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Biomedical subjects

Randal P Ching

Publications and source records attributed to Randal P Ching.

17 recordsLinked to original sources
PubMed2006

Rate dependence of hydraulic resistance in human lumbar vertebral bodies.

STUDY DESIGN: Twenty-one intact human lumbar vertebral bodies (L3 and L4) were used to determine the changes in measured intraosseous pressure for 2 volumetric flow rates and to calculate hydraulic resistance in both cases. OBJECTIVE: To evaluate changes in hydraulic resistance in intact vertebral bodies under different rates of flow. SUMMARY OF BACKGROUND DATA: Hydraulic resistance has been implicated in the creation of high-speed vertebral injuries, such as burst fracture, but no previous study has measured hydraulic resistance under high-speed loading conditions. Previous work in whole bone preparations showed that hydraulic resistance was constant under low-speed conditions. The authors hypothesized that: (1) measured pressure would increase with increasing input flow rates, and (2) hydraulic resistance would remain constant at increased input flow rates. METHODS: Using 2 input velocity conditions (10 mm/s and 2500 mm/s), resultant pressures were measured and hydraulic resistance calculated. Trabecular architecture was determined using micro-computerized tomography after testing. RESULTS: Measured pressure increased with increasing input flow rates. However, average hydraulic resistance decreased significantly when comparing low-speed (3.40 +/- 1.58kPa*s/mL) and high-speed (0.16 +/- 0.08kPa*s/mL) groups. CONCLUSIONS: Current hydraulic resistance results contradict previous findings. The observed decrease in hydraulic resistance suggests that, during high-speed injury events, marrow flow may damage the trabeculae and thereby weaken the vertebra.

Aged↗
PubMed2006

Effect of foot shape on the three-dimensional position of foot bones.

To eliminate some of the ambiguity in describing foot shape, we developed three-dimensional (3D), objective measures of foot type based on computerized tomography (CT) scans. Feet were classified via clinical examination as pes cavus (high arch), neutrally aligned (normal arch), asymptomatic pes planus (flat arch with no pain), or symptomatic pes planus (flat arch with pain). We enrolled 10 subjects of each foot type; if both feet were of the same foot type, then each foot was scanned (n=65 total). Partial weightbearing (20% body weight) CT scans were performed. We generated embedded coordinate systems for each foot bone by assuming uniform density and calculating the inertial matrix. Cardan angles were used to describe five bone-to-bone relationships, resulting in 15 angular measurements. Significant differences were found among foot types for 12 of the angles. The angles were also used to develop a classification tree analysis, which determined the correct foot type for 64 of the 65 feet. Our measure provides insight into how foot bone architecture differs between foot types. The classification tree analysis demonstrated that objective measures can be used to discriminate between feet with high, normal, and low arches.

Biomechanical Phenomena↗
PubMed2006

Developmental biomechanics of the cervical spine: Tension and compression.

Epidemiological data and clinical indicia reveal devastating consequences associated with pediatric neck injuries. Unfortunately, neither injury prevention nor clinical management strategies will be able to effectively reduce these injuries or their effects on children, without an understanding of the cervical spine developmental biomechanics. Thus, we investigated the relationship between spinal development and the functional (stiffness) and failure biomechanical characteristics of the cervical spine in a baboon model. A correlation study design was used to define the relationships between spinal tissue maturation and spinal biomechanics in both tension and compression. Eighteen baboon cervical spine specimens distributed across the developmental spectrum (1-26 human equivalent years) were dissected into osteoligamentous functional spinal units. Using a servo-hydraulic MTS, these specimens (Oc-C2, C3-C4, C5-C6, C7-T1) were non-destructively tested in tension and compression and then displaced to failure in tension while measuring the six-axes of loads and displacements. The functions describing the developmental biomechanical response of the cervical spine for stiffness and normalized stiffness exhibited a significant direct relationship in both tension and compression loading. Similarly, the tensile failure load and normalized failure load demonstrated significant maturational increases. Further, differences in biomechanical response were observed between the spinal levels examined and all levels exhibited clinically relevant failure patterns. These data support our understanding of the child cervical spine from a developmental biomechanics perspective and facilitate the development of injury prevention or management schema for the mitigation of child spine injuries and their deleterious effects.

Aging↗
PubMed2006

Effect of loading rate on the compressive mechanics of the immature baboon cervical spine.

Thirty-four cervical spine segments were harvested from 12 juvenile male baboons and compressed to failure at displacement rates of 5, 50, 500, or 5000 mm/s. Compressive stiffness, failure load, and failure displacement were measured for comparison across loading rate groups. Stiffness showed a significant concomitant increase with loading rate, increasing by 62% between rates of 5 and 5000 mm/s. Failure load also demonstrated an increasing relationship with loading rate, while displacement at failure showed no rate dependence. These data may help in the development of improved pediatric automotive safety standards and more biofidelic physical and computational models.

Animals↗
PubMed2004

Effect of displacement rate on the tensile mechanics of pediatric cervical functional spinal units.

This study examined the effect of loading (displacement) rate on the tensile mechanics of cervical spine functional spinal units. A total of 40 isolated functional spinal units (two vertebrae and the adjoining soft tissues) from juvenile male baboons (10+/-0.6-human equivalent years old) were subjected to tensile loading spanning four orders of magnitude from 0.5 to 5000 mm/s. The stiffness, ultimate failure load, and corresponding displacement at failure were measured for each specimen and normalized by spinal geometry to examine the material properties as well as the structural properties. The tensile stiffness, failure load, normalized stiffness, and normalized failure load significantly increased (ANOVA, p<0.001) with increasing displacement rate. From the slowest to fastest loading rate, a two-fold increase in stiffness and four-fold increase in failure load were observed. The tensile failure strains (1.07+/-0.31 mm/mm strain) were not significantly correlated with loading rate (ANOVA, p=0.146). Both the functional (non-destructive stiffness and normalized stiffness) and failure mechanics of isolated functional spinal units exhibited a power-law relationship with displacement rate. Modeling efforts utilizing these rate-dependent characteristics will enhance our understanding of the tensile viscoelastic response of the spine and enable improved dynamic injury prevention schemes.

Animals↗
PubMed2004

Neural space integrity of the lower cervical spine: effect of anterior lesions.

STUDY DESIGN: A repeated measures study design was used to evaluate intervertebral foramen and spinal canal neural space integrity subsequent to sequential surgical anterior lesions of the lower cervical spine in a human cadaver model. OBJECTIVE: To investigate the degree to which sequential ablation of anterior vertebral elements places the neural structures at risk of injury. SUMMARY OF BACKGROUND DATA: Classic instability management utilizing functional-structural criteria has been widely examined associating specific lesions or pathologies to a degree of mechanical instability. Unfortunately, these studies have not assessed the neuroprotective role of the vertebral column. METHODS: Eight human cadaveric lower cervical spines were instrumented with transducers to measure geometrical changes in the intervertebral foramen and spinal canal. Sequential lesions were performed anteriorly on the anterior and middle column structures (C4-C5 disc and C5 vertebra), and their effects on neural space integrity and range of motion were measured under physiologic loading. RESULTS: Range of motion significantly increased with successively more destructive lesions, whereas the spinal canal exhibited few changes. Intervertebral foramen integrity was statistically reduced for corpectomy (66% intact), hemivertebrectomy (62% intact) and full vertebrectomy (57% intact) lesions when loaded in concomitant extension and ipsilateral bending (4 Nm). CONCLUSIONS: Lesions more extensive than a surgical discectomy have significant effects on the cervical neural foramens specifically when the spine is placed in extension, ipsilateral bending, and coupled ipsilateral bending and extension. Our study establishes a quantitative relationship between the risk of neural structure compression and anterior lesions of the spinal column under physiologic loading.

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PubMed2004

Spinal maturation affects vertebral compressive mechanics and vBMD with sex dependence.

The effects of natural aging on the mechanics of the spine are far better understood for the mature adult spine than for the developing (immature) spine. Throughout its chondrification and ossification, the vertebra, which is the primary structural unit of the spine, undergoes enormous cellular, biochemical, and structural changes that should strongly influence its biomechanical response to external forces. Unfortunately, very little data exist for the mechanics of immature vertebrae. Vertebral maturation was therefore investigated in 22 baboon thoracic specimens to elucidate its relationship with biomechanics and volumetric bone mineral density (vBMD). Cadaveric baboon vertebrae were used due to the limited availability of human tissues in the pediatric age range. The specimen ages ranged between 1 and 30 human-equivalent years based on skeletal maturity. Isolated ninth thoracic vertebrae (T9) were subjected to compressive loading to document their compressive mechanical properties (yield load, stiffness, yield strength, and elastic modulus) and ashed to determine their volumetric bone mineral density. Spinal maturation was discovered to significantly increase vBMD (P < 0.0001) and compressive mechanics (stiffness, bulk elastic modulus, failure load, and bulk strength, P < 0.001) in a sex-dependent manner. Vertebral stiffness increased from 1218 N/mm at 1 year to 3534 N/mm at 30 years with a second order polynomial "maturation" relationship. Volumetric bone mineral density and vertebral cross-sectional area together described the developmental patterns of stiffness and yield load of isolated vertebrae. Sex differences were observed throughout development, demonstrating differing growth patterns to accommodate mechanical loading whereby males develop larger size vertebrae and females achieve their mechanical stiffness and strength through greater bone mineral density.

Age Factors↗
PubMed2003

Effect of loading rate on endplate and vertebral body strength in human lumbar vertebrae.

Previous studies have implied that increases in loading rate resulted in changes in vertebral mechanical properties and these changes were causative factors in the different fracture types seen with high-speed events. Thus many researchers have explored the vertebral body response under various loading rate conditions. No other study has investigated the role of the endplate in high-speed vertebral injuries. The current study determined changes in the endplate and vertebral body strength with increases in displacement rate. The endplate and vertebral body failure loads in individual lumbar vertebrae were documented for two displacement rates: 10 and 2500 mm/s. Using cross-sectional areas from the endplate and vertebral body, failure stresses for both components were calculated and compared. Both the endplate and vertebral body failure loads increased significantly with increased loading rate (p<0.005). Although the vertebral body failure stress increased significantly with loading rate as well (p<0.01), the endplate stresses did not (p>0.35). In addition, the endplate and vertebral strengths were not significantly different under high-speed loading (p>0.60), which inhibits possible predictions as to which bony component would fail initially during a high-speed injury event. It is possible that load distribution may contribute more to the fracture patterns seen at high speeds over vertebral component strength.

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PubMed2003

Muscular imbalances resulting in a clawed hallux.

A clawed hallux is a deformity of the great toe resulting from a muscular imbalance. Using a cadaveric foot-loading frame, we quantitatively assessed the role of the peroneus longus (PL), extensor hallucis longus (EHL), and flexor hallucis longus (FHL) on position and pressure distribution of the first ray by simulating muscle imbalances. The experimental protocol included applying seven different combinations of simulated disproportionate loads ("overpulls") for these three muscles using midstance force values derived from the literature. This study quantified the angular change in the joints of the first ray and measured the plantar pressure beneath the head of the first metatarsal and the hallux. The results indicated that the peroneus longus was statistically the greatest contributor to the elevation of plantar pressure beneath the first metatarsal, while the EHL and FHL were primarily responsible for the angular changes resulting in the clawed hallux deformity.

Aged↗
PubMed2002

Internal pressure measurements during burst fracture formation in human lumbar vertebrae.

STUDY DESIGN: In a laboratory study, 21 human lumbar spine segments were used to determine whether intraosseous pressure increases occur during axial-compressive loading conditions under two displacement rates. OBJECTIVE: To determine whether an intraosseous pressure rise is associated with burst fracture formation. SUMMARY OF BACKGROUND DATA: Burst fractures are high-speed injuries usually associated with neurologic deficit. An internal pressure rise has been implicated as a critical factor in burst fracture formation. The authors hypothesize that the internal pressure increases with increasing input velocity. METHODS: The internal pressure changes were measured in spine segments using two displacement rates: 10 mm/s (slow speed) and 2500 mm/s (high speed). Failure load and energy absorption were determined for both groups. The resultant fracture types were determined from postinjury radiographs. RESULTS: The initial peak internal pressure decreased from slow- to high-speed tests (P < 0.01). Overall peak pressure, failure load, and energy absorbed at failure were not significantly different. Slow-speed tests resulted in compression fractures, whereas high-speed tests resulted in burst and compression fractures. CONCLUSIONS: The current research did not support the current theory of burst fracture formation. There was a decrease in measured internal pressure from the slow- to high-speed groups, and burst fractures still were produced. The theory could be potentially modified to suggest that the nucleus entering the vertebral body acts as a wedge, splitting the vertebral body apart and enabling the bony fragments to be pushed into the canal space.

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PubMed2002

Neural space integrity of the lower cervical spine: effect of normal range of motion.

STUDY DESIGN: An experimental investigation of intervertebral foramen and spinal canal neural space integrity was performed throughout physiologic range of motion of the lower cervical spine in intact human cadaver specimens. OBJECTIVE: To investigate cervical positions that might place the neural tissues of the spine in heightened risk of injury. To meet this objective the following hypotheses were tested: 1) spinal canal integrity varies with specific normal range of motion positions of the lower cervical spine, and 2) intervertebral foramen integrity is dependent on and unique for different physiologic positions of the lower cervical spine. SUMMARY OF BACKGROUND DATA: Cervical spine injuries are frequently associated with compressive damage to neurologic tissues and consequently poor clinical outcomes. Neurologic injury typically occurs from disc, ligamentous, or bony occlusion of the spinal canal and intervertebral foraminal spaces dynamically during an injury event or with abnormal alignment and position after the injury event. Prior studies have shown pressure and geometric changes in cervical spine neural spaces in certain cervical spine positions. However, to the authors' knowledge, this is the first research effort aimed at elucidating the integrity of the cervical spine neural spaces throughout the normal physiologic range of motion. METHODS: The authors instrumented 17 fresh-frozen unembalmed cadaveric human cervical spines (C3-C7) with specially designed intervertebral foramen occlusion transducers and a spinal canal occlusion transducer. The specimens were loaded with pure bending moments to produce simulated physiologic motions of the lower cervical spine. The resulting occlusion profiles for the intervertebral foramen and spinal canal were recorded along with the 6-degree of freedom position of the cervical spine. Because these occlusion measurements describe the ability of the spine to preserve the space for the neural structures, the authors define this neuroprotective role of the vertebral column as neural space integrity. RESULTS: The range of motion developed experimentally in this study compared well with published reports of normal cervical motion. Thus, subsequent changes in neural space integrity may be regarded as resulting from normal human cervical spine motion. No significant change in the spinal canal space was detected for any physiologic motion; however, intervertebral foramen integrity was significantly altered in extension, ipsilateral bending, combined ipsilateral bending and extension, and combined contralateral bending with extension when compared with intact upright neutral position. CONCLUSIONS: This study defines the range of neural space integrity associated with simulated physiologic motion of the lower cervical spine in an experimental setting. This information may be useful in comparing neural space changes in pathologic conditions and may enhance refinement of neurologic injury prevention strategies.

Biomechanical Phenomena↗
PubMed2002

Hydraulic resistance and permeability in human lumbar vertebral bodies.

Hydraulic resistance (HR) was measured for ten intact human lumbar vertebrae to further understand the mechanisms of fluid flow through porous bone. Oil was forced through the vertebral bodies under various volumetric flow rates and the resultant pressure was measured The pressure-flow relationship for each specimen was linear. Therefore, HR was constant with a mean of 2.22 +/- 1.45 kPa*sec/ml. The mean permeability of the intact vertebral bodies was 4.90x10(-10) +/- 4.45x10(-10) m2. These results indicate that this methodology is valid for whole bone samples and enables the exploration of the effects of HR on the creation of high-speed fractures.

Aged↗
PubMed2002

Compressive tolerance of the maturing cervical spine.

While a number of experiments have reported injury thresholds for the adult cervical spine in compression, the compressive failure tolerance of the child spine has not been characterized. In order to develop useful safety measures for children, the biomechanical effects of maturation must be evaluated. Hence, this study examined the effects of spinal development on the compressive mechanics of the cervical spine. An animal model was used due to the lack of human tissues in the pediatric age range. Twenty-two fresh cadaveric baboon cervical spines (all male) were dissected into two functional spinal unit segments: Occiput-C2, C3-C5, C6-T1. The specimens ranged in age from 1 to 30-human equivalent years based upon radiographic assessment of their skeletal maturity. Dynamic (1.0-m/sec) haversine displacement inputs up to 70% strain were imparted on each specimen and the resulting loads were recorded. Significant increases in the compressive failure load were observed with increased maturation of the spinal tissues (ANOVA, p = 0.003). Differences were also observed between the spinal levels examined. The lower cervical spine, C6-T1, had the smallest failure load for specimens greater than 8-human-equivalent years, while the upper cervical spine was the most susceptible to injury at less than 8-human-equivalent years. The compressive failures generated are consistent with those observed clinically, consisting of primarily burst fractures and physis (growth plate) failures. These data clearly suggest that spinal compressive tolerance is directly related to maturation. Therefore, through scaling, these data may provide tolerance values applicable to anthropomorphic test dummies and computational models aimed at injury prevention for the pediatric occupant.

Journal Article↗
PubMed2002

Tolerance of the cervical spine to eccentric axial compression.

Cervical spine injury resulting from compressive impact loading is a particularly devastating musculoskeletal injury due to the frequency of neurologic involvement. The objective of this research was to investigate the effect of axial eccentricity on the tolerance of the cervical spine. Two functional spinal unit segments (3 adjacent vertebra and their intervening discs and soft-tissues) were dissected from the lower cervical spine of twenty-four human cadaver cervical spines and randomly assigned to one of three loading groups. The eight specimens were tested to failure in compression, compression-flexion, and compression-extension under displacement control on a high-rate MTS load frame. The resulting six-axis loads were measured and evaluated by injury mechanism (group). Statistically distinct (p < 0.01) injury mechanisms, in terms of measured axial eccentricity, were produced by each of the eccentric axial compression inputs (compression-flexion, compression-extension, and compression). The axial force at failure for the compression and compression-extension loading environments were nearly equal and significantly (p < 0.01) larger (4-times) than their counterpart in the compression-flexion group. Failure data were compared with the neck injury criteria (Nij) recently proposed by the NHTSA using the 50th percentile male and 5th percentile female injury reference values. The compression and compression-extension mechanisms produced Nij values near 1.0. The compression-flexion series resulted in significantly lower Nij values at failure (approx. 0.3, p < 0.01). The results of this study provide tolerance data for the cervical spine subjected to different compressive loading environments and may be used to enhance injury reference computations facilitating neck injury prevention.

Journal Article↗
PubMedDate not supplied

Foot and ankle ligament morphometry.

This study primarily measured and established a morphometric spectrum of cross-sectional areas for foot and ankle ligaments with the use of a new freeze-fracture technique that was independent of ligament cross-sectional shape. Ligament morphometry measurements were made on a total of 121 bone-ligament-bone preparations that were harvested from 26 fresh (unembalmed) male cadaver feet. We used the traditional digital caliper method to measure length and the freeze-fracture technique to measure cross-sectional area. Cross-sectional area values ranged from 21.36 to 170.48 mm(2) and length values from 5.01 to 37.45 mm. In addition, area-to-length ratios ranged from 0.60 to 27.02 mm. Compared with the freeze-fracture technique, the digital caliper method, which assumed that ligament cross-sectional shape was rectangular, resulted in an approximately 35% difference in cross-sectional area.

Adult↗
PubMedDate not supplied

A three-dimensional, anatomically detailed foot model: a foundation for a finite element simulation and means of quantifying foot-bone position.

We generated an anatomically detailed, three-dimensional (3-D) reconstruction of a human foot from 286 computerized topographic (CT) images. For each bone, 2-D cross-sectional data were obtained and aligned to form a stacked image model. We calculated the inertial matrix of each bone from the stacked image model and used it to determine the principal axes. Relative angles between the principal axes of the bones were employed to describe the shape of the foot, i.e., the relationships between the bones of the foot. A 3-D surface model was generated from the stacked image models and a detailed 3-D mesh for each bone was created. Additionally, the representative geometry of the plantar soft tissue was obtained from the CT scans, while the geometries of the cartilage between bones were obtained from the 3-D surface bone models. This model served dual purposes: it formed the anatomical foundation for a future finite element model of the human foot and we used it to objectively quantify foot shape using the relationships between the principal axes of the foot bones.

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