Regional structure-function relationships of lumbar cartilage endplates.

Cartilage endplates (CEPs) act as protective mechanical barriers for intervertebral discs (IVDs), yet their heterogeneous structure-function relationships are poorly understood. This study addressed this gap by characterizing and correlating the regional biphasic mechanical properties and biochemical composition of human lumbar CEPs. Samples from central, lateral, anterior, and posterior portions of the disc (n = 8/region) were mechanically tested under confined compression to quantify swelling pressure, equilibrium aggregate modulus, and hydraulic permeability. These properties were correlated with CEP porosity and glycosaminoglycan (s-GAG) content, which were obtained by biochemical assays of the same specimens. Both swelling pressure (142.79 ± 85.89 kPa) and aggregate modulus (1864.10 ± 1240.99 kPa) were found to be regionally dependent (p = 0.0001 and p = 0.0067, respectively) in the CEP and trended lowest in the central location. No significant regional dependence was observed for CEP permeability (1.35 ± 0.97 * 10-16 m4/Ns). Porosity measurements correlated significantly with swelling pressure (r = -0.40, p = 0.0227), aggregate modulus (r = -0.49, p = 0.0046), and permeability (r = 0.36, p = 0.0421), and appeared to be the primary indicator of CEP biphasic mechanical properties. Second harmonic generation microscopy also revealed regional patterns of collagen fiber anchoring, with fibers inserting the CEP perpendicularly in the central region and at off-axial directions in peripheral regions. These results suggest that CEP tissue has regionally dependent mechanical properties which are likely due to the regional variation in porosity and matrix structure. This work advances our understanding of healthy baseline endplate biomechanics and lays a groundwork for further understanding the role of CEPs in IVD degeneration.

The influence of loss to follow-up in autism screening research: Taking stock and moving forward.

BACKGROUND: How best to improve the early detection of autism spectrum disorder (ASD) is the subject of significant controversy. Some argue that universal ASD screeners are highly accurate, whereas others argue that evidence for this claim is insufficient. Relatedly, there is no clear consensus as to the optimal role of screening for making referral decisions for evaluation and treatment. Published screening research can meaningfully inform these questions-but only through careful consideration of children who do not complete diagnostic follow-up. METHODS: We developed two simulation models that re-analyze the results of a large-scale validation study of the M-CHAT-R/F by Robins et al. (2014, Pediatrics, 133, 37). Model #1 re-analyzes screener accuracy across six scenarios, each reflecting different assumptions regarding loss to follow-up. Model #2 builds on this by closely examining differential attrition at each point of the multi-step detection process. RESULTS: Estimates of sensitivity ranged from 40% to 94% across scenarios, demonstrating that estimates of accuracy depend on assumptions regarding the diagnostic status of children who were lost to follow-up. Across a range of plausible assumptions, data also suggest that children with undiagnosed ASD may be more likely to complete follow-up than children without ASD, highlighting the role of clinicians and caregivers in the detection process. CONCLUSIONS: Using simulation modeling as a quantitative method to examine potential bias in screening studies, analyses suggest that ASD screening tools may be less accurate than is often reported. Models also demonstrate the critical importance of every step in a detection process-including steps that determine whether children should complete an additional evaluation. We conclude that parent and clinician decision-making regarding follow-up may contribute more to detection than is widely assumed.

Causal mediation and sensitivity analysis for mixed-scale data.

The goal of causal mediation analysis, often described within the potential outcomes framework, is to decompose the effect of an exposure on an outcome of interest along different causal pathways. Using the assumption of sequential ignorability to attain non-parametric identification, Imai et al. (2010) proposed a flexible approach to measuring mediation effects, focusing on parametric and semiparametric normal/Bernoulli models for the outcome and mediator. Less attention has been paid to the case where the outcome and/or mediator model are mixed-scale, ordinal, or otherwise fall outside the normal/Bernoulli setting. We develop a simple, but flexible, parametric modeling framework to accommodate the common situation where the responses are mixed continuous and binary, and, apply it to a zero-one inflated beta model for the outcome and mediator. Applying our proposed methods to the publicly-available JOBS II dataset, we (i) argue for the need for non-normal models, (ii) show how to estimate both average and quantile mediation effects for boundary-censored data, and (iii) show how to conduct a meaningful sensitivity analysis by introducing unidentified, scientifically meaningful, sensitivity parameters.

Deep historical borrowing framework to prospectively and simultaneously synthesize control information in confirmatory clinical trials with multiple endpoints.

In current clinical trial development, historical information is receiving more attention as it provides utility beyond sample size calculation. Meta-analytic-predictive (MAP) priors and robust MAP priors have been proposed for prospectively borrowing historical data on a single endpoint. To simultaneously synthesize control information from multiple endpoints in confirmatory clinical trials, we propose to approximate posterior probabilities from a Bayesian hierarchical model and estimate critical values by deep learning to construct pre-specified strategies for hypothesis testing. This feature is important to ensure study integrity by establishing prospective decision functions before the trial conduct. Simulations are performed to show that our method properly controls family-wise error rate and preserves power as compared with a typical practice of choosing constant critical values given a subset of null space. Satisfactory performance under prior-data conflict is also demonstrated. We further illustrate our method using a case study in Immunology.

Fatalism, Social Support and Self-Management Perceptions among Rural African Americans Living with Diabetes and Pre-Diabetes.

Diabetes is a public health problem and a major risk factor for cardiovascular disease, the leading cause of death in the United States. Diabetes is prevalent among underserved rural populations. The purposes of this study were to perform secondary analyses of existing clinical trial data to determine whether a diabetes health promotion and disease risk reduction intervention had an effect on diabetes fatalism, social support, and perceived diabetes self-management and to provide precise estimates of the mean levels of these variables in an understudied population. Data were collected during a cluster randomized trial implemented among African American participants (n = 146) in a rural, southern area and analyzed using a linear mixed model. The results indicated that the intervention had no significant effect on perceived diabetes management (p = 0.8), diabetes fatalism (p = 0.3), or social support (p = 0.4). However, the estimates showed that, in the population, diabetes fatalism levels were moderate (95% CI = (27.6, 31.3)), and levels of social support (CI = (4.0, 4.4)) and perceived diabetes self-management (CI = (27.7, 29.3)) were high. These findings suggest that diabetes fatalism, social support, and self-management perceptions influence diabetes self-care and rural health outcomes and should be addressed in diabetes interventions.

Sexual dimorphisms in three-dimensional masticatory muscle attachment morphometry regulates temporomandibular joint mechanics.

Temporomandibular joint (TMJ) disorders disproportionally affect females, with female to male prevalence varying from 3:1 to 8:1. Sexual dimorphisms in masticatory muscle attachment morphometry and association with craniofacial size, critical for understanding sex-differences in TMJ function, have not been reported. The objective of this study was to determine sex-specific differences in three-dimensional (3D) TMJ muscle attachment morphometry and craniofacial sizes and their impact on TMJ mechanics. Human cadaveric TMJ muscle attachment morphometry and craniofacial anthropometry (10Males; 11Females) were determined by previously developed 3D digitization and imaging-based methods. Sex-differences in muscle attachment morphometry and craniofacial anthropometry, and their correlation were determined, respectively using multivariate general linear and linear regression statistical models. Subject-specific musculoskeletal models of the mandible were developed to determine effects of sexual dimorphisms in mandibular size and TMJ muscle attachment morphometry on joint loading during static biting. There were significant sex-differences in craniofacial size (p = 0.024) and TMJ muscle attachment morphometry (p < 0.001). TMJ muscle attachment morphometry was significantly correlated with craniofacial size. TMJ contact forces estimated from biomechanical models were significantly, 23% on average (p < 0.001), greater for females compared to those for males when generating the same bite forces. There were significant linear correlations between TMJ contact force and both 3D mandibular length (R2 = 0.48, p < 0.001) and muscle force moment arm ratio (R2 = 0.68, p < 0.001). Sexual dimorphisms in masticatory muscle morphology and craniofacial sizes play critical roles in subject-specific TMJ biomechanics. Sex-specific differences in the TMJ mechanical environment should be further investigated concerning mechanical fatigue of TMJ discs associated with TMJ disorders.

Depth- and direction-dependent changes in solute transport following cross-linking with riboflavin and UVA light in ex vivo porcine cornea.

Diffusion is an important mechanism of transport for nutrients and drugs throughout the avascular corneal stroma. The purpose of this study was to investigate the depth- and direction-dependent changes in stromal transport properties and their relationship to changes in collagen structure following ultraviolet A (UVA)-riboflavin induced corneal collagen cross-linking (CXL). After cross-linking in ex vivo porcine eyes, fluorescence recovery after photobleaching (FRAP) was performed to measure fluorescein diffusion in the nasal-temporal (NT) and anterior-posterior (AP) directions at corneal depths of 100, 200, and 300 µm. Second harmonic generation (SHG) imaging was also performed at these three corneal depths to quantify fiber alignment. For additional confirmation, an electrical conductivity method was employed to quantify ion permeability in the AP direction in corneal buttons and immunohistochemistry (IHC) was used to image collagen structure. Cross-linked corneas were compared to a control treatment that received the riboflavin solution without UVA light (SHAM). The results of FRAP revealed that fluorescein diffusivity decreased from 23.39 ± 11.60 µm2/s in the SHAM group to 19.87 ± 10.10 µm2/s in the CXL group. This change was dependent on depth and direction: the decrease was more pronounced in the 100 µm depth (P = 0.0005) and AP direction (P = 0.001) when compared to the effect in deeper locations and in the NT direction, respectively. Conductivity experiments confirmed a decrease in solute transport in the AP direction (P < 0.0001). FRAP also detected diffusional anisotropy in the porcine cornea: the fluorescein diffusivity in the NT direction was higher than the diffusivity in the AP direction. This anisotropy was increased following CXL treatment. Both SHG and IHC revealed a qualitative decrease in collagen crimping following CXL. Analysis of SHG images revealed an increase in coherency in the anterior 200 µm of CXL treated corneas when compared to SHAM treated corneas (P < 0.01). In conclusion, CXL results in a decrease in stromal solute transport, and this decrease is concentrated in the most anterior region and AP direction. Solute transport in the porcine cornea is anisotropic, and an increase in anisotropy with CXL may be explained by a decrease in collagen crimping.

Acculturation and Health Beliefs: Interactions Between Host and Heritage Culture Underlie Latina/o Caregivers' Beliefs About HPV Vaccination.

This study examined the interactive effects of acculturation (host culture acquisition) and enculturation (heritage culture retention) on Latina/o caregivers' beliefs about their child completing the human papillomavirus vaccine series. Participants were 161 caregiver-child dyads from Florida. Using multiple regression, caregiver knowledge and health beliefs (perceived threat, benefits, barriers, subjective norms, and self-efficacy) about series completion were predicted from caregivers' scores on acculturation, enculturation, and their interaction, controlling for sociodemographics. Acculturation and enculturation interacted to predict knowledge, benefits, barriers, and self-efficacy. Caregivers with high acculturation scores generally supported series completion, regardless of their enculturation score. However, when acculturation was low, caregivers who retained more (vs. less) of their heritage culture were more knowledgeable and held more favorable beliefs about series completion. Findings highlight the importance of independently assessing acculturation and enculturation in Latina/o immigrant populations. Overlooking enculturation may lead to incomplete conclusions about acculturation and health.

Cardiovascular disease risk among rural residents living with diabetes and prediabetes: A cluster randomized trial.

OBJECTIVE: Diabetes is a major health problem that is closely linked with cardiovascular disease (CVD), the leading cause of death in the United States. The purpose of this analysis was to determine the effect of a culturally relevant diabetes health promotion program on diabetes knowledge and self-reported self-care behaviors. DESIGN: A cluster randomized controlled trial was conducted in 12 rural church settings. Seven churches were randomized to the intervention group and five to the control group. SAMPLE: The sample included 146 African American participants diagnosed with diabetes and prediabetes. INTERVENTION: The intervention group participants (n = 75) received the diabetes health program, and those in the control group (n = 71) group received a publicly available diabetes health brochure. MEASURES: Data were collected about diabetes knowledge, self-care activities, fatalism, and social support. RESULTS: Linear mixed model was the statistical test used to analyze group differences. Compared with the control group, the intervention group showed significant changes from pretest to posttest for diabetes knowledge and behaviors associated with diet and blood glucose testing. CONCLUSION: Health promotion programs implemented by public health nurses among rural groups at increased risk for developing CVD can facilitate understanding about strategies to reduce disease risk.

Temporomandibular Joint Condyle-Disc Morphometric Sexual Dimorphisms Independent of Skull Scaling.

PURPOSE: Approximately 2 to 4% of the US population have been estimated to seek treatment for temporomandibular symptoms, predominately women. The study purpose was to determine whether sex-specific differences in temporomandibular morphometry result from scaling with sex differences in skull size and shape or intrinsic sex-specific differences. MATERIALS AND METHODS: A total of 22 (11 male [aged 74.5 ± 9.1 years]; 11 female [aged 73.6 ± 12.8 years]) human cadaveric heads with no history of temporomandibular disc derangement underwent cone beam computed tomography and high-resolution magnetic resonance imaging scanning to determine 3-dimensional cephalometric parameters and temporomandibular morphometric outcomes. Regression models between morphometric outcomes and cephalometric parameters were developed, and intrinsic sex-specific differences in temporomandibular morphometry normalized by cephalometric parameters were determined. Subject-specific finite element (FE) models of the extreme male and extreme female conditions were developed to predict variations in articular disc stress-strain under the same joint loading. RESULTS: In some cases, sex differences in temporomandibular morphometric parameters could be explained by linear scaling with skull size and shape; however, scaling alone could not fully account for some differences between sexes, indicating intrinsic sex-specific differences. The intrinsic sex-specific differences in temporomandibular morphometry included an increased condylar medial length and mediolateral disc lengths in men and a longer anteroposterior disc length in women. Considering the extreme male and female temporomandibular morphometry observed in the present study, subject-specific FE models resulted in sex differences, with the extreme male joint having a broadly distributed stress field and peak stress of 5.28 MPa. The extreme female joint had a concentrated stress field and peak stress of 7.37 MPa. CONCLUSIONS: Intrinsic sex-specific differences independent of scaling with donor skull size were identified in temporomandibular morphometry. Understanding intrinsic sex-specific morphometric differences is critical to determining the temporomandibular biomechanics given the effect of anatomy on joint contact mechanics and stress-strain distributions and requires further study as one potential factor for the increased predisposition of women to temporomandibular disc derangement.

Predictors of Human Papillomavirus Vaccine Completion Among Low-Income Latina/o Adolescents.

PURPOSE: The purpose of this longitudinal study was to identify individual and interpersonal factors associated with human papillomavirus (HPV) vaccine series completion in a sample of low-income Latina/o adolescent girls and boys. METHODS: Caregiver-adolescent dyads (N = 161) were recruited from a rural Federally Qualified Health Center in southwest Florida when the adolescent (aged 11-17 years) received the first dose of HPV vaccine. Dyads completed a baseline assessment that measured demographic and cultural characteristics, past medical history, provider-patient communication, HPV knowledge, health beliefs about completing the series, and the adolescent's experience receiving the first dose. Using multivariable logistic regression, we identified caregiver- and adolescent-related factors associated with series completion (receipt of three doses of HPV vaccine within 1 year of initiation) as indicated in the adolescent's medical record and state immunization registry. RESULTS: Within 1 year of initiation, 57% (n = 92) completed the three-dose series. Missed opportunities for completion were observed for 20% of the sample who returned to the clinic. Caregiver-related predictors of completion included education, self-efficacy to complete the series, and knowledge of the required number of doses. Adolescent-related predictors included age, influenza vaccination within the past 2 years, having a chronic medical condition, reason for the baseline visit, and receipt of written information about HPV vaccination from a health care provider. CONCLUSIONS: Findings highlight important opportunities for improving completion of the HPV vaccine series among Latina/o adolescents. Intervention efforts should involve health care providers and parent-adolescent dyads and prioritize evidence-based strategies for reducing missed opportunities for series completion.

Influencing cardiovascular health habits in the rural, deep south: results of a cluster randomized trial.

Cardiovascular disease (CVD) is a major cause of death among people living in the United States. Populations, especially minorities, living in the rural South are disproportionately affected by CVD and have greater CVD risk, morbidity and mortality. Culturally relevant cardiovascular health programs implemented in rural community settings can potentially reduce CVD risk and facilitate health behavior modification. The purpose of this study was to examine the effects of a cardiovascular health promotion intervention on the health habits of a group of rural African American adults. The study had a cluster randomized controlled trial design involving 12 rural churches that served as statistical clusters. From the churches (n = 6) randomized to the intervention group, 115 participants were enrolled, received the 6-week health program and completed pretest-posttest measures. The 114 participants from the control group churches (n = 6) did not receive the health program and completed the same pretest-posttest measures. The linear mixed model was used to compare group differences from pretest to posttest. The educational health intervention positively influenced select dietary and confidence factors that may contribute toward CVD risk reduction.

Improving Cardiovascular Disease Knowledge among Rural Participants: The Results of a Cluster Randomized Trial.

Cardiovascular disease (CVD) is a major cause of death and disability, especially among people living in the rural, southern United States. Rural African Americans are often diagnosed with CVD earlier in life, and they bear a disproportionate burden of CVD risk factors, morbidity, and mortality. Health equity among historically underserved, rural populations can potentially be attained through culturally relevant interventions that teach people skills to stay well and avoid CVD-related risk and diagnoses. The purpose of this secondary analysis was to determine the effect of an evidence-based intervention on cardiovascular health knowledge and the stages of change toward the action and maintenance phases. The pre-test-post-test data were obtained during a cluster randomized trial involving twelve rural churches that were randomized to intervention (n = 6) and control (n = 6) groups. Participants (n = 115) in the intervention group received a cardiovascular health intervention, and those (n = 114) in the control group could receive the intervention following the study’s completion. The data were analyzed using a linear mixed model to compare group differences from pre-test to post-test. The cardiovascular health promotion intervention significantly improved cardiovascular health knowledge and was associated with advancements in the stages of change toward the action and maintenance phases.

Promoting Heart Health Among Rural African Americans.

BACKGROUND: Cardiovascular disease is a major cause of death for people living in the United States. African Americans bear a disproportionate burden of cardiovascular disease. Interventions designed to target multiple risk factors may facilitate elimination of cardiovascular disease health disparities. OBJECTIVE: The purpose of this study was to evaluate a culturally relevant cardiovascular health promotion intervention that could potentially reduce cardiovascular disease risk among a group of rural African American adults by improving intentions, attitudes, norms, and self-efficacy to increase produce consumption, reduce dietary saturated fat intake, and increase exercise. METHODS: A cluster randomized controlled trial design was used to evaluate the effect of the "With Every Heartbeat Is Life" cardiovascular health promotion program among rural African Americans. The African American congregants of 12 rural churches located in northern Florida were randomly assigned to either an intervention group that received a culturally relevant cardiovascular health promotion intervention or a control group. Data analysis using linear mixed model was performed to compare group differences from pretest to posttest. RESULTS: The cardiovascular health promotion intervention had a positive influence on the intentions, attitudes, norms, and self-efficacy of rural African Americans to increase produce consumption and reduce dietary saturated fat. The intervention also enhanced participants' attitudes and self-efficacy regarding exercise. CONCLUSION: The culturally relevant cardiovascular health promotion program presented to cluster groups of rural African American participants had positive influences on psychosocial variables associated with engaging in cardiovascular health recommendations. Nurse-led interventions in community settings can potentially reduce cardiovascular disease risk.

Quantifying Baseline Fixed Charge Density in Healthy Human Cartilage Endplate: A Two-point Electrical Conductivity Method.

STUDY DESIGN: Regional measurements of fixed charge densities (FCDs) of healthy human cartilage endplate (CEP) using a two-point electrical conductivity approach. OBJECTIVE: The aim of this study was to determine the FCDs at four different regions (central, lateral, anterior, and posterior) of human CEP, and correlate the FCDs with tissue biochemical composition. SUMMARY OF BACKGROUND DATA: The CEP, a thin layer of hyaline cartilage on the cranial and caudal surfaces of the intervertebral disc, plays an irreplaceable role in maintaining the unique physiological mechano-electrochemical environment inside the disc. FCD, arising from the carboxyl and sulfate groups of the glycosaminoglycans (GAG) in the extracellular matrix of the disc, is a key regulator of the disc ionic and osmotic environment through physicochemical and electrokinetic effects. Although FCDs in the annulus fibrosus (AF) and nucleus pulposus (NP) have been reported, quantitative baseline FCD in healthy human CEP has not been reported. METHODS: CEP specimens were regionally isolated from human lumbar spines. FCD and ion diffusivity were concurrently investigated using a two-point electrical conductivity method. Biochemical assays were used to quantify regional GAG and water content. RESULTS: FCD in healthy human CEP was region-dependent, with FCD lowest in the lateral region (P = 0.044). Cross-region FCD was 30% to 60% smaller than FCD in NP, but similar to the AF and articular cartilage (AC). CEP FCD (average: 0.12 ±â€Š0.03 mEq/g wet tissue) was correlated with GAG content (average: 31.24 ±â€Š5.06 µg/mg wet tissue) (P = 0.005). In addition, the cross-region ion diffusivity in healthy CEP (2.97 ±â€Š1.00 × 10 cm/s) was much smaller than the AF and NP. CONCLUSION: Healthy human CEP acts as a biomechanical interface, distributing loads between the bony vertebral body and soft disc tissues and as a gateway impeding rapid solute diffusion through the disc. LEVEL OF EVIDENCE: N/A.

Tensile biomechanical properties of human temporomandibular joint disc: Effects of direction, region and sex.

Approximately 30% of temporomandibular joint (TMJ) disorders include degenerative changes to the articular disc, with sex-specific differences in prevalence and severity. Limited tensile biomechanical properties of human TMJ discs have been reported. Stress relaxation tests were conducted on TMJ disc specimens harvested bilaterally from six males and six females (68.9±7.9 years), with step-strain increments of 5%, 10%, 15%, 20% and 30%, at 1% strain-per-second. Stress versus strain plots were constructed, and Young׳s Modulus, Instantaneous Modulus and Relaxed Modulus were determined. The effects of direction, region, and sex were examined. Regional effects were significant (p<0.01) for Young׳s Modulus and Instantaneous Modulus. Anteroposteriorly, the central region was significantly stiffer than medial and lateral regions. Mediolaterally, the posterior region was significantly stiffer than central and anterior regions. In the central region, anteroposteriorly directed specimens were significantly stiffer compared to mediolateral specimens (p<0.04). TMJ disc stiffness, indicated by Young׳s Modulus and Instantaneous Modulus, was higher in directions corresponding to high fiber alignment. Additionally, human TMJ discs were stiffer for females compared to males, with higher Young׳s Modulus and Instantaneous Modulus, and female TMJ discs relaxed less. However, sex effects were not statistically significant. Using second-harmonic generation microscopy, regional collagen fiber organization was identified as a potentially significant factor in determining the biomechanical properties for any combination of direction and region. These findings establish structure-function relationships between collagen fiber direction and organization with biomechanical response to tensile loading, and may provide insights into the prevalence of TMJ disorders among women.

Region and strain-dependent diffusivities of glucose and lactate in healthy human cartilage endplate.

The cartilage endplate (CEP) is implicated as the main pathway of nutrient supply to the healthy human intervertebral disc (IVD). In this study, the diffusivities of nutrient/metabolite solutes in healthy CEP were assessed, and further correlated with tissue biochemical composition and structure. The CEPs from non-degenerated human IVD were divided into four regions: central, lateral, anterior, and posterior. The diffusivities of glucose and lactate were measured with a custom diffusion cell apparatus under 0%, 10%, and 20% compressive strains. Biochemical assays were conducted to quantify the water and glycosaminoglycan (GAG) contents. The Safranin-O and Ehrlich׳s hematoxylin and eosin staining and scanning electron microscopy (SEM) were performed to reveal the tissue structure of the CEP. Average diffusivities of glucose and lactate in healthy CEP were 2.68±0.93×10-7cm2/s and 4.52±1.47×10-7cm2/s, respectively. Solute diffusivities were region-dependent (p<0.0001) with the highest values in the central region, and mechanical strains impeded solute diffusion in the CEP (p<0.0001). The solute diffusivities were significantly correlated with the tissue porosities (glucose: p<0.0001, r=0.581; lactate: p<0.0001, r=0.534). Histological and SEM studies further revealed that the collagen fibers in healthy CEP are more compacted than those in the nucleus pulposus (NP) and annulus fibrosus (AF) and show no clear orientation. Compared to human AF and NP, much smaller solute diffusivities in human CEP suggested that it acts as a gateway for solute diffusion through the disc, maintaining the balance of nutritional environment in healthy human disc under mechanical loading and preventing the progression of disc degeneration.

A Bayesian mixture model for missing data in marine mammal growth analysis.

Much of what is known about bottle nose dolphin (Tursiops truncatus) anatomy and physiology is based on necropsies from stranding events. Measurements of total body length, total body mass, and age are used to estimate growth. It is more feasible to retrieve and transport smaller animals for total body mass measurement than larger animals, introducing a systematic bias in sampling. Adverse weather events, volunteer availability, and other unforeseen circumstances also contribute to incomplete measurement. We have developed a Bayesian mixture model to describe growth in detected stranded animals using data from both those that are fully measured and those not fully measured. Our approach uses a shared random effect to link the missingness mechanism (i.e. full/partial measurement) to distinct growth curves in the fully and partially measured populations, thereby enabling drawing of strength for estimation. We use simulation to compare our model to complete case analysis and two common multiple imputation methods according to model mean square error. Results indicate that our mixture model provides better fit both when the two populations are present and when they are not. The feasibility and utility of our new method is demonstrated by application to South Carolina strandings data.

The region-dependent biomechanical and biochemical properties of bovine cartilaginous endplate.

Regional biomechanical and biochemical properties of bovine cartilaginous endplate (CEP) and its role in disc mechanics and nutrition were determined. The equilibrium aggregate modulus and hydraulic permeability between the central and lateral regions were examined by confined compression testing. Biochemical assays were conducted to quantify the amount of water, collagen, and glycosaminoglycan (GAG). The equilibrium aggregate modulus of the CEP in the central region (0.23 ± 0.15 MPa) was significantly lower than for the lateral region (0.83 ± 0. 26 MPa). No significant regional difference was found for the permeability of the CEP (central region: 0.13 ± 0.07×10(-15)m(4)/Ns and lateral region: 0.09 ± 0.03 × 10(-15)m(4)/Ns). CEPs were an average of 75.6% water by wet weight, 41.1% collagen, and 20.4% GAG by dry weight in the central region, as well as an average of 70.2% water by wet weight, 73.8% collagen, and 11.7% GAG by dry weight in the lateral region. Regional differences observed for the equilibrium aggregate modulus were likely due to the regional variation in biochemical composition. The lateral bovine endplate is much stiffer and may share a greater portion of the load. Compared with the nucleus pulposus (NP) and annulus fibrosus (AF), a smaller hydraulic permeability was found for the CEP in both the central and lateral regions, which could be due to its lower water content and higher collagen content. Our results suggest that the CEP may block rapid fluid exchange and solute convection, allow pressurization of the interstitial fluid, and play a significant role in nutrient supply in response to loading.