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H Weinans

Publications and source records attributed to H Weinans.

59 records · Page 4Linked to original sources
PubMed1989

Adaptive bone remodeling and biomechanical design considerations for noncemented total hip arthroplasty.

Clinical problems with noncemented total hip arthroplasty (THA) stems, directly or indirectly related to load transfer, include mid-thigh pain due to relative (micro) motions or excessive endosteal interface stresses, subsidence and loosening due to inadequate primary stability and fit, and proximal femoral bone atrophy due to stress shielding. In this article, the load-transfer mechanisms associated with noncemented THA stems and their resulting stress patterns are discussed in relation to design features, bonding characteristics, and materials choice. Nonlinear finite-element models and computer simulation programs for strain-adaptive bone remodeling have been used for this study. Canal-filling, fully bonded metal stems have been found likely to cause proximal bone atrophy, possibly leading to long-term failure of the implant/bone composite. The use of flexible (isoelastic) materials and/or press-fit fixation reduces stress shielding, but also reduces the potential for interface stability. The stem material, the stem shape, and the coating geometry interact in relation to the load-transfer mechanism, and it is suggested that optimal combinations of these characteristics can be determined through the computer simulation methods presented.

Adaptation, Physiological↗
PubMed1987

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. 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. 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.

Adaptation, Physiological↗
PubMedDate not supplied

ESB Research Award 1992. The mechanism of bone remodeling and resorption around press-fitted THA stems.

A major problem threatening the long-term integrity of total hip replacement is the loss of proximal bone often found around noncemented stems in the long term. It is generally accepted that 'stress shielding' is the cause for this problem: after implantation of the prosthesis the surrounding bone is partially 'shielding' from load carrying and starts to resorb. One of the proposed answers to this problem is the application of press-fitted stems. These smooth-surfaced implants are thought to provoke higher proximal bone loading, and, hence, less stress shielding than bonded implants, because they are wedged into the femur every time when loaded. However, in a two-year experiment in dogs, similar amounts of resorption of the proximal cortex were found around press-fitted and bonded implants. The question arises how similar resorption patterns can develop under completely different stress conditions, and whether this phenomenon can be explained by adaptive bone remodeling theories based on Wolff's law. In the present study an answer was sought for this question. An advanced iterative computer simulation model was used to analyze the remodeling process in the animal experiment. Three-dimensional finite element models were constructed from the animal experimental configuration, in which smooth, press-fitted stems were applied unilaterally in the canine. The FE model was integrated with iterative remodeling procedures, validated in earlier studies. In the model an appropriate non-linear representation of the loose bone-implant interface was realized, also capable of simulating the proximal interface gap that was found around the uncoated implants. The simulation models predicted similar amounts of proximal bone loss and distal bone densification as found in the animal model. Hence, the cortical bone loss could indeed be predicted by the strain-adaptive bone remodeling theory. By unraveling the simulation process, the question stated above could be answered. Densification of the distal bone bed during the initial remodeling process was found to cause reduced axial stem displacement (elastic subsidence), decreasing the wedging effect of the stem and, hence, decreasing the loading of the proximal bone, resulting in proximal bone loss. Hence, whereas in the case of bonded stems the proximal resorption process develops monotonously to a new equilibrium, the process around smooth, press-fitted stems develops nonmonotonously. This is due primarily to the unbonded interface conditions and the development of a proximal fibrous membrane. The remodeling process then gradually causes the stem to be jammed in the distal diaphyses (proximal 'stress bypass').

Alloys↗
PubMedDate not supplied

Quantification of subchondral bone changes in a murine osteoarthritis model using micro-CT.

In the past few years there has been a considerable interest in the role of bone in osteoarthritis. Despite the increasing evidence of the involvement of bone in osteoarthritis, it remains very difficult to attribute the cause or effect of changes in subchondral bone to the process of osteoarthritis. Although osteoarthritis in mice provides a useful model to study changes in the subchondral bone, detailed quantification of these changes is lacking. Therefore, the goal of this study was to quantify subchondral bone changes in a murine osteoarthritis model by use of micro-computed tomography (micro-CT). We induced osteoarthritis-like characteristics in the knee joints of mice using collagenase injections, and after four weeks we calculated various 3D morphometric parameters in the epiphysis of the proximal tibia. The collagenase injections caused cartilage damage, visible in histological sections, particularly on the medial tibial plateau. Micro-CT analysis revealed that the thickness of the subchondral bone plate was decreased both at the lateral and the medial side. The trabecular compartment demonstrated a small but significant reduction in bone volume fraction compared to the contralateral control joints. Trabeculae in the collagenase-injected joints were thinner but their shape remained rod-like. Furthermore, the connectivity between trabeculae was reduced and the trabecular spacing was increased. In conclusion, four weeks after induction of osteoarthritis in the murine knee subtle but significant changes in subchondral bone architecture could be detected and quantified in 3D with micro-CT analysis.

Animals↗