Functional aspects of strepsirrhine lumbar vertebral bodies and spinous processes

The relationship between form and function in the lumbar vertebral column has been well documented among platyrrhines and especially catarrhines, while functional studies of postcranial morphology among strepsirrhines have concentrated predominantly on the limbs. This morphometric study investigates biomechanically relevant attributes of the lumbar vertebral morphology of 20 species of extant strepsirrhines. With this extensive sample, our goal is to address the influence of positional behavior on lumbar vertebral form while also assessing the effects of body size and phylogenetic history. The results reveal distinctions in lumbar vertebral morphology among strepsirrhines in functional association with their habitual postures and primary locomotor behaviors. In general, strepsirrhines that emphasize pronograde posture and quadrupedal locomotion combined with leaping (from a pronograde position) have the relatively longest lumbar regions and lumbar vertebral bodies, features promoting sagittal spinal flexibility. Indrids and galagonids that rely primarily on vertical clinging and leaping with orthograde posture share a relatively short (i.e., stable and resistant to bending) lumbar region, although the length of individual lumbar vertebral bodies varies phylogenetically and possibly allometrically. The other two vertical clingers and leapers, Hapalemur and Lepilemur, more closely resemble the pronograde, quadrupedal taxa. The specialized, suspensory lorids have relatively short lumbar regions as well, but the lengths of their lumbar regions are influenced by body size, and Arctocebus has dramatically longer vertebral bodies than do the other lorids. Lumbar morphology among galagonids appears to reflect a strong phylogenetic signal superimposed on a functional one. In general, relative length of the spinous processes follows a positively allometric trend, although lorids (especially the larger-bodied forms) have relatively short spinous processes for their body size, in accordance with their positional repertoire. The results of the study broaden our understanding of postcranial adaptation in primates, while providing an extensive comparative database for interpreting vertebral morphology in fossil primates.     

Ligament insertions into the human lumbar vertebral body.

The insertion of the annulus fibrosus and of the perivertebral ligaments into the lumbar vertebral body is studied by histology and microradiography, in post-mortem human material from 0 to 34 years of age. The annulus lamellosus is attached to the edge ring, whose origin is endochondral, and ends in a calcified cartilage. The perivertebral ligaments are fixed to the cortex, that derives from those ligaments; they join the vertebral body via bundle bone.     

Hydraulic permeability and activation energy of human keratinocytes at subzero temperatures

Studies on isolated human keratinocytes provide a model for design of optimal freeze-thaw protocols for skin cryopreservation and banking. Nucleated keratinocytes from the basal layer of split thickness human cadaveric skin were separated by a combined trypsin and DNAse digestion and suspended in Dulbecco's minimal essential medium with fetal calf serum. A small volume of suspension was frozen on a microprocessor controlled cryostage. Extracellular ice was nucleated at predetermined subzero temperatures, and the temperature was held constant for the duration of the experiment. The osmotic response of the cells to the formation of extracellular ice was recorded on 35-mm photographic film. Selected serial frames were digitized for automated computer evaluation of metric parameters of specific cells. Changes in the apparent cell volume were quantified over a period of several minutes to obtain dehydration curves associated with exposure to concentrated extracellular electrolytes. The Kedem-Katchalsky coupled flow transport model was statistically fit to the data using a personal computer. Values for the permeability coefficients were adjusted to optimize the correlation between the theory and the data. An activation energy of 44.8 kJ/mol and a water permeability of 0.035 micron (atm.min) at 0 degrees C were derived from the data measured over a temperature range from -2 to -9 degrees C.     

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.     

Experimental and theoretical investigation of directional permeability of human vertebral cancellous bone for cement infiltration

The use of acrylic polymers in infiltrating the porous bone structure is an emerging procedure for the augmentation of osteoporotic vertebrae. Although this procedure is employed frequently, it is performed based on empirical knowledge, and therefore, does not take into consideration the porosity-dependent permeability of human vertebral cancellous bone. The purpose of this study was to: (a). experimentally and theoretically investigate interdependence of the vertebral cancellous bone permeability and porosity, and (b). examine if the bone permeability of spinal cancellous bone can be predicted using bone mineral density measurements. If these relations can be established, they can be useful in optimizing the injection conditions for predicable cement infiltration. To determine the porosity-dependent and directional permeability, 34 bone cores-20 samples in the superior-inferior (SI) direction and 14 in the anterior-posterior (AP) direction-were cut from 20 lumbar vertebrae and infiltrated with silicone oil with a viscosity matching that of PMMA. The permeability of the cores was determined based on Darcy's law. The mean permeability of SI and AP cores was 4.45+/-1.72 x 10(-8) and 3.44+/-1.26 x 10(-8)m(2), respectively. An interesting finding of this study was that the permeability of the AP cores was approximately 78% of that of SI cores, though the porosity of the SI and AP cores taken from the same vertebra was approximately equal. In addition, we provided a theoretical model for the porosity-dependent permeability that accurately described non-linear dependency of the bone permeability and porosity in both directions. Although the relation of the bone permeability and porosity was established, bone mineral density was a weak predictor of the bone permeability. The experimental and theoretical results of this study can be used to understand polymer flow in cement infiltration procedures.     

Mid-sagittal dimensions of cervical vertebral bodies.

A series of lateral radiographs of the cervical spinal column was evaluated in order to determine vertebral body dimensions. The sample included males (N=30) and females (N=31) 18 to 24 years old, comprising three stature percentile ranges (1-20; 40-60; 80-99) of the U.S. adult population. A two-dimensional analysis of vertebral body height (average distance between superior-inferior surgaces), depth (average distance between anteriorposterior surfaces), and area (average height X average depth) revealed minimal effects due to stature. In all subjects, average depth exceeded average height for vertebral bodies C3 through C7. Upon combining stature groups, both sexes revealed maximum average values for these dimensions at the seventh cervical vertebral body. Minimum average height occurred at C5 whereas minimum average depth was found at C3. Significant correlation (alpha greater than 0.05) was found for males between ponderal index and height and depth of the C7 vertebra. Male head weight correlated significantly with C3, C4, C5 and C6 vertebral body height and with C3, C5 and C6 vertebral body depth. For females, C7 height and C6 depth correlated significantly with ponderal index and head weight respectively. Probable biomechanical relationships of specific cervical vertebral bodies are noted     

Embedding of human vertebral bodies leads to higher ultimate load and altered damage localisation under axial compression

Computer tomography (CT)-based finite element (FE) models of vertebral bodies assess fracture load in vitro better than dual energy X-ray absorptiometry, but boundary conditions affect stress distribution under the endplates that may influence ultimate load and damage localisation under post-yield strains. Therefore, HRpQCT-based homogenised FE models of 12 vertebral bodies were subjected to axial compression with two distinct boundary conditions: embedding in polymethylmethalcrylate (PMMA) and bonding to a healthy intervertebral disc (IVD) with distinct hyperelastic properties for nucleus and annulus. Bone volume fraction and fabric assessed from HRpQCT data were used to determine the elastic, plastic and damage behaviour of bone. Ultimate forces obtained with PMMA were 22% higher than with IVD but correlated highly (R² = 0.99). At ultimate force, distinct fractions of damage were computed in the endplates (PMMA: 6%, IVD: 70%), cortex and trabecular sub-regions, which confirms previous observations that in contrast to PMMA embedding, failure initiated underneath the nuclei in healthy IVDs. In conclusion, axial loading of vertebral bodies via PMMA embedding versus healthy IVD overestimates ultimate load and leads to distinct damage localisation and failure pattern.     

Hydraulic resistance of two sorghums varying in drought resistance

Genotypes of sorghum [Sorghum bicolor (L.) Moench] vary in drought resistance. Yet it is not known if their hydraulic resistances vary. The objective of this study was to determine if the hydraulic resistance of a drought-resistant sorghum was the same as that of a drought-sensitive sorghum. Leaf water and osmotic potentials were measured daily, during a 14-d period, in leaves of a drought-resistant (‘KS9’) and a drought-sensitive (‘IA25’) sorghum, which had the roots in pots with a commercial potting soil that was either well watered or allowed to dry. Soil water potential, adaxial stomatal resistance, and transpiration rate were determined daily. Hydraulic resistance of the plants was calculated from the slope of the line relating soil water potential minus leaf water potential versus transpiration rate. When the soil was not watered, the drought-sensitive sorghum had a water potential that averaged −0.50 MPa lower and an osmotic potential that averaged −0.57 MPa lower, but a similar adaxial stomatal resistance (1.19 s mm⁻¹), compared with the drought-resistant sorghum. Seven days after the beginning of the experiment, the water potential of the soil with the drought-sensitive sorghum was −0.25 MPa lower than that of the soil with the drought-resistant sorghum. With the water-limited conditions, the drought-sensitive sorghum depleted the soil-water reserve more quickly and died 2 d before the drought-resistant sorghum. Under well watered conditions, the two sorghums had similar water potentials (−1.64 MPa), osmotic potentials (−2.83 MPa), and adaxial stomatal resistances (0.78 s mm⁻¹). The calculated hydraulic resistance of the two sorghums did not differ and averaged 3.4 × 10⁷ MPa s m⁻¹. The results suggested that the variation in susceptibility to drought between the two genotypes was due to differences in rate of soil-water extraction. Contribution No. 86-249-J from the Kansas Agricultural Experiment Station. The paper is dedicated to the memory of Dr Dan M Rodgers.     

Modulation of mitochondrial permeability transition pore affects multidrug resistance in human hepatocellular carcinoma cells

Multidrug resistance (MDR) is a critical problem in the chemotherapy of cancers. Human hepatocellular carcinoma (HCC) responds poorly to chemotherapy owing to its potent MDR. Chemotherapeutic drugs primarily act by inducing apoptosis of cancer cells, and defects in apoptosis may result in MDR. Mitochondrial permeability transition (mPT) is implicated as an important event in the control of cell death or survival and mPT represents a target for the development of cytotoxic drugs. This study aimed to investigate the effects of selective opener (Atractyloside glycoside, ATR) and inhibitor (Cyclosporine A, CsA) of mitochondrial permeability transition pore (mPTP) on a CDDP-resistant HCC cell line (SK-Hep1 cells). In this study, a stable MDR phenotype characterization of SK-Hep1 cell line (SK-Hep1/CDDP cells) was established and used to investigate the role of mPTP in MDR. Results suggested that ATR accelerated the decrease of mitochondrial membrane potential (ΔΨm), reduced the Bax activity, and increased the apoptosis of SK-Hep1/CDDP cells; while CsA inhibited mPTP opening, reduced and delayed the decline of mitochondrial membrane potential, and increased the Bax activity, leading to increased tolerance of SK-Hep1/CDDP cells to apoptosis induction. However, mPTP activity had no effect on the expression of MDR1 in cells,meanwhile the P-gp translocation to mitochondria was increased, and functionally activated. In conclusion, selective modulation of mPTP can affect MDR in human HCC cells. Therefore, activation of mPTP may provide a new strategy to sensitize cancer cells to chemotherapeutic drugs and to reverse the MDR in cancer cells.     

Parametric finite element analysis of vertebral bodies affected by tumors

The vertebral column is the most frequent site of metastatic involvement of the skeleton. Due to the proximity to the spinal cord, from 5% to 10% of all cancer patients develop neurologic manifestations. As a consequence, fracture risk prediction has significant clinical importance. In this study, we model the metastatically involved vertebra so as to parametrically investigate the effects of tumor size, material properties and compressive loading rate on vertebral strength. A two-dimensional axisymmetric finite element model of a spinal motion segment consisting of the first lumbar vertebral body (no posterior elements) and adjacent intervertebral disc was developed to allow the inclusion of a centrally located tumor in the vertebral body. After evaluating elastic, mixed, and poroelastic formulations, we concluded that the poroelastic representation was most suitable for modeling the metastatically involved vertebra's response to compressive load. Maximum principal strains were used to localize regions of potential vertebral trabecular bone failure. Radial and axial vertebral body displacements were used as relative indicators of spinal canal encroachment and endplate failure. Increased tumor size and loading rate, and reduced trabecular bone density all elevated axial and radial displacements and maximum tensile strains. The results of this parametric study suggest that vertebral tumor size and bone density contribute significantly to a patients risk for vertebral fracture and should be incorporated in clinical assessment paradigms.     

A patient-specific computer tomography-based finite element methodology to calculate the six dimensional stiffness matrix of human vertebral bodies

In most finite element (FE) studies of vertebral bodies, axial compression is the loading mode of choice to investigate structural properties, but this might not adequately reflect the various loads to which the spine is subjected during daily activities or the increased fracture risk associated with shearing or bending loads. This work aims at proposing a patient-specific computer tomography (CT)-based methodology, using the currently most advanced, clinically applicable finite element approach to perform a structural investigation of the vertebral body by calculation of its full six dimensional (6D) stiffness matrix. FE models were created from voxel images after smoothing of the peripheral voxels and extrusion of a cortical shell, with material laws describing heterogeneous, anisotropic elasticity for trabecular bone, isotropic elasticity for the cortex based on experimental data. Validated against experimental axial stiffness, these models were loaded in the six canonical modes and their 6D stiffness matrix calculated. Results show that, on average, the major vertebral rigidities correlated well or excellently with the axial rigidity but that weaker correlations were observed for the minor coupling rigidities and for the image-based density measurements. This suggests that axial rigidity is representative of the overall stiffness of the vertebral body and that finite element analysis brings more insight in vertebral fragility than densitometric approaches. Finally, this extended patient-specific FE methodology provides a more complete quantification of structural properties for clinical studies at the spine.     

Magnetic resonance (MR) evaluation of bone marrow in vertebral bodies.

Magnetic Resonance (MR) imaging was used to examine the hematopoietic bone marrow in the vertebral bodies of eight healthy subjects, and of 35 cancer patients who had been previously treated with radiation therapy. MR was instrumental in distinguishing viable hematopoietic tissue (red marrow) from adipose tissue (yellow marrow), whose presence reflected the extent of radiation-induced bone marrow injury. Different water content in proliferating hematopoietic tissue and adipose tissue enabled clear distinction of the two components even inside the same vertebral body. Three patterns of bone marrow viability were observed in irradiated patients: 1. Patients undergoing therapy at the time of MR study, and patients who had received low-intermediate dose several years before MR examination showed no alteration as compared with healthy controls (i.e. homogeneous presence of red marrow). 2. Patients who had received low-intermediate dose few years before MR, showed either partial re-colonization of yellow marrow or almost complete ablation of active red marrow with rare areas of re-colonization. 3. Patients who had received high dose, showed complete depletion of red marrow (fatty substitution) independently of the length of time elapsed since radiation therapy. Therefore, bone marrow recovery after radiation therapy was associate with two variables: received dose and length of time allowed for re-colonization by surviving hematopoietic tissue. In conclusion, our results provide evidence that MR can be purposively used to study composition and distribution of normal bone marrow, and to asses the extent of radiation-induced bone marrow injury; to monitor bone marrow recovery (or the lack of it); and in the general follow-up of treated cancer patients.