Bone Tissue - Meshless Methods in Biomechanics - page 219

maximize the resistance and minimize the weight. Bones perform several bio
functions [ 1 ], such as:
Mechanical Functions:
Support—The skeleton provide a frame that keeps the body supported.
Protection—Bones serve to protect internal organs and soft tissues.
Movement—Bones, muscles, tendons, ligaments and joints function are combined
together to generate and transfer forces so that located body parts, or the entire
body, may be manipulated.
Metabolic Functions:
Mineral repository—Bones are an important mineral repository (calcium and
phosphorus).
Blood cells producer—In the red marrow (hematopoietic) erythrocytes (red blood
cells), leucocytes (with blood cells) and platelets are produced.
Energy repository—In the yellow marrow fat cells can be found, an energy depot.
Besides all this, the bone is a living tissue, in constant mutation, experimenting
a continuous reconstruction and reformulation along its life span, due to
mechanical, nutritional and endocrine stimulus [ 1 ]. This chapter describes the
structure, the material composition and the mechanical properties of the bone
tissue. Biologic material laws suitable to simulate the bone tissue are presented, as
well as a new developed phenomenological law. Afterwards the bone tissue
remodelling algorithm used in this topic is presented.
6.1.1 Bone Morphology
The human skeleton structure has more than 200 bones classified, by shape, in four
major types: long bone, short bone, flat bone and irregular bone [ 1 ]. These bone
types are represented in Fig. 6.1 .
In the diaphysis zone, the outer shell of the long bone is cortical bone (compact
bone) and in the centre it can be found the medullar cavity, which contains in
adulthood yellow marrow (mainly fat cells). In the epiphyses the outer shell of
cortical bone is thin and in the core it can be found trabecular bone (spongy bone)
and red marrow. The red marrow, unlike the yellow marrow which is just a soft
tissue with energy depot functions, is a hematopoietic tissue and it is the site of
production of red cells, platelets and most of the white blood cells. These features
are represented in Fig. 6.2 .
Short bones are characterized to be small and to have no preferential dimension.
These bones consist of cancellous tissue (trabecular bone) enclosed within a thin
layer of cortical bone. Examples are the carpals, the tarsals and the bones in the
ankle and in the wrist.