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C H A P T E R 1 5 Spinal Stenosis with Spondylolisthesis
85
seems logical that un-instrumented posterolateral fusion could provide a
good compromise between the two options.
9
Though much of the morbidity associated with preparation of the fusion bed would remain (increased
dissection and pain, increased anesthesia time, and blood loss), the additional trauma and time of instrumentation placement would be avoided.
Prospective studies of patients with degenerative spondylolisthesis who
underwent decompression and uninstrumented dorsolateral fusion versus patients undergoing decompression alone have in fact demonstrated
significantly better outcomes. Of note, although this procedure is associated
with a high pseudoarthrosis rate (up to 36%), this did not affect patient
outcomes. This is thought to be the result of stiffening of the spine and
motion restriction due to a stable pseudarthrosis.
11,12
The procedure does have some disadvantages. As mentioned above,
the patient must still undergo the extensive dissection of the lateral areas
over the transverse processes. The fusion itself is negatively impacted by the
relatively poor vascularity of the transverse processes as well as the constant
intertransverse graft motion during activities of daily living secondary to
the intervening juxtaposed paraspinous and quadratus lumborum muscles.
Finally, dorsolateral fusion requires consolidation of bone over a fairly large
distance (several centimeters) between transverse processes.
Fusion with Biologics
Newer biologics have given the surgeon the advantage of relatively improved
fusion rates using less invasive techniques. Numerous prospective randomized studies of recombinant bone morphogenetic proteins (recombinant human bone morphogenetic protein-2 [rhBMP-2] and recombinant
human bone morphogenetic protein-7 [rhBMP-7]) have been performed.
The safety, effectiveness, and radiographic outcomes of OP-1 (BMP-7)
putty with autogenous iliac crest bone graft used for laminectomy and
noninstrumented posterolateral fusion for symptomatic lumbar stenosis
associated with degenerative spondylolisthesis have been reported and are
encouraging.
A prospective randomized controlled multicenter clinical study with a
2-year follow-up has reported clinical success, defined as a 20% improvement in the preoperative Oswestry score. Success was achieved in 85%
of patients treated with OP-1 putty versus 64% of patients treated with
autograft. In addition, a successful posterolateral fusion was achieved in
55% of patients treated with OP-1 putty and in 40% of patients treated
with autograft. Importantly, a 36-item Medical Outcomes Study ShortForm General Health Survey (SF-36). SF-36 scores showed similar clinical
improvement in both groups.
A second prospective randomized clinical study has evaluated the
use of rhBMP-2 to achieve posterolateral spine fusion in patients with a
grade I spondylolisthesis and single level degenerative disc disease that
were scheduled to undergo single level posterolateral lumbar arthrodesis.
The study compared patients undergoing autogenous iliac crest bone graft
with pedicle screw instrumentation, rhBMP-2 with pedicle screw instrumentation, and rhBMP-2 only with no instrumentation. The study demonstrated a radiographic fusion rate of 40% in the autogenous iliac crest bone
graft with pedicle screw instrumentation, 100% in patients that received
rhBMP-2 with pedicle screw instrumentation, and 100% in the rhBMP2–only group.
13
More importantly, the clinical outcomes improved faster
and to a greater degree in the rhBMP-2–only group. The surgical time was
significantly less secondary to the elimination of the time required for bone
graft harvest and placement of internal fixation.
Decompression and Posterolateral Fusion with Instrumentation
The most effective method of achieving “stability” following decompression is the addition of instrumentation.
11
A prospective randomized study
comparing the results of decompression and arthrodesis alone with those of
decompression and arthrodesis combined with instrumentation has shown
that the addition of spinal instrumentation improved the fusion rate (82%,
instrumented versus 45%, noninstrumented).
4
Although achieving a solid
fusion appeared to be less important, since no significant difference was
found in clinical outcomes, more recent longer term (5- to 14-year) followup studies have reported that patients with pseudarthrosis did not do as
well as those that achieved solid fusion.
4,11
The complication rates, revision
rates, radiographic results, and patient satisfaction at 5-year follow-up were
reviewed for patients following segmental posterior instrumented fusion
with decompression in patients with lumbar degenerative spondylolisthesis
and showed that no patient had a neurologic deficit, evidence of symptomatic
pseudarthrosis (i.e., pain, lucency, loose instrumentation), or recurrent stenosis at the fused segment.
7
Unfortunately, posterolateral fusion requires a large dissection for the
preparation of the fusion bed, which is associated with increased pain,
bleeding, time in surgery, and recovery. In addition to this, instrumentation
further increases the morbidity of the surgery.
12
Facet Fusion
Facet joints normally function by bearing load and allowing motion, while
restricting excessive motion. Fusion of the facet can be accomplished with or
without instrumentation, and can substantially reduce the pain and morbidity associated with posterolateral fusion. Though studies have demonstrated
that instrumented facet fusions can have a 96% fusion rate by CT scan, this
is not as strong as a posterolateral fusion, and a functional outcome assessment was not reported.
Uninstrumented facet fusions are becoming more popular because of
their simplicity and minimal additional dissection requirement. They can
be performed using locally harvested autograft placed into the facet joint
or with allograft bone dowels that are currently available from several
companies. Unfortunately, no powerful studies are available on the effectiveness of uninstrumented facet fusion in stabilizing the spine.
Because a varying degree of disruption of the facet capsule (which in
itself is stabilizing) must occur to perform a facet fusion, a negative to this
procedure is that if a fusion does not occur, the spine will have in fact
lost stability from the procedure. Additionally, if wide decompressions
are performed, the added stress placed on the facet joint can lead to fractureof the thinned pars interarticularis and complete incompetency of the
joint. Obviously, if any type of facet fusion is going to be attempted, care
should be taken to preserve as much of the pars interarticularis as possible
bilaterally.
Fusion with Transforaminal Lumbar Interbody Graft
The addition of interbody support helps to restore the biomechanical advantages of a solid anterior column and provides an increased fusion surface
area. These advantages could translate into an increased rate of fusion and
improved patient outcomes. Unfortunately, no prospective randomized
studies have been performed comparing decompression with transforaminal
lumbar interbody fusion to decompression with instrumented posterolateral
fusion. Until such a study is performed, it will be more difficult to justify the
added dissection and anesthesia time required in an older patient population.
Nonfusion Options
Laminectomy
Many studies have demonstrated the efficacy of dorsal decompression for
alleviating the symptoms of spinal stenosis.
1-3
Although laminectomy is a
relatively well-tolerated procedure, the incidence of postoperative instability (increased translation and loss of alignment) has been reported to be
as high as 50% in patients undergoing laminectomy for spinal stenosis and
even higher in patients with degenerative spondylolisthesis.
5,10
The standard surgical treatment for lumbar spinal stenosis consists of
a decompressive laminectomy accompanied by partial medial facetectomy
and foraminotomy, as needed. It is important to preserve as much of the
facet joint as possible. Similarly, preservation of the pars interarticularis is
essential to maintain stability and minimize the need for instrumentation.
Therefore it is often helpful to expose and visualize the pars interarticularis
in order to avoid its inadvertent disruption during the decompression.
When performed properly, the risk of postoperative instability following
this procedure is less than 2% in patients without degenerative scoliosis. The
risk of instability increases in patients with degenerative scoliosis, especially
as the magnitude of the curve increases. Patients with curves greater than
20 degrees are at a higher risk of curve progression and often require
prophylactic fusion. The risk of worsening postoperative spondylolisthesis
also increases with the number of levels decompressed, ranging from 6% for
2 levels to 15% for 3 or more levels.
86
P A R T I I Basic Science of the Aging Spine
Laminotomy or Interlaminar Fenestration
Interlaminar fenestration or laminotomy can provide significant neural
decompression in select patients with minimal structural disruption, and
can be especially useful in the treatment of lateral recess stenosis. These
procedures emphasize the preservation of stabilizing structures such as the
interspinous and supraspinous ligaments, spinous processes, and functionally important parts of facet joints. Interlaminar fenestration is accomplished
by trimming bone around the interlaminar spaces of involved segments
along with removal of the ligamentum flavum and medial portion of the
facet joint. The fenestration extends laterally to decompress affected nerve
roots with the preservation of the adjoining laminae, spinous processes,
interspinous ligaments, and facet joints.
Foraminotomy
Foraminotomy is often required when the neural foramen is narrowed as a
result of disc space collapse or facet arthropathy. As with other decompressive procedures, aggressive foraminotomy can destabilize the spine, especially in the presence of degenerative scoliosis or spondylolisthesis, and can
result in an increase in the magnitude of slip or rate of curve progression.
Therefore care must be taken to minimize facet disruption by limiting the
facetectomy to the medial one third of the facet joint and to preserve the
pars interarticularis if possible. Decompression of the nerve root on the concavity of a curve, which often has significant foraminal narrowing, is often
challenging and may not be feasible.
Restorative Laminoplasty
Biomechanically, the vertebral arch, supraspinous and interspinous ligaments provide a tethering constraint during anterior flexion and support
for the dorsolumbar fascia and muscles. In order for the posterior elements to provide support, the supraspinous and interspinous ligaments
with their bony attachments must be intact. It has been demonstrated that
extensive laminectomy can lead to instability if these points of attachment
are removed.
Spinal canal enlargement by restorative laminoplasty, in which osteotomized vertebral arches are repositioned rather than removed, can provide
an acceptable alternative to fusion. Theoretically, this method of decompression could be more effective in preventing postoperative instability
than multilevel fenestration, because it involves less extensive dissection
of the laminae and facet joints. As an alternative to decompression with
fusion, it has been used in patients with both degenerative spondylolisthesis and degenerative scoliosis with 2-year follow-up studies showing
no exacerbation of spondylolisthesis or scoliosis, nor the onset of other
instability
Whereas favorable results have been demonstrated using laminoplasty,
2-year outcome studies have demonstrated that symptomatic improvement
is less likely in patients with degenerative scoliosis, particularly with more
severe scoliosis. Notably, the number of restored vertebral arches has not
been found to have significant correlations on overall improvement rate.
Similarly it has not been shown to be effective in patients with degenerative spondylolisthesis. Its benefit in lateral spondylolisthesis has not been
evaluated.
Minimally Invasive Techniques
Minimally invasive surgery (MIS) is becoming more popular in the
treatment of many spinal disorders. With these techniques, a decompressive laminectomy, laminotomy, or foraminotomy is performed with
minimal tissue dissection via the use of special retractor systems, unilateral approaches, and endoscopes. These techniques can be used to insert
spinal instrumentation, or for decompression procedures alone. Although
MIS decompression has many theoretical advantages with respect to
minimizing tissue disruption and preserving stability, such benefits have
not been conclusively proven. In addition, they can be associated with
a steep learning curve and prolonged operative time, which may be an
important issue in the elderly and medically fragile patient. As with any
surgical procedure performed through a small portal, orientation can be
difficult, and therefore an unintentionally aggressive facet resection or
damage to the pars interarticularis could occur if landmarks are not properly recognized.
Motion-Sparing Technologies
Recently, new technologies have become available that are primarily categorized as “motion preservation devices” but may have some use in minimizing
destabilization while decompressing the stenotic patient. The literature is
sparse and has mixed results on many of these device’s efficacy. More followup is needed to determine their ultimate role and utility in patients with
spondylolisthesis.
The goal of surgery with many of these devices is to provide semirigid
stabilization, interspinous widening, or both, in an attempt to stabilize the
spine, provide for neural decompression, and avoid the need for fusion. They
mainly come in two varieties: interspinous process distraction devices and
semirigid fixation between pedicle screws. A prospective study of patients
with degenerative spondylolisthesis who underwent decompression of the
spine, with and without stabilization, using the Graf system (Surgicraft,
Worcestershire, UK) reported no statistically significant difference between
decompression alone and decompression with stabilization using the Graf
system. Additionally, stabilization using the Graf system was not effective
in reducing the recurrence of leg symptoms. Another prospective clinical
study evaluated whether elastic stabilization with the Dynesys system
(Zimmer Spine, Minneapolis, Minn.) provided enough stability to prevent
progression of spondylolisthesis after decompression for spinal stenosis with
degenerative spondylolisthesis. Radiographically, no significant progression
of spondylolisthesis was detected. The authors concluded that in an elderly
population with spinal stenosis and associated degenerative spondylolisthesis, dynamic stabilization with this system in addition to decompression
results in clinical outcomes similar to those seen with established protocols using decompression and fusion with pedicle screws. Of note, although
the implant failure rate was fairly high (17%), none of these instances were
clinically symptomatic.
Interspinous distraction devices prevent extension of the instrumented
level and try to replicate the relief the patient obtains when they lean forward in flexion. A randomized controlled study of such a device, X STOP
(St. Francis Medical Technologies, Alameda, Calif.), in patients with neurogenic claudication and degenerative spondylolisthesis, reported overall
clinical success in 63% of the patients treated with the X STOP versus 13%
success in the nonsurgical group. A common cause of failure of these devices
is that their modulus of elasticity is usually far greater than the adjacent
spinous processes, which leads to subsidence of the device into the spinous
processes as well as fracture of the bone.
CONCLUSION
Degenerative spondylolisthesis and spinal stenosis commonly occur in tandem and often cause back and radicular leg pain or neurogenic claudication.
It is most common in elderly women at L4-L5. It is also most common
in a patient population with multiple comorbidities and poor bone quality.
Though many with this condition who undergo laminectomy also require
fusion, decompressive surgery without instrumented fusion is an option in
select patients and is better tolerated with less perioperative morbidity in
this population of medically fragile patients.
The severity of a patient’s symptoms and the presence of any neurological deficits must be taken into account. Evaluation of these patients should
include determining the presence or absence of associated degenerative
scoliosis and characteristics of the listhesis that portend less stability (lateral
listhesis). In patients with an associated scoliosis, the magnitude and progression of the curve must be determined.
While traditional laminectomy can usually be performed without destabilizing the spine, care must be taken to spare the pars interarticularis and
as much of the facet(s) as possible. Procedures such as laminotomy, interlaminar fenestration, foraminotomy, and restorative laminoplasty may be
sufficient for neural decompression without significantly compromising
structural integrity. Likewise, newer minimally invasive techniques have the
potential to preserve more structurally important soft tissue. The ultimate
role that these procedures play in the surgical treatment of patients with
spinal stenosis and degenerative scoliosis remains to be proven.
When decompressive procedures are performed without fusion, a radical
decompression should be avoided at the base or apex of a curve in order to
minimize risk of curve progression. Curves that are greater than 20degrees,
C H A P T E R 1 5 Spinal Stenosis with Spondylolisthesis
87
demonstrate progressive deformity, or fit both criteria, are not good candidates for decompression without fusion. Finally, patients with significant
axial pain are less likely to experience improvement in their back pain without concomitant fusion. Recent short-term studies have also shown the
efficacy of adding biologics to aid in obtaining a solid fusion. Future technologies, such as dynamic stabilization and interspinous distraction devices,
will require long-term prospective studies to prove their role in managing
the patient with degenerative scoliosis and spondylolisthesis.
References
1. D.K. Sengupta, H.N. Herkowitz, Lumbar spinal stenosis. Treatment strategies and indications for surgery, Orthop. Clin. North Am. 34 (2003) 281.
2. J.N. Katz, S.J. Lipson, M.G. Larson, et al., The outcome of decompressive laminectomy for
degenerative lumbar stenosis, J. Bone Joint Surg. Am. 73 (1991) 809.
3. A.J. Caputy, A.J. Luessenhop, Long-term evaluation of decompressive surgery for degenerative lumbar stenosis, J. Neurosurg. 77 (1992) 669.
4. K.H. Bridwell, T.A. Sedgewick, M.F. O’Brien, et al., The role of fusion and instrumentation
in the treatment of degenerative spondylolisthesis with spinal stenosis, J. Spinal Disord. 6
(1993) 461.
5. S. Matsunaga, K. Ijiri, K. Hayashi, Nonsurgically managed patients with degenerative
spondylolisthesis: a 10- to 18-year follow-up study, J. Neurosurg. 93 (2000) 194.
6. R.J. Benz, Z.G. Ibrahim, P. Afshar, et al., Predicting complications in elderly patients
undergoing lumbar decompression, Clin. Orthop. Relat. Res. (2001) 116.
7. M.Y. Wang, B.A. Green, S. Shah, et al., Complications associated with lumbar stenosis
surgery in patients older than 75 years of age, Neurosurg. Focus 14 (2003) e7.
8. J.S. Fischgrund, The argument for instrumented decompressive posterolateral fusion for
patients with degenerative spondylolisthesis and spinal stenosis, Spine 29 (2004) 173.
9. F.M. Phillips, The argument for noninstrumented posterolateral fusion for patients with spinal stenosis and degenerative spondylolisthesis, Spine 29 (2004) 170.
10. D.R. Murphy, E.L. Hurwitz, A.A. Gregory, R. Clary, A non-surgical approach to the
management of lumbar spinal stenosis: a prospective observational cohort study, BMC
Musculoskelet. Disord. 7 (2006) 16.
11. M.B. Kornblum, J.S. Fischgrund, H.N. Herkowitz, et al., Degenerative lumbar spon-
dylolisthesis with spinal stenosis: a prospective long-term study comparing fusion and
pseudarthrosis, Spine 29 (2004) 726.
12. Z. Ghogawala, E.C. Benzel, S. Amin-Hanjani, et al., Prospective outcomes evaluation after
decompression with or without instrumented fusion for lumbar stenosis and degenerative
Grade I spondylolisthesis, J Neurosurg Spine 1 (2004) 267.
13. S. Boden, J. Kang, H. Sandhu, et al., Use of recombinant human bone morphogenetic
protein-2 to achieve posterolateral lumbar spine fusion in humans: A prospective, randomized clinical pilot trial 2002 Volvo Award in clinical studies, Spine 27 (2002) 2662.
Imaging of the Aging Spine
Colin S. Poon, Navid Zenooz, and Gordon Sze
16
k e y p o i n t s
Radiography is suited for evaluation of spine alignment. Lateral flexion and
extension views are commonly used for assessment of segmental instability.
MRI provides the most comprehensive imaging evaluation of the aging spine.
Fat-suppressed imaging sequences are particularly valuable for imaging of
spine trauma, inflammation, infection, and neoplasm. For inflammation,
infection, and neoplasm, contrast enhanced T1-weighted imaging sequences
can provide additional information.
Nuclear bone scan is sensitive but not specific for evaluation of most active
spine diseases.
Radiography with lateral flexion and extension views is most commonly
used for follow-up of postoperative spine. CT provides better assessment
of hardware placement and postoperative complications. MRI and nuclear
bone scan can be used for problem solving in patients with postoperative
complications, and persistent or new symptoms.
Although the aging spine can be affected by a wide spectrum of diseases
including neoplasm, infection, trauma, and degenerative disease, the latter
by far is the most important in terms of disease burden and socioeconomic
impact in the aging population. Back pain, with or without radiculopathy,
is the most common indication for imaging of the spine. Patients with
debilitating degenerative disease are often treated by surgery or other interventional procedures. Many of these patients will continue to have active
complaints and require imaging follow-up. For these reasons, this chapter
will focus on imaging of degenerative disease. Many other pathological conditions including trauma, infection and neoplasm can also affect the aging
spine. An awareness of the imaging application in these diseases is important because a major role for early imaging of back pain is the exclusion of
these “red flag” conditions. The imaging of these other diseases and postoperative spine, as well as a discussion of imaging techniques, are included in
the Appendix (on the website) to serve as an introduction to these topics.
Degenerative disease of the spine most commonly involves the lumbar
spine, followed by the cervical spine. Manifestations of degenerative spine
disease include intervertebral disc degeneration, disruption of the annulus
fibrosus, herniation of the nucleus pulposus, vertebral endplate changes,
osteophyte formations, facet arthropathy, formation of juxta-articular cysts,
degenerative spondylolisthesis, and spinal stenosis.
Intervertebral Disc Degeneration
On radiography (Figure 16-1) , intervertebral disc degeneration is indirectly
inferred from loss of the normal disc space height. Gas may be seen in the
disc space, due to a negative pressure within the degenerative disc causing
extraction of nitrogen from extracellular space. This is commonly referred
to as vacuum phenomenon. The vacuum phenomenon can be accentuated
during extension of the spine and reduced during flexion. Vertebral endplate
irregularity is often seen, with or without associated sclerotic changes at the
endplates.
With the wide availability of MRI, CT is rarely requested for the primary
evaluation of degenerative disc disease, except in patients with contraindications for MRI examination. Similar to radiography, CT can demonstrate
L3
IMAGING OF DEGENERATIVE SPINE DISEASE
Correlation between imaging morphology of degenerative disease and clinical symptoms can be poor, particularly for the most common complaint of
pain. The reasons of the discrepancy are not clear, but several factors may
come into play. Subjective complaints such as pain may be due to inflammatory response in the surrounding soft tissues, rather than mass effect that
can be visualized directly on imaging. In addition, degenerative changes may
indirectly compress the nerve roots by distorting their normal surrounding
soft tissue structures, such as epidural fat, rather than compress the nerves
directly. Imaging usually provides only a static snapshot of the anatomical
structures. For example, most imaging studies are acquired with the patient
supine, which is most likely different from the posture of the patients when
they experience their symptoms. Although specialized units such as upright
MRI scanners are now available to address these issues, their use is not
yet widely adopted. Notwithstanding its limitations, imaging provides an
important means for evaluation of the spine.
88
L5
F IG UR E 1 6 -1 Radiographic features of degenerative disc disease. Disc
space narrowing and subtle cartilaginous endplate sclerosis are present at L4-L5.
C H A P T E R 1 6 Imaging of the Aging Spine
89
disc space loss, endplate irregularity or sclerotic changes, and vacuum phenomenon. However, CT also allows direct visualization of disc bulging and
disc herniation (Figure 16-2) , although with a lesser soft tissue contrast
compared to MRI. When more accurate depiction of disc bulging and disc
herniation is required, CT myelography can be performed (Figure 16-3) .
MRI provides the best soft tissue details of degenerative disc disease. In
young healthy patients, the intervertebral discs demonstrate hyperintensity
on T2-weighted images. With aging, there is loss of this hyperintensity due
to a decrease of water content and changes in proteoglycan composition
(Figure 16-4). There is decreased disc height and the endplates may
become irregular. Gas from vacuum phenomenon may fill the space of
a degenerative disc, which may demonstrate hypointensity on both T1and T2-weighted images. Alternatively, the space may be filled with fluid,
which is seen as hyperintensity on T2-weighted images. A degenerative
disc may also calcify, which can give hypointensity or hyperintensity on
T1-weighted images, depending on the type and concentration of calcification. A degenerative disc may also enhance secondary to the presence of
granulation tissues.
Fissures of the annulus fibrosus may be seen in the intervertebral discs.
On MRI, annular disruptions (also referred as fissures) may be seen as a
small high intensity zone within the outer annulus (Figure 16-5) .
One of the primary advantages of MRI is the direct visualization of disc
bulging or herniation, and its associated mass effect on the nervous structures. At a particular disc level, a disc can have bulging and one or more
areas of herniation seen on the same occasion. In 2001, multiple societies
reached a consensus to standardize the nomenclature and classification of
disc pathology.
1
This work is currently being revised (A. Williams, S.Rothman, R. Murtagh, G. Sze, in progress). The consensus was initially developed for lumbar disc disease but is generalized to disc disease in the rest
of the spine. Normal disc space is defined craniocaudally by the vertebral
body endplates, and circumferentially by the ring apophysis of the vertebral
bodies. In the newly revised consensus, a disc bulge refers to diffuse displacement of disc material beyond the normal disc space, and covers greater than
25% of the normal disc space circumference (i.e, greater than 90 degrees of
the circumference) (Figure 16-6, A) . Disc displacement covering 25% or
less of the circumference is called herniation. When the width of the base
of the disc herniation is greater than any other measurements in the same
plane of the herniation, it is called a protrusion (Figure 16-6, B). When
any of the measurements of the herniation is greater than the width at its
base, the herniation is described as an extrusion (Figure16-6, C and D). In
essence, a protrusion is a disc herniation with a wide base, whereas an extrusion is a narrow-based disc herniation with appearance sometimes resembling toothpaste that is squeezed out of its container. Migration refers to
herniated disc material that is displaced above or below the level of the disc.
When the disc extrusion is separated from the parent disc, it is referred to
as a sequestration. Sequestered disc often demonstrates T2 hyperintensity
compared to its disc of origin. This may be secondary to the presence of
granulation tissue, immune response, or inflammation.
2
Most disc sequestrations are seen in the epidural space, but rarely, they may migrate into the
intradural space or posterior to the thecal sac. Herniated disc may be contained by the annulus fibrosus (subannular) or the posterior longitudinal
ligament (subligamentous) (Figure 16-6, D), although the distinction some-
times can be difficult.
Disc material can also herniate through the vertebral cartilaginous endplates into the adjacent vertebral bone marrow. Intravertebral (intraosseous) herniation is often called Schmorl’s node (Figure 16-7) and has been
reported in 38% to 75% of the population. Most of these are seen as incidental findings.
Vertebral Marrow Changes and Osteophyte Formation
Disc degeneration often leads to changes of the bone marrow adjacent
to the cartilaginous endplates bordering the disc. MRI can demonstrate
three patterns of bone marrow signal changes that have been classified by
Modic et al
3
(Figure 16-8) . The vertebral marrow changes can convert
from one type to another with time. In many patients, the vertebral marrow changes actually appear in a mixed pattern. The clinical and pathophysiological significance of vertebral marrow changes have been subject
to debate. Some reports have suggested that type I change is likely to be
inflammatory in origin and is more strongly associated with active low
back symptoms and segmental instability.
4
It has also been suggested that
patients with type I marrow changes respond better to fusion compared
to those without or with other types of endplate changes, and that persistence of type I marrow changes after fusion is associated with a worse
outcome.
5
Osteophyte formation is commonly seen in the aging spine. Osteophytes
refer to abnormal bony outgrowth that is believed to be induced by abnormal mechanical stress. They are often located at the edge of the annulus
fibrosus and adjacent apophyses, and are best seen on radiographs or CT.
Osteophytes at the outer rim of the vertebral endplates and associated with
degenerative disease are commonly referred to as spondylosis deformans.
Facet Arthropathy
Degenerative changes of the facet joints in the spine resemble that of other
synovial joints in the rest of the body. Although radiography can demonstrate the bone changes associated with osteoarthritis, including joint space
narrowing as a result of thinning of articular cartilage, subchondral sclerosis,
marginal osteophyte formation, facet hypertrophy, and hyperostosis, these
findings are best demonstrated on CT (see Figures 16-2 and 16-3). Very
often, gas from vacuum phenomenon can also be seen on radiography or
CT. MRI does not provide as much bony detail, but facet hypertrophy is
F IG UR E 1 6- 2 CT of intervertebral disc degeneration.
A, Reformatted sagittal CT image in bone window showing
severe disc degeneration including severe disc space loss, lucency
within the disc space consistent with gas (vacuum phenomenon),
and sclerosis at the adjacent endplates (white arrow). The facet
joint also demonstrates irregular hypertrophy, osteophytes and
loss of joint space (open arrow). Degeneration of these structures
T
A
B
lead to instability, resulting in anterolisthesis of L4 over L5. B,
Axial image in soft tissue window demonstrates diffuse disc bulging (white arrows), thickening of the ligamentum flavum (black
arrows), and facet arthropathic changes that include joint space
narrowing, facet hypertrophy, and vacuum phenomenon in the
facet joints (open arrow). These changes lead to severe spinal
canal stenosis, with the thecal sac (T) severely compressed anteriorly and posterolaterally.
90
P A R T I I Basic Science of the Aging Spine
F IG UR E 1 6- 3 CT myelogram. A, Axial
image at the L3-L4 intervertebral level demonstrates a left central disc protrusion (open
arrow), causing stenosis and impingement of
the nerve roots at the left lateral recess. By
comparison, the right L4 nerve root at right
lateral recess (white arrow) is floating freely
within the thecal sac. B, At the L2-L3 level,
there is severe spinal stenosis as a result of disc
bulging, ligamentum flavum hypertrophy, and
facet arthropathic changes that include facet
hypertrophy and sclerosis (circle), resulting in
almost complete obliteration of the cerebrospinal fluid space (arrow).
A
B
L3
F I GU R E 1 6- 4 Disc degeneration seen on MRI (T2-weighted image) (same patient as Figure 16-1).
There is disc space narrowing and loss of the normal T2 hyperintensity of the L4-L5 disc. Bulging of the disc with
a small protrusion into the spinal canal is also shown (arrow). Compare the L4-L5 disc with the normal appearance of the discs at L2-L3 and L3-L4 levels.
F IG UR E 1 6- 5 Annular disruption seen as a high intensity zone (arrow) on T2 weighted images.
C H A P T E R 1 6 Imaging of the Aging Spine
91
*
A
C
B
L3
D
*
F IG UR E 16 -6 Disc bulging and herniation. A,
Diffuse disc bulging. The disc extends beyond the margin of the ring apophysis (arrows) circumferentially. B,
Disc protrusion. Note the width of the base (arrow) is
larger than any other dimensions of the disc herniation.
Degenerative facet hypertrophy is also noted (asterisks).
C, Disc extrusion. The width of the base (white arrow)
is narrower than any other dimensions. The nerve root
at the left lateral recess is impinged by the extruded
disc. Compare this with the corresponding free nerve
root on the right (open arrow). D, Subligamentous disc
extrusion. Note the narrow width of the base and the
location of the disc extrusion (white arrow) underneath
the lifted posterior longitudinal ligament (black arrows).
F I GU R E 16 - 7 Schmorl’s node (arrow) at superior endplate of L4 vertebra. On this sagittal
T2-weighted image, loss of the normal bright signal and bulging of the L3-L4 and L4-L5 discs are
also noted.
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P A R T I I Basic Science of the Aging Spine
A
D
G
B
E
F IG UR E 16 -8 Degenerative vertebral endplate changes (arrows) as classified by Modic et al3
Type I marrow change demonstrates T1 hypointensity,(A) T2 hyperintensity (B) and enhances with gadolinium. (C) It represents replacement of normal hematopoietic marrow by fibrovascular tissue. Type II marrow change demonstrates hyperintensity on both T1- (D) and T2-weighted (E) images. It is secondary to
conversion of hematopoietic marrow to fatty marrow. Type III change demonstrates hypointensity on both
T1- (F) and T2-weighted (G) images. It represents replacement of hematopoietic marrow by sclerosis. There
is no abnormal enhancement associated with type II or type III changes (not shown).
C
F
easily demonstrated (see Figure 16-6, B). In addition, MRI may demon-
strate joint space effusion and inflammatory changes (synovitis) that can be
associated with osteoarthritis (Figure 16-9). Synovitis is best demonstrated
on fat-suppressed T2-weighted or postgadolinium MRI sequences.
The uncovertebral joints associated with the lower five cervical vertebral
bodies are also commonly associated with arthropathic changes. The uncinate process may undergo hypertrophy and spur formation that can project
into the neural foramina and spinal canal, leading to narrowing of the neuroforamina and spinal canal stenosis (Figure 16-10) .
Juxta-articular cysts are often seen associated with facet arthropathy.
They include synovial and ganglion cysts. Compared to synovial cysts,
ganglion cysts do not have synovial lining and do not communicate with
the joint space. However, on imaging, it is difficult to make the distinction
and they are often simply referred to as juxta-articular cysts. The cysts are
usually located in the posterolateral epidural space of the spinal canal. Occasionally, they may be completely outside of the spinal canal (Figure 16-11).
They can calcify and sometimes can be confused with other pathological
entities such as a disc herniation or a mass. However, the recognition of
continuity of a lesion with adjacent degenerative facet joint should strongly
suggest the diagnosis. On MRI, their signal intensity is variable and depends
on whether they contain proteinaceous material or hemorrhage. Gas may
be present in synovial cysts, as they communicate with facet joints that may
C H A P T E R 1 6 Imaging of the Aging Spine
93
contain gas from vacuum phenomenon. The cyst walls may contain hemorrhage or calcification. There may be contrast enhancement in the cyst wall
or surrounding soft tissues if inflammatory response is present.
Spondylolisthesis and Segmental Instability of the Spine
Spondylolisthesis, scoliosis, and segmental instability can result from
degeneration of the stabilizing structures in the spine, including intervertebral discs, vertebral bodies, facet joints, joint capsules, and ligaments (see
Figure16-2). It is important to exclude other underlying pathologies, such
as defect of the pars interarticularis or fracture. This consideration is particularly important when the anterolisthesis is greater than grade 1 (25% of the
vertebral body diameter), or the degenerative changes are disproportionately
mild to account for the high grade spondylolisthesis. Pars interarticularis
defect can be detected using oblique radiography or CT. For occult pars
defect or occult fracture, a nuclear bone scan may aid in their detection.
Segmental instability of the spine can be seen as spine deformity or
spondylolisthesis that increases with spine motion and progresses over time.
Standing radiography that includes anteroposterior and lateral projections
L4
L5
F IG UR E 16 - 9 Enhancement may be present in degenerative disease
of the facet joints (arrows). Other degenerative changes of the facet joints may
also include facet hypertrophy, joint space narrowing, and joint effusion.
with flexion and extension of the spine provides the most easily available
imaging tool for evaluation of spine instability.
There are currently no standardized methods or criteria for diagnosis
of spine instability.
4 mm for sagittal translation have been used to infer instability in some
6
studies.
Sagittal rotation is measured as the variation of angle between two
7
However, values of 10 degrees for sagittal rotation and
6
opposite vertebral endplates observed during flexion and extension on lateral projection, and sagittal translation is measured as the variation of distance between the lines that follow the posterior cortices of two adjacent
vertebrae. To minimize the effect of radiographic magnification, the absolute
distance can be given as a percentage of the anteroposterior width of the
superior vertebra.
Reproducibility of measurement of segmental instability is difficult,
and is subject to many factors, including patient positioning, angulation of
x-ray beam, radiographic magnification effect that varies with the distance
of the anatomical structures from the x-ray detector, and patient’s level of
cooperation.
Radiography can also demonstrate other indirect signs of instability,
such as vacuum phenomenon and traction osteophytes. Traction osteophytes appear as horizontal osteophytes that arise typically on adjacent vertebral bodies below the rims of the endplate, approximately 2 to 3 mm from
the edge of the intervertebral disc
8
(Figure 16-12) .
Instability is difficult to demonstrate directly on routine MRI and CT.
Many imaging features can suggest instability indirectly, including spondylolisthesis, degenerative endplate changes, vacuum phenomenon, and degenerative disc disease. However, these imaging features are neither sensitive nor
specific and can also be seen in degenerative spine disease without instability.
Spinal Stenosis
Spinal canal stenosis and foraminal stenosis are common consequences of
degenerative disease of the spine. Patients with congenital anomalies, such
as short pedicles, are particularly at risk of developing spinal stenosis. Spinal stenosis is best evaluated with MRI because of its ability to assess both
bony and soft tissue structures that can narrow the spinal canal or neural
foramina (Figures 16-13 and 16-14). Direct impingement on the spinal
cord or nerve roots can be easily seen on MRI. Disc bulging, disc herniation,
degenerative changes of the facet and uncovertebral joints, thickening of
the ligamentum flavum, epidural lipomatosis and spondylolisthesis can all
lead to narrowing of the spinal canal and neural foramina. Although sagittal
images can provide a general overview of spinal canal stenosis, axial images
are essential for an accurate assessment of the degree of stenosis.
The central spinal canal can be narrowed anteriorly by disc bulge or
herniation and vertebral osteophytes. Posterolaterally, it may be narrowed
by facet disease and ligamentum flavum hypertrophy. Epidural lipomatosis tends to favor the posterior epidural space but may also be seen
C5
A
F IG UR E 1 6- 10 Uncovertebral joint degenerative disease causing neural foraminal narrowing. Axial CT image (A)and reformatted coronal CT image
(B) at C6-C7 intervertebral level demonstrate spur formation at the uncovertebral joints (black arrows) projecting into the neural foramina, causing foraminal stenosis.
Compare this with the normal uncovertebral joints at the other levels (white arrows). C, Axial T2-weighted MR image in a different patient demonstrates osteophytes
at the posterior vertebral margin and uncovertebral joints (short arrows). A small disc protrusion is also noted at the left lateral recess (open arrow). There is narrowing
of the bilateral neural foramina, worse on the left, causing impingement of the left exiting nerve root. Long arrow, right exiting nerve root.
B
C
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P A R T I I Basic Science of the Aging Spine
circumferentially. These abnormalities lead to distortion of the normally
round or oval shape of the spinal canal and thecal sac. With worsening stenosis, the spinal canal and thecal sac may become triangularly shaped or flattened. There may be effacement of cerebrospinal fluid space located between
the degenerative processes, causing spinal stenosis and impingement of the
spinal cord or nerve roots.
Grading of spinal canal stenosis can be performed according to the
recommendation of the Combined Task Forces of the North American
Spine Society, American Society of Spine Radiology, and American Society
of Neuroradiology.1 Spinal canal compromise of less than one third of
the normal canal is graded as “mild,” between one third and two thirds is
“moderate,” and over two thirds is “severe.” Neural foraminal stenosis can be
assessed on axial images and lateral sagittal images, using a grading scheme
similar to that for central spinal canal.
Severe spinal canal stenosis can lead to compression of the spinal cord.
This can result in ischemia and edema, which may eventually lead to irreversible damage and myelomalacia (Figure 16-15). Myelomalacia can
be seen as T2 hyperintense signal of the spinal cord. Cystic changes and
F IG UR E 16 -1 1 Synovial cyst. Axial T2-weighted MR image demon-
strates degenerative changes of the bilateral facet joints, which contain a small
amount of effusion. On the right; a small synovial cyst (arrow) is seen in continuity with the right facet joint.
C
F IG UR E 16 -1 2 Lateral radiography of lumbar spine demonstrates a
traction spur (arrow), which is an indirect sign of segmental instability. (From
Leone A, Guglielmi G, Cassar-Pullicino VN, Bonomo L. Lumbar intervertebral
instability. Radiology 2007; 245(1): 62-77, Figure 5.)
L4
S1
A
F IG UR E 1 6- 1 3 Spinal canal and neuroforaminal stenosis. A, Sagittal T2-weighted image demonstrates disc bulging at the L5-S1 level and spinal ste-
nosis (arrow). B, Axial T2-weighted image at L5-S1 level demonstrates severe spinal stenosis with nerve root impingement as a result of congenital shortening of the
pedicles (note the short distance between the facets and the vertebral body) and superimposed degenerative changes including disc bulging and facet arthropathic
changes. Small arrows, disc bulging; long arrow, annular disruption; (open arrow), facet hypertrophy and joint effusion. C, Sagittal T1-weighted image in another
patient demonstrates anterolisthesis of L5 over S1 secondary to spondylolysis at L5 (open arrow). The L5 nerve root exiting the L5-S1 neuroforamen is compressed
(arrow). Compare this with the free L3 nerve root exiting the L3-L4 neuroforamen (open arrowhead), which is completely surrounded by normal epidural fat.
B
C