There is no universally accepted definition of osteoporosis. One of the most convincing is that proposed by the NIH in 19931, according to which osteoporosis is a generalised disease of the skeleton, characterised by a reduction in bone mass and a deterioration in the microarchitecture of the bone, which results in an increase in bone fragility and a greater tendency to fractures. The loss of bone mass and the deterioration of the microarchitecture are consequences of an alteration in the phenomenon of bone renewal, whose fundamental protagonist is what is called a “unit of bone remodelling”. Osteoporosis is therefore, ultimately nothing but a functional alteration in this unit.
Subsequent to the NIH definition, it has been felt necessary to introduce a new concept, that of bone quality2, which was not reflected in it. This concept includes both those aspects related to bone structure as well as those related to the characteristics of bone tissue (intrinsic properties of bone material). It is possible that an alteration in the quality of bone material is involved in the tendency to osteoporotic fractures, but in general its importance –in relation to bone mass and to those structural aspects– is less. Thus it can be accepted that the definition indicated earlier continues to be valid.
The skeleton is an organ of support, and as such it is exposed to the processes of deterioration which all structures which have to bear mechanical load suffer. But differently from inert support structures (columns, beams, etc), bone is a living organ, with capacity for renewal, and for maintaining its conditions of resistance. This renewal takes place in a permanently and has been given the name “bone remodelling”3,4. The speed at which it occurs is known as “bone turnover”.Read More