Bone graft for spine fusion
Bone graft for spinal fusion surgeries may either be harvested
from the patient (autologous bone) or from a cadaver
(allograft bone).
Autologous bone is harvested from the patient's
pelvic bone (iliac crest) and provides the spinal fusion with a calcium scaffolding for the new bone to grow
on (conduction). In addition, autologous bone also
contains
bone-growing cells (osteoblasts) and bone-growing
proteins (bone morphogenic proteins).
Allograft bone simply provides a calcium scaffolding
and does not have any bone-growing cells or bone-growing
proteins. In the lumbar spine, allograft bone is restricted
for use in ALIF or PLIF procedures in which bone graft
is placed in compression (the compression aids the healing
process for the bone). In a posterolateral gutter spine fusion,
in which the bone is placed in tension, allograft
bone by itself will not heal well (although allograft
chips combined with autograft may be used to
extend the harvested bone graft).
Autologous bone, in which the bone is harvested from
the patient’s body during spine surgery, has the obvious
disadvantage of higher post-operative pain. Most of
the pain associated with bone graft harvesting is either
from too much muscle stripping or from cutting the small
sensory nerves (cluneals) that lie in the fat layer
over the pelvis (iliac crest). With careful surgical
technique, both of these pitfalls may be avoided.
In posterolateral gutter spine fusion and PLIF procedures,
a single incision can be used for the spinal fusion
surgery and to harvest the bone from the pelvis (iliac
crest). The pelvis can be approached through a plane
that has no nerves or blood vessels, and only the top
portion of the crest needs to be stripped of its muscles
(gluteal muscles). Use of this surgical technique minimizes
the blood loss and post-operative pain associated with
bone graft harvesting.
Bone harvested for ALIF procedures is done through
a separate incision (one inch to two inches long) over
the iliac crest. Again, only the very top portion of
the iliac crest needs to be removed and the soft cancellous
(spongy) bone from in between the cortical (hard) layers
of bone is scooped out.
Scooping the bone out of the pelvic bone does not result
in a lot of pain because there are no nerve fibers inside
the bone. However, care must be taken to avoid the sensory
nerve in this region (lateral femoral cutaneous nerve)
as damage to this nerve can produce pain and numbness
in the front of the thigh (meralgia parasthetica). In
general, this approach should be associated with minimal
post-operative pain or discomfort because limited soft
tissue stripping is needed.
There are currently several products on the market
and in development that act either as a bone graft extender
or substitute. Demineralized bone matrix (bone
that has had the calcium removed) has been available
for the past several years. It carries some of the bone
morphogenic proteins that the body uses to induce bone
formation. There are also calcium hydroxyappetite products
or coral, both of which have structures similar to bone
and act as scaffolding for new bone.
There has been a lot of excitement among spine surgeons
awaiting the new bone morphogenic protein products
that are expected to be strong inducers of bone growth
(osteoinductive). These new products will be relatively
expensive, but will probably be able to grow bone even
better than the patient’s own bone and bone graft
harvesting may no longer be necessary.
By: Peter
F. Ullrich, Jr., MD
September 8, 1999 (Updated March 30, 2001)
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