kinematics have been experimentally described using human volunteers, full-body cadaver specimens, and isolated and intact head-neck specimens. However, forces and moments at the cervico-thoracic junction have not been clearly delineated. An experimental investigation was performed using ten intact head-neck complexes to delineate the loading at the base of the cervical spine and angular acceleration of the head in whiplash. A pendulum-minisled apparatus was used to simulate whiplash acceleration of the thorax at four impact severities. Lower neck loads were measured using a six-axis load cell attached between the minisled and head-neck specimens, and head angular motion was measured with an angular rate sensor attached to the lateral side of the head. Shear and axial force, extension moment, and head angular acceleration increased with impact severity. Shear force was significantly larger than axial force (p < 0.0001). Shear force reached its maximum value at 46 msec. Maximum extension moment occurred between 7 and 22 msec after maximum shear force. Maximum angular acceleration of the head occurred 2 to 18 msec later. Maximum axial force occurred last (106 msec). All four kinetic components reached maximum values during cervical S-curvature, with maximum shear force and extension moment occurring before the attainment of maximum S-curvature. Results of the present investigation indicate that shear force and extension moment at the cervico-thoracic junction drive the non-physiologic cervical S-curvature responsible for whiplash injury and underscore the importance of understanding cervical kinematics and the underlying kinetics.

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

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↗

PubMed2002

Intervertebral rotations as a function of rear impact loading.

Rear impact loading of the cervical spine results in a complicated biomechanical problem due to the complex geometry and viscoclastic material properties of this anatomy. Although a number of investigations have been performed to understand the biomechanics of rear impact, the dependence of segmental kinematics on cervical level and input velocity has not been clearly outlined. An experimental investigation was performed for this purpose using 10 isolated head-neck specimens. Segmental motions of the cervical spine were obtained for levels C2-C3 to C6-C7 at rear impact velocities of 2.1, 4.6, 6.6, and 9.3 km/h. Increases in segmental motion from baseline kinematics were compared for the three higher velocity tests. Results indicated greater increase in magnitude of segmental motion for levels C5-C6 and C6-C7 at higher input velocities than all other investigated levels. This finding helps to define the kinematics of the cervical spine leading to whiplash injury.

Analysis of Variance↗

PubMed2002

Small female and large male responses in rear impact.

The objective of this study was to conduct rear impact sled tests using 5(th), 50(th), and 95(th) percentile Hybrid III dummies and evaluate proposed injury criteria. Head restraint positions of differing height (750, 800 mm) and backset (0, 50, 100 mm) 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 dummy rear impact response. Event I was coincident with the torso bottoming out the seat cushion, Event II occurred at the time of the peak neck flexion moment, and Event III occurred at the time of maximum head to head restraint involvement. 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, the N(ij) and N(km) did not exhibit such clear trends. The 50(th) 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 5(th) and 95(th) 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.

Accidents, Traffic↗