Implementation of boundary conditions in modeling the femur is critical for the evaluation of distal intramedullary nailing

In previous numerical and experimental studies of the intramedullary nail implanted human femur several simplifications to model the boundary and loading conditions during pre-clinical testing have been proposed. The distal end of the femur was fixed in the majority of studies dealing with the biomechanics of the lower extremity, be it numerical or experimental, which resulted in obviously non-physiological deflections. Per contra, Speirs et al. (2007) proclaimed physiological deflections as a result of constraining the femur in a novel statically determinate fashion in combination with using a complex set of muscle forces. In tandem with this, we have shown that not only the deflections but also the stress and strain predictions turn out to be much lower in magnitude, as a result of using the latter approach. To illustrate the dramatic change in results, we compared these results with those of two other models employing commonly used boundary and loading conditions in retrograde stabilization of a distal diaphyseal fracture. The model used herewith resulted in more realistic femoral cortical strains, lower stresses on both the nail and the screws, as well as such deflections in the overall structure

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

Twente Spine Model: Development, validation, and application of a complete and coherent musculoskeletal model of the human spine

A comprehensive assessment of the spinal loads throughout the spine can advance our understanding of its functioning but is largely unavailable. Musculoskeletal modeling offers a non-invasive means to estimate in vivo spinal loads and can thus provide clinical insights into the spine’s functioning. The primary objective of this dissertation was to develop a validated, complete and coherent musculoskeletal model of the entire human spine for investigating the spinal loads. Firstly, an anatomical dataset (the Twente Spine Dataset) including necessary musculoskeletal parameters for creating this model was measured. For each muscle-tendon element, locations of the attachment sites at the origin, insertion, and via points were digitized, and morphological parameters consisting of the fiber length, tendon length, sarcomere length, optimal fiber length, pennation angle, mass, and physiological cross-sectional area were measured. Next, a complete and coherent musculoskeletal model of the entire human spine (the Twente Spine Model) was developed based on the previously acquired anatomical dataset. In this model, cervical, thoracic, and lumbar vertebrae, a flexible ribcage, and comprehensive muscular anatomy were incorporated. An inverse dynamics based static optimization routine minimizing muscle fatigue was used for calculating muscle and joint forces during basic neck and trunk movements. For validation of the predicted internal loads, quasi-static trunk tasks as measured in previous in vivo studies were simulated, and calculated intradiscal pressures at thoracic and lumbar discs and normalized resultant loads were compared. Subsequently, the sensitivity of muscle and intervertebral disc force computations against potential errors in modeling muscle attachment sites (muscle origin, insertion, and via points) were investigated. For this, every muscle attachment location was perturbed in the Twente Spine Model during upright standing, flexion, lateral bending, and axial rotation of the trunk. The changes in the T6/T7, T12/L1, and L4/L5 disc forces were analyzed, and an overall sensitivity index value was calculated for every perturbed muscle. Furthermore, electromyographic activities and trunk movements during isometric and dynamic trunk activities were simultaneously measured. Finally, musculoskeletal and patient-specific finite element models were used in combination to investigate if modeling more physiological load regimes can significantly affect the vertebral fracture risk prediction

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

The 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 thorough investigation of the spinal loads in a complete and coherent musculoskeletal model of the human spine

Although in vivospinal loads have been previously measured, existing data are limited to certain lumbar and thoracic levels. A detailed investigation of spinal loads would assist with injury prevention and implant design but is unavailable. In this study, we developed a complete and coherent musculoskeletal model of the entire human spine and studied the intervertebral disc compression forces for physiological movements on three anatomical planes. This model incorporates the individual vertebrae at the cervical, thoracic, and lumbar regions, a flexible ribcage, and complete muscle anatomy. Intradiscal pressures were estimated from predicted compressive forces, and these were generally in close agreement with previously measured data. We found that compressive forces at the trunk discs increased during trunk lateral bending and axial rotation of the trunk. During flexion, compressive forces increased in the thoracolumbar and lumbar regions and slightly decreased at the middle thoracic discs. In extension, the forces generally decreased at the thoracolumbar and lumbar discs whereas they slightly increased at the upper and middle thoracic discs. Furthermore, similar to a previous biomechanical model of the cervical spine, our model predicted increased compression forces in neck flexion, lateral bending, and axial rotation, and decreased forces in neck extension