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uncemented stem impossible without correction. Several
strategies have been used to solve this problem: (1) leave
the deformity unaddressed and use a small cemented
stem; (2) use a proximal femoral allograft and (3) correct
the deformity and use an uncemented stem.
Hardware can be very difficult to remove. Small intra-
medullary nails or rods are typical and it can be dif-
ficult to attach a vice grips for removal (
Figure 49.3
).
13
Removal may require extensive burring around the rod
entry and exit sites and the use of a slap hammer. This
procedure can be more difficult than expected because
the rods may have been in place since childhood and can
be overgrown. It may also be difficult to obtain purchase
on the rods for extraction. Too much force may result
in fracturing the femur, in which case stem placement
would become very challenging.
The use of an extended trochanteric osteotomy can
be very helpful in visualizing the implant and the defor-
mity correction. To correct the deformity on the medial
fragment of the proximal femur, a second osteotomy
will have to be made on the medial cortex of the femur.
Cables should then be wrapped around the bone of the
proximal femur. This second osteotomy should be made
at a more proximal level than the first to allow for correc-
tion of the varus deformity of the femur.
Different stems can be used for this technique. The
implant must be distally stabilized in the femur below
the osteotomy site. Fluted tapered implants, avail-
able in modular or nonmodular varieties (either of
which can work in this situation) can be helpful in this
regard. Careful templating is a must to determine pre-
operatively where the osteotomies should be placed and
what implants may it. An intraoperative radiograph is
required to ensure the correct implant it.
Poor bone quality makes femoral implant placement
difficult. Prophylactic cabling below the osteotomy
ensures that additional fractures are not propagated at
the time of implant insertion. The OI bone is quite brittle
and is at high risk for fracture during this procedure.
Knee
Knee replacement is made more difficult by the pres-
ence of deformity, hardware and ligamentous laxity.
22
If
the femur has a deformity, a full-length standing radio-
graph should be obtained so that implant positioning
can be determined before surgery. The use of intraopera-
tive fluoroscopy can be helpful to ensure that the oste-
otomies are made as templated. Another option is to use
computer guidance to help in alignment.
23
However, care
should be taken with the extra pin holes needed to use
the guidance device because they can be sites of future
fractures. In some cases, it may be decided that deformity
correction cannot be made through knee replacement and
that an osteotomy and correction should be considered as
a first step. Torsional deformity can make determination
of the rotation of the femoral and tibial implants difficult.
Malrotation may lead to poor patellar tracking.
As in hip replacement, the removal of hardware
(which can include tibia rods that may extend to the
ankle) may be necessary but can be difficult. Severe
deformity can also lead to poor soft tissue coverage over
the knee. If ignored, this situation can lead to wound-
healing problems. Skin expanders have been successfully
used to improve the soft tissue coverage around the knee
in such cases.
12
Ligamentous laxity may make balancing of the knee
difficult or impossible, and this aspect should be care-
fully considered during the planning stage. The use of
extra constraint, even to the extent of using a rotating
hinge-type replacement, may be necessary. However,
such implants require stems, and stem placement may be
challenging in a bowed bone. The hinged replacements
are also quite large in the tibia, which may create diffi-
culties in sizing the implants to the bone. Preparation for
these difficulties should be planned in advance so that
the maximal number of options can be present during
surgery.
CONCLUSION
Hip and knee replacements are challenging in patients
with OI. Brittle bone leads to higher rates of intraopera-
tive fractures. Deformity and pre-existing hardware lead
FIGURE 49.3
This anteroposterior radiograph of the hip shows
an intramedullary rod that would need to be removed before
arthroplasty.
