Bma Illustrated Medical Dictionary

and also occurs with asthmaand chronic

obstructive pulmonary disease (see pul-

monary disease, chronic obstructive).

orthopticsTechniques used mainly in

children to measure and evaluate squint,

including eye exercises, assessment of

monocular and binocular vision, and

measures to combat amblyopia.

orthoticsUse of appliances to support

or correct weakened or deformed joints.

osAn anatomical term for a bone; also

refers to an opening in the body, as in

the cervical os (entrance to the uterus).

Osgood–Schlatter diseasePainful en-

largementand tenderness of the tibial

tuberosity (the bony prominence of the

tibia), which occurs most commonly in

boys aged between 10 and 14. It results

from excessive, repetitive pulling of the

quadriceps muscle, due to repeated exer-

cise. The disorder often clears up without

treatment; severe pain may require

physiotherapyor immobilization of the

knee in a plastercast.

osmosisThe passage of a solvent from a

weaker solution to a more concentrated

one through a semipermeable membrane.

All body cells are surrounded by such

membranes, which allow water, salts, sim-

ple sugars (such as glucose), and amino

acids(but not proteins) to pass through.

Therefore, osmosis plays an important

part in regulating the distribution of water

and other substances in body tissues.

ossicle A small bone, especially any of the

3 tiny bones in the middle ear(malleus,

incus, and stapes) that conduct sound

from the eardrum to the inner ear.

OSSICLE

orthodontic appliancesFixed or re-

movable devices, commonly known as

braces, worn to correct malocclusion, or

to reposition overcrowded or buck teeth.

Usually fitted during childhood and

adolescence, they move teeth using

sustained gentle pressure. A fixed appli-

ance has brackets attached to the teeth

through which an arch wire is threaded

and tightened to exert pressure. These

are usually kept in place for about a year,

after which time a retainer plate may be

needed to hold the teeth in place until

tooth and jaw growth has finished.

Removable appliances, consisting of a

plastic plate with attachments that

anchor over the back teeth, are used

when only one or a few teeth need cor-

recting. They apply force by means of

springs, wire bows, screws, or rubber

bands fitted to the plate.

orthodonticsA branch of dentistry

concerned with preventing and treating

malocclusion. The procedures are usually

performed while teeth are developing

and still relatively manoeuvrable, but

can also be of benefit in adulthood.

An orthodontist may first make mod-

els of the teeth (see impression, dental)

and take X-raysof the head and jaws.

Certain teeth, often premolars, may be

extracted to make room for the remain-

ing teeth. Poorly positioned teeth are

then moved by gentle pressure exerted

by orthodontic appliances.

orthognathic surgeryAn operation to

correct deformity of the jaw and the

severe malocclusionthat is invariably

associated with it. The bones of the jaw

are repositioned under general anaesthe-

sia, and often require splinting (see

splinting, dental) until they heal.

orthopaedicsThe branch of surgery con-

cerned with disorders of the bonesand

jointsand their associated muscles,ten-

dons, and ligaments. Procedures include

setting broken bones and applying casts;

treating dislocations, slipped discs,

arthritis, and back problems; treating

bone tumours and birth defects of the

skeleton; and repairing or replacing hip,

knee, or finger joints.

orthopnoeaDifficulty in breathing when

lying flat. Orthopnoea is a symptom of

heart failure and pulmonary oedema,

ORTHODONTIC APPLIANCES OSSICLE

O

Incus

Malleus

Stapes

LOCATION

OSSICLES

OF EAR

Outer

ear Inner ear

Middle ear

Eardrum