Microstructural And Mechanical Properties Of Human Ribs Joseph

The joints between the vertebra and ribs allow more motion than those at the
sternum. This is necessary to facilitate respiration by allowing the ribs to move and
altering the total volume of the thorax. The allowable motion of the ribs with respect to the
vertebrae increases downward along the spine, with the eleventh and twelfth ribs being the
most mobile in terms of the joint itself.
The mechanical aspects of the ribs and their articulations between the sternum and
vertebrae are an important part of this study. The articulations between each rib and the
sternum create a fixed type of end condition. This fixed end condition allows the
production of a bending or torsional moment at the attachment site. This may prove to be
an important factor when considering the effects this may have in the way the
microstructure of the rib adapts during the life of an individual. The articulations of the
ribs with the vertebral column may be classified as more of a pinned condition. This
condition allows the rib to rotate slightly, but translation is limited, therefore, the
production of torsional forces in the posterior portion of the rib is limited. The differences
between the articulations of the rib at each end may effect the microstructural adaptation
that occurs during life.
Bone Microstructure
The human rib is composed of cancellous bone surrounded by a thin cortical shell.
The cancellous core is created by an array of plates and columns of trabeculae. This
produces a structure with variable porosity and intercommunicating pores filled with bone
marrow. The classification of bone from compact to cancellous is dependent on its
porosity. The range of porosity for compact bone is 5% to 30% and 30% to over 90% for
cancellous bone (Carter and Hayes 1977). Cortical bone is responsible for providing the
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