Biomechanical aspects of hydroxylapatite coatings on femoral hip prostheses

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Adaptive bone-remodeling theory applied to prosthetic-design analysis

The subject of this article is the development and application of computer-simulation methods to predict stress-related adaptive bone remodeling, in accordance with ‘Wolff's Law’. These models are based on the Finite Element Method (FEM) in combination with numerical formulations of adaptive bone-remodeling theories.\ud \ud In the adaptive remodeling models presented, the Strain Energy Density (SED) is used as a feed-back control variable to determine shape or bone density adaptations to alternative functional requirements, whereby homeostatic SED distribution is assumed as the remodeling objective.\ud \ud These models are applied to investigate the relation between ‘stress shielding’ and bone resorption in the femoral cortex around intramedullary prostheses, such as used in Total Hip Arthroplasty (THA). It is shown that the amount of bone resorption depends mainly on the rigidity and the bonding characteristics of the implant. Homeostatic SED can be obtained when the resorption process occurs at the periosteal surface, rather than inside the cortex, provided that the stem is adequately flexible

Prospects of computer models for the prediction of osteoporotic bone fracture risk

Bone fractures are major problems for osteoporosis patients. To avoid such fractures, more information is needed about the factors that determine the bone fracture risk. In this chapter, it is discussed how recently developed finite element computer models that can represent the trabecular architecture in full detail can provide such information. It is concluded that a computer modeling approach to this problem is feasible, required and promising. It is expected that, eventually, such models can be used as a basis for an accurate diagnosis of the bone fracture risk

Mechanical stability of trabecular bone morphology as a measure for osteoporosis

A new technique for assessing the mechanical stability of trabecular bone was introduced. This technique uses a full three dimensional reconstruction of a trabecular bone specimen and a finite element model to calculate the local stress distribution within the trabeculae. A little bone was artificially removed in the model at highly loaded locations and the changed stress distributions were determined. The changes in these distributions are indicative for the mechanical stability (change in fracture risk) of the trabecular architecture with respect to small changes in mass. The authors propose that this method can be used to measure the mechanical efficacy of a trabecular architecture in terms of fracture risk, thereby defining osteoporosis in a quantitative wa

The role of imaging in early hip OA

SummaryHip osteoarthritis (OA) is characterized by cartilage degradation, subchondral bone sclerosis and osteophyte formation. Nowadays, OA is thought to develop via different etiologies that all lead to a similar form of end stage joint degradation. One of these subtypes is related to an abnormal shaped hip joint, like acetabular dysplasia and a cam deformity. These bony abnormalities are highly predictive for development of hip OA, but they are likely to already be present from childhood. This suggests that these deformations induce OA changes in the hip, well before extensive hip degradation becomes present three to four decades later. Accurate detection and successful characterization of these early OA events might lead to better treatment options for hip OA besides nowadays available invasive joint replacement surgery. However, current diagnostic imaging techniques like radiographs or plain magnetic resonance imaging (MRI), are not sensitive enough to detect these subtle early OA changes. Nor are they able to disentangle intertwined and overlapping cascades from different OA subtypes, and neither can they predict OA progression. New and more sensitive imaging techniques might enable us to detect first OA changes on a cellular level, providing us with new opportunities for early intervention. In this respect, shape analysis using radiography, MRI, computed tomography (CT), single photon emission computed tomography (SPECT)/CT, and positron emission tomography (PET) might prove promising techniques and be more suited to detect early pathological changes in the hip joint. A broad application of these techniques might give us more understanding what can be considered physiological adaptation of the hip, or when early OA really starts. With a more clear definition of early OA, more homogenous patient populations can be selected and help with the development of new disease modifying OA interventions