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Mechanics of bone and bone-implant system

The relationship between structure, mechanical properties and ultrasound transmission in bone

This research is part of the IDO/04/005-project: “quantitative analysis of biological tissues using ultrasound waves aimed at tissue characterization.” The focus is on the relation between mechanical strength of and the ultrasound (US) transmission through porous trabecular bone. Quantification of the micro-architecture using histomorphometrical parameters, is used to link both phenomena. The microstructure is linked to mechanical properties using µCT-scans and FE models. A simplified skeleton-based FE model, which uses local structural properties as meshing parameters, was developed for this purpose. This model will be used to simulate US propagation as well, enabling us to directly link microstructure to both strength and wave propagation and thus bridging the existing knowledge gap. If the link US transmission – bone strength is quantified it can be used clinically to asses bone competence with US measurements. Metabolic bone diseases, like osteoporosis, can then be monitored and diagnosed safe and noninvasively.

Jozef Vanderoost

Patient-specific image-based analyses of bone competence

Preventing femoral fractures is an important goal in osteoporosis research. In order to evaluate a person’s fracture risk and to quantify response to treatment bone competence is best assessed by bone strength. Finite element (FE) modelling based on medical imaging is considered a very promising technique for the assessment of in vivo femoral bone strength. An important structural parameter that contributes to this global femoral strength is the orthotropic internal trabecular architecture. Based on in vivo CT scans (figure), it is possible to estimate these structural properties and to use them to build FE models that predict femoral strength accurately.

Leen Lenaerts

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Bone remodeling in the human forearm

Local changes at the distal radius will be assessed in a large cohort of patients, using data obtained with an HRpQCT scanner. An accurate method of image registration will be developed to measure structural changes in bone microarchitecture and to identify the areas of bone remodelling in subsequent HRpQCT data of the distal radius, containing a 1 cm slab of bone. Subsequently, bone remodeling algorithms, developed by collaborators will be applied to models that are based on the in vivo data set. The models will require accurate estimates of bone loading at the boundaries of the 1 cm slab of bone. Finite element models based on scans of the distal half of the forearm will be used to assess the local boundary conditions for the area of interest. For validation of the remodeling simulations, the results of will be compared to the patient measurements.

Ingrid Knippels

 

The assessment and treatment of peri- and inter-prosthetic (IP) fractures of the femur following a total hip arthroplasty (THA) or total knee arthroplasty (TKA)

The assessment and treatment of peri- and inter-prosthetic (IP) fractures of the femur following a total hip arthroplasty (THA) or total knee arthroplasty (TKA) remains a challenge. Revision surgeries, rising in incidence due to the aging population, frequently request longer replacement prosthesis stems which decreases the interprosthetic gap. The hypothesis stated by orthopedic surgeons is that this may induce a stress riser that could lead to an even higher susceptibility for peri-prosthetic fractures of the femur. Nevertheless, the influence of the interprosthetic gap distance on the femoral biomechanical properties has never been really substantiated and quantified.
Therefore, the following aims were included in this research: (1) to evaluate the effect of the interprosthetic gap distance on the biomechanical properties of the femur (2) to describe the inter-prosthetic fracture morphology (3) to evaluate the stability of 3 lateral plate constructs used to reconstruct peri- and inter-prosthetic fractures, (4) to investigate whether gap size would influence the stability of long plate-and-screw constructs and (5) to investigate whether anterior strut allograft would improve the stability of these plate-and-screw reconstructions.
In the first phase, an experimental study will be performed using relevant gap sizes, prostheses and plate fixation systems in combination with synthetic biomechanical relevant femoral bones (Sawbones, Pacific Research Laboratories, Sweden). After these experiments, creation of a finite element model will provide experiment validation and further insight in the IP-fractures problematic.

 

Thomas Quirynen
 

Micro-scale mechanical characterization of cortical bone

Physical laws dictate that the competence of bone at macro-scale depends on its microstructure and its tissue quality. A physics-based approach to prediction of whole bone competence necessitates evaluation of bone microstructure and tissue quality. Recently, with the introduction of the BioDent instrument (Active Life Scientific, USA) the reference-point-indentation (RPI) technique can now be employed to mechanically characterize bone tissue quality in-vivo. RPI, coupled with in-vivo characterization of bone microstructure using high-resolution computed tomography, can be used to construct micro-finite-element (μFE) based models of subject-specific whole bone mechanical behavior. This framework has the potential to significantly alter the current paradigm in clinical assessment of bone fracture risk, which is based on bone density. In the light of several studies that have shown bone density to be an unreliable predictor of whole bone competence, the importance of the physics-based approach is emphasized. This project aims to use BioDent to mechanically characterize long bones from mouse models, grouped separately by age, sex, diet, muscular loading and in-bred genetic strain. These tests will be analyzed using micromechanics based models to derive constitutive properties of bone tissue, which can then be used in μFE models of whole bones to predict whole bone behavior.

Pinaki Bhattacharya

 

Patient-specific predictions for bone treatments

It has been known for years that long bones of the human body adapt their density and architecture to mechanical loading. Since the 1980s, mathematical models have been developed in order predict this mechanical adaptation of human bones. These algorithms have been implemented in finite element simulations and applied to various bones such as femur. The goal of my project is to predict bone density distribution in proximal femur for subject-specific geometries and loading conditions. Patient-oriented medicine is an emerging area of research and has received much attention in recent years. Subject-specific prediction of bone density in the proximal femur would allow designing individualized implants and surgical methods. Additionally it could shed more light on mechanisms behind onset of disease such as osteoporosis. At KU Leuven, I am involved in the European Industry-Academia Partnership and Pathways (IAPP) project titled CAD-BONE in collaboration with University of Zaragoza (Spain) and the company Materialise (Belgium)

Ali Vahdati

 

Does The Osteocyte Lacuna Affect Bone Adaptive Response In Aging?

Osteoporosis is by far the most common bone disease, resulting in nearly four million osteoporotic bone fractures in Europe each year. Hence, there a strong socio-economic need to reduce the number of fractures. Low bone mass, the hallmark of osteoporosis, is a consequence of a negative balance in the bone remodeling process. This proposal is aiming at improving our understanding of this age-related bone loss preceding bone fracture. The osteocytes (OCY), the most abundant bone cell type, play a key role in the remodeling process by directing the osteoblast (bone building cells) and the osteoclasts (bone removing cells). Supported by recent evidence that OCYs can modify their micro-environment, we hypothesize that changes in the OCY lacunar morphology lead to changes in the stress conditions experienced by the OCY, giving rise to a modified response to mechanical loading.
Assessing the role of the lacunar morphology may lead to the development of new strategies towards improving bone quality and fracture prevention as well as elucidating a pathway in the etiology of osteoporosis.


A reconstructed image of a mouse fibula, acquired using desktop µCT:

 

Haniyeh Hemmatian