Modeling and remodeling in bone tissue
Abstract (summary)
Bone tissue, the main material the skeleton consists of, has remarkable properties. Two macroscopically different types are distinguished. The first type is cortical or compact bone, which is a rather dense tissue. The second type is trabecular or cancellous bone. This is a porous tissue with a complex three-dimensional structure consisting of struts and plates, called trabeculae. Already in 1892 Wolff found that the orientation of these trabeculae coincides with the direction of the stress trajectories. He proposed that bone loading is somehow sensed and that bone adapts its structure accordingly. This principle of functional adaptation is generally known as ‘Wolff's Law’. It occurs in conditions of disuse when bone is lost, and in intense physical usage when bone mass increases, but also during growth, after fracture healing and in relation with implant incorporation, when the orientation of trabeculae changes. The ability of the bone to adapt to mechanical loads is brought about by continuous bone resorption and bone formation. If these processes occur at different locations, the bone structure is altered. This is called modeling. In a homeostatic equilibrium resorption and formation are balanced. In that case old bone is continuously replaced by new tissue, ensuring the maintenance of mechanical integrity of bone tissue without any global changes in the architecture. This is called remodeling. The modeling and remodeling processes are conducted by specialized bone-resorbing and bone-forming cells, called osteoblasts and osteoblasts respectively. The pathways by which mechanical forces are expressed in osteoclast and osteoblast activity is currently one of the main unresolved issues in bone mechanobiology.
For this dissertation we studied the modeling and remodeling processes as modulated by mechanical forces. We demonstrated that many of the phenomena as they occur in the bone tissue can be explained by a remarkably simple theory, based on the assumptions that osteocytes, which reside in the bone tissue matrix, are mechanosensitive cells capable of sending biochemical messengers to the bone surface. These signals stimulate osteoblasts to form bone whereas they inhibit resorption by osteoclasts. (Abstract shortened by UMI.)
Indexing (details)
Biomedical engineering