1. Interspinous process spacers are implants placed between adjacent lumbar spinous processes as a less invasive alternative to spinal fusion surgery. They are designed to preserve motion while reducing pain by decreasing pressure on spinal discs and facets. 2. Biomechanical studies show that spacers reduce intradiscal pressure and facet joint contact area at implanted levels without affecting adjacent segments. Clinical reports also suggest spacers provide short-term symptom improvement for appropriately selected patients. 3. However, concerns exist that the spacers may cause local pain over time and weaken spinal stability by disrupting ligaments and maintaining facet joints in distraction. Further research is still needed to establish the long-term efficacy and safety of interspin

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2. Interspinous
Process Spacers

3. The concept of using the
vertebral spinous process
to secure an implanted
device is not new.
The Knowles device,
introduced in the 1950s,
consisted of a steel
cylinder designed
for temporary insertion
between adjacent
lumbar spinous processes
in the patient with acute
disk herniation.
Whitesides TE Jr, Spine 2003

4. Subsequent interspinous
process devices have been
designed for longer-term
implantation for managing
various conditions, including:
spinal stenosis,
disk herniation,
segmental instability,
degenerative disk disease.

5. In some patients, the
devices are intended
for use in conjunction
with more traditional
spinal fusion surgery.
Tsuji H et al, J Spinal Disord 1990
Senegas J, Eur Spine J 2002

6. Rationale for the Use of Interspinous
Process Spacers
The interspinous
process spacer
is a motion-preserving
spinal implant
designed to provide
symptomatic relief
to selected patients
without the need
for spinal fusion

7. Theoretic indications
for
interspinous process
spacer devices include:
spinal stenosis
with and without
degenerative
spondylolisthesis,
as well as
chronic discogenic low back
pain.
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8. These implants
have been proposed as a
“dynamic stabilization”
alternative to
rigid instrumented fusion,
with the advantages of :
a more limited and
less morbid surgical
procedure that may confer
less risk of adjacent
segment degeneration.
Minns RJ,et al, Spine 1997

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The pathophysiology
of spinal degeneration
remains a matter
of controversy;
however, a popular
hypothesis suggests that
the spondylotic sequence
begins with:
progressive disk desiccation,
bulging, and
collapse.

10. Low-grade
segmental instability
may subsequently
result in:
facet joint subluxation
and
hypertrophy,
as well as
in progressive thickening
of the ligamentum
flavum.

11. The risk of developing
symptomatic stenosis,
typically in the sixth decade
of life or later,
is increased
in the patient with pre-existing:
developmental stenosis
or
a trefoil-shaped spinal canal.

12. Neural dysfunction
has been attributed:
to direct compression
of the cauda equina
and
lumbosacral nerve roots as
they travel within the:
canal,
lateral recesses,
and
neuroforamen.

13. Presumably,
compression
results in:
disruption of the
vascular supply,
neural metabolism,
and
axonal processes.

14. The postural
dependency
of:
neurogenic claudication
and
stenosis related symptoms
is the result of
the anatomic effects of :
flexion
and
extension
on the spinal canal
and
foraminal dimensions.

15. During lumbar
extension,
the ligamentum flavum
buckles anteriorly,
while
the posterior annulus
bulges posteriorly;
Both contribute to
further reduction
in the size of the central
canal
and
lateral recesses

16. Neuroforaminal
narrowing
occurs:
as the facet capsule
is pushed anteriorly
by the superior
articular facet of the
caudal vertebra
Mayoux-Benhamou MA ,et al, Surg
Radiol Anat 1989

17. Conversely,
flexion
is associated with:
a relative increase
in the area of the
spinal canal
as buckling of the
ligamentum
flavum is relieved.

18. Interspinous
process spacer
technology
is designed to take
advantage of
the marked postural
dependence
of symptoms
that exists
in many patients
with spinal stenosis.

19. The device is
interposed between
adjacent
spinous
processes
following limited
surgical exposure of
the posterior lumbar
spine.

20. The implant
maintains the
treated level :
in modest flexion
and
limits extension
without limiting
either:
axial rotation
or
lateral bending.
Lindsey DP, et al, Spine 2003

21. In general,
normal cross-sectional
area of the dural sac
in the lumbar region
is 150 to 200 mm2
stenotic symptoms
may be associated
with a decrease in
area to <100 mm2.
Ullrich CG, et al, Radiology 1980

22. Computed tomography
studies suggest that
lumbar flexion
increases the area of the
spinal canal by 11%.
By comparison,
in vivo magnetic resonance
imaging evaluation
of patients
following implantation of
an interspinous process
spacer
has suggested a mean
22.3% increase
in cross-sectional area
of the dural sac.
Inufusa A,, et al, Spine 1996
Lee J, et al, J Spinal Disord Tech 2004

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Interspinous process
spacer implants also
are being promoted
for use in managing
low back pain caused
by degenerative disk
disease.

24. The mechanism of
pain generation
associated with
disk degeneration
remains unclear,
and
surgical treatment of
this condition
remains controversial.

25. The patient with chronic
severe low back pain
unresponsive to
nonsurgical management
is commonly treated:
with spinal fusion,
usually
with rigid implant fixation
systems,
including pedicle screws
and
interbody cages.

26. Interspinous proce s s
spacer implants
have been proposed:
as a dynamic stabilization
alternative to
rigid instrumented fusion,
with the advantages
of
a more limited and
less morbid surgical
procedure that may confer
less risk of adjacent segment
degeneration.
Minns RJ, et al, Spine 1997

27. Initial
biomechanical
studies in cadaveric
spines indicate that
the interspinous process
spacer reduces:
intradiskal pressure and
posterior annular pressure
at the implanted level.
Lee J, et al, J Spinal Disord Tech 2004

28. In neutral sagittal
alignment,
posterior annular
pressure
is reduced by 38%,
while
nuclear pressure
is reduced by 20%.
Swanson KE, et al, Spine 2003

29. With extension,
pressure reduction
is 63% and 41%,
respectively.
Pressures at
adjacent levels
do not appear to be
significantly affected.
Swanson KE, et al, Spine 2003

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Senegas J, Eur. Spine 2002

31. Biomechanincs of the
interspinous spacer
DIAM

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37. Low back pain
originating in
pathologic facet joints
(facetogenic pain) is
another controversial topic.
Some investigators have
suggested that more than
15% of chronic low back
pain originates from
pathologic facet joints;
others are skeptical that the
facet joints are a significant
pain generator.
Dreyer SJ, et al, Arch Phys Med Rehabil 1996
Berven S, et al, Semin Neurol 2002

38. Biomechanically,
depending on
position and
the presence of
associated arthrosis,
the lumbar facet joints
are thought to
transmit 25% to 47%
of axial load.
Shirazi-Adl A, et al, J Biomech 1987
YangKH, et al, Spine 1984

39. In cadaveric studies,
interspinous process
spacer implants
reduced:
facet joint contact area
by 46%, and
mean pressure by 39%,
at the implanted level,
with no significant effect
on pressures at adjacent
levels.
Wiseman CM, et al, Spine 2005

40. Consequently,
some proponents of
interspinous process
spacer technology
have suggested a
potential role for these
implants in managing
facetogenic pain.

41. Functional Anatomy of
the Posterior Column
In terms of potential
sites for implant
attachment,
the spinous process
has been identified
as the weakest
component
of vertebral anatomy.
Coe JD, et al, Spine 1990
Shepherd DE, et al, Spine 2000

42. The mean load
to fracture
has been reported
to be between
339 to 405 N
and is one half
to one fifth that
of spinal laminae.
Spinous process
bone strength has been
found to:
correlate linearly
with bone mineral density.
Coe JD, et al, Spine 1990
Shepherd DE, et al, Spine 2000

43. Anatomically, the
interspinous ligament is
composed of three distinct
regions:
dorsal,
middle, and
ventral.
Of these,
the middle region
is the area in which
ruptures typically occur.
Heylings DJ, et al, J Anat 1978
Rissanen PM, et al, Acta Orthop Scand Suppl 1960

44. Histologically,
the ligament consists of
multiple fibrous cords
composed of intermingled
collagen and elastic fiber
bands arranged in parallel
and zig zag fashion.
In many individuals,
the supraspinous ligament
is completely absent
at the L4-5 and L5-S1
levels.
Coe JD, et al, Spine 1990
Shepherd DE, et al, Spine 2000
Barros EM, et al, Spine J 2002

45. Controversy and Concerns
Numerous concerns exist
regarding interspinous
process spacer technology.
Some concerns are theoretical
and involve the potential of
interspinous process spacer
implants
to cause local pain and
contribute to segmental
destabilization.
Others involve
the true clinical efficacy and
durability of benefit from these
devices.

46. Interspinous process spacer
implants are designed to:
produce increased
segmental kyphosis
(spinal process flexion) at the
treated level.
Concern has been raised
regarding the potentially
deleterious effect
of local kyphosis on
adjacent segments.
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47. The spinous process
normally serves as:
an origin and
insertion site for muscles
and ligaments;
it is designed to resist
tensile forces.
It does not normally
function as a compressive
load-bearing structure.

48. In the patient with:
advanced spondylosis
and
disk degeneration,
adjacent spinous
processes can abut one
another:
with formation of a bursa
and
the potential
for local pain generation.

49. It is possible that:
compression
loading
of the spinous
processes
and
cyclic device motion
may lead to:
local tissue changes
and
pain generation.

50. Placement of
interspinous
process spacer
implants may:
disrupt and
potentially weaken the
interspinous ligament and
further destabilize the
implanted level,
particularly in terms of its
ability to resist
flexion-associated
tension forces.

51. Lumbar segmental
stability
is maximized by locking
of the facet joints,
which has been
demonstrated to occur
with approximately
50 to 100 N
of compression.
Papp T, et al, Spine 1997

52. By maintaining these
joints in
relative distraction,
there is concern that
interspinous
process
spacers
may
decrease overall
stability.

53. Although biomechanical
studies have suggested:
no significant effect on
segmental range of motion
in terms of
rotation and
lateral bend
at the instrumented level,
these cadaveric
studies
were performed at low
and controlled loads
and may not accurately
reflect in vivo forces.
Lindsey DP, et al, Spine 2003

54. A study of
interspinous process
spacer placement
following
graded
facetectomy
demonstrated
a marked increase
in lateral bending
motion
at the implanted
level.
Fuchs PD, et al, Spine 2005

55. CCoonncclluussiioonnss

56. Intespinous spacers succeed in :
1. Disc deloading
2. Facets deloading
3. Reduction of the extension
4. Increase dimensions of the
foramens
Disc decompression
Senegas J, Eur. Spine 2002

57. The rationale
behind interspinous
process spacer
devices appears to
be :
sound and
is well-supported by
biomechanical
studies.

58. Surgery
to implant
an interspinous
process spacer
is less invasive
than standard
laminectomy.

59. Early clinical reports
suggest
promising
short-term results
when these devices
are properly applied
in appropriately
selected patients.

60. Overall,
clinical efficacy
appears to be
moderate,
with most patients
experiencing
measurable
improvement
in symptoms
and
function
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61. However, a large
minority of patients
fails to experience
adequate relief,
and
concern remains
regarding the
durability of clinical
improvement in those
experiencing short-term
symptomatic
improvement.

62. Currently,
it seems likely that there is
a role for interspinous process
spacer technology
in specific sub-populations of
patients, such as those with:
persistent symptoms despite
nonsurgical treatment and
with borderline anatomic
stenosis,
or
those who are severely
debilitated by medical
contraindications that prohibit
more definitive decompressive
surgery.

63. Appropriate
candidates for these
devices are:
patients with
neurogenic
claudication
symptoms
that are relieved by:
forward flexion of the
spine and
who have no significant
pain at rest.