Biomechanical Paradigms Research Articles

Clinical impairments and their associations to sagittal plane motion in children with cerebral palsy: a statistical parametric mapping study

Synthetic grafts are often satisfactory employed in cardiac and vascular surgery, including expanded poly(ethylene terephthalate) or expanded poly(tetrafluoroethylene). However, accumulating evidences suggest the emergence of worrisome issues concerning the long-term fate of prosthetic grafts as large vessel replacement. Disadvantages related to the use of synthetic grafts can be traced in their inability of mimicking the elasto-mechanical characteristics of the native vascular tissue, local suture overstress leading to several prosthesis-related complications and retrograde deleterious effects on valve competence, cardiac function and perfusion. Motivated by this, in the present work it is analyzed – by means of both elemental biomechanical paradigms and more accurate in silico Finite Element simulations – the physical interaction among aorta, autograft and widely adopted synthetic (Dacron) prostheses utilized in transposition of pulmonary artery, highlighting the crucial role played by somehow unexpected stress fields kindled in the vessel walls and around suture regions, which could be traced as prodromal to the triggering of anomalous remodelling processes and alterations of needed surgical outcomes. Theoretical results are finally compared with histological and surgical data related to a significant experimental animal campaign conducted by performing pulmonary artery transpositions in 30 two-month old growing lambs, followed up during growth for six months. The in vivo observations demonstrate the effectiveness of the proposed biomechanical hypothesis and open the way for possible engineering-guided strategies to support and optimize surgical procedures.

A Biomechanical Paradigm Shift: Part I: Transforming Lower Extremity Biomechanics Terminology, Nomenclature and Science as an Upgrade to “STJ Neutral” and “Normal” Biomechanics

Biomechanical Obstructions to Biomechanical Research and Practice need to be enshrined as Iconic Precursors and Replaced with a Paradigm Shift in order to allow Lower Extremity Biomechanics to Acculturate Onwards and Upwards as an Evidence Based Science.

Biomechanical paradigm and interpretation of female pelvic floor conditions before a treatment.

BackgroundFurther progress in restoring a woman’s health may be possible if a patient with a damaged pelvic floor could undergo medical imaging and biomechanical diagnostic tests. The results of such tests could contribute to the analysis of multiple treatment options and suggest the optimal one for that patient.AimTo develop a new approach for the biomechanical characterization of vaginal conditions, muscles, and connective tissues in the female pelvic floor.MethodsVaginal tactile imaging (VTI) allows biomechanical assessment of the soft tissue along the entire length of the anterior, posterior, and lateral vaginal walls at rest, with manually applied deflection pressures and with muscle contraction, muscle relaxation, and Valsalva maneuver. VTI allows a large body of measurements to evaluate individual variations in tissue elasticity, support defects, as well as pelvic muscle function. Presuming that 1) the female pelvic floor organs are suspended by ligaments against which muscles contract to open or close the outlets and 2) damaged ligaments weaken the support and may reduce the force of muscle contraction, we made an attempt to characterize multiple pelvic floor structures from VTI data.ResultsAll of the 138 women enrolled in the study were successfully examined with the VTI. The study subjects have had normal pelvic support or pelvic organ prolapse (stages I–IV). The average age of this group of subjects was 60±15 years. We transposed a set of 31 VTI parameters into a quantitative characterization of pelvic muscles and ligamentous structures. Interpretation of the acquired VTI data for normal pelvic floor support and prolapse conditions is proposed based on biomechanical assessment of the functional anatomy.ConclusionVaginal tactile imaging allows biomechanical characterization of female pelvic floor structures and tissues in vivo, which may help to optimize treatment of the diseased conditions such as prolapse, incontinence, atrophy, and some forms of pelvic pain.

Dal gesto alla parola. Riflessioni intorno alla "postura" dell'educare

The body is the focal point of all knowledge. Knowledge is always a knowledge of the body. The educational relationship is a relationship between bodies. Words have a body, the writing has a body, the tongue is a motor act. Despite all this, the educating body size is still not thematized by pedagogical reflection. Referring to the perspective inaugurated by the pedagogy of the body, the essay aims to reflect on the constituent aspects of a bodily vision of educational processes, developing its own reflection on the concept of posture, to extend its meaning, and not just metaphorically, way beyond the narrow semantic spaces which the biomechanical paradigm has long relegated. A reflection that weaves knowledge and interdisciplinary awareness, to try to unravel as in gesture (of touch, of seeing, of listening, of voice) lies much more than educating the sense of what we tend to grant him reductively.

Compliance mismatch and compressive wall stresses drive anomalous remodelling of pulmonary trunks reinforced with Dacron grafts

Synthetic grafts are often satisfactory employed in cardiac and vascular surgery, including expanded poly(ethylene terephthalate) or expanded poly(tetrafluoroethylene). However, accumulating evidences suggest the emergence of worrisome issues concerning the long-term fate of prosthetic grafts as large vessel replacement. Disadvantages related to the use of synthetic grafts can be traced in their inability of mimicking the elasto-mechanical characteristics of the native vascular tissue, local suture overstress leading to several prosthesis-related complications and retrograde deleterious effects on valve competence, cardiac function and perfusion. Motivated by this, in the present work it is analyzed – by means of both elemental biomechanical paradigms and more accurate in silico Finite Element simulations – the physical interaction among aorta, autograft and widely adopted synthetic (Dacron) prostheses utilized in transposition of pulmonary artery, highlighting the crucial role played by somehow unexpected stress fields kindled in the vessel walls and around suture regions, which could be traced as prodromal to the triggering of anomalous remodelling processes and alterations of needed surgical outcomes. Theoretical results are finally compared with histological and surgical data related to a significant experimental animal campaign conducted by performing pulmonary artery transpositions in 30 two-month old growing lambs, followed up during growth for six months. The in vivo observations demonstrate the effectiveness of the proposed biomechanical hypothesis and open the way for possible engineering-guided strategies to support and optimize surgical procedures.

A biomechanical paradigm for axonal insult within the optic nerve head in aging and glaucoma

This article is dedicated to Rosario Hernandez for her warm support of my own work and her genuine enthusiasm for the work of her colleagues throughout her career. I first met Rosario as a research fellow in Harry Quigley’s laboratory between 1991 and 1993. Along with Harry, John Morrison, Elaine Johnson, Abe Clark, Colm O’Brien and many others, Rosario’s work has provided lamina cribrosa astrocyte cellular mechanisms that are biomechanically plausible and in so doing provided credibility to early notions of the optic nerve head (ONH) as a biomechanical structure. We owe a large intellectual debt to Rosario for her dogged persistence in the characterization of the ONH astrocyte and lamina cribrosacyte in age and disease. Two questions run through her work and remain of central importance today. First, how do astrocytes respond to and alter the biomechanical environment of the ONH and the physiologic stresses created therein? Second, how do these physiologic demands on the astrocyte influence their ability to deliver the support to retinal ganglion cell axon transport and flow against the translaminar pressure gradient? The purpose of this article is to summarize what is known about the biomechanical determinants of retinal ganglion cell axon physiology within the ONH in the optic neuropathy of aging and Glaucoma. My goal is to provide a biomechanical framework for this discussion. This framework assumes that the ONH astrocytes and glia fundamentally support and influence both the lamina cribrosa extracellular matrix and retinal ganglion cell axon physiology. Rosario Hernandez was one of the first investigators to recognize the implications of this unique circumstance. Many of the ideas contained herein have been initially presented within or derived from her work (Hernandez, M.R., 2000. The optic nerve head in glaucoma: role of astrocytes in tissue remodeling. Prog Retin Eye Res. 19, 297–321.; Hernandez, M.R., Pena, J.D., 1997. The optic nerve head in glaucomatous optic neuropathy. Arch Ophthalmol. 115, 389–395.).

Glaucomatous cupping of the lamina cribrosa: A review of the evidence for active progressive remodeling as a mechanism

The purpose of this review is to examine the literature in an attempt to elucidate a biomechanical basis for glaucomatous cupping. In particular, this work focuses on the role of biomechanics in driving connective tissue remodeling in the progression of laminar morphology from a normal state to that of an excavated glaucomatous state. While there are multiple contributing factors to the pathogenesis of glaucoma, we focus on laminar extracellular matrix (ECM) remodeling in glaucoma and the feedback mechanisms and signals that may guide progressive laminar cupping. We review the literature on the potential mechanisms of glaucomatous changes in the laminar ECM at the anatomic, structural, cellular and subcellular levels in the context of the biomechanical paradigm of glaucomatous onset and progression. Several conclusions can be drawn from this review. First, extensive remodeling of the lamina cribrosa ECM occurs in primary open angle glaucoma. Second, there is surprisingly little evidence to support acute mechanical damage to the lamina as the principal mechanism of cupping. Third, ONH astrocytes and lamina cribrosa cells can sense their mechanical environment and respond to mechanical stimuli by remodeling the ECM. Fourth, there is evidence suggesting that chronic remodeling of the lamina results in a progressive posterior migration of the laminar insertion into the canal wall, which eventually results in the posterior lamina inserting into the pia mater. Finally, modeling studies suggest that laminar remodeling may be a biomechanical feedback mechanism through which cells modify their environment in an attempt to return to a homeostatic mechanical environment. It is plausible that biomechanics-driven connective tissue remodeling is a mechanism in the progression of laminar morphology from a normal state to that of a cupped, excavated glaucomatous state.

Vascular disease is associated with facet joint osteoarthritis

Epidemiologic studies have demonstrated associations between vascular disease and spinal degeneration. We sought to examine whether vascular disease was associated with lumbar spine facet joint osteoarthritis (FJ OA) in a community-based population. 441 participants from the Framingham Heart Study multi-detector computed tomography (MDCT) Study were included in this ancillary study. We used a quantitative summary measure of abdominal aortic calcification (AAC) from the parent study as a marker for vascular disease. AAC was categorized into tertiles of 'no' (reference), 'low', and 'high' calcification. FJ OA was evaluated on computerised tomography (CT) scans using a four-grade scale. For analytic purposes, FJ OA was dichotomized as moderate FJ OA of at least one joint from L2-S1 vs no moderate FJ OA. We examined the association of AAC and FJ OA using logistic regression before and after adjusting for age, sex and body mass index (BMI). Furthermore, we examined the independent effect of AAC on FJ OA after including the known cardiovascular risk factors; diabetes, hypertension, hypercholesterolemia, and smoking. Low AAC (OR 3.84 [2.33-6.34]; P<or=0.0001) and high AAC (9.84 [5.29-18.3]; <or=0.0001) were strongly associated with FJ OA, compared with the reference group. After adjusting for age, sex, and BMI, the association with FJ OA was attenuated for both low AAC (1.81 [1.01-3.27]; P=0.05) and high AAC (2.63 [0.99-5.23]; P=0.05). BMI and age were independently and significantly associated with FJ OA. The addition of cardiovascular risk factors to the model did not substantially change parameter estimates for either AAC tertile. AACs were associated with FJ OA in this community-based population, when adjusting for epidemiologic factors associated with spinal degeneration, and cardiovascular risk factors. Potentially modifiable risk factors for facet degeneration unrelated to conventional biomechanical paradigms may exist. This study is limited by cross-sectional design; longitudinal studies are needed.

Cytochromes CYP1A1 and CYP1B1: new pieces in the puzzle to understand the biomechanical paradigm of atherosclerosis

Atherosclerosis is epidemiologically linked and causally related to the presence of ‘risk factors’. Despite their diversity, major risk factors for cardiovascular disease such as hypercholesterolaemia, diabetes, hypertension, physical inactivity, obesity, and tobacco smoking share a common ‘systemic’ mechanism of action, i.e. they act on the entire inner surface of the arterial vascular tree. The cellular and molecular effects of such systemic risk factors, acting through biohumoral mediators, can account for the greater or lesser propensity of different individuals to atherosclerotic vascular disease (the ‘biohumoral’ paradigm).1,2 Atherosclerosis is, however, focal and discrete in location and has clear preferences for certain sites of the vasculature, such as branching points, bifurcations, or the convex side of curved arteries. In addition, some arteries are more prone to atherosclerosis than others (e.g. the carotid artery vs. the subclavian artery, epicardial coronary arteries vs. intramyocardial arteries), and there are preferential locations even within extremely close areas in the same artery, such as in the region of the carotid bifurcation. The ‘site-specific’ location of the process is a golden opportunity, and perhaps a ‘Holy Grail’ for atherosclerosis research. It is usually explained by the action of particular types of shear stress imposed on the arterial wall by flow regimens of the circulating blood.3 In recent years, much progress has been gained in understanding how shear stress is transduced within the artery wall in order to protect from or promote atherogenesis (the ‘biomechanical’ paradigm). Crucial to this understanding is the identification of endothelial responses to shear stress, by which endothelial cells can sense and integrate haemodynamic stimuli and react to them. The arterial endothelium is exposed to three main varieties of haemodynamic forces:4,5 (a) the pressure generated by hydrostatic forces towards the vessel wall; (b) circumferential tensions or stress, resulting from … *Corresponding author. Tel: +39 0871 415 12; fax: +39 0871 402 817. E-mail : rdecater{at}unich.it

4SY09-1 Biochemical and biomechanical paradigms of endothelial activation in health and disease

4SY09-1 Biochemical and biomechanical paradigms of endothelial activation in health and disease

Spastic hypertonia: mechanisms and measurement.

Spastic hypertonia has been defined as a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes (muscle tone) with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex, as one component of the upper motor neuron syndrome. Heightened muscle tone may be the result of changes intrinsic to the muscle or to altered reflex properties. Increased motoneuronal excitability and/or enhanced stretch-evoked synaptic excitation of motoneurons are mechanisms that might enhance stretch reflexes. Two distinct parameters may be altered in the pathologic stretch reflex--the "set point," or angular threshold of the stretch reflex, and the reflex "gain," or the amount of force required to extend the limb in proportion to the increasing joint angle. Earlier studies fail to dissociate the contributions of reflex threshold and reflex gain. Recent investigations suggest that spastic hypertonia may be the result of a decrease in stretch reflex threshold without significant increase in reflex gain, as was previously believed. Various clinical scales, biomechanical paradigms, pendulum models, and electrophysiologic studies have been used to quantify spastic hypertonia. Biomechanical methods seem to correlate most closely with the clinical state. Spastic hypertonia is but one component of the upper motor neuron syndrome, whose features also include loss of dexterity, weakness, fatigability, and various reflex release phenomena. These other features of the upper motor neuron syndrome may well be more disabling to the patient than changes in muscle tone.