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18 Lumbar Spinal Stenosis
18.1 General Considerations
I. In t r o d u ct ion .
A. De n it ion : n ar row in g of t h e s p in al ca n al (ce n t r a l s t e n o s is), lat e r a l re ce ss (la t e ra l
recess stenosis), or foramen (foraminal stenosis) with neural impingement that
produces symptoms of neurogenic claudication or radiculopathy.
B. De ge n e r at ive sp in a l s t e n o sis e vid en ce d o n im a gin g s t u d ie s is s ig n i ca n t o n ly i f
clinically sym ptom atic.
C. Mo r e co m m o n a ft e r t h e ft h d e c a d e .
D. Men m ore a ected t h an w om en.
E. Asso c ia t e d w it h d isk d e ge n e r a t io n .
II. Class i cat ion .
A. Co n ge n it al: u su ally d eve lo p m e n t a l a n d p r im a r ily ce n t ra l ca n a l st e n os is (Fig. 18.1).
a
Fi g . 1 8 . 1 ( a , b ) Me as u re m e n t s o f t he b o ny
b
anatomy and spinal canal.
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1. Characteristics.
a. Earlier clinical presentation (fourth and fth decade).
b. Multilevel involvement.
c. Fewer degenerative changes on imaging.
d. Subtle anatomical changes that may compress the thecal sac.
2. Radiographic ndings.
a. Smaller cross-sectional spinal canal area.
b. Shorter anterior-posterior (AP) pedicle length.
c. The midline, axial AP canal diam eter, medial–lateral vertebral body
width, and sagittal AP canal diameters are smaller.
d. Smaller AP pedicle length to vertebral body ratio.
e. No di erence in the AP vertebral body diameter, vertebral body height,
canal w idth, or pedicle width.
B. Ac q u i r ed (m o st co m m on in t h e s i x t h d e c a d e ).
1. Degenerative stenosis.
a. Central stenosis.
(1) Enlargem ent of the inferior articular process, ligam entum avum ,
and intervertebral disk protrusion or herniation.
b. Lateral stenosis.
(1) Enlargem ent of the superior articular process and ligam entum
avum.
c. Foram inal stenosis.
(1) Narrow ing of the foram en secondary to far lateral disk herniation and
pars hypertrophy in isthmic spondylolisthesis.
2. Degenerative spondylolisthesis.
a. For example, at the L4–L5 level, the L5 nerve is entrapped between
the inferior articular process of L4 and the posterior aspect of the body
of L5.
3. Combined.
a. Disk herniation, superimposed on a degenerative or congenitally stenotic
canal.
4. Iatrogenic.
a. Postlaminectomy, postfusion, post–disk surgery.
5. Posttraumatic.
a. Secondary to retropulsion of bone in a burst fracture and fracture
dislocation.
6. Miscellaneous.
a. Paget’s disease, uorosis.
b. Dwar sm (achondroplastic).
III. Pat h ogen esis.
A. Var iat io n s o f t he sp in a l ca n al m ay p r e d isp o s e t o sp in al st e n o sis .
1. Three types of spinal canal.
a. Round canal.
b. Oval canal.
c. Trefoil canal (15%).
(1) Napoleon hat shape.
(2) A trefoil canal predisposes to lateral recess stenosis.
18 Lum bar Spinal Stenosis 199
B. Disk d ege n e r a t io n :
1. Aging versus degeneration.
2. Changes in the collagen, proteoglycans, and water content.
C. Fa c e t jo in t in vo lve m e n t :
1. Follows disk degeneration.
2. Joint cartilage loss, hypertrophy, osteophytes, and subluxation.
D. Thre e - join t com p lex:
1. Two posterior facet joints and the disk are all involved in the pathogenesis.
2. Degenerative changes of the three-joint complex secondary to repeated
rotational and compression injuries.
3. Intervertebral disks develop circumferential and radial tears with a loss of
disk height.
4. Posterior joints undergo synovitis, cartilage destruction, and osteophyte
for m at ion .
a. Results in capsular laxity, ligamentum avum hypertrophy or buckling,
and joint instability or subluxation.
5. Instability:
a. Degenerative spondylolisthesis.
b. Retrolisthesis.
c. Degenerative scoliosis.
d. Rotatory subluxation.
E. L4 or L5 n er ve s a r e m o re t yp ic a lly a e c t e d :
1. Greater compressive and shear stresses.
2. Pedicles of the lower lumbar spine have convex inferior borders as compared
with the concave inferior border in the upper lumbar spine.
3. Disk degeneration is most common at L4–L5 and L5–S1.
F. N e u r a l c o m p r e s s i o n :
1. Anatomical site of compression:
a. Cauda equina and thecal sac (central canal).
b. Traversing nerve root (lateral recess).
c. Dorsal root ganglion (intervertebral foram en).
d. Spinal nerve (extraforaminal).
2. The cauda equina is compressed centrally from the anteroposterior direction
at the intervertebral disk level..
a. Bulging disk anteriorly.
b. Ligamentum avum and facet joints posteriorly.
3. The nerve root can be compressed at multiple anatomical locations (Fig. 18.2).
a. Entrance zone.
(1) Posterolateral herniated disk.
(2) Hypertrophic superior articular process.
b. Middle zone.
(1) Pars interarticularis (spondylolysis).
4. Exit zone (foramen) (Fig. 18.3):
a. Anatomy.
(1) Bounded by vertebral body and disk anteriorly, pedicles superiorly
and inferiorly, and pars, ligamentum avum, and tip of superior
articular process posteriorly.
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Fi g . 1 8 . 2 Va r i o u s a n a t o m i c a l l o c a t i o n s f o r n e r v e r o o t c o m p r e s s i o n .
18 Lum bar Spinal Stenosis 201
a b
Fi g . 1 8 . 3 ( a ) Anatomical location of the nerve root within the neuroforamen. (b) Neuroforaminal
stenosis with nerve root impingement secondary to facet hypertrophy and osteophytic compression
secondary to the superior articular process.
(2) Laterally herniated disk or annulus.
(3) Superior facet subluxation may compress the nerve against the
pedicle, body, or bulging annulus.
b. Extraforaminal compression.
(1) Extreme lateral or extraforam inal herniated disk.
(2) Also known as far-out syndrom e.
(a) The exiting nerve root is com pressed between the transverse
processes of L5 and the sacral ala in spondylolisthesis (L5–S1).
(3) Transverse process fracture or bone graft anterior to the transverse
processes.
5. Dimensions of stenosis (Fig. 18.4):
a. Central.
(1) Absolute stenosis: midsagittal lum bar diam eter < 10 mm.
(2) Relative stenosis: 10 to 13.5 mm .
b. Lateral recess.
(1) Less than 3 to 4 mm .
c. Foram en.
(1) Foram inal height < 15 mm .
(2) Posterior disk height < 3 mm (80% likelihood of nerve root
compression).
6. Pathophysiology of radiculopathy:
a. Combination of compression and in ammation.
(1) Com pression alone m ay not cause pain.
(2) In am matory mediators:
(a) Phospholipase A2.
(b) Neuropeptides.
b. Dynamic instability.
(1) Spinal canal and foram en.
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18 Lumbar Spinal Stenosis
a b
Fi g . 1 8 . 4 ( a ) Cross-sectional view of the normal anatomy of the neural structures within the spinal
canal. (b) Computed tomographic myelography demonstrating central stenosis with signi cant ligamentum avum hypertrophy.
c. Venous stasis.
d. Arterial ischemia.
e. Nutritional de cit.
(1) Abnorm al cerebrospinal ow.
f. Perce n t con st rict ion of cau d a e qu in a.
(1) Twent y- ve percent: no de cits.
(2) Fifty percent or greater: motor de cits and complete loss of
somatosensory evoked potentials (SSEPs).
IV. Clin ical n d ings.
A. Pa in .
1. Variable:
a. Monoradiculopathy.
b. Bilateral neurogenic claudication.
c. At ypical leg pain.
d. Cauda equina symptoms.
2. Typically in the lower back, buttock, and lower extremities.
3. Pain is worse with standing and walking.
4. Relieved by rest, exed posture, and sitting.
5. The history is the key in making the diagnosis of spinal stenosis.
B. Cla u d ica t io n -like s y m p to m s in 5 0 %.
1. One must rule out vascular claudication.
2. In vascular claudication:
a. Relief after rest is more prompt.
b. Flexion of the spine does not relieve symptoms.
(1) For exam ple, bicycling and walking uphill m ay not cause neurogenic
claudication because th e spine is exed.
3. Vascular and neurogenic claudication may coexist.
18 Lum bar Spinal Stenosis 203
C. Ph ys i c a l e xa m in at io n .
1. Paucity of objective ndings.
2. The sciatic tension sign is often negative.
3. Neurological de cits may or may not be present.
4. The m ost important sign is painful and limited extension.
5. Thorough abdominal and vascular examination should be done routinely.
a. Vascular changes may demonstrate lower extremity ulcer formation, hair
loss, edem a, and skin m ot tling.
D. Diagn ost ic tools.
1. Plain radiographs.
a. Disk space narrowing or degenerative disk disease.
b. End plate osteophytes and sclerosis.
c. Facet enlargement or osteophyte form ation.
d. Narrowed neuroforaminal canal.
e. Loss of lumbar lordosis.
2. Magnetic resonance imaging (Fig. 18.5).
a. Best modality for evaluating lumbar spinal stenosis.
b. Excellent for soft tissue details, but bony margins are better
demonstrated by CT scans.
E. Con ge n it a l st e n os is .
1. Lumbar spinal stenosis typically a ects individuals over 60 years of age, but
younger patients with congenital stenosis present in the fourth and fth
decades.
2. The presenting symptoms are somewhat di erent in that many su er with
low back pain (LBP) w ith or without neurogenic claudication.
Fi g . 1 8 . 5 Ma g ne t ic re so na nce im ag ing d em on strating spinal stenosis secondary to a herniated
lum ba r d isk. (Fro m Im ho f H, e d. Spinal Im ag ing
[Direct Diagnosis in Radiology]. Stut tgart, Germany: Georg Thieme Verlag; 2008: Fig. 3.35.
Re p r o d u c e d w i t h p e r m i s s i o n . )
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18 Lumbar Spinal Stenosis
3. LBP is typically worse with standing and walking as compared with
diskogenic LBP, which is typically worse with sitting.
4. The spinal canal is narrow at multiple levels with short pedicles. The sagittal
canal to vertebra ratio is < 0.4 (Singh et al).
5. The patients with congenital stenosis presenting with “neurogenic LBP”
are frequently misdiagnosed as diskogenic LBP and are given inappropriate
treatment.
6. Treatment is initially conservative as for other stenotic patients, but if there
is no respon se, m ultilevel lam inectomy is recom m ended rather than fusion .
V. D i e r e n t i a l d i a g n o s e s .
A. Tra u m a (sp r a in s, st r ain s, com p r ess io n fr a ct u r es).
B. In fe ct io n s (ve r te b r a l o st e o m ye l i t is ).
C. In a m m a t or y d iso rd e r s .
D. Congen it al defect s (ach on d rop lasia).
E. Me t a b olic (o st e o p o r os is , Pa ge t ’s d ise a s e ).
F. De g e n e r a t i v e ( d i s k h e r n i a t i o n , fa c e t s y n d r o m e ) .
G. Neop la sm s (in t r a sp in al, b o n e t u m o r s, an d m et ast as is).
H. Neurological disorders (peripheral neu ropathies).
I. Cir cu la t or y (abd om in al aor t ic a n e u r ysm , va scu la r cla u d icat ion ).
J. My o fa s cia l s y n d r o m e s .
K. Ps ych o n e u ro t ic p r o b le m s .
VI. Tre at m e n t.
A. Co n se r va t ive .
1. Nonsteroidal anti-in ammatory drugs.
2. Lumbosacral corsets.
3. Flexion exercises.
4. Epidural or foraminal injection.
B. Su r ge r y.
1. Indications.
a. Cauda equina syndrome.
b. Progressive motor weakness.
c. Limb pain that is unresponsive to conservative treatment and if
symptoms signi cantly a ect quality of life.
2. Surgical techniques (Fig. 18.6).
a. Decompression: the key is adequate decompression while preserving
stability of the motion segment by undercutting the facet joint and
preserving the pars interarticularis. For multilevel decompression, care
must be taken to preserve the pars interarticularis in the upper lumbar
spine, because the pars is m ore medial. Therefore, lam inectomy is more
lateral at the facets, which is the location for lateral recess sten osis, an d
more medial or narrower at the pars.
(1) Central stenosis:
(a) Lam inectomy (Fig. 18.7).
(2) Lateral recess:
(a) Remove an overgrow n superior facet by undercutting.
(3) Foram inal decompression: foram inal decom pression requires more
facet rem ova l, bu t e ve r y e or t m u st be m a d e to p rese r ve t h e facet join t
18 Lum bar Spinal Stenosis 205
Fi g . 1 8 . 6 St e p s fo r a lu m b ar la m in e c t o m y.
as much as possible by undercutting and using special instruments,
such as a curved foram inotomy rongeur or rasp (Fig. 18.8).
(a) If the nerve root is tight after lam inectomy and facet
undercutting, additional sites may be responsible for nerve
compression.
i. Su perior facet again st posterior vertebral body.
ii. Su perior facet again st pedicle.
iii. Superior facet or pedicle again st bu lging lateral annulus.
iv. In fer ior facet and ver tebral body (d egenerat ive
spondylolisthesis).
v. Tr a n sve r se p roce sses of L5 an d sa cral ala (“far-ou t syn drom e ”).
b. Lumbar fusion:
(1) Approaches.
(a) Posterior: posterolateral fusion, posterior lum bar interbody
fusion , and tran sforam in al lum bar interbody fu sion.
(b) Anterior: anterior lum bar interbody fusion , extrem e lateral
lum bar interbody fusion.
(2) Fusion is recom m ended when there is stenosis in conjunction with
the following conditions:
(a) Unstable degenerative scoliosis or kyphosis.
i. Progressive curves.
ii. Cur ves > 20°.
iii. Loss of sagit tal balance and lum bar lordosis.
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18 Lumbar Spinal Stenosis
b
a
c
d e
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