Jason Moore

Sensitivity of THOR and Hybrid III dummy lower neck loads to belt systems in frontal impact.

Objectives: To determine head–neck biomechanics with a focus on lower neck injury metrics in frontal impact. The mid- and large-size Hybrid III dummies and the mid-size Test device for Human Occupant Restraint (THOR) were positioned on a buck. Tests were conducted at low, medium, and high (3.3, 6.7, and 15.7 m/s) change in velocities using 3 restraint types: normal 3-point belt with no pretension (type A), 10-cm pretension (type B), and 200 N pretension (type C). Repeat tests were conducted. Measured vertical and shear forces and sagittal bending moments were evaluated at the upper and lower regions of the neck to different types of belt systems and at different change in velocities. Peak values normalized with respect to the belt type A were used in the comparative analysis. Metrics transformed to the occipital condyles and T1 were also evaluated. Results: All dummies showed good repeatability. Peak measured and transformed upper and lower neck moments were greatest in the large-size dummy. The mid-size Hybrid III dummy responded with greater forces and moments than the THOR. Regardless of dummy type, anthropometry, and velocity, peak lower neck moments were more sensitive to belt types than peak lower neck forces. A similar pattern was apparent for upper neck data. Moments in the THOR were more sensitive than moments in the mid-size Hybrid III dummy. Conclusions: This study offers quantitative generic restraint-based data and addresses response differences between dummies and dummies of the same family. Because of increased sensitivity to belt types at the upper and lower necks for both forces and moments, the THOR appears to be an improvement to better assess injury potential to rear seat occupants wherein frontal impact air bags do not exist.

Role of disc area and trabecular bone density on lumbar spinal column fracture risk curves under vertical impact

While studies have been conducted using human cadaver lumbar spines to understand injury biomechanics in terms of stability/energy to fracture, and physiological responses under pure-moment/follower loads, data are sparse for inferior-to-superior impacts. Injuries occur under this mode from underbody blasts. OBJECTIVES determine role of age, disc area, and trabecular bone density on tolerances/risk curves under vertical loading from a controlled group of specimens. T12-S1 columns were obtained, pretest X-rays and CTs taken, load cells attached to both ends, impacts applied at S1-end using custom vertical accelerator device, and posttest X-ray, CT, and dissections done. BMD of L2-L4 vertebrae were obtained from QCT. Survival analysis-based Human Injury Probability Curves (HIPCs) were derived using proximal and distal forces. Age, area, and BMD were covariates. Forces were considered uncensored, representing the load carrying capacity. The Akaike Information Criterion was used to determine optimal distributions. The mean forces, ±95% confidence intervals, and Normalized Confidence Interval Size (NCIS) were computed. The Lognormal distribution was the optimal function for both forces. Age, area, and BMD were not significant (p > 0.05) covariates for distal forces, while only BMD was significant for proximal forces. The NCIS was the lowest for force-BMD covariate HIPC. The HIPCs for both genders at 35 and 45 years were based on population BMDs. These HIPCs serve as human tolerance criteria for automotive, military, and other applications. In this controlled group of samples, BMD is a better predictor-covariate that characterizes lumbar column injury under inferior-to-superior impacts.

Non-Destructive and Failure Responses of Cervical Spine Artificial Disc Surgery for Military Applications

Ossification patters, non-destructive and failure responses of cervical artificial discs were determined using an in vivo Caprine model. The animals were anesthetized, discectomies were done at C3–C4, and Bryan disc, ProDisc-C, or anterior discectomy and fusion with plating (ACDF) was done. They were euthanized after monitoring for six months. Non-destructive loads were applied to the excised cervical columns in flexion, extension and lateral bending, combined with compression. The failure test was done under compression-flexion. X-rays and computed tomography scans were used to determine fusion. Force-displacement data for both artificial discs were grouped based on the presence or absence of heterotopic ossifications. They were compared with the ACDF specimens. Heterotopic ossifications occurred in both discs. Patterns of ossification were similar to those reported in civilian patients. Force-displacement responses of ossified spines were stiffer in all modes for both discs. However, differences were non-uniform. Biomechanical corridors are presented for all cases. The present preliminary study should be extended to discern the role of the disc type, loading mode and spinal level in future research.Copyright

Lumbar Spinal Mechanics in Pure Bending: Influence of Gender, Spinal Level, and Degeneration Grade

Gender differences have been identified in normal and traumatic motions of the spine. In the cervical region, spinal motions in females were significantly greater than in males during identical dynamic acceleration pulses [1]. Static cervical range of motion was also shown to be greater in female volunteers [2]. In the thoracic region, gender differences were identified in compressive and tensile elastic moduli [3]. Although male volunteers had slightly greater lumbar spine mobility, the difference was not statistically significant [4]. Another study reported that female lumbar specimens were somewhat more flexible than male specimens [5]. Lumbar spinal motions are clinically important in the diagnosis of abnormalities and instability. Increased motions occur secondary to instability and may indicate a need for spinal stabilization. However, although previous studies have provided baseline data for lumbar motions [6], possible variations in spinal motions between males and females may lead to inaccurate diagnosis. Therefore, the purpose of this investigation was to define lumbar spinal motions on a level-by-level basis to determine statistically significant differences between males and females and at varying levels of degeneration.© 2009 ASME