Is BMU-Coupling a Strain-Regulated Phenomenon? A Finite Element Analysis

Abstract

Histologically, two types of bone reconstruction are distinguished: modeling and remodeling. Modeling changes the amount of bone and determines its geometrical form in relation to the prevailing mechanical loads and their resulting deformation (strain). Remodeling renews existing bone in a sequence of resorption and formation. However, in both processes the cells responsible for resorption and formation are the same: osteoclasts and osteoblasts. We studied if there is a relation between the activity of these cells and the deformation of the local bone tissue during remodeling. Two finite element models were built on a microscopic, supracellular level: (1) a secondary osteon in cortical bone and (2) a Howship's lacuna in a trabecula. Both models were loaded in the ''natural,'' that is, longitudinal direction. Equivalent strains were determined as a measure for the deformation of the bone tissue. In the first model, the strain field around the osteon showed a region of decreased deformation in front of the tunnel, just where osteoclasts excavate cortical bone tissue. Behind the cutting cone, elevated strain levels appear in the tunnel wall at locations where osteoblasts are active. The second model showed that a local excavation of a loaded trabecula leads to higher strains at the bottom of the lacuna, where resorption is stopped and osteoblasts are recruited to refill the gap. However, in the direction of loading reduced strain levels appear, just where resorption continues to proceed along the trabecular surface. We conclude that at the tissue level, strain distributions occur during the remodeling process that show a relationship to the activity of osteoblasts and osteoclasts. This suggests that BMU coupling, that is, the subsequent activation of osteoclasts and osteoblasts during remodeling, is a strain-regulated phenomenon. (J Bone Miner Res 2000;15: 301-307)

Normal Bone Anatomy and Physiology

“…TGF-␤ released from bone matrix decreases osteoclast resorption by inhibiting RANKL production by osteoblasts. The reversal phase has also been proposed to be mediated by the strain gradient in the lacunae (20,21). As osteoclasts resorb cortical bone in a cutting cone, strain is reduced in front and increased behind, and in Howship's lacunae, strain is highest at the base and less in surrounding bone at the edges of the lacunae.…”

Mechanisms of osteocyte stimulation in osteoporosis

“…Bone lining cells, osteoblasts and osteocytes, have been proposed to act as mechanosensors within bone tissue (Cowin et al 1991;Lanyon 1993;Mullender and Huiskes 1997). Osteocytes are the most widely accepted candidates for sensing mechanical stresses in bone (Ajubi et al 1996;Burger and Veldhuijzen 1993a;Carter and Caler 1985;Cowin et al 1991;Huiskes et al 2000;KleinNulend et al 1995;Lanyon 1993;Mullender and Huiskes 1995;Mullender and Huiskes 1997;Mullender et al 1994;Smit and Burger 2000;Weinbaum et al 1994;Westbroek et al 2000).…”

The Alternation of Peri-Implant Bone Response Exposed to Static Lateral Load

“…According to some previous studies, osteocytes are proposed to be mechanical sensor cells. (29)(30)(31)(32) The load leads to deformation of the bone, which stimulates the alteration of the cell signal of osteocytes (29) . In addition, strong load may cause microcracks in the bone, which induces apoptosis of osteocytes (33)(34)(35) .…”