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Rotation of the cervical spine beyond its normal range of motion is a leading cause of fall-related spinal cord injuries (SCIs) in older adults. This rotation is constrained, in part, by the spinal ligaments. The experimentally measured properties of these ligaments are tabulated in literature, including sex-specific properties; however, their influence on the rotation kinematics of the cervical spine has not been compared. We examined how different mechanical properties of spinal ligaments, including sex-specific properties, affected the rotational kinematics of the cervical spine using finite element analysis (FEA). Ligament properties most influenced the rotation of the lower cervical spine, with increased ligament stiffness reducing rotation. Ligament deformation remained mostly in the toe region of their force-displacement curves, emphasizing the need to incorporate non-linear ligament behavior in FEA. Predictions made using one set of experimental properties (Property 1) better-matched experimental kinematic data. Using sex-specific properties had a moderate effect (6% in extension, –3% in flexion) on rotation, with a greater impact on extension. Ligament properties also affected the segmental distribution of rotation, causing a variability of 3–21% at different levels. We emphasized the need to incorporate tailored approaches to FEA to obtain clinically relevant results when modeling flexion/extension rotation.

Age-related alterations of gene expression of transforming growth factor β1 (TGF-β1) and its receptors (TβRs) in tissues derived from rat intervertebral discs were assessed together with TGF-β1-dependent proteoglycan synthesis by the cultured disc cells. Disc tissues and cells were individually harvested from two sites of the coccygeal vertebrae, namely the nucleus pulposus (NP) and annulus fibrosus (AF), which are major distinct components of the intervertebral discs. Semi-quantitative RT-PCR analysis indicated that the level of gene expression of TGF-β1/TGF-β1 receptor type I (TβR-I) of NP decreased with age. In AF, the level of TGF-β1/TβRs gene expression did not apparently differ with age. Consistent with the RT-PCR results, stimulation of proteoglycan synthesis by TGF-β1 in NP cells decreased with age. Proteoglycan synthesis by AF cells was also stimulated by TGF-β1. However, levels of this stimulation by AF cells were identical. The present findings indicate that the genetic expression of TGF-β1/TβR-I and TGF-β1-dependent proteoglycan synthesis decreased with age in NP cells, and further suggest that a loss of proteoglycan synthesis with age in the intervertebral disc is at least in part due to the transcriptional down regulation of TGF-β1/TβR-I and decreased synthetic ability of proteoglycans in response to TGF-β1 by NP cells.

The effect of aging on long bone mechanical properties and bone formative capacity was characterized in the male Fisher 344 rat. The femurs of rats from three age groups (4 mo., 12 mo. and 28 mo.) were tested in three-point bending to determine their structural properties. The apparent material properties were then calculated by adjusting for bone geometry. Bone formation was assessed by dynamic histomorphometry of both cortical and cancellous bone as well as by Northern blot analysis for the expression of the osteoblast phenotypic proteins osteopontin (OP), osteocalcin (OC), type I collagen (COL) and alkaline phosphatase (AP). Aging resulted in a decline in the apparent material properties that was associated with a compensatory alteration of bone geometry that preserved structural strength and stiffness. Histomorphometric analysis revealed significant age-related decreases in cancellous bone volume, trabecular number and increased trabecular separation suggesting the existence of senile osteopenia in the proximal tibia of the male Fisher 344 rat. A significant decline in bone formation rate (BFR), but not mineral apposition rate, suggests that a reduction in osteoblast number, but not osteoblast activity, contributes to age-related bone loss. The decline in BFR with aging was reflected in a decreased mRNA expression for OP, OC and COL but not AP. Further, the pattern of mRNA expression was consistent with reduced osteoblast differentiation with aging. The present study indicates the age-related decline in material properties of long bones is paralleled by a decrease in osteogenesis.

The purposes of this study were to investigate the activation of neck muscles during movement of the head from the neutral position to the maximum points and back to the neutral position. The experiment was designed to compare between groups. There were in total 26 subjects: 11 in the young group (mean age 24.3 years old) and 15 in the middle-age group (mean age 55.9 years old) were recruited. The active ROM, velocity, and surface EMG activities of the left and right sternocleidomastoid (SCM) muscles were recorded during repetitive cervical movements in the six directions of flexion/extension, right/left rotation and side-bending. The data were evaluated with repeated-measures analysis of variance (ANOVA). The active ROM and maximum force in both flexion and extension were significantly lower for the middle-age group than for the young group. However, the integrated EMG values for the left and right SCM muscles during movement of the head to and from the maximum points of the ROM in three cardinal planes were significantly greater in the middle-age group than in the young group. Whether these over-activation of SCM is related to degeneration of the cervical spines requires further investigation.

Purpose: The aim of this study is to investigate deterioration in mechanical integrity of the collagen network of bovine bone formed by non-enzymatic glycation (NEG), a process that mimics aging by microindentation technique. Methods: Young and old bovine cortical bone specimens were rested in solutions for four weeks for the process of NEG and were grouped as ribosylated and non-ribosylated. A series of indentations were made on bone specimens weekly for each of 3-masses of 50 g, 100 g and 200 g for 10 s to detect the effect of indentation load and for each of five durations of 5 s, 10 s, 20 s, 30 s for 100 g to study the effect of indentation duration. The applied load was increased to 300 g, 500 g, 1000 g and 2000 g for 10 s to be able to make microcracks. Specimens were tested in the wet and dry state to study the effects of hydration on microhardness measurement. Results: Loads of 50 g, 100 g and 200 g for 10 s were able to differ ribosylated bone from non-ribosylated bone for the young and old bovine bones. Microhardness values increased with increasing incubation period. Microhardness of dry specimens were found to be statistically higher than that of wet specimens. Presence of extrinsic toughening mechanisms including crack bridging due to uncracked ligaments and collagen fibers were directly observed by scanning electron microscope (SEM). Ribosylated bone was found to have lower number of collagen bridging compared to non-ribosylated bovine bone. Conclusion: Microhardness test by these are able to discriminate non-modified collagen structure from modified collagen. On the other hand, it is found that microindentation was not able to discriminate the degree of NEG.

Mandibular symphyseal distraction osteogenesis is a clinical procedure utilized in orthodontics for solving problems of dental overcrowding on the mandibular arch. A critical issue is to evaluate the optimal duration of the latency period between the osteotomy and the first aperture of distraction device. In fact, the latency period should change with the patient's age. To this end, a computational mechanobiological model has been developed in order to find optimal durations of latency period for young, adult, and elder patients. The model is implemented in a finite element framework simulating the process of tissue differentiation in the bone callus formed after osteotomy. The biophysical stimulus regulating the tissue differentiation process is hypothesized to be a function of the octahedral shear strain and interstitial fluid flow velocity. The resulting spatial distribution of stiffness properties in the callus region is analyzed in order to assess the risk of premature bone union of osteotomy edges. The three-dimensional (3D) finite element model (FEM) of human mandible is reconstructed from computed tomography (CT) scans and also includes a tooth-borne device. Under unilateral occlusion, the mandible is submitted to full mastication loading or to mastication forces reduced by 70%. The results show that optimal durations of the latency period for preventing premature bone union are about 5–6 days for the young patient, 7–8 days for the adult patient, and 9–10 days for the elder patient. These durations seem rather insensitive to the magnitude of mastication forces. Finally, distraction force values predicted by the present mechanobiological model are in good agreement with data reported in the literature.

A forward trunk lean sometimes occurs to compensate for quadriceps muscle weakness. Since muscle weakness in the lower extremities is commonly observed in the elderly, quadriceps weakness may trigger age-related postural change. The objective of this study was to ascertain the association between forward trunk lean during walking and musculoskeletal strength in females aged between 46 and 79 years. Musculoskeletal functions (range of joint motion, degree of kyphosis, muscle strength) and joint moments during walking were measured for 13 females. Subjects who showed greater joint moments during walking tended to lean more. Moderate association was seen between mean trunk angle during walking and knee extension moment (r = 0.535, p = 0.060). There was no statistically significant correlation between the strength of the quadriceps muscle and the mean trunk angle in walking subjects (r = 0.095, p = 0.758). These observations suggested that muscle weakness in the quadriceps is largely independent of leaning of the trunk for this sample of subjects. Other factors may change the posture to a stoop, such as severe thoracic kyphosis, poor balance control, or fear of falling.

Aim of this paper is to develop an automated system for the classification and characterization of carotid wall status and to develop a robust system based on local texture descriptors. A database of 200 longitudinal ultrasound images of carotid artery is used. One-hundred images with Intima-Media Thickness (IMT) value higher than 0.8mm are considered as high risk. Six different rectangular pixel neighborhoods were considered: four areas centered on the selected element, with sizes $7\times 15$, $15\times 7$, $7\times 3$, and $3\times 7$ pixels, and two noncentered areas with sizes $7\times 3$ pixels upwards and downwards. We have extracted various texture descriptors (31 based on the co-occurrence gray level matrix, 13 based on the spatial gray level dependence matrix, and 20 based on the gray level run length matrix (GLRLM) from neighborhood. We have used Quick Reduct Algorithm to select 12 most discriminant features from extracted 211 features. Each pixel is then assigned to the vessel lumen, to the intima-media complex, or to the adventitia by using an integrated system of three feed-forward neural networks. The boundaries between the three regions are used to estimate the IMT value. The texture features associated with GLRLM are found to be clinically most significant. We have obtained an overall classification accuracy of 79.5%, sensitivity of 87%, and specificity of 72%. We observed a unique classification pattern between low risk and high risk images: in the latter ones, a considerable number of pixels of the intima–media complex ($31.2\%\pm 14.4\%$) was classified as belonging to the adventitia. This percentage is statistically higher than that of low risk images ($18.2\%\pm 11.8\%$; $p<0.001$). Locally extracted and pixel-based descriptors are able to capture the inner characteristics of the carotid wall. The presence of misclassified pixels in the intima–media complex is associated to higher cardiovascular risk.

Accelerometry is now a well-established method for monitoring human body movements, and is increasingly being used for gait analysis under nonlaboratory conditions because of its low-cost and unobtrusive nature. In order to encourage its use in the clinical setting such as for assessing functional declines due to aging or disease, an extensive database of healthy gait is needed. This paper presents reference data for 245 normal Japanese adults (126 men and 119 women aged 40–86 years) obtained from indoor walk tests by using a trunk-mounted acceleration sensor. Seven gait parameters were extracted from the acceleration data measured at fast, normal, and slow gait for 5m and 10m walkways. The effects of age on cadence, speed, and step length were consistent with those observed in previous studies. Scaled speed and acceleration were closely correlated with each other, and exhibited similar gender- and age-associated behavior, indicating that they could be used interchangeably in gait analysis. A comparison of these parameters between different walkways revealed a significant effect of walkway length. Our parameters may provide a useful reference database for the clinical analysis of not only healthy gait but also impaired gait for the 10m walkway as well as for the shorter 5m walkway.

Proprioception while standing is important for the balance control, but the proprioception has not been investigated in the unconstrained standing conditions. The purpose of this study was to investigate the effects of age and gender on the thresholds of perception and muscle response in response to the support surface rotation. The experiment was designed so that the thresholds depend mainly on the proprioception, i.e., quasistatic condition (0.2^∘/s rotation of the platform) with eyes closed. Fifty-two healthy subjects (half young and half elderly) participated in this study. A platform was developed which can be rotated in four directions. Perception threshold angle was registered from subjects’ pressing a button. Muscle response threshold angle was determined as the earlier onset of EMG in lower limb muscles. Two standing conditions (feet together and natural stance) were tested. Repeated-measures ANOVA showed that both thresholds increased with age. Post hoc tests revealed (1) that the perception threshold was greater for women than men in the elderly and (2) both thresholds of the elderly were greater for the feet-together stance than natural stance. Inferior perception sensitivity of platform rotation in elderly women may be associated with inferior performance in cortical postural control and greater fall ratio compared to elderly men, which suggests the need of proprioception trainings.

Purpose: This study investigated the effects of grinding, polishing and aging on physical properties using self-made zirconia and commonly used ultraclear ceramic materials and glass ceramics in the clinic. Methods: The samples were prepared using 3% yttria-stabilized zirconia ceramic (3Y-TZP) powder containing alumina, which was granulated by ball milling. Then, it is pressed into a circular sheet together with Upcera and Wieland materials. The glass ceramic materials are molded. Finally, all materials were subjected to hydrothermal aging. Results: The self-made zirconia had better permeability than the commonly used ultratransparent ceramic materials and glass ceramics. The polishing after grinding improved the surface morphology and roughness of tooth transparent ceramic materials; Polishing after grinding improved the aging resistance of zirconia materials. The bending strength of self-made samples was less than that of two kinds of ceramics commonly used in clinic, but greater than that of glass ceramics. Aging improved the bending strength of zirconia. Conclusions: The self-made zirconia had better permeability than ultratransparent all-ceramic materials and glass ceramics, and its bending strength was better than that of glass ceramics. Grinding and polishing could improve not only the surface morphology and roughness but also the strength and aging resistance.

The biomechanical properties of arteries play a crucial role in governing the overall hemodynamic function of the circulatory system. The nonuniformity in elastic and geometric structures of the blood vessels adds on to the complexity in dealing with pulsatile natures of blood pressure and flow. Short-term or chronic changes in arterial wall properties subjecting to distending pressure and perfusing flow make quantification of arterial compliance especially important in its use in describing the overall arterial function. This paper will first review the methodologies of determining arterial compliance in systole, in diastole and varying throughout the entire cardiac cycle. The stroke volume-to-pulse pressure method, the linear Windkessel model-based approaches and the nonlinear pressure-dependent compliance model method to derive arterial compliance are presented. The clinical relevance and implications are highlighted accordingly, in particular, the consequences of hypertension and aging.