The Minimally Invasive Surgical Treatment of Back
Pain
by Dr. Harel Deutsch
Back pain is an extremely prevalent condition. The
economics of back pain are staggering. An analysis of
back pain costs in the Netherlands demonstrated back
pain costs accounted for 1.7 % of GNP. While the direct
medical costs were $368 million, the indirect costs
were $4.6 billion. The indirect costs including work
absenteeism and chronic disability accounted for 93%
of the total back pain costs.(1) Aggregate annual productivity
losses from chronic backache in the United States are
approximately $28 billion or $1,230 per male worker
and $773 per female worker.(2) Work absences due to
back pain occur in up to 5.62% of the population.(3)
Despite the personal and economic implications, an
effective treatment has remained elusive. Our understanding
of back pain has been incomplete. The widespread availability
of MRI imaging over the past 15 years has significantly
improved our diagnostic capability. Parallel improvements
in surgical technology have extended our ability to
address spine related pathology. A new paradigm of back
pain has emerged with a significant improvement in patient
outcome. Minimally invasive surgical techniques and
newly developed bio-engineered products now allow us
to treat identifiable spine problems with small incisions
and allow for a quicker recovery.
Back pain etiology
 |
| (Figure
1) Disc degeneration:
A. Normal anatomy, B. Early degeneration with loss
of disc height and disc bulging, C. Late disc degeneration
with further loss of disc height, formation of posterior
and anterior osteophytes, facet hypertrophy, and
foraminal stenosis. |
To some extent, back pain represents an important physiological
message. Our vertebrae and intervertebral discs compromise
joints designed to move in a constrained fashion. If
movement occurs beyond the normal ability of the joint,
the result is pain. Excessive axial loading of the spine
also results in physiological pain. Back pain becomes
a problem when such pain is generated under normal daily
activities. In the majority of patients, these conditions
occur because of degenerative changes. Normal wear-and-tear
can result in progressive disc dehydration, height loss,
and bulging. In the majority of people, degeneration
causes some well-tolerated pain. In others, the pain
can significantly affect a person’s ability to
carry out day-to-day functions. (Figure 1) X-rays demonstrate
the loss of disc height. (Figure 2) MRIs demonstrate
disc dehydration and loss of height as well as disc
bulging and reactive changes within the vertebral endplates.
(Figure 3)
 |
| (Figure
2) X-ray showing
collapse of the L5-S1 disc space. |
Degenerative changes typically start in a person’s
20s. These changes rarely become symptomatic unless
one level degenerates excessively. In younger symptomatic
patients (age 20-65 years), degeneration usually predominantly
affects one level. In older patients (>65), widespread
spine degeneration and degenerative scoliosis are more
common. Degenerative disc and facet joint changes can
result in entrapment of exiting nerve roots and a resulting
radiculopathy.
In the majority of back pain patients, the clinical
course is characterized by relatively mild symptoms
interspersed with repeated exacerbations of lower back
pain. Episodes can be severe but usually resolve with
conservative treatment including analgesics and rest.
In others, degeneration can result in constant unremitting
pain.
Back pain usually represents a nonspecific diagnosis
given to a whole complex of symptoms. Pain originating
from a degenerative disc usually presents as the classical
axial lower back pain. Discogenic pain tends to specifically
worsen with prolonged sitting and standing and is relieved
by unloading the spine and lying down. The sitting position
results in more axial compressive forces than standing
and therefore is usually more symptomatic in discogenic
pain. Degenerative disc changes are often not well visualized
on radiographs or even CT scanning. MRI scans on the
other hand are often extremely effective in visualizing
the intervertebral disc. Disc dehydration appears as
a low intensity signal on T2-weighted imaging. Adjacent
sclerotic changes in the vertebral body arising from
increased localized axial loading are also evident.
 |
| (Figure
3) Sagittal T2
MRI imaging showing a degenerated L5-S1 disc with
disc narrowing and bone endplate changes. |
The segmental spinal joint includes the intervertebral
joints and the posterior facet joints. Facet degeneration
can lead to referred pain to the buttock and hip area
that may simulate a radiculopathy in some cases. Referred
facet pain does not generally extend below the knee.
Degenerative joint changes result in the guarding or
tensing of paraspinal muscles. Reactive changes and
fatigue in the paraspinal muscles can result in myofascial
pain syndromes characterized by paraspinal muscle tenderness
and fatigue. Patients can have elements of all three
pain syndromes simultaneously. Degenerative changes
can also lead to nerve root impingement and an associated
radiculopathy.
Treatment
Conservative therapy
The first line of treatment for back pain remains conservative
therapy. Extensive research has gone into determining
the best initial course of action. Bedrest was the classical
treatment for acute back pain previously. Multiple randomized
controlled studies have demonstrated that strict bedrest
is not beneficial in an acute episode and may be slightly
harmful.(4) For acute back pain, exercise has been shown
to be ineffective. For chronic lower back pain, exercise
and physical therapy have been demonstrated to be effective.(5)
Other interventions such as weight loss in the appropriate
patient, are very successful. Caudal and selective epidural
injections have limited success in short-term pain relief.(6)
Conservative interventions have few side-effects and
are worth trying prior to committing to surgical correction.
Surgery
Surgery for axial back pain involves stabilizing the
degenerated joint. Not all patients with back pain who
have failed conservative therapy are candidates for
surgery. Imaging studies, especially MRI scans need
to corroborate a specific degenerative segment. Because
the lumbar vertebrae provide limited nonessential mobility,
we can sacrifice mobility in order to restore the spine’s
structural integrity. The amount of mobility sacrificed
by fusing one level is generally minimal. Initial attempts
to stabilize the spine involved onlay fusion where bone
graft was laid down over the posterior spine. Onlay
fusion was infrequently successful. The development
of spinal instrumentation allowed for immediate spine
stabilization. Stabilization techniques have steadily
improved. Further understanding concerning the importance
of interbody stabilization and fusion has resulted in
even better surgical outcomes.
Minimally Invasive Surgery
 |
| (Figure
4) Minimally invasive
lumbar fixation. A. Placement of the muscle dilator,
B. Removal of facet joint, C. Discectomy, D. Placement
of interbody graft, E. Pedicle screw placement,
F. Placement of rod. |
Traditional spinal stabilization surgeries are fairly
large surgeries and involve long recovery times and
injury to local paraspinal muscle groups. Newer technologies
have allowed us to perform the same interbody spine
stabilization with smaller incisions and less dissection.
(Figure 4) The result is less paraspinal muscle damage
and quicker recovery with excellent success rates. Sequential
dilators are introduced to dilate the paraspinal muscles
and provide exposure to the spine. The dilators allow
for the placement of a tube approximately 20 mm in diameter
by 7 cm in length. Surgery is performed through this
limited access port. Once the dilators are removed,
the muscle returns to its physiological position. Less
muscle damage results in less postoperative swelling
and pain. Less muscle damage also prevents long-term
muscle deinnervation and atrophy. The paraspinal muscles
serve an important role in stabilizing the lumbar spine.
Titanium screws to stabilize the spine can be introduced
percutaneously. (Figure 6) The titanium screws provide
immediate stability and facilitate bone fusion by immobilizing
the spine much as a cast can immobilize a long bone
fracture. (Figure 5)
The addition of bone morphogenic protein (Infuse®)
has also increased success rates. Infuse is a bio-engineered
molecule that is able to signal the patient’s own
cells to form bone. The use of Infuse has increased
spinal surgery fusion rates and improved outcomes.(7)
The use of Infuse also allows surgeons to avoid harvesting
iliac crest bone and thus speeds recovery. Previous
posterolateral fusion rates as low as 40-60% have been
reported. With the use of Infuse in an anterior spinal
interbody fusion study, fusion rates were close to 100%.
Additionally fusion seemed to occur earlier (within
3 months) rather than 1-2 years after surgery.
 |
| (Figure
5) Minimally invasive
lumbar fixation. A. Placement of the muscle dilator,
B. Removal of facet joint, C. Discectomy, D. Placement
of interbody graft, E. Pedicle screw placement,
F. Placement of rod. |
Increased understanding of back pain and MRI scans
allows physicians to target the pain generator more
specifically. Rather than fusing multiple levels physicians
can now address the level causing the pain. Initially,
spine fusion involved the placement of posterior pedicle
screws to stabilize the spine. Results with pedicle
screws alone were somewhat mixed. Newer techniques such
as the transforaminal interbody fusion (TLIF) require
actual removal of the lumbar disc material and replacement
with a spacer in addition to the placement of pedicle
screws. Minimally invasive techniques allow a TLIF to
be performed with minimal blood loss. Patients’
length of stay in the hospital is dramatically reduced
to 1 to 2 days. Complications are limited and infections
are very rare because of the lack of dead space to foster
fluid collection.
 |
| (Figure
6) Interbody spacer
and pedicle screws placed through a tubular retractor |
The overall results with minimally invasive spine surgery
are similar to open surgery with about 80% of patients
realizing a substantial improvement. After surgery,
patients can return to a full lifestyle within a few
weeks of surgery.
Conclusion
Back pain remains an important medical consideration.
Previously, limited understanding of the spine and back
pain has led to an incomplete treatment paradigm. Advances
in imaging and improved interpretation of MRI imaging
have resulted in a greater understanding of spine degeneration.
Carefully selected patients with back pain who have
failed other treatments may be candidates for surgery.
Rapid advances in spinal stabilization technology have
also resulted in improved patient outcome. Minimally
invasive technology now allows for quicker patient recovery
and satisfaction. Minimally invasive techniques minimize
adjacent muscle and tissue damage. Clinical results
are similar to open procedures with about 80% of patients
experiencing significant improvement in their axial
back pain. Minimally invasive techniques are being applied
to other spine problems such as tumors and fractures
of the spine.
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