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and the patient begins to weight bear again. Most expe-
rienced surgeons managing OI patients attempt to limit
these types of fractures by using lightweight splinting or
casting materials and by employing the shortest dura-
tion of immobilization possible. Rehabilitation following
fractures or osteotomies, including early water therapy
where the buoyancy of the body limits the weight bear-
ing while allowing muscle and joint function, is also
believed to help avoid disuse osteoporosis.
Other Extremity Issues in OI
The bones are not the only tissues affected in OI.
Children with OI frequently have hypermobile joints,
occasional with impressive ligamentous laxity. This can
make positioning of the limbs for function even more
challenging, as deformity in the long bones poorly posi-
tions the joints, and then ligamentous laxity in addition
to bone deformities can accentuate the malalignment.
Children with OI also commonly have lower than nor-
mal muscle tone and strength - perhaps an intrinsic
consequence of abnormal collagen in muscle or related
to the altered biomechanics and inefficient lever arms
around joints in the setting of limb deformity. Bracing
can be used to hold hypermobile joints in a biomechani-
cally appropriate position, with an added benefit being
provision of more support to the abnormal bones.
FIGURE 47.1
Severe anterolateral bowing of the tibia can prevent
the foot from being able to achieve a plantigrade position for weight
bearing.
PROBLEMS CAUSED BY LIMB
DEFORMITY
studies, however, question the ability of surgical long
bone realignment of the lower extremities to improve
ambulatory status. The ability to ambulate is based on
multiple factors in addition to limb alignment, such as
muscle strength and coordination, ligamentous stabil-
ity and neurological control. Treatment interventions
for children with OI need to be tailored based on defor-
mity and the child's functional level. Smaller amounts of
deformity that do not interfere with limb function can be
better tolerated and may be amendable to non-operative
treatment and/or observation for progression of defor-
mity, while a larger degree of deformity may be best
addressed surgically.
Any deformity that causes loss of the mechanical axis
of the bone results in increased stress at the apex of the
deformity. This can lead not only to fracture, but also to
inability to place the limb in space for stance or appro-
priate function. As an example, severe anterolateral bow-
ing of the tibia can result in an inability to place the foot
plantigrade on the ground (
Figure 47.1
). Thus, during
surgical realignment procedures, the goal should be cor-
rection of the mechanical axis, as residual bowing will
increase the risks of refracture and progressive deformity
(
Figure 47.2
). Deformity of the upper extremity is better
tolerated, as the less constrained shoulder joint allows
abundant compensatory motion, resulting in the abil-
ity to place the hand in space despite deformity of the
humerus or forearm. In the lower extremity, deformities
of bone are less well tolerated. The femur and tibia sup-
port more weight than in the upper extremity, and have
joints with more constraints, such as the hip or knee.
Severe bowing can lead to recurrent fractures of the limb.
Frequent splinting or casting can also impede develop-
ment of gait or other milestones in infants and toddlers
who otherwise have the neurological development that
would allow achievement of these milestones. Some
T
REATMENT OF DEFORMIT
Y
Medical Management of Deformity
The use of bisphosphonates became widespread for
the treatment of OI in children in the early 1990s. While
multiple randomized controlled studies have shown that
bisphosphonates use can reduce the number of fractures,
there are no data that specifically document a reduction
