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Anterior
Lumbar Interbody Fusion |
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Spinal
fusions are indicated for patients with low back and/or
leg pain due to degenerative disc disease or instability
that is refractory to conservative treatments. Why a
degenerated disc produces symptoms is somewhat unclear.
As the disc loses water (which appears as darkness on
the MRI), it begins lose height which produces redundancy
in its covering (annulus,
see anatomy). |
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| L5-S1
degenerative disc disease: note darkness of disc
indicating loss of water content. |
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This
may produce chronic tearing of the disc covering and
pain. As the vertebra settle due to disc height loss,
contact pressure on the posterior joints (facets) increases
which incites inflammation and pain. Currently, spinal
fusion is the only proven surgical techniques which
improves the pain of
degenerative disc disease.
In
the past, most fusions were performed posteriorly utilizing
autologous bone and commonly supplemented with fixation
devices such as pedicle screws and rods. Posterior
fixation devices have been shown to enhance fusion
rates and facilitate postoperative patient mobilization.
Wide exposure of the posterior spinal elements
is required for implantation of these devices with
resultant damage to the paraspinous musculature.
Often times this muscular damage may limit the ultimate
benefits of the fusion operation.
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Settling
of the vertebra due to disc degeneration produces
abnormal motion and may contribute to pain. |
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cages are inserted. Bone placed within the cages
causes adjacent vertebra to heal together, eliminating
motion, and decreasing symptoms. |
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In
response to the shortcomings of posterior spinal fusion,
new anterior fusion techniques have been developed.
As one of the Food and Drug Administration investigators
for these new techniques, I would like to share my
experience with an anterior fusion fixation device
which I feel will revolutionize our current thinking
in spine surgery.
An anterior subumbilical incision measuring approximately 2 inches long is made
horizontally in the abdominal wall between the rectus musculature. No muscle
is cut or distorted during the spinal approach. A abdominal retroperitoneal approach
to the lumbar spine is achieved. Very little bleeding is encountered during exposure
of the spine. The device is packer with autologous bone and inserted, usually
in 30 minutes.
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| Anterior
Interbody Fusion done with allograft bone and rhBMP
growth factors. |
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Postoperatively
the patients are allowed to ambulate the night of surgery
and are discharged on postoperative day two. This is
compared with 5-7 hospital days with standard posterior
fusions and 4-5 hours of operative time. Blood loss
is minimal and patients rarely require transfusions.
In 1995, I was asked by the cage manufacturer to do a safety and efficacy study
on anterior interbody fusion devices for the purpose of gaining FDA approval.
65 patients were done on the initial study. All patients had only one level fused.
All patients fused, and 98% of patients reported good and excellent results.
All patients had relief of preoperative symptoms. There were no infections and
only one patient was returned to the operating room for minor bleeding.
Since that time, I have done approximately 400 of these procedures with similar
results. What has been learned is that if more than one level is fused with an
anterior interbody fusion technique, the results degrade proportional to the
number of levels attempted. Two level fusions are successful in select patients,
but three level anterior interbody fusions without posterior augmentation, should
rarely, in my opinion, be attempted.
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Three
views of bone inside the cages completely healed.
In the lower CT, bone is seen bridging the two
vertebra together. |
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Two
main categories of devices are available. Cages made
of titanium and allograft (cadaver bone) are FDA approved
and implanted in the United States. I have used both
successfully and have come to appreciate the relative
benefits of each device. Allografts have the theoretical
advantage of healing primarily to the vertebra whereas
titanium can only act as a carrier for bone placed
within it. Allografts degrade postoperative MRI scans
less than metal cages which is important if the patient
should need studies in the future. Both cages types
require CT scans to conclusively assess complete fusion
within the device. Allografts have a theoretical disadvantage
as being a carrier of infection or target of rejections
but these complications, as far as I know, have not
been reported.
Theoretically, as a patient becomes older and relatively osteoporotic, a metallic
cage could collapse into the adjacent vertebra. Because allografts are incorporated,
this probably would not happen. Before surgery, I present both options to my
patients and allow them to decide the best choice for them.
Many patients ask about laparoscopic placement of cages. I do not do
it for the following reasons. My operative time with open procedures
is 60-90 minutes. Laparoscopy, in anyone's hands, takes much longer.
The limiting factor in incision size is the size of the device for both
procedures and since the device is equal size, in my hands, the incisions
are about the same. The published complication rates are much higher
for laparoscopic cases even in the most experienced hands. Finally, since
most insurance plans will currently allow patients to stay in the hospital
for 1-2 days following one of these procedures, the theoretical advantage
of allowing patients to be discharged sooner with laparoscopy , may benefit
all parties except the patient.
Related links:
Normal spinal anatomy
Abnormal spinal anatomy
Spinal
Balance and Adjacent Segment Degeneration
Read
the latest research on Anterior Interbody Fusions
Back FAQ's
Pre-surgery FAQ's
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