Webster's New World Medical Dictionary

stereotactic radiation therapy
See 
radiation
therapy, stereotactic.
stereotactic radiotherapy
See 
radiation ther-
apy, stereotactic.
stereotactic surgery
Surgery in which a system
of three-dimensional coordinates is used to locate
the site to be operated on.
stereotaxis
Use of a computer and scanning
devices to create three-dimensional pictures.
Stereotaxis can be used to direct a biopsy, external
radiation, or the insertion of radiation implants.
sternal rib
See 
rib, true.
sternotomy
A surgical incision made through the
breastbone (sternum), for example, as performed
for access to the heart during surgery.
sternum
The long flat bone in the upper middle
of the front of the chest. The sternum articulates
(comes together) with the cartilages of the first
seven ribs and with the clavicle (collarbone) on
either side. The sternum consists of three parts: the
manubrium (the upper segment of the sternum, a
flattened, roughly triangular bone), the corpus
(body) of the sternum, and the xiphoid process (the
little tail of the sternum than points down). These
sections of the sternum arise as separate bones, and
they may fuse partially or completely with one
another. Also known as breastbone.
steroid
One of a large group of chemical sub-
stances classified by a specific carbon structure.
Steroids include drugs used to relieve swelling and
inflammation, such as prednisone and cortisone;
vitamin D; and some sex hormones, such as testos-
terone and estradiol.
steroid abuse
Use of substances containing
steroids to increase muscle mass. Steroids can have
many side effects when misused, including psychi-
atric problems, liver tumors, reduction in the size of
male genitals, sterility, and heart damage.
stethoscope
An instrument that is used to trans-
mit low-volume sounds such as a heartbeat (or
intestinal, venous, or fetal sounds) to the ear of the
listener. A stethoscope may consist of two ear pieces
connected by means of flexible tubing to a
diaphragm that is placed against the skin of the
patient. The stethoscope has become one of the
symbols of the medical profession. The origins of
the stethoscope can be traced back to the French
physician Laënnec, who in 1819 invented a crude
model that consisted of a wooden box that served to
help physicians hear the sounds within the chest
cavity. It has undergone many modifications since
then.