Effects of intervertebral disk behavior on the load distribution and fracture risk of the vertebral body

Osteoporosis is characterized by low bone mass and an increased fracture risk. Measurements of bone mass alone, however, will not provide adequate information about the fracture risk, because the trabecular architecture or spatial distribution of the bone density has an important effect on the strength. We have developed a method to estimate the tissue strength of trabecular bone directly from 3D reconstructed axial CT-scans in combination with a finite element model. The method provides the stress distribution throughout the structure which can be used as a measure for the strength and fracture risk of the bone. A matter of concern with this method are the external loading conditions placed on the vertebral body, which might be strongly affected by the behavior of the intervertebral disk. In this study we have tested the effects of various intervertebral disk models on the load distribution through the vertebral body. A 3D model of a vertebral body was developed based on serial axial CT-scans which were converted to a 3D finite element model. The model was augmented with intervertebral disks at the upper and lower endplates. The disks contained a nucleus and an annulus region. The properties of the nucleus were varied to study the effects of a healthy disk with a functional nucleus pulposus and a degenerated disk with virtually no load bearing of the nucleus pulposus. The methods introduced in this study can be used to estimate load transfer through the vertebral body directly from CT-scans and, thereby, assessing the fracture risk of the bone and thus the status of osteoporosi

Sensitivity of muscle and intervertebral disc force computations to variations in muscle attachment sites

Item does not contain fulltextThe current paper aims at assessing the sensitivity of muscle and intervertebral disc force computations against potential errors in modeling muscle attachment sites. We perturbed each attachment location in a complete and coherent musculoskeletal model of the human spine and quantified the changes in muscle and disc forces during standing upright, flexion, lateral bending, and axial rotation of the trunk. Although the majority of the muscles caused minor changes (less than 5%) in the disc forces, certain muscle groups, for example, quadratus lumborum, altered the shear and compressive forces as high as 353% and 17%, respectively. Furthermore, percent changes were higher in the shear forces than in the compressive forces. Our analyses identified certain muscles in the rib cage (intercostales interni and intercostales externi) and lumbar spine (quadratus lumborum and longissimus thoracis) as being more influential for computing muscle and disc forces. Furthermore, the disc forces at the L4/L5 joint were the most sensitive against muscle attachment sites, followed by T6/T7 and T12/L1 joints. Presented findings suggest that modeling muscle attachment sites based on solely anatomical illustrations might lead to erroneous evaluation of internal forces and promote using anatomical datasets where these locations were accurately measured. When developing a personalized model of the spine, certain care should also be paid especially for the muscles indicated in this work

Twente spine model:A complete and coherent dataset for musculo-skeletal modeling of the lumbar region of the human spine

Item does not contain fulltextMusculo-skeletal modeling can greatly help in understanding normal and pathological functioning of the spine. For such models to produce reliable muscle and joint force estimations, an adequate set of musculo-skeletal data is necessary. In this study, we present a complete and coherent dataset for the lumbar spine, based on medical images and dissection measurements from one embalmed human cadaver. We divided muscles into muscle-tendon elements, digitized their attachments at the bones and measured morphological parameters. In total, we measured 11 muscles from one body side, using 96 elements. For every muscle element, we measured three-dimensional coordinates of its attachments, fiber length, tendon length, sarcomere length, optimal fiber length, pennation angle, mass, and physiological cross-sectional area together with the geometry of the lumbar spine. Results were consistent with other anatomical studies and included new data for the serratus posterior inferior muscle. The dataset presented in this paper enables a complete and coherent musculo-skeletal model for the lumbar spine and will improve the current state-of-the art in predicting spinal loading

Gene-expression profiles and oncogenes in pediatric T-cell acute lymphoblastic leukemia

Blood consists of serum and three other main ingredients: erythrocytes (red blood cells), thrombocytes (platelets) and leukocytes (white blood cells). Leukocytes normally compose less than 1% of the blood volume but have important functions in our defense against foreign and endogenous pathogens. Many different leukocytes can be distinguished, the main types being lymphocytes (~75% T-cells, ~25% B-cells), monocytes and granulocytes. All these different blood cells arise through distinct and tightly controlled developmental stages from hematopoietic precursor cells, which reside in the bone marrow and thymus (Figure 1). However, sequential mutations, chromosomal rearrangements and epigenetic changes can cause a precursor cell to be blocked from further differentiation and to start proliferate in a uncontrollable manner which results in cancer. Uncontrolled proliferation of blood precursor cells is called leukemia. Different types of leukemia are distinguished based on their lineage of origin; myeloid or lymphoblastic leukemia. Lymphoblastic leukemia can be further divided into Bcell precursor (BCP) or T-cell lymphoblastic leukemia. In acute lymphoblastic leukemia malignant cells are arrested at a relative immature stage whereas in chronic lymphocytic leukemia, cells have a more differentiated phenotype