Bone inclu
des cavities in various length scales, from nanoporosities occurring between the collagen fibrils an
d the mineral crystals all the way to macrocavities like the me
dullary cavity. In particular, bone is permeate
d by a vast number of channels (the lacunar-canalicular system), that re
duce the stiffness an
d, more importantly, the strength of the bone that they permeate. These consequences are presumably a price worth paying for the ability of the lacunar-canalicular system to
detect changes in the strain environment within the bone material an
d, when
deleterious, to trigger processes like mo
deling or remo
deling which ¡®rectify¡¯ it. Here we review the size an
d density of the various types of cavities in bone, an
d discuss their effect on the mechanical properties of cortical bone.
In this respect the bones of advanced teleost fish species (probably the majority of all vertebrate species) are an unsolved conundrum because they lack bone cells (and therefore lacunae and canaliculi) in their skeleton. Yet, despite being acellular, some of these fish can undergo considerable remodeling in at least some parts of their skeleton. We address, but do not solve this mystery.