This study is important because it indicates that microcracks may be bad for fluid flow which stimulates bone growth but good for cartilage growth as if fluid is not flowing than it is building up pressure and pressure is more conducive to chondrogenesis. This indicates that a method to induce fluid flow such as clamping/tapping should be higher duration and more “fatigue loading” based to insure the induction of microcracks. Fatigue loading is the act of inducing bone damage not by a sudden large damage but by sustained bouts of loading over time.
Influence of interstitial bone microcracks on strain-induced fluid flow.
“microcracks act as a stimulus for bone remodelling, initiating resorption by osteoclasts and new bone formation by osteoblasts. Microcracks alter the fluid flow and convective transport through the bone tissue. [We evaluate] the strain-induced interstitial fluid velocities developing in osteons in presence of a microcrack in the interstitial bone tissue. Based on Biot theory in the low-frequency range, a poroelastic model is carried out to study the hydro-mechanical behaviour of cracked osteonal tissue. the presence of a microcrack in the interstitial osteonal tissue may drastically reduce the fluid velocity inside the neighbouring osteons{So maybe microcracks will increase hydrostatic pressure as hydrostatic pressure is the pressure exterted by a fluid at rest}. This fluid inactive zone inside osteons can cover up to 10% of their surface. Consequently, the fluid environment of bone mechano-sensitive cells is locally modified.”
“Cortical bone constitutes the outer shell of long bones. This live entity is continuously renewed by bone cells in response due to the loading generated by daily activity”
“microdamage occurring inside the osteonal volume may generate a cell-transducing mechanism based on ruptured osteocyte processes. Concomitantly, microcracks are likely to alter the fluid flow and convective transport through the bone tissue and thus modify the hydraulic vicinity of the sensitive cells”
“the drag force caused by the pericellular fibres is thought to activate the cellular biochemical response through the interactions with the cytoskeleton”
“the pressure inversely increases from its Haversian reference to reach its maximum in the interstitial tissues.”
“the presence of the microcrack strongly modifies the fluid flow velocities in the osteons located in the immediate vicinity of the damage. It may generate an “inactive zone” inside the osteon wherein the fluid velocities are relatively low and thus the osteocytes stimulation too”<-But even though fluid flow may be low hydrostatic pressure may be high which may be better for chondrogenesis.