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Incidence and Impact
Low
back pain is extremely common in today's society. Seventy-five
percent of all people will experience back pain at some time
in their lives. The total cost in lost productivity is enormous.
Back pain is the second leading cause of absenteeism from work,
after the common cold and accounts for 15% of sick leaves. Back
injuries cause 100 million lost days of work annually, and are
the most costly injury for employers. The cost of a back pain
injury claim far surpasses others. The average total cost per
claim in 1989, was $18,365.00. Time plays an important role in  back
pain recovery. After 52 weeks
of back injury disability and absenteeism, only 25% of injured
workers return to work. After two years of disability, the return
rate is zero. For 85% of back pain sufferers, the primary site
of injury is the lower lumbar spine.
The good news is that the vast majority of back-injured patients,
probably greater than 90%, will recover completely without surgical
treatment. Only 2 to 3% of the population with back
pain have a herniated disc and only 1% have compression
of a nerve root (leg symptoms).
Chronic Low Back Pain/Failed Back
Treating
chronic low back pain that has proven refractory to non-operative
management can be challenging. The results of previous surgical
treatments are often sobering. Re-operation rates on the spine
have been reported at 6.9 - 37.7%. Heithoff et al, reported 25,000
- 50,000 failed back surgery syndrome cases occurring each year.
For the aforementioned reasons the appropriate diagnosis, efficient
treatment, and when indicated well - executed surgery, are of
absolute necessity. Otherwise it is all too easy to add to the
chronic "failed back" patient population.
 Causes of Low Back Pain
Some
of the common causes of back problems are disc injury (e.g.,
herniation and internal disc disruption, IDD) and degenerative
discs. Disc
degeneration
affects about 12 million people in the United States, of which
most are between the ages of 20 and 65. Approximately ten percent
of patients with degenerative discs are candidates for some type
of spinal surgery.
The
intervertebral disc serves as a shock absorber, load distributor
and spacer. As we age the disc normally undergoes degenerative
change. The disc loses its ability to hold water, resulting in
decreased ability to absorb shock and a narrowing of the nerve
openings in the sides of the spine, which may pinch the nerves.
The result is increased disc stiffness often accompanied by back
and leg pain. The degenerative changes within the disc are universal
and account for the majority of chronic low back pain seen in spine clinics.
Unfortunately there is not a 1:1 association of disc degeneration
to pain. In one study 52% of degenerative discs were found to
be the source of the patients back pain. The MRIis a
relatively sensitive test for the detection of degenerative changes
within the intervertebral disc, but is incapable of providing
a pain association.
 Discography
Additional testing is required to assign a "pain generator"
status to the individual disc. Discography is accepted
as the disc evaluation "procedure-of-choice". Discography
investigates, and establishes the intervertebral discs role in
the production of the patient's low back pain.
At
times in the past the value of discography has been questioned.
Current literature supports discography's worth as a diagnostic
tool used to investigate painful spinal conditions.
Discography Candidates
Who
is a candidate and when is discography indicated?
A patient
who experiences persistent spinal (cervical, thoracic, lumbar)
pain.
A disc
abnormality is suspected.
Non-invasive
tests have failed to provide an explanation or source of pain.
A pain
correlation is desired.
Patients
who have continued pain despite previous surgery are often discography
candidates. There are many variations of the discography procedure.
The method most commonly utilized at KU Medical Center is that
of provocative discography. Provocative discography is the instillation
of sterile saline (not dye) into the disc looking for reproduction
of the patient's pain. Exact pain reduction supports the discs
role as a "pain generator", documenting a specific
diagnosis, and allows more aggressive intervention.
History of Discography
Discography
was originally performed with dye, when existing imaging techniques
did not provide information on the disc's internal architecture.
In most present cases we utilize the MRI to identify disc abnormalities
and the discogram to assign a "pain generator" status.
Historically,
Lindblom (1940's) injected cadaveric specimens with red lead
containing dyes and examined the pattern of distribution within
the disc. Erlacher (1952), studied 200 cadaver disc specimens
and found that discography accurately represented the disc anatomy.
The discs were sectioned and studied for correlation. Wiley (1968)
reported on 1092 patients, finding discography a valuable tool
with very few complications. In one study of the MRI, significant
disc abnormalities were demonstrated in 28% of symptom and pain-free
individuals (28% false-positive rate). Clearly a procedure is
needed to further define the MRI findings as contributing to
the patient's symptoms. Discography is the only method that directly
relates a radiographic image to the patient's pain.
Walsh
et al (1990), performed provocative discography on ten asymptomatic
pain-free volunteers. No pain was produced on injection. However,
50% demonstrated abnormal dye patterns. He felt the pain correlation
the procedure had a specificity of 100%. Simmon's et al's (1990),
suggested that treating painful spinal conditions based only
on MRI results could lead to under treatment.
Colhoun
et al (1988), studied the success of fusions performed with a
discography proven pain correlation. Patient satisfaction was
achieved in 88%. When the correlation was absent the satisfaction
with the fusion procedure dropped to 52%. Discography has also
been documented as helpful in diagnosing pseudarthrosis (failure-of-fusion),
Byrd (1992).
Indications for Discography
We
believe in the following indication, for discography:
Failed
conservative therapy
Diagnostic
tests - inconclusive (equivocal or inconsistent)
Persistence
of severe symptoms - surgery a consideration
Discography
is an outpatient procedure, performed under biplanar fluoroscopy,
local anesthesia and sterile conditions. When performed correctly
and in "experienced hands" the main complication is
a short period of increased pain. In short, discography has proven
itself to be an invaluable diagnostic modality reserved for the
investigation of painful spinal conditions where other non-invasive
studies have been unable to provide or confused the diagnosis
to allow further more aggressive treatment.
Interbody Cage Fusion
Once
the disc has been established as the source of the patients chronic,
refractory to conservative care, incapacitating, low back pain,
one of the most exciting advances in spine surgery becomes available
as a treatment modality.
The new interbody
fusion systems utilize an innovative threaded titanium cage
for spinal fusion. The technique is less invasive than other
methods. The cages are small, hollow threaded titanium cylinders
used to restore the degenerated disc space to or near its original
height, relieving any pressure on the patient's nerves. The clinical
outcomes of the cage interbody fusion study, which were reviewed
by the FDA, have shown significant reductions in pain and increases
in activity levels compared to other fusion methods.
 During the surgery, portions of
the painful disc and a small amount of bone are removed, allowing implant insertion.
A small amount of bone is then taken from the pelvis and packed inside the cage
implants. This allows the bone to grow through and around the implant fusing the
vertebral bodies and relieves the patient's pain. The interbody cage fusion system
is implanted from the front (anterior) when possible, as recovery and postoperative
pain are lessened. However, the decision on surgical approach is based upon the
patient's condition.
Advantages of Interbody Cage Fusion
Based
upon the findings of the FDA clinical study and comparisons to
other fusion methods, the cage interbody fusion system offers
many advantages over traditional fusion methods.
The
following are some of the advantages:
The
procedure has been found to have a low overall complication rate.
The
amount of blood loss during surgery can be much less than other
types of spinal fusion.
Postoperative
pain may be minimized through a decrease in the amount of surgical
intervention.
Operative
procedure and length of stay in the hospital can be less than
other fusion methods.
Return
to daily activities can be much quicker.
Results of Interbody Cage Fusion Procedure 
These
findings follow the general trend in medical care toward less
invasive surgical techniques that provide better outcomes for
patients. The first FDA controlled clinical study on interbody
cage fusions includes 947 patients. The clinical success rates
for patients at two years after surgery were measured in the
following areas:
Measurement
Patients
reporting favorable outcome - 89%
Function
maintained or improved - 94%
Pain
improvement - 85%
Strength
maintained or improved - 94%
Fusion
rate - 91%
As the numbers
reflect, an exciting advance compared to previously available
techniques.
Material provided
by Dr. Glenn M. Amundson
Used by Permission
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