Glossary of Terms

Here is an alphabetical list of medical terms and other words or phrases you may encounter while seeking healthcare:

pertaining to the ends of the extremities

surgical removal of adenoids

lymphatic tissue forming a prominence of the wall of the pharyngeal recess of the nasopharynx


removal of amniotic fluid by syringe placed through uterus and amniotic membrane for the use of genetic testing or testing of fetal lung maturity.

immobility of a joint

before or in front of; in anatomy; the abdominal side of a person

Atlantoaxial instability
instability of the union between the first and second cervical vertebrae

a wasting or decrease in size

assessment of hearing

Autosomal dominant
referring to inheritance of a genetic trait; a trait that is expressed whenever the gene is present and unrelated to the sex of the individual

Autosomal recessive
referring to inheritance of a genetic trait, a trait that is only expressed when an individual has both genes for this trait and unrelated to the sex of the individual

Avascular necrosis (Legg Perthes)
death of tissue or bone due to lack of blood supply

not harmful, not recurrent or progressive

bilevel positive airway pressure; a way to provide adequate oxygen to a person with sleep apnea

Bone age
an estimate of biological age based on radiological findings. May be used to determine how much more growth potential an individual has.

abnormal shortening of fingers and/or toes

continuous positive airway pressure; a treatment for sleep apnea which works to increase the level of oxygen saturation of the blood during sleep

permanent flexion (bent) of fingers or toes

a connective tissue that forms part of the skeleton; provides a model embryologically in which most bones develop

opacity (unclear) of the lens of the eye causing severe visual impairment

Central apnea
temporary cessation (stopping) of breathing due to a problem related to the central nervous system (brain)

Cerebrospinal fluid (CSF)
a water cushion surrounding the brain and spinal cord protecting them from physical impact. Excess amounts of CSF or decreased flow of CSF between the brain and spinal cord can be indicators of a neurological problem.

pertaining to or the region of the neck

Cervicomedullary junction
the junction between the base of the skull and brain stem and the cervical spine and spinal cord.

Chorionic villus sampling (CVS)
a prenatal test in which small pieces of the placenta are removed to genetically test the fetus.

the packages of material in the nucleus of every cell made up of DNA in which an individual's genes are encoded.

ongoing; denoting a disease that is long term or life long with slow progression

Cleft palate
a palate (roof of the mouth) with a congenital opening

description of information founded directly on observation and treatment of patients.

a neurological finding observed as a spasmodic reflex in the ankle due to a compression or injury of the spinal cord.

Club feet
a congenital malformation of the feet in which they are rotated in and on the side towards to the other foot. This is usually treated with corrective casting.

a protein found in connective tissue of multiple systems of the body.

Computed tomograpy scan (CT scan or CAT scan)
a technology for quickly imaging bone, soft tissue and blood vessels

Conductive hearing loss
hearing loss due to some type of blockage or structural abnormality of the ear which prevents the sound waves from reaching the inner ear.

present at birth.

Connective tissue
tissues of the body that bind together bones, muscles and other body parts.

Corneal clouding
clouding of the outer layer of the eyeball due to deposits of a cellular material

Coxa vara
a deformity at the hip joint that occurs when the head of the femur is at an angle of less than 120 to the shaft of the femur, causing the femur to not fit into the hip socket correctly

pertaining to the skull and face

the removal of pressure. In skeletal dysplasias, most often refers to a surgical procedure performed on the spine to reduce pressure on the spinal cord created by the abnormally formed vertebrae and skull.

Deep tendon reflexes
a reflex which can indicate pressure on or injury of the spinal cord.

a cause of progressive deterioration

a process by which the blood is not carrying as much oxygen as it optimally could

pertaining to a diagnosis; usually refers to a characteristic or criteria which is critical for a specific diagnosis.

Disproportionate (short stature)
a size or ratio different from what is considered to be normal. Disproportionate short stature is when one part of the body (e.g. the trunk) is short in comparison to another part (e.g. the limbs)

farthest from the center (i.e. the hands are distal in relation to the upper arm (humerus))

abnormal development of tissue (including bone, muscle, etc.)

Ear, Nose and Throat
see Head and Neck Surgery

Enamel hypoplasia
underdevelopment or lack of development of tooth enamel

of the trachea (tube which connects larynx to lungs for the purpose of breathing)

a cellular substance which facilitates a specific chemical reaction. When an enzyme is missing or in decreased quantity, the specific reaction plus all those that occur subsequently (as part of a chain of reactions) will not occur correctly or at all and therefore subsequent physiologic problems will arise

of the epiphysis; the epiphysis is the center of ossification at the end of the long bones

Eustachian tube
auditory tube that connects the ears to the nasopharynx. Eustachian tube dysfunction results in poor drainage from the ears to the nasopharynx

movement that pulls apart both ends of any part

long (upper) bone of the thigh

outer and smaller bone of the lower leg (calf)

act of binding or condition of being bent decreasing the angle between the bones forming a joint.

Flexion contractures
the fixation of a joint in a fixed position (inability to fully straighten or extend at a joint)

Foramen magnum
opening at the base of the skull through which the spinal cord passes from the brain into the spinal column

Frontal bossing
prominence of the forehead

union/coming together of two body parts; two permanently joined body parts which were previously separate due to natural processes or surgical intervention (e.g. fusion of cervical vertebrae to provide stability).

the way in which a person walks

Gastresophageal reflux (GE reflux)
a return or backward flow of stomach contents up through the esophagus

regions of DNA that code for proteins, which determine an individual's development and traits and are inherited from generation to generation

pertaining to genes and reproduction

Genu valgus
knock knees; in turning of legs that bring knees close together or possibly touching while standing and/or walking. Knock knees has to do with how the knee lines itself up with the hip and ankle. In a child with knock knees though, when the knees touch, the ankles are separated by a good distance.

Genu varum
bowlegged; curvature of the legs resulting in increased space between the knees usually due to the overgrowth of the fibula in relation to the tibia. The fibula "bows" in order to accommodate for the shorter tibia.

Germline mosaicism
the presence of reproductive cells (sperm or egg) of different genetic make-up. For example, an average-statured parent may some reproductive cells with the mutation for achondroplasia. This would give them a chance of having more than one child with achondroplasia.

wedging of vertebra in a kyphotic curve of the spine.

Head and Neck surgery
medical specialty previously called ENT (ear, nose and throat) that focuses on the surgical management of issues of the head and neck

two different versions of a specific gene. As in achondroplasia, one gene without a mutation and one with the mutation for achondroplasia.

having two identical versions of a specific gene. Homozygous or double dominant achondroplasia occurs when a child has two copies of the gene for achondroplasia

bone of the upper arm connecting the shoulder to the elbow.

increased accumulation of cerebrospinal fluid (CSF) within the ventricles fo the brain. Can indicate a blockage to the flow of CSF.

excessive joint movement that permits increased mobility (flexibility)

increased action of the reflexes; can be an indicator for a neurological complication

abnormally increased distance between eyes

increased in size of an organ or body structure

abnormally decreased amount of phosphate circulating in blood

underdevelopment of tissue or organ

episode of decreased rate and depth of breathing

decreased or low muscle tone

insertion of a tube into any organ; usually refers to insertion of a tube in the larynx/trachea to provide air for respiration.

local, temporary deficiency of blood supply due to obstruction

Joint dislocation
temporary displacement (usually) at the point of juncture between two bones of a bone from its usual position in the joint

an exaggeration or angulation of the normal posterior curve of the spine; an outward curve of the mid spine

the surgical excision (removal) of a vertebral posterior arch. In skeletal dysplasias, this is most often done to decrease pressure on the spinal cord at that level.

strong fibrous connective tissue which connects the end of the bones at a joint and binds them together, facilitating or limiting motion

Ligamentous laxity
looseness of the ligaments

the lower part of the spine/back but not including the vertebrae that extend into the pelvis

pertaining to the region of the spine including the lumbar and sacral vertebrae

abnormally large size of head. This maybe normal for the child's condition or an indicator or problems with brain development.

Magnetic Resonance Imaging (MRI)
type of diagnostic imaging that uses electromagnetic imaging and allows evaluation of tissues and fluid in addition to bone. This imaging providing two dimensional cuts through the body part being study which allows a physician to develop a three dimensional sense of the anatomy of that part. Often used to study the brain and spine as well as joints.

malposition and imperfect contact of the mandibular (lower) and maxillary (upper) teeth.

horseshoe-shaped bone forming the lower jaw

a paired bone that forms the skeletal base of the upper face, roof of mouth, sides of the nasal cavity and floor of the eye orbits. Part of the maxilla supports the upper teeth and is called the upper jaw.

shortening of the middle of the bone (usually referring to the long bones)

the portion of a developing long bone that is between the diaphysis (shaft) and the epiphysis; the growing portion of the bone

with significantly short or small limbs

Middle ear effusion
escape of fluid into the middle ear (behind the eardrum).

Midface hypoplasia
underdevelopmemt or undergrowth of the midface (between, but not including, forehead and mandible)

Milestones (developmental)
a significant development event or accomplishment, such as sitting, walking, talking, etc. There are standards for accomplishing developmental milestones by age. Children with skeletal dysplasias and other medical conditions may accomplish these milestones at a slower pace or in a different manner than average children.

Mixed hearing loss
hearing loss that is both conductive as well as having a sensorineural component

a group of rare genetically determined disorders caused by the body's inability to produce certain enzymes, resulting in an abnormal deposit of complex sugars in tissues and cells. This process causes progressive damage which can range in severity from strictly bone and joint involvement to massive complications in all organ systems.

a change in a gene potentially capable of being transmitted to offspring and possibly causing a different characteristic or medical condition in an individual

condition of the spinal cord, usually causing neurologic symptoms and findings.


incision of the tympanic membrane (eardrum). Often done for the placement of tubes to encourage draining of fluid caught behind the eardrum and often resulting in recurrent ear infections.

Natural history
the understood course of a medical condition, usually with a wide range of severity between affected individuals

of or pertaining to the nervous system, including the brain, spinal cord and nerves.

the medical specialty with expertise in the nervous system

Obstructive apnea
temporary cessation (stopping) of breathing due to a problem related to an obstruction or blockage of oxygen getting to the lungs. Usually due to structural problems of the face and/or neck. In the skeletal dysplasias, common causes include small nasal passages, redundant pharyngeal tissue, large tonsils and/or adenoids.

Occipital frontal circumference
head circumference. The measurement of the distance around the skull. There are standards for head circumference that have been created by age and sex. Achondroplasia has specific growth curves that have been developed for monitoring head circumference.

Odontoid (process)
a toothlike process that stabilizes the connection between the head and the neck. It sticks up through the first and second cervical vertebrae, providing support as the head moves backwards and forwards.

Odontoid hypoplasia
underdevelopment of the odontoid process which can lead to instability of the cervical spine at the junction with the skull

the medical specialty with expertise in preventing and correcting abnormalities of the skeleton and other supporting structures including joints, muscles, and connective tissue.

arthritis (inflammation of a joint) marked by progressive deterioration of the joints and/or vertebrae

decrease in the amount of bone tissue

disease process that decreases the density of bone, making the bones more susceptible to breaks

an operation in which the bone is cut through. This type of operation is often used to correct deformities of the legs, such as bowlegs or knock knees.

Otitis media
inflammation and/or infection of the middle ear

Overnight oximetry
see polysomnography

Pectus carinatum
a condition in which the sternum is abnormally prominent or sticks out; pigeon breast

Pectus excavatum
a condition in which the sternum is abnormally depressed

the bony structure that supports the vertebral columns and contains the hip sockets

Pes planus
flat feet

bones of the fingers and toes

medical specialty also known as Physical Medicine and Rehabilitation (curing of medical symptoms by natural methods, such as physical therapy, exercise, heat/cold, etc.

Physical therapy
medical specialty of rehabilitation in order to restore physical function and prevent disability

flat vertebrae

more than 5 fingers and/or toes

continuous study of respiration during sleep

referring to in the rear or toward the back; situated behind

mental or physical developmental earlier than the average age

Prenatal diagnosis
tests (amniocentesis, ultrasound, chorionic villus sampling (CVS)) used to diagnosis medical conditions in pregnancy

Pressure equalizing tubes (PE tubes)
ventilating tubes; small tubes placed in the eardrum (tympanic membrane) to allow for drainage of fluid that has collected behind the eardrum.

changing position to face downward; lying down or turning the arm and hand so that the palm faces downward

Proportionate short stature
short stature in which the trunk and the limbs are in equal or similar proportion

near the center

of or relating to the lungs and respiration

Pulmonary hypoplasia
underdevelopment of the lungs

the medical specialty of respiration

Radial head dislocation
displacement of the radial head from its usual position in the joint at the point of juncture between the radius and the humerus (elbow)

Radial head subluxation
partial or incomplete dislocation of the radial head

the medical specialty of diagnostic imaging and interpretation

the shorter of the two bones of the lower arm on the side of the thumb

the process of treating and training a person with a disability to achieve maximum function and independence.

Restrictive lung disease
decreased pulmonary function secondary to decreased size of the chest cavity and/or lungs

Retinal detachment
separation of the inner sensory layer of the retina to the outer epithelium (outer surface of eyeball) which can lead to blurred vision, light flashes, loss of visual acuity, etc. Individuals with skeletal dysplasias involving connective tissue are usually monitored closely for this complication, as repair may be possible.

proximal shortening; shortening at the end of the bone closest to the trunk (humerus, femur)

a condition affecting that development of bone either due to a deficiency of vitamin D or a genetic defect leads to the inability to utilize vitamin D. In both cases, the condition can be treated

of the lowest part of the spine

the vertebrae complex below the lumbar region of the spine that connects the vertebral column to the pelvis

a lateral (sideways) curve of the spine usually consisting of two curves - the abnormal one and another to compensate for it.

Sensorineural hearing loss
hearing loss due to a problem with sending signals from the ear to the brain

medical symptoms or conditions that result from having a specific disease. For example, bowed legs and lumbar stenosis are sequelae of achondroplasia.

Sleep apnea
temporary, often repeated, cessation of breathing during sleep

Sleep study
see polysomnography

Somatosensory evoked potentials (SSEP)
study of nerves to assess their functional state

random, occurring occasionally; in genetics, not inherited, new

partial or incomplete dislocation

the motion of turning of the palm of the hand so that it faces upward

Talipes equinovarus
a deformity of the feet in which the foot is extended and the individual walks on their toes

referring to the chest and middle region of the spine (vertebrae to which the ribs are attached)

region of the spine at the juncture of the thoracic and lumbar vertebrae

the inner and larger bone of the lower leg

surgical removal of the tonsils

having three prongs, resembling a trident fork

of or related to the trunk

tympanic membrane

the longer of the two bones of the lower arm on the side of the 5th finger.

diagnostic imaging using sound waves. Most often used to evaluate fetuses in utero, but also used for evaluation of the brain and other organs.

Ventriculo-peritoneal shunt (VP shunt)
a medical device placed in a ventricle of the brain and draining to the chest which diverts fluid from the brain and prevents the development of hydrocephalus

increased size of the ventricles in the brain

X-linked dominant (XLD)
referring to inheritance of a genetic trait; a trait that is expressed whenever the gene is present and is inherited on the X chromosome

X-linked recessive (XLR)
referring to inheritance of a genetic trait; a trait that is expressed whenever the gene is present and depending on the sex of the individual. In XLR conditions, a male will always be affected and females may be unaffected or more mildly affected as they have a second X chromosome which will help to compensate for the abnormality on the other X chromosome.