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

The modelling and mechanical consequences of fibrous-tissue formation around femoral hip prostheses

On the longer term, bone resorption around the prosthesis may occur, at least when acrylic cement is used for fixation, resulting in a soft fibrous tissue layer between cement and bone. The mechanical behavior of a fibrous-tissue interface connection will therefore be governed by the following effects: 1) reduced compliance; 2) material nonlinearity of the tissue itself; 3) loosening on tension; 4) slip in shear; 5) time dependency. In the present analysis, a (nonlinear) 2-D finite element method model (using quasi 3-D structural characteristics) of femoral hip replacement was used to study the consequences of the effects 1 through 4 on the load-transfer mechanism, the stress patterns and the relative motions occurring between implant and bone. [9 Refs; In English

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

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