The most cut-resistant neck guard for preventing lacerations to the neck.

OBJECTIVE: To evaluate the effectiveness of a variety of neck guard brands when contacted by a sharpened hockey skate blade. DESIGN: Analytic experimental. SETTING: Laboratory. PARTICIPANTS: Neck surrogate. INTERVENTIONS: Forty-six samples of 14 different types of neck guards were tested on a custom-made laceration machine using a neck surrogate. Closed-cell polyethylene foam was placed between the neck surrogate and the protective device. MAIN OUTCOME MEASURES: The effectiveness of the neck guard was evaluated by observation of the foam after the simulated slicing action of the skate blade. Two sets of tests were performed on each device sample including low and high force. For low-force tests, initial compression loads of 100, 200, and 300 N were applied between the neck surrogate for each of 2 orientations of the blade at 45 and 90 degrees. For high-force tests, representing a more severe simulation, the applied load was increased to 600 N and a blade angle fixed at 45 degrees. All tests were performed at a blade speed of 5 m/s. RESULTS: Only 1 product, the Bauer N7 Nectech, failed during the 300-N compression tests. All of the neck guards failed during 600-N test condition except for the Skate Armor device and 1 of the 3 Reebok 11K devices. CONCLUSIONS: A skate blade angle of 45 degrees increased the likelihood of a neck laceration compared with a skate blade angle of 90 degrees due to decreased contact area. Damage to the neck guard is not an indicator of the cut resistance of a neck guard. Neck protectors with Spectra fibers were the most cut resistant. CLINICAL RELEVANCE: The study provides data for the selection of neck guards and neck guard materials that can reduce lacerations to the neck.

Three-dimensional adult male head and skull contours.

OBJECTIVE: Traumatic brain injury (TBI) is a major public health issue, affecting millions of people annually. Anthropomorphic test devices (ATDs) and finite element models (FEMs) provide a means of understanding factors leading to TBI, potentially reducing the occurrence. Thus, there is a need to ensure that these tools accurately model humans. For example, the Hybrid III was not based on 3-dimensional human head shape data. The objective of this study is to produce average head and skull contours for an average U.S. male that can be used for ATDs and FEMs. METHODS: Computed tomography (CT) scans of adult male heads were obtained from a database provided by the University of Virginia Center for Applied Biomechanics. An orthographic viewer was used to extract head and skull contours from the CT scans. Landmarks were measured graphically using HyperMesh (Altair, HyperWorks). To determine the head occipital condyle (OC) centroid, surface meshes of the OCs were made and the centroid of the surfaces was calculated. The Hybrid III contour was obtained using a MicroScribe Digitizer (Solution Technologies, Inc., Oella, MD). Comparisons of the average male and ATD contours were performed using 2 methods: (1) the midsagittal and midcoronal ATD contours relative to the OC centroid were compared to the corresponding 1 SD range of the average male contours; (2) the ATD sagittal contour was translated relative to the average male sagittal contour to minimize the area between the 2 contours. RESULTS: Average male head and skull contours were created. Landmark measurements were made for the dorsum sellae, nasion skin, nasion bone, infraorbital foramen, and external auditory meatus, all relative to the OC centroid. The Hybrid III midsagittal contour was outside the 1 SD range for 15.2 percent of the average male head contour but only by a maximum distance of 1.5 mm, whereas the Hybrid III midcoronal head contour was outside the 1 SD range for 12.2 percent of the average male head contour by a maximum distance of 2 mm. Minimization of the area between the midsagittal contours resulted in only 2.3 mm of translation, corroborating the good correlation between the contours established by initial comparison. CONCLUSIONS: Three-dimensional average male head and skull contours were created and measurements of landmark locations were made. It was found that the 50th percentile male Hybrid III corresponds well to the average male head contour and validated its 3D shape. Average adult head and skull contours and landmark data are available for public research use at http://biomechanics.pratt.duke.edu/data .

Tensile failure properties of the perinatal, neonatal, and pediatric cadaveric cervical spine.

STUDY DESIGN: Biomechanical tensile testing of perinatal, neonatal, and pediatric cadaveric cervical spines to failure. OBJECTIVE: To assess the tensile failure properties of the cervical spine from birth to adulthood. SUMMARY OF BACKGROUND DATA: Pediatric cervical spine biomechanical studies have been few due to the limited availability of pediatric cadavers. Therefore, scaled data based on human adult and juvenile animal studies have been used to augment the limited pediatric cadaver data. Despite these efforts, substantial uncertainty remains in our understanding of pediatric cervical spine biomechanics. METHODS: A total of 24 cadaveric osteoligamentous head-neck complexes, 20 weeks gestation to 18 years, were sectioned into segments (occiput-C2 [O-C2], C4-C5, and C6-C7) and tested in tension to determine axial stiffness, displacement at failure, and load-to-failure. RESULTS: Tensile stiffness-to-failure (N/mm) increased by age (O-C2: 23-fold, neonate: 22 ± 7, 18 yr: 504; C4-C5: 7-fold, neonate: 71 ± 14, 18 yr: 509; C6-C7: 7-fold, neonate: 64 ± 17, 18 yr: 456). Load-to-failure (N) increased by age (O-C2: 13-fold, neonate: 228 ± 40, 18 yr: 2888; C4-C5: 9-fold, neonate: 207 ± 63, 18 yr: 1831; C6-C7: 10-fold, neonate: 174 ± 41, 18 yr: 1720). Normalized displacement at failure (mm/mm) decreased by age (O-C2: 6-fold, neonate: 0.34 ± 0.076, 18 yr: 0.059; C4-C5: 3-fold, neonate: 0.092 ± 0.015, 18 yr: 0.035; C6-C7: 2-fold, neonate: 0.088 ± 0.019, 18 yr: 0.037). CONCLUSION: Cervical spine tensile stiffness-to-failure and load-to-failure increased nonlinearly, whereas normalized displacement at failure decreased nonlinearly, from birth to adulthood. Pronounced ligamentous laxity observed at younger ages in the O-C2 segment quantitatively supports the prevalence of spinal cord injury without radiographic abnormality in the pediatric population. This study provides important and previously unavailable data for validating pediatric cervical spine models, for evaluating current scaling techniques and animal surrogate models, and for the development of more biofidelic pediatric crash test dummies.

Evaluation of pediatric skull fracture imaging techniques.

Radiologic imaging is crucial in the diagnosis of skull fracture, but there is some doubt as to whether different imaging modalities can accurately identify fractures present on a human skull. While studies have been performed to evaluate the efficacy of radiologic imaging at other anatomical locations, there have been no systematic studies comparing various CT techniques, including high resolution imaging with and without 3D reconstructions to conventional radiologic imaging in children, we investigated which imaging modalities: high-resolution CT scan with 3D projections, clinical-resolution CT scans or X-rays, best showed fracture occurrence in a pediatric human cadaver skull by having an expert pediatric radiologist examine radiologic images from fractured skulls. The skulls used were taken from pediatric cadavers ranging in age from 5 months to 16 years. We evaluated the sensitivity and specificity for the imaging modalities using dissection findings as the gold standard. We found that high-resolution CT scans with 3D projections and conventional CT provided the most accurate fracture diagnosis (single-fracture sensitivity of 71%) followed by X-rays (single-fracture sensitivity of 63%). Linear fractures outsider the region of the sutures were more identifiable than diastatic fractures, though the incidence of false positives was greater for linear fractures. In the two cases where multiple fractures were present on the same anatomical skull location, the radiologist was less likely to identify the presence of additional fractures than a single fracture. Overall, the high-resolution and clinical-resolution CT scans had the similar accuracy for detecting skull fractures while the use of the X-ray was both less accurate and had a lower specificity.

The mechanical and morphological properties of 6 year-old cranial bone.

Traumatic Brain Injury (TBI) is a leading cause of mortality and morbidity for children in the United States. The unavailability of pediatric cadavers makes it difficult to study and characterize the mechanical behavior of the pediatric skull. Computer based finite element modeling could provide valuable insights, but the utility of these models depends upon the accuracy of cranial material property inputs. In this study, 47 samples from one six year-old human cranium were tested to failure via four point bending to study the effects of strain rate and the structure of skull bone on modulus of elasticity and failure properties for both cranial bone and suture. The results show that strain rate does not have a statistically meaningful effect on the mechanical properties of the six year-old skull over the range of strain rates studied (average low rate of 0.045 s(-1), average medium rate of 0.44 s(-1), and an average high rate of 2.2 s(-1)), but that these properties do depend on the growth patterns and morphology of the skull. The thickness of the bone was found to vary with structure. The bending stiffness (per unit width) for tri-layer bone (12.32±5.18 Nm(2)/m) was significantly higher than that of cortical bone and sutures (5.58±1.46 Nm(2)/m and 3.70±1.88 Nm(2)/m respectively). The modulus of elasticity was 9.87±1.24 GPa for cranial cortical bone and 1.10±0.53 GPa for sutures. The effective elastic modulus of tri-layer bone was 3.69±0.92 GPa. Accurate models of the pediatric skull should account for the differences amongst these three distinct tissues in the six year-old skull.

Pediatric head contours and inertial properties for ATD design.

Child head trauma in the United States is responsible for 30% of all childhood injury deaths with costs estimated at $10 billion per year. The common tools for studying this problem are the child anthropomorphic test devices (ATDs). The headform sizes and structural properties of child ATDs are based on various anthropometric studies and scaled Hybrid III mass and center of gravity (CG) properties. The goals of this study were to produce pediatric head and skull contours, provide estimates of pediatric head mass, mass moment of inertia and CG locations, and compare the head contours with the current child ATD head designs. To that end, computer tomography (CT) scans from one hundred eighty-five children in twelve age groups were analyzed to develop three-dimensional head and skull contours. The contours were averaged to estimate head and skull contours for children aged 1-month to 10-years. Inertial properties were estimated from a small sample of post- mortem human subjects (PMHSs). This paper provides new equations for estimating the moments of inertia and anatomical landmarks in the head. There were reasonable agreement between the estimates for head masses obtained from analysis of the CT scans of the PMHS heads and the estimates obtained using the volumetric scaling rule used in ATD design work. The regression of the pediatric head sizes was found to be non-linear, with different regression slope for ages 1M to 18M and 18M to 120M. The 12M CRABI and 36M Hybrid III heads were found to be different by 10 and 18mm, respectively, from the average human CT contours due to the differences in the occipital condyle placement relative to the nasion.

Use of a three-dimensional, normative database of pediatric craniofacial morphology for modern anthropometric analysis.

BACKGROUND: Surgical correction of cranial abnormalities, including craniosynostosis, requires knowledge of normal skull shape to appreciate dysmorphic variations. However, the inability of current anthropometric techniques to adequately characterize three-dimensional cranial shape severely limits morphologic study. The authors previously introduced three-dimensional vector analysis, a quantitative method that maps cranial form from computed tomography data. In this article, the authors report its role in the development and validation of a normative database of pediatric cranial morphology and in clinical analysis of craniosynostosis. METHODS: Normal pediatric craniofacial computed tomography data sets were acquired retrospectively from the Duke University Picture Archive and Communications System. Age increments ranging from 1 to 72 months were predetermined for scan acquisition. Three-dimensional vector analysis was performed on individual data sets, generating a set of point clouds. Averages and standard deviations for the age and gender bins of point clouds were used to create normative three-dimensional models. Anthropometric measurements from three-dimensional vector analysis models were compared with published matched data. Preoperative and postoperative morphologies of a sagittal synostosis case were analyzed using three-dimensional vector analysis and the normative database. RESULTS: Three- and two-dimensional representations were created to define age-incremental normative models. Length and width dimensions agreed with previously published data. Detailed morphologic analysis is provided for a case of sagittal synostosis by applying age- and gender-matched data. CONCLUSIONS: Three-dimensional vector analysis provides accurate, comprehensive description of cranial morphology with quantitative graphic output. The method enables development of an extensive pediatric normative craniofacial database. Future application of these data will facilitate analysis of cranial anomalies and assist with clinical assessment.

Tensile mechanical properties of the perinatal and pediatric PMHS osteoligamentous cervical spine.

Pediatric cervical spine biomechanics have been under-researched due to the limited availability of pediatric post-mortem human subjects (PMHS). Scaled data based on human adult and juvenile animal studies have been utilized to augment the limited pediatric PMHS data that exists. Despite these efforts, a significant void in pediatric cervical spine biomechanics remains. Eighteen PMHS osteoligamentous head-neck complexes ranging in age from 20 weeks gestational to 14 years were tested in tension. The tests were initially conducted on the whole cervical spine and then the spines were sectioned into three segments that included two lower cervical spine segments (C4-C5 and C6-C7) and one upper cervical spine segment (O-C2). After non-destructive tests were conducted, each segment was failed in tension. The tensile stiffness of the whole spines ranged from 5.3 to 70.1 N/mm. The perinatal and neonatal specimens had an ultimate strength for the upper cervical spine of 230.9 +/- 38.0 N and for the lower cervical spine of 212.8 +/- 60.9 and 187.1 +/- 39.4 N for the C4-C5 and C6-C7 segments, respectively. The lower cervical segments were significantly weaker and stiffer than the upper cervical spine segments in the older cohort. For the entire cohort of specimens, the stiffness of the upper cervical spine ranged from 7.1 to 199.0 N/mm. The tolerance ranged from 173.6 to 2960 N for the upper cervical spine and from 142 to 1757 N for the lower. There was a statistically significant increase in stiffness and strength with age. The results also suggest that juvenile animal surrogates estimate the stiffness of the human cervical spine fairly well; however, they may not provide accurate estimates of pediatric cervical spine strength.