Bone
graft options for a spine fusion
The bone graft is the material that is used to form
the bridge between two vertebral segments in the spine
to obtain the fusion. Bone grafts can be divided
into three main categories based on where they are
obtained.
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Autograft bone graft is the term
used for the patient’s own bone is used to
for the bone graft in the spine fusion. The
most common donor area is the iliac crest, which
is located in the patient’s pelvis. Local
bone from the area of surgery such as lamina and
spinous process bone are technically considered
to be autograft as well. The iliac crest autograft
is considered to be the gold standard and is most
often used as bone graft in a spine fusion. However,
it does carry the risk of done site morbidity,
or unwanted aftereffects such as postoperative
pain at the donor site (the pelvic rim).
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Allograft bone graft is bone obtained
from cadavers, and comes in many shapes and forms
for use in a spine fusion. There are different
techniques of sterilization as well as different
storage techniques for allograft bone, such as
fresh frozen or freeze-dried. At present,
this is the most commonly used alternative to autograft
bone, and is most commonly used as a bone graft
supplement (to the patient’s own bone) in
the back of the spine in adult patients. It may
also be used in a fusion procedure to treat scoliosis
in adolescent patients.
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Bone graft substitutes are products that
either assist or replace the need for autograft
or allograft bone in a spine fusion. For example,
tricalcium phosphate acts as a structural lattice
for bone formation. Other bone graft substitutes
such as demineralized bone matrix, are used as
graft extenders and can be used to mix with allograft
and increase fusion rates. Bone Morphogenetic
Protein (BMP) is a commercially available protein,
which has been shown (when placed in fusion cages
for interbody fusion) to have the same rate of
fusion as the iliac crest allograft without the
donor site morbidity (unwanted aftereffects, such
as postoperative pain). However,
at present BMP is extremely expensive, and because
it is a relatively new product not all of the potential
long term side effects are known. The addition
of the patient’s bone marrow aspirate (obtained
thru a needle rather than an additional incision)
to allograft, has promise of obtaining better fusion
rates than allograft alone, and may be more cost
effective than other bone graft substitute options.
The choice of which type of bone graft to use is largely
dependent on where the fusion is done in the spine
(in the cervical, thoracic, or lumbar spine), and the
surgical approach to the fusion (anterior or posterior).
A number of other factors also play a role in the decision,
such as whether or not the patient smokes or has other
risk factors that may inhibit a successful fusion.
This article has reviewed many of the different options
available to achieve a spine fusion. All of the
different approaches with spine fusion have certain
risks and complications. One common risk among
all types of spine fusion that is important to keep
in mind is the risk of clinical failure, which means
that despite achieving a successful fusion the patient’s
pain is not alleviated.
By: Ali Araghi, DO
July 21, 2004
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