Biomechanical Issues Research Articles

Biomechanical Modeling of the Rectum for the Design of a Novel Artificial Anal Sphincter

This paper discusses biomechanical issues that are related to the option of a novel artificial anal sphincter around the human rectum. The prosthesis consists of a compression cuff system inside and a reservoir cuff system outside, which is placed around the debilitated sphincter muscle. The micropump shifts fluid between the cuffs and thus takes over the expansion and compression function of the sphincter muscle. However, the human rectum is not a rigid pipe, and motion in it is further complicated by the fact that the bowel is susceptible to damage. With the goal of engineering a safe and reliable machine, the biomechanical properties of the in-vivo porcine rectum are studied and the tissue ischemia is analyzed.

Visualisation of biomechanical data to assist therapeutic rehabilitation

PURPOSE: The biomechanics community have to date had limited success in communicating complex biomechanical data and analyses outside of their field. The authors have created an innovative prototype software tool to visualise objective dynamic movement data captured from older adults undertaking activities of daily living (ADLs). Evaluation of this tool has shown it to be a successful way of communicating the complexity of older adult mobility data in an accessible manner for non-biomechanical specialists and lay audiences(1,2). METHODS: A software tool was developed, which generates a 3D animated human 'stick figure', on which the biomechanical demands of ADLs are represented visually at the joints as a percentage of each individual's maximum capability using a continuous colour gradient from green at 0%, amber at 50%, through to red at 100% (Figure 1). The tool was evaluated using a qualitative methodology of interviews and focus groups, where older adults and professionals viewed a series of visualisations of dynamic movement data(3). RESULTS AND DISCUSSION: Analysis of focus group discussions facilitated by the visualizations revealed new kinds of dialogues about biomechanical issues. The method of visualising and presenting the data clearly enabled people without training in biomechanics, both professionals and lay older people, to access and interpret the biomechanical information, based on their background, knowledge of a field or their personal experience. Further, the common visual medium enabled the sharing of different insights without recourse to specialist terminology or knowledge. New kinds of dialogues occurred in focus groups between older people and professionals about their experiences, based on real understanding of where the mobility problems were occurring. New dialogues also emerged between professionals from a range of different disciplines, crucial for different aspects of the care, wellbeing or design of the built environment for older people. Neither of these would have been possible using current conventions of presenting biomechanical data. The visualisations also appear to allow a deeper understanding of the issues within professions, both in healthcare and in design. These findings have led to new research with five discrete yet complementary studies covering a range of clinical applications of this method for: i) mobility and exercise advice for the healthy older adult; ii) falls prevention; iii) rehabilitation of total knee replacement; iv) to enhance early mobilisation of acute stroke patients and v) to enhance biomechanical diagnosis and fitting of ankle foot orthoses (AFO) in late stage stroke.

Molecular Biomechanics: The Molecular Basis of How Forces Regulate Cellular Function

Recent advances have led to the emergence of molecular biomechanics as an essential element of modern biology. These efforts focus on theoretical and experimental studies of the mechanics of proteins and nucleic acids, and the understanding of the molecular mechanisms of stress transmission, mechanosensing and mechanotransduction in living cells. In particular, single-molecule biomechanics studies of proteins and DNA, and mechanochemical coupling in biomolecular motors have demonstrated the critical importance of molecular mechanics as a new frontier in bioengineering and life sciences. To stimulate a more systematic study of the basic issues in molecular biomechanics, and attract a broader range of researchers to enter this emerging field, here we discuss its significance and relevance, describe the important issues to be addressed and the most critical questions to be answered, summarize both experimental and theoretical/computational challenges, and identify some short-term and long-term goals for the field. The needs to train young researchers in molecular biomechanics with a broader knowledge base, and to bridge and integrate molecular, subcellular and cellular level studies of biomechanics are articulated.

Anatomy & Biomechanics of the Hip

The hip joint is unique anatomically, physiologically, and developmentally; therefore understanding the basic structure and biomechanics of the hip is essential for clinicians, physiotherapists and engineers alike. In this review we outline the function of the key anatomical components of the hip and discuss the relevant related biomechanical issues. Understanding the forces that cross the hip and the details of the anatomy leads to a better understanding of some of the failures of the past and gives credence to current and future solutions.

Three Dimensional Active Contours for the Reconstruction of Abdominal Aortic Aneurysms

An aneurysm is a gradual and progressive ballooning of a blood vessel due to wall degeneration. Rupture of abdominal aortic aneurysm (AAA) constitutes a significant portion of deaths in the US. In this study, we describe a technique to reconstruct AAA geometry from CT images in an inexpensive and streamlined fashion. A 3D reconstruction technique was implemented with a GUI interface in MATLAB using the active contours technique. The lumen and the thrombus of the AAA were segmented individually in two separate protocols and were then joined together into a hybrid surface. This surface was then used to obtain the aortic wall. This method can deal with very poor contrast images where the aortic wall is indistinguishable from the surrounding features. Data obtained from the segmentation of image sets were smoothed in 3D using a Support Vector Machine technique. The segmentation method presented in this paper is inexpensive and has minimal user-dependency in reconstructing AAA geometry (lumen and wall) from patient image sets. The AAA model generated using this segmentation algorithm can be used to study a variety of biomechanical issues remaining in AAA biomechanics including stress estimation, endovascular stent-graft performance, and local drug delivery studies.

An Object-Oriented Approach to Simulating Human Gait Motion Based on Motion Tracking

An Object-Oriented Approach to Simulating Human Gait Motion Based on Motion TrackingAccurate bone motion reconstruction from marker tracking is still an open and challenging issue in biomechanics. Presented in this paper is a novel approach to gait motion reconstruction based on kinematical loops and functional skeleton features extracted from segmented Magnetic Resonance Imaging (MRI) data. The method uses an alternative path for concatenating relative motion starting at the feet and closing at the hip joints. From the evaluation of discrepancies between predicted and geometrically identified functional data, such as hip joint centers, a cost function is generated with which the prediction model can be optimized. The method is based on the object-oriented multibody library MOBILE, which has already been successfully applied to the development of industrial virtual design environments. The approach has been implemented in a general gait visualization environment termedMobile Body.

A Review of the Biomechanics of Intrinsic Replacement in Ulnar Palsy

The actions of the interossei and lumbricals are many and their loss causes significant impairment of hand function. Many procedures have been described to restore intrinsic function following ulnar nerve palsy. There are many biomechanical issues involved in tendon transfers, including choice of muscle-tendon unit, route, insertion site, tension and drag. The surgeon, therefore, should have a good understanding of biomechanical principles to ensure optimal results. In this article the principles of biomechanics are reviewed with specific reference to tendon transfers for intrinsic reconstruction in ulnar palsy, along with their practical implications.

Hip Arthroplasty in a Patient with Congenital Pubic Diastasis and Bladder Exstrophy

We report a total hip arthroplasty performed for arthritis and osteonecrosis in a patient with congenital pubic diastasis and bladder exstrophy. A satisfactory outcome was achieved after appropriate consideration of the technical and biomechanical issues involved.

Treatment of Syndesmosis Disruptions With TightRope Fixation

Open reduction and screw fixation is the current standard treatment for displaced injuries of the ankle syndesmosis. Despite reduction and stable internal fixation, however, these injuries do not uniformly have excellent outcomes. In addition, screw fixation has potential disadvantages. The objective of this article was to provide an overview of the important anatomical and biomechanical issues relating to syndesmosis injuries and to present the surgical technique and potential advantages of fixation with the TightRope implant(Arthrex Inc, Naples, Fla). The shortterm results of an ongoing prospective, randomized clinical trial are also presented.

Dynamic iso-resistive trunk extension simulation: Contributions of the intrinsic and reflexive mechanisms to spinal stability

The effects of external resistance on the recruitment of trunk muscles and the role of intrinsic and reflexive mechanisms to ensure the spinal stability are significant issues in spinal biomechanics. A computational model of spine under the control of 48 anatomically oriented muscle actions was used to simulate iso-resistive trunk movements. Neural excitation of muscles was attained based on inverse dynamics approach along with the stability-based optimization. The effect of muscle spindle reflex response on the trunk movement stability was evaluated upon the application of a perturbation moment. In this study, the trunk extension movement at various resistance levels while extending from 60 degrees flexion to the upright posture was investigated. Incorporation of the stability condition as an additional constraint in the optimization algorithm increased antagonistic activities for all resistance levels demonstrating that the co-activation caused an increase in the intrinsic stiffness of the spine and its stability in a feed-forward manner. During the acceleration phase of the movement, extensors activity increased while flexors activity decreased in response to the higher resistance. The co-activation ratio noticed in the braking phase of the movement increased with higher resistance. In presence of a 30 Nm flexion perturbation moment, reflexive feed-back noticeably decreased the induced deviation of the velocity and position profiles from the desired ones at all resistance levels. The stability-generated co-activation decreased the reflexive response of muscle spindles to the perturbation demonstrating that both intrinsic and reflexive mechanisms contribute to the trunk stability. The rise in muscle co-activation can ameliorate the corruption of afferent neural sensory system at the expense of higher loading of the spine.

Improving EMG-Based Muscle Force Estimation by Using a High-Density EMG Grid and Principal Component Analysis

The accuracy of predictions of muscle force based on electromyography (EMG) is an important issue in biomechanics and kinesiology. Since human skeletal muscles show a high diversity and heterogeneity in their fiber architecture, it is difficult to properly align electrodes to the muscle fiber direction. Against this background, we analyzed the effect of different bipolar configuration directions on EMG-based force estimation. In addition, we investigated whether principal component analysis (PCA) can improve this estimation. High-density surface-EMG from the triceps brachii muscle and the extension force of the elbow were measured in 11 subjects. The root mean square difference (RMSD) between predicted and measured force was determined. We found the best bipolar configuration direction to cause a 13% lower RMSD relative to the worst direction. Optimal results were obtained with electrodes aligned with the expected main muscle fiber direction. We found that PCA reduced RMSD by about 40% compared to conventional bipolar electrodes and by about 12% compared to optimally aligned multiple bipolar electrodes. Thus, PCA contributes to the accuracy of EMG-based estimation of muscle force when using a high-density EMG grid.

Lower body problems and injury in cycling

Summary Cycling is generally regarded as a low impact sport. It has a range of skills and disciplines, but the majority of cyclists are usually involved in the endurance aspect of the sport. The low impact nature, however, does not preclude cyclists from injury and musculoskeletal problems. Apart from the obvious trauma and sequelae involved in a fall from the bike, the prolonged postural adaptations combined with the repetitive limb movement from spending hours cycling seem to be one of the main reasons for lower limb and lower body problems. Those intending to become involved in the diagnosis and treatment of such problems should be aware of the plethora of mechanical and biomechanical issues when assessing an injured cyclist. This review of lower body problems in cycling highlights the typical patterns of injury and points out that to obtain a diagnosis for a cycling related problem a practitioner must evaluate faults in the bicycle as well as the cyclist. It also highlights that, despite some useful biomechanical input, there is a disturbing lack of evidence base for the treatment of some musculoskeletal complaints. This is unhelpful to those seeking more evidence-based practice, and may encourage an anecdotal approach to treatment for cyclists. All practitioners who are involved in the care of these sports people should continue to press for good quality studies so that cycling injuries of the lower limb may treated more efficaciously in the future.

Introduction to Biomechanics Related to Endovascular Repair of Abdominal Aortic Aneurysm

Biomechanical issues of practical relevance to the physician in the clinical management of patients undergoing endovascular repair (EVR) of their abdominal aortic aneurysms (AAA) is discussed. Following a brief description of key terms in vascular biomechanics, background on the current state of knowledge in the biomechanics of AAA pathogenesis and rupture is provided. This is followed by a discussion of key issues of biomechanical relevance in EVR such as the mechanics of endotension, the notion of intraaneurysmal sac pressure and potential pitfalls of techniques used to measure them, mechanics of graft fracture/kinking, and graft migration. The discussions are intended to provide an overview of this field to physicians.

Crown Cover Is Correlated with Relative Density, Tree Slenderness, and Tree Height in Lodgepole Pine

Abstract The objective of this study was to investigate the relationship between tree height, bole slenderness, and relative density with crown shyness (crown interstitial space) in even-aged lodgepole pine. In 10 lodgepole pine stands in Alberta, Canada, ranging in height from 5.6 to 22.1 m, 9–23 triangular plots were established. A plot consisted of three trees that formed the corners of the triangle; all plots were at theoretical crown closure. Within each triangle, the percentage crown closure (% CC) was related to the mean height, slenderness coefficient (SC, tree height/diameter), and relative density (RD) of the trees that defined the triangle. Within the stands less than 12 m in height, % CC was positively correlated with RD. Within most of the stands greater than 15 m, % CC was negatively correlated to SC. Mean % CC declined with increasing stand height. Results suggest that RD is strongly related to % CC in short stands but as trees grow in height, biomechanical issues related to stem form (i.e., SC) probably play a large role in determining the amount of canopy coverage. We suggest that taller trees with high SC are more flexible, resulting in intense crown collisions, crown abrasion, and crown shyness. FOR. SCI. 50(3):356–363.

An in vitro uniaxial stretch model for axonal injury.

We have developed a unique uniaxial stretching device to study axonal injury and neural cell death resulting from brain tissue deformations common in traumatic head injuries. Using displacement control rather than force control, this device is capable of achieving strains >70% and strain rates up to 90 s(-1), well above those currently used for studying axonal injury. We have demonstrated that the deformation of the specimen was uniaxial, uniform and highly reproducible; the prespecified displacement profiles could be realized almost precisely; and adequate cell adhesion could be achieved readily. The entire device can fit into a biological safety cabinet to maintain sterility, and the specimens are convenient for cell culture. This device can be used to investigate a wide range of biomechanical issues involved in diffuse axonal injury.

Fall-related upper body injuries in the older adult: a review of the biomechanical issues

Although the epidemiology of fall-related injuries is well established for the elderly population over 65 years of age, the biomechanics of how, when and why injuries do and do not occur when arresting a fall have received relatively little attention. This paper reviews the epidemiological literature in the MEDLINE data base pertinent to the biomechanics of fall-related injuries, including data on fall rates, fall-related injury rates, fall directions and types of injuries available. It also covers primary sources not listed on MEDLINE, along with the pertinent biomechanics literature. Many falls in older adults are in a forward direction, and as a result the upper extremities are one of the most commonly injured structures, presumably in protecting the head and torso. In this review emphasis is placed on what is, and what is not, known of the biomechanical factors that determine the impact forces and injury risk associated with upper extremity injuries in forward falls. While decreased bone mineral density may be contributory, it is not a reliable predictor of fracture risk. Evidence is presented that fall-related impact forces can be reduced by appropriate volitional arrest strategies. Further theoretical and experimental research is needed to identify appropriate fall-arrest strategies for the elderly, as well as the physical capacities and skills required to do so. Inexpensive interventions might then be developed to teach safe fall-arrest techniques to older individuals.

Pott's disease in Senegal

The purpose of this study is to report our experience on Pott's disease in Senegal, which belongs to the group of least-developed countries .In these countries, tuberculosis is still a public health issue. Regarding spine tuberculosis, we attempted to implement a diagnostic and therapeutic approach appropriate for our conditions of medical practice. The authors reported a retrospective epidemiological and clinical study of 255 patients suffering from tuberculosis of the spine. Theses patients were hospitalized at the University Hospital of Fann in Dakar from January 1986 to July 1998. Sixty percent came from the capital, the mean age was 34.9 years, there were 136 males for 119 females, and antituberculosis immunization were not done every time. Associated extra-spinal tuberculosis, predominantly tuberculosis of the lung, was observed in 28.2 patients (59%). Of 37 patients tested for human immunodeficiency virus (HIV) infection, only one was positive. Patients came late to the hospital, leading to a high percentage of neurological complications (79.2%). Our diagnostic strategy was based on epidemiological and clinical criteria already defined by Martini. Thoracic spine (53.8%) and lumbar sacral spine (21.7%) were the column vertebral segments most frequently involved. All patients received antituberculosis chemotherapy, and only 39 patients underwent surgery with laminectomy without posterior instrumentation. Functional outcome study was done for 89 paraplegic patients: 26 (29%) went to Frankel grade D or E and, among 27 operated patients, nine entered theses grades. Seventeen patients (11.5%) died. We developed the concept of "spinal-cord rescue," which focuses more on neurological rather than biomechanical issues.

The history of surface electromyography.

The history of muscle pain and dysfunction is viewed through the lens of a four factor theory of histologic (tissue related) issues, psychologic (emotional) issues, sensory motor (movement) issues, and biomechanical (postural) issues. The historical antecedents of surface electromyography are reviewed.

New developments in the biomechanics of the diabetic foot.

Biomechanical issues are now widely recognized as being important in the treatment of diabetic foot disease. The purpose of the present review is to identify advances that have occurred since the previous International Conference on the Diabetic Foot in 1995 in the understanding of foot biomechanics in relation to diabetes. Attention continues to be focused on the identification of a threshold plantar pressure that leads to tissue damage. Recent studies have suggested that peak barefoot pressure may be only 65% specific for the development of ulceration. The association between foot deformity and plantar pressure has been the subject of several quantitative studies, but new questions have been raised about the etiology of claw toes. The measurement of shear stress continues to be an elusive goal although several small studies have presented possibly feasible technical approaches. The importance of callus as a precursor to ulceration has been confirmed experimentally and quantitative measures of motor neuropathy have been presented. Although a number of new devices have been introduced as alternatives to the Total Contact Cast, few clinical studies of their efficacy are available yet. New information on the properties of insole materials has been published including data on changes with repeated cycling. Complications of prophylactic surgery have been shown to include a high rate of Charcot fractures. Two new series describing the fixation of such fractures have also been reported. Biomechanical issues have also been addressed in two sets of guidelines for treatment that have recently been published. These many studies confirm the central role of mechanical stress and its relief in the treatment of neuropathic foot problems in diabetes.

On the trabecular "thickness"-number problem.

The decrease in trabecular number with aging and in osteoporosis seems to be naturally irreversible. In one view the resulting loss of bone strength would be irreversible too, but in another view the remaining trabeculae could increase their strength, chiefly by thickening. Whether that can occur has become important for osteoporosis research and management as well as for some biomechanical issues. This article reviews evidence and ideas that concern that matter. It suggests why the second view could be correct although previous studies did not detect it. However, that view still needs the kind of proof the general skeletal science community could accept.