Introduction to Special Conditions of the Flat Bones of the Cranium
The flat bones of the skull are somewhat special. They are generally curved.
Together, they form a sphere which surrounds and protects the brain.
Tab 1 Repair of Bones in the Cranium
When the growth of the cranial flat bones is complete, the osteogenic layer
of the periosteum disappears.
Cracks and/or line fractures of cranial flat bones will usually heal by the
activity of the osteoblasts within the bone.
However, when bone substance is lost and a spatial defect ("hole")
remains, the missing portions of the table(s) will not be replaced.
Osteoblastic activity will repair only the margins of the spatial defect ("hole").
Tab 2 Brain Injury in Young People
In a young individual, the flat bones of the skull are not yet fully
developed. The cranium as a whole is relatively flexible. An injury to the brain,
resulting from a force applied to the cranium, will usually be located immediately below
the location of the applied force.
Tab 3 Brain Injury in Adults
In an older adult, the flat bones of the skull have fully developed and are
more or less fused to each other. The cranium is a relatively solid sphere. An injury to
the brain, resulting from a force applied to the cranium, will usually be found on the
opposite side from the applied force.
Often, the applied force will be diverted around
the sphere to the base of the cranium. There, the diverted force may cause fractures of
the cranium at the apertures (openings) in its base.
Tab 4 Sesamoid Bones
The sesamoid bones are another kind of bone.
Sesamoid bones develop in place within tendons of skeletal muscles where the
tendons sustain excessive pressures. Since the sesamoid bone absorbs these pressures,
it protects the tendon from wear and tear.
The primary example of sesamoid bones is the patella (kneecap).
In the form of a simple pulley mechanism, the tendon of the quadriceps femoris muscle
passes over the distal end of the femur. Located at this point within the tendon is the patella.