Intraspecimen Variability Research Articles

Potential of reproductive traits in functional ecology: A quantitative comparison of variability in floral, fruit, and leaf traits.

Despite their claimed low intraspecific variability, plant reproductive traits are less frequently used in functional ecology. Here we focused on underrepresented plant organs, i.e. flowers and fruits, by comparing their traits with well-established leaf traits. We evaluated 16 functional traits (six floral, six fruit, and four leaf traits) in a randomly selected group of woody species under comparable environmental conditions. We aimed to assess interspecific and intraspecimen variability and explore the potential of the proposed flower and fruit traits for ecological research. Traits related to the dry mass of flowers and fruits exhibited the highest interspecific variability, while carbon content traits in flowers and leaves had the lowest. At a specimen level, specific leaf area revealed the highest variation. Carbon content traits for all organs demonstrated the least intraspecimen variability, with flower carbon content being the least variable. Our study revealed connections between the newly proposed traits and widely recognized functional traits, uncovering intriguing links between the established traits and the floral and fruit traits upon which we focused. This complements the already well-recognized variability in plant form and function with additional insights into reproductive processes.

Low intra-canopy variability of floral traits in temperate woody plants

Floral traits represent a valuable yet underutilized resource for functional ecology. We aimed to examine the variability of six quantitative floral traits (carbon [C] and nitrogen [N] contents, C:N ratio, flower length and width, and dry biomass) among a randomly selected group of 79 temperate woody species at both interspecific and intraspecimen levels. We hypothesized that (1) flower traits are closely related to the evolutionary history of the species, resulting in a strong phylogenetic signal, and (2) flowers collected from the most and the least exposed to sunlight parts of the crown would not differ in trait values. We detected statistically significant phylogenetic signals for all six floral traits under study. We found significant differences between samples from the two light variants only for flower N content and C:N ratio. Given the substantial interspecific and the negligible intra-specimen variability observed, we are convinced that the incorporation of these studied traits, especially those related to flower size (i.e., dry biomass, length, and width), into research on flowering biology and ecology can significantly enrich our comprehension of the plant reproductive processes.

Reliable in vitro method for the evaluation of the primary stability and load transfer of transfemoral prostheses for osseointegrated implantation.

Osseointegrated transfemoral prostheses experience aseptic complications with an incidence between 3% and 30%. The main aseptic risks are implant loosening, adverse bone remodeling, and post-operative periprosthetic fractures. Implant loosening can either be due to a lack of initial (primary) stability of the implant, which hinders bone ingrowth and therefore prevents secondary stability, or, in the long-term, to the progressive resorption of the periprosthetic bone. Post-operative periprosthetic fractures are most often caused by stress concentrations. A method to simultaneously evaluate the primary stability and the load transfer is currently missing. Furthermore, the measurement errors are seldom reported in the literature. In this study a method to reliably quantify the bone implant interaction of osseointegrated transfemoral prostheses in terms of primary stability and load transfer was developed, and its precision was quantified. Micromotions between the prosthesis and the host bone and the strains on the cortical bone were measured on five human cadaveric femurs with a typical commercial osseointegrated implant. To detect the primary stability of the implant and the load transfer, cyclic loads were applied, simulating the peak load during gait. Digital Image Correlation was used to measure displacements and bone strains simultaneously throughout the test. Permanent migrations and inducible micromotions were measured (three translations and three rotations), while, on the same specimen, the full-field strain distribution on the bone surface was measured. The repeatability tests showed that the devised method had an intra-specimen variability smaller than 6μm for the translation, 0.02 degrees for the rotations, and smaller than 60 microstrain for the strain distribution. The inter-specimen variability was larger than the intra-specimen variability due to the natural differences between femurs. Altogether, the measurement uncertainties (intrinsic measurement errors, intra-specimen repeatability and inter-specimen variability) were smaller than critical levels of biomarkers for adverse remodelling and aseptic loosening, thus allowing to discriminate between stable and unstable implants, and to detect critical strain magnitudes in the host bone. In conclusion, this work showed that it is possible to measure the primary stability and the load transfer of an osseointegrated transfemoral prosthesis in a reliable way using a combination of mechanical testing and DIC.

Intra- and Interspecific Variability of Non-Structural Carbohydrates and Phenolic Compounds in Flowers of 70 Temperate Trees and Shrubs

(1) The focus on floral functional traits and their variability has been significantly lower than when compared to other plant organs. Here, we focused on the variability of four novel floral chemical traits. We aimed to assess the level of interspecific variability of total non-structural carbohydrates (TNC) and total phenolic compounds (TPh) in the flowers of woody species. (2) We collected data on 70 species of temperate trees and shrubs. We also assessed the intraspecific level of variability by collecting flowers from the high-light and low-light parts of the crown. (3) We found a phylogenetic signal in the variability of starch and TPh. We did not observe statistically significant differences or biologically significant trends between the high-light and low-light parts of the crown. We detected a low impact of light availability on the intraspecimen variability of the TNC and TPh contents. (4) Low intraspecimen variability allows for a more reliable extrapolation of measurements in cases of interspecific comparisons and can be used to better describe the reproductive strategies of different woody species.

Raman spectroscopy and structural heterogeneity of carbonaceous material in Proterozoic organic-walled microfossils in the North China Craton

Raman spectroscopy is a minimally intrusive and minimally destructive technique that has played an important role in analyzing Precambrian carbonaceous microfossils and microstructures. Previous studies have shown that heterogeneities in structural order of carbonaceous material (CM) as revealed by Raman spectroscopy can be preserved in Proterozoic silicified cyanobacterial fossils. However, such heterogeneities have not been documented in Proterozoic eukaryotic microfossils preserved as carbonaceous compressions. In this study, we used Raman spectroscopy to investigate the structural characteristics of organic-walled microfossils, including eukaryotes preserved as carbonaceous compressions, from the late Paleoproterozoic Ruyang Group and the early Neoproterozoic (Tonian) Liulaobei Formation in the North China Craton. Raman geothermometers indicate that CM experienced low-grade metamorphism with apparent peak metamorphic temperatures of ~200 °C for both the Ruyang and Liulaobei microfossils. Heterogeneities in structural characteristics of CM in eukaryotic microfossils were found among different subcellular structures of Shuiyousphaeridium macroreticulatum and among different taxa from the same stratigraphic horizon. We suggest that these heterogeneities can be attributed to differences in precursor organic compounds; thus, the importance of organic precursors should be considered in CM Raman geothermometry studies, especially in environments where heating events occurred quickly. The Raman data presented here are also consistent with hypotheses that the Ruyang microfossils Dictyosphaera delicata and S. macroreticulatum are biologically conspecific taxa with their vesicle walls having similar CM Raman features, and that the Liulaobei microfossils Leiosphaeridia jacutica and L. tenuissima are distinct taxa despite their similarities in morphologies other than vesicle wall thickness. Although more data are needed to verify the consistency of interspecies, intraspecies, and intraspecimen variability, this study indicates that Raman spectroscopy may have the potential to provide an independent test of early eukaryote taxonomy, which has been traditionally based only on morphological features, and to reveal heterogeneities of CM of early eukaryotic organisms.

Intra-individual variability of dental enamel δ13C and δ18O values in Late Pleistocene cave hyena and cave bear from Perspektywiczna Cave (southern Poland)

An important source of palaeoecological and palaeoenvironmental information is intra-specimen variability of isotopic composition of mammal tooth enamel. It reflects seasonal or behavioral changes in diet and climate occurring during a life of the animal. While well-known in ungulates, in carnivorans this variability is poorly recognized. However, carnivoran remains are amongst the most numerous in the Pleistocene fossil record of terrestrial mammals, so their isotopic signature should be of particular interest. The aim of the study was to verify if enamel of a fossil cave hyena (Crocuta crocuta spelaea) and a cave bear (Ursus ingressus) records any regular inter- or intra-tooth isotopic variability. We examined intra-individual variability of δ13C and δ18O values in permanent cheek teeth enamel of fossil cave hyena and cave bear from the site of the Perspektywiczna Cave (southern Poland). We conclude that the isotopic variability of the cave hyena is low, possibly because enamel mineralization took place when the animals still relied on a uniform milk diet. Only the lowermost parts of P3 and P4 enamel record a shift toward an adult diet. In the case of the cave bear, the sequence of enamel formation records periodic isotopic changes, possibly correlating with the first seasons of the animal life.

The source of sulfate in brachiopod calcite: Insights from μ-XRF imaging and XANES spectroscopy

Geochemical signatures preserved in sedimentary carbonate strata are often used as archives for paleoenvironmental reconstructions. However, diagenetic overprinting and/or muting of primary geochemical signatures complicates the interpretation of these data. To avoid this issue, geochemical techniques strive to target unaltered (or minimally altered) carbonate components. The multi-layer low-Mg calcite shell composition of articulate brachiopods are often the target in such studies because they are commonly more robust to recrystallization than the shells of other biomineralizers. Here, we have combined S K-edge μ-XRF imaging, XANES spectroscopy and petrography to determine the source of sulfate in the calcite lattice (carbonate-associated sulfate; CAS) of ancient and extant brachiopods, in order to establish their suitability for use in reconstructing seawater sulfate δ34S throughout the Phanerozoic. Both the extant brachiopod Terebratalia transversa and fossil brachiopods display intra-specimen variability in sulfate abundance parallel to the primary fabric, likely corresponding to variations in growth rate. XANES spectroscopy identifies a majority of the sulfate as inorganic. Additionally, XANES spectroscopy detected low abundances of both reduced and oxidized organic sulfur species (thiol, thioether, sulfoxide and sulfate esters) in all T. transversa samples and lesser abundances in a few of the fossil brachiopods. In T. transversa, inorganic sulfate and sulfate ester abundance increase towards the hinge of the valves. Bulk δ34SCAS of the samples containing the fossil brachiopods are consistently more positive than time-equivalent brachiopod-only values, likely reflecting a mixture of CAS signals from homogenization of carbonate components differentially affected by depositional environment and diagenesis. In contrast, bulk δ34SCAS of modern T. transversa is approximately 1‰ more positive than coeval seawater. Although organic sulfate esters are found within the brachiopod shells, they are only ever present as trace components. Our findings indicate that the vast majority of sulfate in brachiopod shells is inorganic, sourced from coeval seawater. This result supports the use of brachiopods as a potential archive for a faithful CAS record of seawater sulfate throughout the Phanerozoic. The characterization of in situ organic sulfur compounds in both extant and fossil brachiopods indicates the potential importance of various organic sulfur compounds in mineralogical determination (and therefore fossil preservation) and crystal orientation during brachiopod biomineralization throughout geologic time.

Light Impacts Mg Incorporation in the Benthic Foraminifer Amphistegina lessonii

The ratio of Mg to Ca in foraminiferal calcium carbonate (Mg/Cacc) is a popular tool to reconstruct past sea water temperatures. Its application is being complicated by other environmental factors affecting the Mg/Cacc, including salinity and the ratio between sea water [Mg2+] and [Ca2+]. Furthermore, there is considerable intra-specimen variability in Mg/Ca in the form of alternating high- and low-concentration bands. This banding has recently been linked to diurnal cyclicity, in which bands with relatively high Mg/Ca are precipitated during night time. Here we show that light not only impacts variability due to banding but also significantly affects average chamber Mg/Ca in the large benthic, symbiont-bearing foraminifer Amphistegina lessonii. These ratios are higher in foraminifera that calcify for a longer time in the dark, with a difference in Mg/Ca of 23 mmol/mol between carbonate formed completely in the dark versus completely in the light. We propose that individual timing of chamber formation and thus presence or absence of light during calcification is an important driver of inter-specimen variability in foraminiferal Mg/Ca.

The Source and the Course of the Articular Branches to the T4-T8 Zygapophysial Joints

To define the source and the course of the articular branches to the midthoracic zygapophysial ("z") joints. Cadaveric dissection. The Gross Anatomy Laboratory of the Duke University School of Medicine. Ten human cadaveric thoraces. Gross and stereoscopic dissection of dorsal rami T4-T8 was performed bilaterally on 10 adult embalmed cadavers. The medial and lateral branches were traced to their origins from the dorsal rami, and the course of the articular nerves was documented through digital photography. Radio-opaque wire (20 gauge) was applied to the nerves. Fluoroscopic images were obtained to delineate their radiographic course with respect to osseous landmarks. Forty-eight inferior articular branches were identified. Three (6.3%) originated from the medial branch and 44 (91.7%) from the dorsal ramus. One was indeterminate. Fifty-one superior articular branches were identified. Eight (15.7%) originated from the medial branch and 43 (84.3%) from the dorsal ramus. In 12% of cases (6/50), there was side-to-side asymmetry in the origins of the articular branches. Nerves were commonly suspended in the intertransverse space. The articular branches contacted an osseous structure in only 39% of cases. As previously reported, a "descending branch" was not identified in any specimen. Articular branches to the T4-T8 z-joints have substantial inter- and intraspecimen variability of origin. They typically arise from the dorsal ramus rather than the medial branch and frequently do not contact any osseous structure to allow percutaneous needle placement.

Biomechanical characterization of human dura mater.

A reliable computational model of the human head is necessary for better understanding of the physical mechanisms of traumatic brain injury (TBI), car-crash investigation, development of protective head gear and advancement of dural replacement materials. The performance and biofidelity of these models depend largely on the material description of the different structures present in the head. One of these structures is the dura mater, the protective layer around the brain. We tested five human dura mater specimens, with samples at different locations, using planar biaxial tests. We describe the resulting stress-strain curves using both the anisotropic Gasser-Ogden-Holzapfel (GOH) model and the isotropic one-term Ogden model. The low-strain section of the curves is also described using a Neo-Hookean formulation. The obtained stress-strain curves reveal highly nonlinear but isotropic behaviour. A significant amount of inter- and intra-specimen variability is noticed, whereby the latter does not seem to be influenced by location. The GOH model achieves the best fit of the individual test data. A simple Neo-Hookean model can only be used with extreme caution, as it does not manage to capture the nonlinear effects present even at low strains.

Determination of replicate composite bone material properties using modal analysis

Replicate composite bones are used extensively for in vitro testing of new orthopedic devices. Contrary to tests with cadaveric bone material, which inherently exhibits large variability, they offer a standardized alternative with limited variability. Accurate knowledge of the composite’s material properties is important when interpreting in vitro test results and when using them in FE models of biomechanical constructs.The cortical bone analogue material properties of three different fourth-generation composite bone models were determined by updating FE bone models using experimental and numerical modal analyses results. The influence of the cortical bone analogue material model (isotropic or transversely isotropic) and the inter- and intra-specimen variability were assessed.Isotropic cortical bone analogue material models failed to represent the experimental behavior in a satisfactory way even after updating the elastic material constants. When transversely isotropic material models were used, the updating procedure resulted in a reduction of the longitudinal Young’s modulus from 16.00GPa before updating to an average of 13.96 GPa after updating. The shear modulus was increased from 3.30GPa to an average value of 3.92GPa. The transverse Young’s modulus was lowered from an initial value of 10.00GPa to 9.89GPa. Low inter- and intra-specimen variability was found.

Reconciling single-chamber Mg / Ca with whole-shell δ<sup>18</sup>O in surface to deep-dwelling planktonic foraminifera from the Mozambique Channel

Abstract. Most planktonic foraminifera migrate vertically through the water column during life, meeting a range of depth-related conditions as they grow and calcify. For reconstructing past ocean conditions from geochemical signals recorded in their shells, it is therefore necessary to know vertical habitat preferences. Species with a shallow habitat and limited vertical migration will reflect conditions of the surface mixed layer and short-term and mesoscale (i.e. seasonal) perturbations therein. Species spanning a wider range of depth habitats, however, will contain a more heterogeneous, intra-specimen variability (e.g. Mg / Ca and δ18O), which is less for species calcifying below the thermocline. Obtained single-chamber Mg / Ca ratios are combined with single-specimen δ18O and δ13C of the surface-water inhabitant Globigerinoides ruber, the thermocline-dwelling Neogloboquadrina dutertrei and Pulleniatina obliquiloculata, and the deep dweller Globorotalia scitula from the Mozambique Channel. Species-specific Mg / Ca, δ13C and δ18O data combined with a depth-resolved mass balance model confirm distinctive migration and calcification patterns for each species as a function of hydrography. Whereas single-specimen δ18O rarely reflects changes in depth habitat related to hydrography (e.g. temperature), measured Mg / Ca of the last chambers can only be explained by active migration in response to changes in temperature stratification. Foraminiferal geochemistry and modelled depth habitats shows that the single-chamber Mg / Ca and single shell δ18O are in agreement with each other and in line with the changes in hydrography induced by eddies.

Biomechanical evaluation of a biomimetic spinal construct

BackgroundLaboratory spinal biomechanical tests using human cadaveric or animal spines have limitations in terms of disease transmission, high sample variability, decay and fatigue during extended testing protocols. Therefore, a synthetic biomimetic spine model may be an acceptable substitute. The goal of current study is to evaluate the properties of a synthetic biomimetic spine model; also to assess the mechanical performance of lateral plating following lateral interbody fusion.MethodsThree L3/4 synthetic spinal motion segments were examined using a validated pure moment testing system. Moments (±7.5 Nm) were applied in flexion-extension (FE), lateral bending (LB) and axial rotation (AR) at 1Hz for total 10000 cycles in MTS Bionix. An additional test was performed 12 hours after 10000 cycles. A ±10 Nm cycle was also performed to allow provide comparison to the literature. For implantation evaluation, each model was tested in the 4 following conditions: 1) intact, 2) lateral cage alone, 3) lateral cage and plate 4) anterior cage and plate. Results were analysed using ANOVA with post-hoc Tukey’s HSD test.ResultsRange of motion (ROM) exhibited logarithmic growth with cycle number (increases of 16%, 37.5% and 24.3% in AR, FE and LB respectively). No signification difference (p > 0.1) was detected between 4 cycles, 10000 cycles and 12 hour rest stages. All measured parameters were comparable to that of reported cadaveric values. The ROM for a lateral cage and plate construct was not significantly different to the anterior lumbar interbody construct for FE (p = 1.00), LB (p = 0.995) and AR (p = 0.837).ConclusionsBased on anatomical and biomechanical similarities, the synthetic spine tested here provides a reasonable model to represent the human lumbar spine. Repeated testing did not dramatically alter biomechanics which may allow non-destructive testing between many different procedures and devices without the worry of carry over effects. Small intra-specimen variability and lack of biohazard makes this an attractive alternative for in vitro spine biomechanical testing. It also proved an acceptable surrogate for biomechanical testing, confirming that a lateral lumbar interbody cage and plate construct reduces ROM to a similar degree as anterior lumbar interbody cage and plate constructs.

Modeling of Tooling-Workpiece Interactions on Random Surfaces

Abrasive processes, commonly employed in manufacturing, are difficult to model because they rely on brittle particles with unknown geometry and multiple points of contact. Newly developed microreplicated abrasives allow for control of abrasive grit properties such as size, shape, and distribution. This paper proposes and validates a parametric model of abrasive machining that allows for studying the interaction of this particular tooling with randomly generated surfaces. In this work, the parameters of a probability distribution function that represents the workpiece surface are approximated by profilometry data. Monte Carlo simulation is used to account for inter- and intraspecimen variability. A geometric representation is used to mathematically represent the interaction between workpiece and tool. The results show good correlation between theoretical and actual values. This approach could be used to aid in tool geometry design as well as in process parameter optimization.

Variability of trabecular microstructure is age-, gender-, race- and anatomic site-dependent and affects stiffness and stress distribution properties of human vertebral cancellous bone

Cancellous bone microstructure is an important determinant of the mechanical integrity of vertebrae. The numerous microstructural parameters that have been studied extensively are generally represented as a single value obtained as an average over a sample. The range of the intra-sample variability of cancellous microstructure and its effect on the mechanical properties of bone are less well-understood. The objectives of this study were to investigate the extent to which human cancellous bone microstructure within a vertebra i) is related to bone modulus and stress distribution properties and ii) changes along with age, gender and locations thoracic 12 (T12) vs lumbar 1 (L1). Vertebrae were collected from 15 male (66±15 years) and 25 female (54±16 years) cadavers. Three dimensional finite element models were constructed using microcomputed tomography images of cylindrical specimens. Linear finite element models were used to estimate apparent modulus and stress in the cylinders during uniaxial compression. The intra-specimen mean, standard deviation (SD) and coefficient of variation (CV) of microstructural variables were calculated. Mixed model statistical analysis of the results demonstrated that increases in the intra-specimen variability of the microstructure contribute to increases in the variability of trabecular stresses and decreases in bone stiffness. These effects were independent from the contribution from intra-specimen average of the microstructure. Further, the effects of microstructural variability on bone stiffness and stress variability were not accounted for by connectivity and anisotropy. Microstructural variability properties (SD, CV) generally increased with age, were greater in females than in males and in T12 than in L1. Significant interactions were found between age, gender, vertebra and race. These interactions suggest that microstructural variability properties varied with age differently between genders, races and vertebral levels. The current results collectively demonstrate that microstructural variability has a significant effect on mechanical properties and tissue stress of human vertebral cancellous bone. Considering microstructural variability could improve the understanding of bone fragility and improve assessment of vertebral fracture risk.

Interindividual and intraspecimen variability of 3-D bone microarchitectural parameters in iliac crest biopsies imaged by conventional micro-computed tomography

Bone microarchitecture of the iliac bone is used to characterize the properties of bone tissue in osteoporosis, particularly in pharmacological studies. Trabecular bone is known to be heterogeneous media. For a few years, the analysis of three-dimensional (3-D) bone microarchitecture has been based on micro-computed tomography (micro-CT). To assess the interindividual variability (inter-indVar) and the intrasample variability (intra-sampVar) of iliac crest biopsies, we used a Bordier needle trephine in 35 postmenopausal female cadavers (mean age, 74.4 +/- 10.4 years). Finally, we had at our disposal 32 individual iliac crests to assess the inter-indVar and 21 oriented specimens to assess the intra-sampVar. All the samples were chemically defatted, and the images were performed with a desktop micro-CT with a voxel size of 10.77 microm. We measured trabecular bone parameters: bone volume/tissue volume (BV/TV %), trabecular thickness and spacing (Tb. Th*, Tb.Sp* microm), bone surface/bone volume (BS/BV, 1/mm), the trabecular number (Tb.N, 1/mm), structure model index (SMI), trabecular pattern factor (Tb.Pf), and degree of anisotropy (DA). We also measured cortical bone parameters: cortical thickness (Cort.Th), porosity (PoV/TV), and pore diameter (Po.Dm). For the inter-indVar, we analyzed a fixed volume of interest corresponding to 119.8 mm(3) centered on each iliac crest. To assess the intra-sampVar, we divided the whole trabecular volume into three equal height parts (external, middle, internal). BV/TV, Tb.N, and PoV/TV were negatively correlated with age and Tb.Sp* and SMI were positively correlated. The mean difference of absolute individual variations in percentage with the middle area used as a reference, comparatively to external and internal areas, ranged from 6.6% (Tb.Sp*) to 27.8% (BV/TV), except Tb.Pf, which showed large variability. There was no difference between external and internal areas, with a tendency for lower values of BV/TV, Tb.Th*, and Tb.N in the middle of the iliac crest and higher values of Tb.Sp* and BS/BV. The evaluation of bone microarchitecture of iliac crest samples on micro-CT images is reliable. The heterogeneity of bone inside the iliac crest is noticeable as leading to analyzing the largest possible quantity of bone, with standardized location, according to cortex but without any assumption of orientation.

Variability of Acetylcholinesterase Hyperinnervation Patterns in Distal Rectal Suction Biopsy Specimens in Hirschsprung Disease

Variability in cholinergic innervation may contribute to false-negative and false-positive evaluations for Hirschsprung disease (HD). We compared intraspecimen variability of histochemical acetylcholinesterase (ACE) activity in 62 distal rectal mucosal biopsy specimens from 33 patients with short-segment HD (SSHD), 14 patients with short-segment HD/Down syndrome (SSHD/DS), 10 patients with total colonic aganglionosis (HDTC), and 45 ganglionated control specimens obtained because of clinical suspicion for HD. Specimens were evaluated in 1-mm linear segments for abnormal distribution and abnormal intensity of staining reaction in the lamina propria (LP), muscularis mucosae (MM), numerical excess of small submucosal nerves (SSN), and presence or absence of large submucosal nerves (LSN) defined as >35 microns in diameter. Patients with HD and controls were predominantly infant males. Aggregate length of specimens was 186 mm in HD and 136 mm in controls. We defined multiple patterns and relative frequencies of normal and abnormal ACE reactivity in the muscularis mucosae, submucosal nerves, and innervation in the lamina propria. We verified a hyperinnervation pattern more common in neonates within each subset of HD. Large submucosal nerves >35 microns in diameter are relatively less common in SSHD/DS and HDTC. Eleven of 57 patients with HD had at least 1 mm of normal muscularis mucosae accounting for 19/186 mm examined. Ten percent of control mm had at least 1 submucosal nerve >35 microns in diameter. Intraspecimen variability in ACE patterns, when extreme, can usually be resolved by findings elsewhere in an adequate specimen, minimizing the need for repeat procedures.

Accuracy of Pedicle Screw Placement for Upper and Middle Thoracic Pathologies Without Coronal Plane Spinal Deformity Using Conventional Methods

There is a growing interest in the implantation of pedicle screws into the middle and upper thoracic spine. However, usage of the technique is still under debate for these levels because the pedicles in these regions are small and exhibit a high degree of inter- and intraspecimen variability. Twenty-four consecutive patients treated for upper and middle thoracic pathologies by pedicle screw instrumentation under biplanar or uniplanar fluoroscopy were evaluated retrospectively. The rate of screw misplacement on postoperative computerized tomography and complications caused by misplaced screws were determined. In 24 cases, a total of 113 upper-middle thoracic pedicle screws were inserted. Fifty-one of them were inserted between T2 and T5 with guidance of biplanar fluoroscopy, and 62 were inserted between T6 and T8 with uniplanar fluoroscopy. The rate of misplacement was 20.3% for 113 screws (27.4% for T2 to T5 screws, and 14.5% for 62 T6 to T8 screws). Four screws were incorrectly inserted which could have clinical significance (3.5%), and 1 of them required revision. The difference between the upper and middle thoracic screws was not statistically significant (P=0.089). Screw insertion with laminectomy did not cause significant difference in both upper and middle thoracic regions. Only 2 complications were seen because of screw insertion. Pedicle screw insertion with guidance of fluoroscopy may be a reliable and safe method for upper and middle thoracic pathologies.

Modeling Changes in Intervertebral Disc Mechanics with Degeneration

Mechanical response of the spine to various dynamic loading conditions can be analyzed by way of in vitro and in vivo studies. Ethical concerns, interpretation of conclusions reached in animal studies, and lack of detailed stress distributions in the disc components are the major disadvantages of relying solely on in vivo studies. Intraspecimen variability, difficulty in including muscle activity, and inability to mimic fluid exchange into the disc during unloading are some of the disadvantages of in vitro models. The poroelastic finite element models can provide a method of understanding the relationship between biomechanical performance of the disc due to cyclic loading and disc degeneration. A poroelastic finite element model, including regional variation of strain-dependent permeability and osmotic pressure, was used to study the effect of disc degeneration on biomechanical properties as well as propagation of failure in the disc components when cyclic loading was applied to the lumbar disc. The results predicted that healthy discs were much more flexible than degenerated discs, and the disc stiffness decreased with increasing the number of load cycles independent of degenerative condition. Failure was found to progress as the drained elastic properties of the disc components decreased due to the presence of failure. Poroelastic finite element modeling, including strain-dependent permeability and osmotic pressure, is the most advanced analytical tool currently available that can be used to understand how cyclic loading affects the biomechanical characteristics of a degenerated lumbar disc. However, a complete understanding of behavior of the intervertebral disc will ultimately be achieved only with use of a combination of computational models together with in vitro and in vivo experimental methods. Finite element models of discs with varying degrees of disc degeneration will help clinicians understand the initiation and progression of disc failure and degeneration and will assist in the development of approaches to stimulate the regeneration of disc tissues.

Recent Advances in Analytical Modeling of Lumbar Disc Degeneration

Review of the most recent advances in the development of poro-elastic analytical models that include physiologic parameters used for understanding lumbar disc degeneration due to repetitive loading. To discuss how poro-elastic finite element models that include physiologic parameters such as strain-dependent permeability and porosity and regional variation of poro-elastic material properties of a motion segment can be used to understand the effect of disc degeneration due to cyclic loading on the disc biomechanical properties. Mechanical response of the spine to various dynamic loading conditions can be analyzed using in vitro and in vivo studies. Ethical concerns, interpretation of conclusions reached using animal studies, and lack of detailed stress distributions in the disc components are the major disadvantages in using in vivo studies for understanding disc degeneration process. Intraspecimen variability, noninclusion of muscle activity, and difficulty of influx of fluid into the disc during unloading are some of the disadvantages while using in vitro models to understand disc degeneration. The poro-elastic finite element models can provide a method that can circumvent the disadvantages mentioned above and allow a way to understand the relationship between biomechanical performance of the disc due to cyclic loading and disc degeneration. Several types of finite element model were developed in understanding relationship between disc degeneration and associated changes in biomechanical properties. Simplest among them include material and geometric nonlinearity of the disc and was used to predict failure in the disc anulus and endplates under static loading conditions. Response of the lumbar disc under creep loading was studied using poro-elastic models. These models were further refined by including swelling pressure and variable permeability due to change in porosity under load to understand time-dependent deformation of a lumbar disc in a multiple creep compression expansion loading. Regional variation of strain dependent permeability and osmotic pressure was included to further refine the poro-elastic finite element model. This refined model was used to study the effect of disc degeneration on biomechanical properties when cyclic loading was applied to the lumbar disc. The refined model that included regional variation of strain-dependent permeability and osmotic pressure was validated by comparing diurnal change in total stature measured in vivo. The study showed that disc height loss was larger after considerable number of cyclic loadings both in normal and degenerated discs. Cyclic loading also showed that Grade I discs were much more flexible than Grade IV discs. The disc stiffness also decreased as the load cycle increased. A number of different approaches have been used to address the issue of disc degeneration. Poro-elastic finite element model including strain-dependent permeability and osmotic pressure is the most popular analytical tool currently available that can be used to understand how cyclic loading affects the biomechanical characteristics of a degenerated lumbar disc. However, it is important to note that a complete understanding of the behavior of the intervertebral disc will ultimately be arrived using a combination of analytical models, such as the models presented here, in addition to in vitro and in vivo experimental methods.