what-when-how
In Depth Tutorials and Information
FIGURE 20.6
Hyperplastic callus. (A) A 5-year-old boy sustained a femur shaft fracture. (B) Postoperation 4 weeks after open reduction and intra-
medullary rodding. (C) Postoperation 8 weeks. (D) Postoperation 9 months. (E) Postoperation 18 months.
(Figure C reproduced from
11
with permission.)
non-traumatic radial head dislocation in young children.
Almost all adult patients show RHD, while some imma-
ture patients do not, suggesting the developmental nature
of this pathology. The pathogenic mechanism of RHD
remains to be elucidated. Trauma to the elbow does not
proceed in most cases; hence, the development of RHD
may be attributed to (1) RUIMO, (2) angular deformity of
the forearm bones or (3) bulbous hyperplasia of the proxi-
mal ends of the radius and ulna. RHD may contribute to
the limited range of motion of the forearm and elbow.
previously. In addition, it is not clear yet whether HC
develops exclusively in type V, or whether it develops
in other types of OI. Glorieux et al. wrote that they had
not experienced any HC in any other types of OI; how-
ever, they did not exclude that possibility
1
and neither
has this author. On the other hand, in the literature, some
OI patients with HC were reported to have blue sclera,
suggesting HC in other types.
8
Since these patients were
reported before the concept of type V was established,
however, further investigation is necessary to verify the
occurrence of HC in other types.
HC predominantly affects the long bones, most com-
monly the femur followed by the tibia and humerus.
Iliac involvement was also reported.
27,35
HC should be
differentiated from intraosseous osteosarcoma, paros-
teal osteosarcoma, juxtacortical myositis ossificans and
osteochondroma.
35
CT and MRI may help differentiate
HC from malignant conditions;
35,39
however, awareness
of OI type V and its predisposition of HC are also impor-
tant in differential diagnosis. Clinically, the affected limb
segment has pain, tenderness, diffuse swelling and local
heat during active phase, and the serum alkaline phos-
phatase level increases.
1,33,36,37
HC usually regresses
clinically in months or years; however, it can leave some
radiologic stigmata or bone deformation. No medication,
neither bisphosphonate nor indomethacin, has shown
any influence on the natural course of HC.
27
OI type V patients frequently develop abnormal ossi-
fications other than RUIMO or HC. Some bone segments
develop subperiosteal bone formation, usually without
minor injury or any other plausible causes. It does not
grow as exuberantly as HC, but remains diffuse and lat
(
Figure 20.7A, B, and C
). In its acute phase, clinical mani-
festations seem to vary from patient to patient. Some
complain of severe pain, tenderness and/or limited
motion in neighboring joints that interfere with activi-
ties of daily living, or even disability in walking, but
Hyperplastic Callus Formation (HC) and other
Abnormal Ossifications
HC is a radio-opaque lesion originating from the
surface of a bone segment under the healing process of
a fracture or osteotomy, which is huge compared to the
host bone showing unusual features such as sun-ray
spicules and a butterfly-like appearance (
Figure 20.6
).
33
HC has long been reported in OI patients, starting in
1908.
34
On reviewing their description of cases, many of
them seem to be OI type V.
2-4, 6, 8, 31, 35
Glorieux et al.,
1
in
their first report defining OI type V, included HC as one
of the conspicuous features of this disease entity. In the
reported series of OI type V, the incidence of HC ranged
from 57
1
to 75%,
11
and there are also some anecdotal
case reports of HC in OI type V patients
36,37
or fami-
lies.
38
The incidence of HC is dependent upon the dura-
tion of observation or the age of the patient. HC usually
develops in association with fractures
27
or osteotomy;
4
however, spontaneous onset without any documented
fractures or osteotomy was also observed.
27,37
Not all OI
type V patients develop HC, nor do all the fractures in
those who have developed HC end up with HC. Zeitlin
et al.
27
reported that only nine fractures developed HC
among 35 fractures in the lower extremities of OI type
V patients who had had at least one episode of HC
