Webster's New World Medical Dictionary

fourth ventricle
One cavity in a system of four
communicating cavities within the brain, which are
continuous with the central canal of the spinal cord.
The fourth ventricle is the most inferior (lowest) of
these. It extends from the aqueduct of the midbrain
to the central canal of the upper end of the spinal
cord, with which it communicates via the foramina
of Luschka and the foramen of Magendie. It is filled
with cerebrospinal fluid that is formed by structures
called choroid plexuses located in the walls and
roofs of the ventricle.
fraction, ejection
See 
ejection fraction.
fracture
A break in bone or cartilage. Although
usually a result of trauma, a fracture can be the
result of an acquired disease of bone, such as osteo-
porosis, or of abnormal formation of bone in a con-
genital disease of bone, such as osteogenesis
imperfecta (“brittle bone disease”). Fractures are
classified according to their character and location
(for example, greenstick fracture of the radius).
fracture, buckle
See 
fracture, torus.
fracture, clay-shoveler’s
An uncommon break-
age of the spine, of the vertebrae from the lower
neck or upper back, that results from stress. Clay-
shoveler’s fracture usually occurs in laborers who
rapidly lift heavy weights with their arms extended,
such as in shoveling. Symptoms of clay-shoveler’s
fracture include burning, knife-like pain at the level
of the fractured spine, between the upper shoulder
blades. Clay-shoveler’s fracture is diagnosed via X-
ray examination of the spine. Most patients require
no treatment other than rest and avoidance of activ-
ities that stress the area of the fracture. Occasionally
surgical removal of the tip of the broken spine is
performed for those with long-standing pain.