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About
OI
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Causes
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Fractures
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Definition
Osteogenesis imperfecta (OI)
is a generalized connective tissue disorder characterized
mainly by multiple bone fractures, and blue
sclerae.
General information and
aetiology
Collagen is the protein
substance of the white fibres of skin, tendon, bone and
cartilage. In the disorder osteogenesis
imperfecta, due to a
hereditable genetic defect, the body has a lessened
ability to synthesise type 1 collagen. resulting in a
generalised decrease in bone mass
[osteopaenia].
OI is divided into five
types:
Type 1 is the mildest
form of the disease and most patients have distinctly
blue sclerae (the usually white area of the eye). They
are further subclassified into type 1A with normal
dentition (teeth formation), and type 1B where dentition
is abnormal.
Type II is lethal in utero
or shortly after birth. It is subclassified, by severity,
into five separate grades.
Type III is intermediate in
severity between types I and II. It is more severe than
type I, but the sclerae are only slightly blue in
infancy, and are white in adulthood. The condition tends
to become progressively more severe with age.
Type IV is similar to type
III except that it does not tend to become more severe
with age.
Incidence
33 per million
- type 1 - 70%
- type II - 2%
- type III - 20%
- type IV - 5%
Other features associated with
osteogenesis
imperfecta
1. Bone fragility
The fragility of bones in
type I patients may be severe enough to limit
physical activity, or so slight that individuals are
unaware of any disability.
In type II patients bones
and other connective tissue structures are so fragile
that massive injuries can result in utero, or during
delivery.
In types III and IV,
multiple fractures from minor physical stress can
produce progressive and severe deformities.
2. Ocular changes
The sclerae can be normal,
slightly bluish, or bright blue. Blue sclerae may be
an inherited trait in some families without evidence
of bone fragility.
3. Dentinogenesis imperfecta
The teeth may be normal,
moderately discoloured, or grossly abnormal in both
colour and shape. The first teeth are usually smaller
than normal, while the permanent teeth are frequently
bell-shaped and restricted at the base. The teeth may
fracture readily and need to be extracted.
Similar tooth defects may occur
in families without OI.
4. Hearing loss
Hearing loss is common,
usually beginning during the second decade of life and
detectable in 90% of subjects over the age of 30
years.
Hearing loss of conductive or
mixed type occurs in about 50% of patients, beginning
in the late teens and gradually leading to profound
deafness, tinnitus, and vertigo by the end of the
fourth to fifth decade.
5. Associated features
Other connective tissues
of the body may also be involved. Some have thin skin
that scars extensively. Others have extreme joint
laxity with permanent joint dislocations.
Cardiovascular manifestations
such as aortic regurgitation, floppy mitral valves,
and mitral incompetence may be present.
Care and Management
Despite numerous fractures
resulting in pain, restricted movement and diminished
growth, many adults with severe forms of O.I. lead
productive and happy lives. Once the condition has been
confirmed it is managed according to its severity and
risk for skeletal fractures.
Fractures in OI can be treated with
the standard methods appropriate for the type of fracture
and the age, and usually heal satisfactorily with
evidence of good callus formation and without deformity.
Fractures of the long bones, especially of the femur, may
require internal fixation including intra-medullary
nailing, to straighten them. Regular hearing evaluations
after adolescence are recommended. In some cases,
calipers, braces and other supports may be necessary to
protect the brittle bones.
A long-term physical therapy
exercise program to strengthen the paraspinal muscles,
together with adequate calcium intake, and perhaps
calcitonin or fluoride administration, may be
specifically indicated.
References
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