Wat een biomechanisch model zo spannend maakt

Afscheidscollege Prof.dr.ir. Chris J. Snijders, Hoogleraar Medische Technologie Erasmus Universiteit Rotterdam en Afdelingshoofd Biomedische Natuurkunde en Technologie, Erasmus MC. Uitgesproken 3 november 200

Medische technologie in de Medische Faculteit te Rotterdam

Rede, uitgesproken bij de aanvaarding van het ambt van Gewoon Hoogleraar in de Medische Technologie aan de Faculteit der Geneeskunde van de Erasmus Universiteit Rotterdam, op 14 november 198

Influence of activities in the comprehensive community sport clubs on the mental health of children : With special reference to the enjoyment

textabstractThis study deals primarily with the stability of the base of the spine. The sacroiliac joints are vulnerable to shear loading on account of their predominantly flat surfaces. This raises the question of what mechanisms are brought into action to prevent dislocation of the sacroiliac joints when they are loaded by the weight of the upper part of the body and by trunk muscle forces. First a model is introduced to compare load transfer in joints with spherical and with flat joint surfaces. Next we consider a biomechanical model for the equilibrium of the sacrum under load, describing a self-bracing effect that protects the sacroiliac joints against shear according to ‘the sacroiliac joint compression theory’, which has been demonstrated in vitro. The model shows joint stability by the application of bending moments and the configuration of the pelvic arch. The model includes a large number of muscles (e.g. the gluteus maximus and piriformis muscles), ligaments (e.g. the sacrotuberous, sacrospinal, and dorsal and interosseous sacroiliac ligaments) as well as the coarse texture and the ridges and grooves of the joint surfaces

A biomechanical model for the analysis of the cervical spine in static postures

To gain a better understanding of the forces working on the cervical spine, a spatial biomechanical computer model was developed. The first part of our research was concerned with the development of a kinematic model to establish the axes of rotation and the mutual position of the head and vertebrae with regard to flexion, extension, lateroflexion and torsion. The next step was the introduction of lines of action of muscle forces and an external load, created by gravity and accelerations in different directions, working on the centre of gravity of the head and possibly a helmet. Although the results of our calculations should be interpreted cautiously in the present stage of our research, some conclusions can be drawn with respect to different head positions. During flexion muscle forces and joint reaction forces increase, except the force between the odontoid and the ligamentum transversum atlantis. This force shows a minimum during moderate flexion. The joint reaction forces on the levels C0-C1, C1-C2, and C7-T1 reach minimum values during extension, each in different stages of extension. Axial rotation less than 35° does not need great muscle forces, axial rotation further than 35° causes muscle forces and joint reaction forces to increase fast. While performing, lateral flexion muscle forces and joint reaction forces must increase rapidly to balance the head. We obtained some indications that the order of magnitude of the calculated forces is correct

Prevention of fracture at the distal locking site of the gamma nail. A biomechanical study

To investigate the origin of fractures at the distal locking site of the Gamma nail, we loaded ten paired human cadaver femora fixed with a Gamma nail in torsion until they fractured. When an awl was hammered in to start the hole for distal locking a fissure appeared in the lateral cortex of all the femora, and the mean torsional load to create a fracture was reduced by 57.8% compared with that in a control group in which the distal locking hole had been started with a centre drill. When an additional drill hole was made, the mean failure load in torsion decreased by 35.7%. We strongly recommend that an awl should not be used at the distal locking site of the Gamma nail; we recommend the use of a centre drill. Additional drill holes should be avoided because they act as stress raisers

Chronic instability of the foot and foot geometry: A radiographic study

Multiple factors are involved in chronic lateral instability of the ankle. The geometry of the foot may be of importance. A cavovarus foot may predispose to lateral ligament injuries. In the present study, standardized lateral X-rays were obtained of the feet of patients with chronic instability and of a control group. Four parameters were used: (1) the tarsal index as described by Benink; (2) the talocalcaneal angle; (3) the talometatarsal angle; and (4) the calcaneal angle. No relationship between lateral instability of the foot and foot geometry was found. The talocalcaneal angle as defined in this study was found to be a less appropriate parameter in measuring the longitudinal foot arch

Transfer of lumbosacral load to iliac bones and legs Part 2: Loading of the sacroiliac joints when lifting in a stooped posture

We developed a biomechanical model of load transfer by the sacroiliac joints in relation to posture. A description is given of two ways in which the transfer of lumbar load to the pelvis in a stooped posture can take place. One way concerns ligament and muscle forces that act on the sacrum, raising the tendency of the sacrum to flex in relation to the hip bones. The other refers to ligament and muscle forces acting on the iliac crests, raising the tendency of the sacrum to shift in caudal direction in relation to the hip bones. Both loading modes deal with the self-bracing mechanism that comes into action to prevent shear in the sacroiliac joints. When a person is lifting a load while in a stooped posture, the force raised by gravity acting in a plane perpendicular to the spine and the sacrum becomes of interest. In this situation a belt such as used by weight lifters may contribute to the stability of the sacroiliac joints. Verification of the biomechanical model is based on anatomical studies and on load application to human specimens. Magnetic resonance imaging pictures have been taken to verify geometry in vivo

Third-Party Effects

Most theories about effects of social embeddedness on trust define mechanisms that assume someone’s decision to trust is based on the reputation of the person to be trusted or on other available information. However, there is little empirical evidence about how subjects use the information that is available to them. In this chapter, we derive hypotheses about the effects of reputation and other information on trust from a range of theories and we devise an experiment that allows for testing these hypotheses simultaneously. We focus on the following mechanisms: learning, imitation, social comparison, and control. The results show that actors learn particularly from their own past experiences. Considering third-party information, imitation seems to be especially important

Understanding peripartum pelvic pain: Implications of a patient survey

Study Design. An analysis was made of the self-reported medical histories of patients with peripartum pelvic pain. Objectives. To compile an inventory of the disabilities of patients with peripartum pelvic pain, analyze factors associated with the risk for development of the disease, and to formulate a hypothesis on pathogenesis and specific preventive and therapeutic measures. Summary of Background Data. Pregnancy is an important risk factor for development of chronic low back pain. Understanding the pathogenesis of pelvic and low back pain during pregnancy and delivery could be useful in understanding and managing nonspecific low back pain. Methods. By means of a questionnaire, background data were collected among patients of the Dutch Association for Patients With Pelvic Complaints in Relation to Symphysiolysis. Results were compared with the general population. Subgroups were compared with each other. Results. Peripartum pelvic pain seriously interferes with many activities of daily living such us standing, walking, sitting, and all other activities in which the pelvis is involved. Most patients experience a relapse around menstruation and during a subsequent pregnancy. Occurrence of peripartum pelvic pain was associated with twin pregnancy, first pregnancy, higher ago at first pregnancy, larger weight of the baby, forceps or vacuum extraction, fundus expression, and a flexed position of the woman during childbirth; a negative association was observed with cesarean section. Conclusions. It is hypothesized that peripartum pelvic pain is caused by strain of ligaments in the pelvis and lower spine resulting from a combination of damage to ligaments (recently or in the past), hormonal effects, muscle weakness, and the weight of the fetus

Oblique abdominal muscle activity in standing and in sitting on hard and soft seats

The activity of the oblique abdominal muscles was investigated with the trunk in unconstrained, symmetrical and static postures. Electromyographic recordings in six healthy subjects revealed that in all subjects the activity of both the internal and the external obliques is significantly higher in unconstrained standing than in supine posture. Activity of the internal oblique was higher than that of the external oblique abdominal. The sacrospinal, gluteus maximus and biceps femoris muscles showed practically no activity in unconstrained erect posture. During unconstrained sitting both oblique abdominals are active. In most subjects the activity of the oblique abdominals was significantly smaller when sitting on a soft car seat than when sitting on an office chair with a hard seat. The possibility is discussed that contraction of the oblique abdominals in unconstrained standing and sitting may help in stabilizing the basis of the spine and particularly the sacroiliac joints. During standing and sitting the oblique abdominal muscles apparently have a significant role in sustaining gravity loads