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by foreshortened vertebral segment heights, which can
result in anchors nearly abutting one another. In addi-
tion, OI patients tend to have pedicles that are thinner
and irregular in cross-section. As a result, fluoroscopic
imaging can be difficult. Lastly, the surgeon should be
aware that dural fragility and/or ectasia are seen in some
patients with OI, which renders them susceptible to
dural leakage.
There are numerous strategies that help to ensure
success when performing spine procedures in OI
patients. First, one must consider the forces exerted on
the instrumentation and ramifications for a patient with
weak bone structure, such as those with OI. If the need
for surgery is anticipated, it would be beneficial to begin
bisphosphonate treatment a year or more prior to sur-
gery to optimize bone mass for surgery (
Figure 43.4
).
Screws should be inserted into as many pedicles as pos-
sible to distribute this load and prevent excessive force
on any one vertebral segment, which could result in
fracture or screw pullout. Related to screw placement,
it is important to preoperatively estimate the depths
of chosen pedicle screw sites on radiographs, as tactile
feedback may be difficult. Furthermore, rods that are
chosen should have a stiffness that matches the expected
correction of the spine. Excessive stiffness can result in
anchor cut-out, while rods that are too flexible may not
result in the desired correction. In some cases, rods from
cervical or pediatric applications may be appropriate. To
circumvent some of the difficulties posed by structur-
ally weak bone, adjunctive usage of vertebral cement or
extensive use of allograft may be indicated.
Since patients with kyphosis generally have scolio-
sis, kyphosis correction is often indicated. In rare cases
where significant correction of kyphosis is indicated,
anterior column support should be used to prevent cut-
out of implants. In one extreme example, cervical kypho-
sis was treated with anterior C3 and C4 corpectomies
with subsequent interbody cage placement and plate
fixation via a modified anterolateral approach.
27
Although these strategies can prove useful, surgeons
should be aware that not all patients with OI can be
helped by spinal fusion. Success can be estimated by pre-
operative radiographic study of bone quality. Those with
minimal or absent long-bone cortices or “crumpled” ribs
may not have bone strong enough to support an implant.
Therefore, the authors recommend that surgeons assess
cortical thickness with computed tomography (CT)
when deciding whether to proceed with posterior spinal
fusion. Possible surgical complications include breakage
of lamina or pedicles by implants, inability to instrument
spine due to severe osteoporosis, instrumentation failure
postoperatively resulting in loss of correction, late pseu-
doarthrosis and excessive blood loss.
41,43
A combination of the techniques covered in the pre-
ceding paragraphs may prove to be the most effective
treatment strategy to avoid complications. This is best
exemplified by a case presented by Pan et al. The patient
had type IV OI and significant kyphoscoliosis, with an
upper curve of 110°, a lower curve of 65° and a thoracic
kyphosis of 107°. One year before surgery, treatment
was started with cyclic pamidronate disodium treat-
ment. For the 42 days prior to surgery, preoperative
halo-gravity traction was used to straighten the spine.
During the actual procedure, a three-rod technique was
utilized. This involved fixing each rod to five or six ped-
icle screws, which allowed for adequate distribution of
the load over many vertebral segments. Finally, allograft
bone was laid on the decorticated posterior surfaces of
the vertebrae. The combination of bisphosphonate use,
halo-gravity traction, distribution of the load over multi-
ple vertebral bodies, and extensive allograft use resulted
in upper and lower curves of 68° and 45°, respectively,
with a thoracic kyphosis of 39°. This correction was vir-
tually retained one and a half years after the procedure.
Correction also resulted in a significant improvement in
pulmonary function.
41
In summary, abnormalities may exist at any level of
the spine in patients with OI. Periodic history and physi-
cal examination will guide the imaging and appropriate
conservative treatment under the care of an experienced
physician who carries the picture of the whole patient
in mind. As complications are frequent and correction is
modest, careful judgment and a preventive approach are
most appropriate.
References
