Physeal Fractures
Salter-Harris Classification
Keywords
Epiphysis an expansion at the
end of a long bone that develops from a secondary ossification
centre; it is separated from the shaft of the bone by physeal
cartilage during the period of growth. A capital epiphysis is
located at the end of a long bone, such as the femur.
Metaphysis the shaft of a long bone, between the ends
(epiphysis). The diaphysis consists of compact bone enclosing the
medullary cavity.
Growth Plate the cartilaginous physis
or advancing frontier of cellular activity in the endochondral
ossification
of
long bones. This plate or
synchondrosis
has clearly delimited zones and eventually comes to be located
between the epiphysis and
diaphysis of
tubular bones. The four defined zones of the growth plate include,
the reserve zone, in which cartilage cells are few and
randomly situated; the proliferating zone, in which matrix is
produced and cell proliferation occurs; the hypertrophic zone, which
can be subdivided into three other zones (maturation, degeneration,
provisional calcification; and the zones of primary and secondary
spongiosa.
Background: Salter-Harris
fractures are fractures through a growth plate; therefore, they are
unique to pediatric patients. Several types of fractures have been
categorized by the involvement of the physis, metaphysis, and
epiphysis. The classification of the injury is important because it
affect the treatment of the patient and provides clues to possible
long-term complications.
Pathophysiology: The histologic features of the physis are
important for understanding the prognosis of physeal fractures. The
germinal layer of the cartilage is on the epiphysis and derives
nutrition from the epiphyseal vessels. Cartilage cells grow from the
epiphysis towards the metaphysis, forming columns of cells that
degenerate, fragment, and undergo hypertrophy. The fragments of
cells mineralize. This is the zone of provisional calcification
forming the metaphyseal border, and is not bone. Note that no
circulation exists in the cartilage zone.
Neovascularization occurs from the metaphysis towards the epiphysis.
Endothelial cells transform into osteoblasts and use the degenerate
cell debris to form primary immature bone. This immature bone
progressively is remodeled to mature woven bone and further is
remodeled by cutting cones to form mature haversian system bone.
Damage to either epiphyseal or metaphyseal vascular supply disrupts
bone growth; however, damage to the layer of cartilage may not be
significant if the surfaces are reapposed, and vascular supply to
the growing cartilage is not permanently interrupted. When the 2
vascular beds touch, the physis is closed (fused) and no further
bone growth is possible.
Age: Salter-Harris fractures are injuries through the physis.
Therefore, by definition, they must occur before the physis closes.
Typically, physis closure occurs during the teenage years.
Clinical Details: The classification of Salter-Harris
fractures is used to describe the extent and site of the epiphyseal
injuries. The basic types of injuries include the following:
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Salter – Harris classification,
Table 1. Salter – Harris classification of growth plate
injuries.
| Type I: |
Pure epiphyseal separation, with the fracture
isolated to the growth plate itself.
In the type I injury, a
shearing or avulsion force causes a cleavage through the zone of
hypertrophic cells. The prognosis is favourable. The type I
injury is especially frequent as a result of birth injury.
Frequently spontaneous reduction of the separated fragments
takes place. In such instances, radiographs may reveal soft
tissue swelling and minimal widening or irregularity of the
growth plate.
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| Type II: |
Growth plate is slit for a variable distance by a shearing
or avulsion force before the fracture enters the metaphyseal
bone and separates a small fragment of the bone.
Type II is the most common type
of growth plate injury. The small separated fragment of bone is
termed the
Thurston Holland sign (presence of a small separated fragment of
bone from the growth plate appearance is also known as the shiny
corner sign)
or corner sign. Because of intact
periosteum, the fracture fragment is usually reduced easily.
Common sites of involvement are the distal ends of the radius,
tibia, fibula, femur and ulna. Generally the prognosis after
this injury is good.
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| Type III: |
Fracture line extends vertically through the epiphysis and
growth plate to the hypertrophic zone and then horizontally
across the growth plate itself, usually on one side or the
other.
Type III injuries are especially
common in the medial or lateral portion of the distal part of
the tibia. Displacement is generally minimal, and growth arrest
and deformities are rare. |
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| Type IV: |
Fracture that extends across the epiphysis, the growth plate
and the metaphysis producing a fragment that consists of a
portion of both the epiphysis and the metaphysis.
Type IV injuries are encountered
most frequently in the distal ends of the humerus and tibia. A
type IV injury may require open reduction and careful
realignment so that growth arrest and joint deformity are not
encountered at a later date. |
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| Type V: |
Injury to the vascular supply in the germinal cells of the
plate occurs without any immediate radiographic signs.
Although type V injuries may not
be evident immediately, subsequent radiographic examination may
indicate diminished or absent bone growth, which can produce
angular deformity. |
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In addition to the five classic types, several other types of
injury to the growth plate or neighbouring bone are seen that were
not described by Salter and Harris.
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Type VI |
Type VI results from an injury (e.g. physical trauma, burn, or
infection) to the perichondrium that produces reactive bone
formation external to the growth plate.
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Type VI |
Type VI results from an injury (e.g. physical trauma, burn, or
infection) to the perichondrium that produces reactive bone
formation external to the growth plate.
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Type VII |
Type VII consists of epiphyseal changes in the absence of
involvement of the growth plate or metaphysis, such as transchondral
fractures and
osteochondritis dissecans.
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| Type
VIII |
A type VIII injury affects metaphyseal growth and remodelling
mechanisms in the immature skeleton, related primarily to effects on
the blood supply.
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| Type
IX |
In type IX, an injury to the periosteum of the diaphysis in rare
circumstances may result in disruption of normal diaphyseal growth
and remodelling. |
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Useful Links
http://www.vh.org/adult/provider/radiology/bone2/L2Slide13.html
http://www.amershamhealth.com/medcyclopaedia/Volume%20III%201/Salter%20%20Harris%20classification.asp
http://www.emedicine.com/radio/topic613.htm
Images from Brian Tidy at
http://www.radiographersreporting.com/
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