Prevantion of implants failure

1. George Sapkas
Emeritus Professor of Orthopaedics
Prevention of
Implants Failure
in Adult Scoliosis
Surgery

2. Spino – Pelvic
Parameters

3. Incidence Angle (Duval-Beaupere)
Normal Values No 709 subjects
PI= 52.60 +- 10.4 (31 to 83.5)
PT= 13 +- 6.8
SS=39.6 +- 7.9
There is no difference between Men and Women
Normal Values
PT should be <PI/2
SS should be > PI/2
Interpretation of Pelvic Parameters
Anatomical Constant. Every one has his/her own
Pelvic Incidence Angle for the whole life.
(Stops Increased after Skeletal Maturity)
It is a characteristic of the Sagittal width of Pelvis
There is no good or bad PI

4. Gravity line
and
Sagittal Vertical
Axis
(SVA)
Femoral head
S1 Gravity Line
Center
of
Gravity
C7
Plumb
SVA

5. Sagittal-Coronal
balance - imbalance
S1
Coronal imbalance
Sagittal imbalance

6. Goals of surgical treatment
• Restoration of sagittal and coronal balance
in a patient with fixed spinal deformity
• Achievement of solid arthrodesis
• Rigid internal fixation to permit a brace-
free mobilization
• Relief of axial and radicular pain
Devlin J.V., Surg. Techn. Odf the spine 2003

7. • The surgical treatment
of sagittal and coronal
imbalance is complex
and demanding.
• Long instrumentations
and vertebral
osteotomies are
frequently needed to
restore balance of the
spine.

8. • Different types of vertebral osteotomies can be
performed these include:
o Ponte osteotomy (PO)
o Smith–Peterson osteotomy (SPO)
o Pedicle Subtraction Osteotomy (PSO)
o Posterior Vertebral decancellation osteotomy
(eggshell decancellation)
o Posterior Vertebral Column resection (PVCR).
o Anterior Osteotomy(ies) and
Posterior Corrective osteotomy(ies)
and stabilization

9. • A high rate of
complications can be
anticipated, especially
when PSO or PVCR
are performed:
o reaching short-term
rates of nearly 30 %
and
o different patterns of
long-term failures and
complications.
PSO
Keith H. Bridwell, et al Spine 2003

10. Implants Failure

11. • The literature related to:
o Complications
o failures
o revisions
• after surgery for sagittal
and coronal imbalance
is scarce.
Failures and revisions in surgery for sagittal imbalance:
analysis of factors influencing failure
P. Berjano et al, Eur Spine J. 2013
Sagittal Decompensation After Corrective
Osteotomy for Lumbar Degenerative Kyphosis
Sang-Hun Lee, MD, et al, Spine 2011
Complications and Outcomes of Pedicle Subtraction
Osteotomies for Fixed Sagittal Imbalance
Keith H. Bridwell, et al Spine 2003

12. Insufficient
correction
P. Berjano et al, Eur Spine J. 2013
Davis L. Reames, MD, et al Spinal Disord Tech 2015
PJK
Spondylodesia bellow the top
of kyphosis

13. • The final sagittal balance
obtained with surgery is a
key factor in determining
the success of the
procedure.
• Sagittal balance has been
evaluated with these
parameters:
o Pelvic tilt
o Gravity line and SVA
7.5cm

14. • A patient with an
anteriorly displaced
gravity line has,
as a consequence:
o increased mechanical stress
on the posterior implant:
o the translation of the mass
anteriorly causes
a)an increase in the moment
arm of the trunk mass with
respect to the rod.
b) increasing the cyclic bending
stress on it.

15. • Muscular fatigue
o causes pain in a long-term
muscular work,
and
o the deterioration
of sagittal imbalance
• can lead to a fatigue
or
• breakage of the implant.

16. 1year pop
Additionally,
• a) Tensile forces
(that are worst resisted
by the rods compared to
neutral or compression
forces)
are increased
posteriorly.
• b) Tensile forces
through the posterior
graft
cause bone
resorption
and
reduce the chance
of obtaining solid
fusion

17. • A practical consequence
is the need to perform
o an adequate preoperative
planning, with
calculation
of the site
and
o the amount of correction
necessary
to restore the position
of the gravity line
related to the spine.

18. • Intra-operative
measurement of the
amount of correction
obtained before final
tightening of the implants
is necessary.
• In most cases
extra manipulation needed
to obtain
the desired correction.

19. Posterior column
discontinuity in PSO
P. Berjano et al, Eur Spine J. 2013

20. • The Pedicle Subtraction
Osteotomy (PSO)
is a very effective
technique
to increase lordosis.
• With this wedge
osteotomy
it is possible
to obtain a correction of
as much as 35o
per osteotomy site.
35o
PSO

21. • Though it is a very
powerful option
to improve lumbar
lordosis,
PSO shows some
limits.
• One of these
is the wide resection
of the posterior
bony elements
needed to perform
the osteotomy. Ibrahim Obeid et al Eur. Spine J. 2012

22. • This often results
in a lack of continuity
of the posterior elements.
• This gap in the posterior
column after
the correction
o can cause a failure
of the postero-lateral
fusion process,
because
o insufficient
bony bed can be
available to incorporate
bone graft
at the level of osteotomy Ibrahim Obeid et al Eur. Spine J. 2012

23. • An additional factor of
instability
is
o the combination
around
the osteotomy level
• the lack of continuity
of posterior elements
with
• intact (flexible)
discs around.
Ibrahim Obeid et al Eur. Spine J. 2012

24. • This represents a scenario:
o of huge instability
o concentration of mechanical
stress,
o with stiff and long constructs
above and below the
osteotomy site
and
o an unprotected area
where the rods take
most of the mechanical stress
at the
osteotomy level.
Ibrahim Obeid et al Eur. Spine J. 2012

25. Furthermore, after a PSO
a)the osteotomized vertebral
level cannot be instrumented
with
* pedicle screws,
* sublaminar wires
* hooks,
bringing another factor of
instability.
b)If pseudoarthrosis occurs,
the rods will inevitably
break because
o of cyclic load
o and fatigue stress

26. Rod diameter
P. Berjano et al, Eur Spine J. 2013

27. • The rods used
in the degenerative pathology
have been originally
designed for adolescent
deformity surgery.
• The 5.5 mm diameter rods
provide:
o an adequate resistance
to correction maneuvers
during surgery
and
o can be easily bent in lordosis to
connect the screws after PSO.
5.5 mm
6 mm

28. • The 6 mm
diameter rods
o have a greater
stiffness
and
o resistance to breakage.

29. • The increased stiffness is
insufficient when fusion
is not obtained.
• The continuous stress
on the rods:
o in case
of post-operative
unbalanced spine
or
o in case of
pseudoarthrosis leads
in any case
to rod breakage.

30. Pe. Ag.
F 72
3/10/22
1 yr F-up
• Instrumentation will fail
o if balance
and
o fusion
are not obtained
after surgery.
• Six millimeter Co – Cr rods
or double rods
are however preferred
in this kind of surgery,
because of their
greater resistance to fatigue
stresses.

31. • Probably
o a specific instrumentation
for degenerative
spine surgery,
o with new materials
o and geometry
could improve
the resistance of the rods,
leading to a greater
resistance to stresses.
Titanium rod
Co- Cr rod

32. Rod bending
P. Berjano et al, Eur Spine J. 2013

33. • In order
o to engage
the rods on the screws
o to provide
adequate correction,
o the surgeon
frequently needs
to perform
an aggressive bending
of the rods
at the level of the
osteotomy
from straight rods.

34. • In specific cases
like PSO
o at the L4 level
(the most frequent
preference currently
to reproduce
the physiological
curvature
of the lumbar spine,
that concentrates
most of the lordosis
between L4 and S1)
o typically requires
bending the rod
nearly 90o
in a short 4-cm
segment.

35. • A short radius bending
of the rod causes
o compressive stress in
the concavity
and
o distractive stress
in the convexity,
which can cause
stress risers to form.
Tensile forces Compressive forces

36. • The combination
o of a short radius
bending,
o lever marks,
o distractive forces,
o increased flexion
moment arm on the rod
and
o reduced stiffness
of the spine
at the level of the
osteotomy
o is probably the cause of
the high observed
incidence
of rod breakage.

37. Insufficient distal foundation
P. Berjano et al, Eur Spine J. 2013

38. Distal foundation 1st sacral vertebra

39. Distal foundation 1st sacral vertebra and Interbody Cages
Diverted sacral screws
TLIF
S1
L2
TLIF
L5
L4
L3

40. • Current strategy
includes pelvic
instrumentation
in all cases of sagittal
imbalance correction
with surgery extending
to S1.
• This increases the lever
on the pelvis
and allows
for more aggressive
correction
of the loss of lordosis,
without increasing the
risk
of acute intraoperative
or delayed failure
of the fixation at S1

41. a)The different
orientation
in the axial plane
of the divergent
pelvic screws
b)with respect to the S1
convergent screws
c)is the key
in increasing
pullout resistance
of the construct.
Darryl Lau et al, Spine 2014

42. Proximal Junctional
Kyphosis

43. Spinal deformities
(Kyphosis – Scoliosis)
related to osteoporosis

45. 82 82

47. Kyphotic deformity

48. Ponte osteotomies

49. Sacral – Iliac fixation

50. Tether system
Hook
Screws

51. Cemented vertebrae and double rods

52. Cemented vertebrae above spondylodesia

53. Conclusions

54. • Patients with
o an SVA correction
of 4cm with surgery
did not need revision
surgery
o whereas those with
PJK requiring
revisions had
SVA > 8 cm
Han Jo Kim et al, Spine 2014
4.7cm

55. • Patients with
insufficient correction
had:
o Sagittal Vertical Axis
higher than 5 cm
o Pelvic Tilt higher than
20o.

56. • Patients with
Proximal Junctional
Kyphosis (PJK)
requiring revision
o were older
and
o had higher
postoperative lumbar
lordosis (LL)
and
o larger SVA corrections
than patients
without PJK
Han Jo Kim et al, Spine 2014 Darryl Lau et al, Spine 2014
Kyphoplasty

57. • In adult scoliosis,
a)older patients
with large
corrections in their
LL and SVA
• b)were at high risk
for developing
PJK,
• c)requiring
revision surgery.
Han Jo Kim et al, Spine 2014

58. • Long fusions,
• a)often associated
with vertebral
osteotomies,
b)are needed to
restore
an adequate
alignment
of the spine.
P. Berjano et al, Eur. Spine Journal 2013

59. • Many factors
can have a role
o in the final outcomes
and
o can influence the
risk of failure,
o with need of revision
surgery.
P. Berjano et al, Eur. Spine Journal 2013
imbalanced
balanced

60. • Adequate
o preoperative planning
and
o calculation
of the amount
of correction needed
is of paramount importance,
o as is intra-operative
measurement
to assure the final
achievement of planning.
P. Berjano et al, Eur. Spine Journal 2013

61. • The choice of
o rod diameter
and
o rod alloy
and
o a careful contouring,
avoiding the creation of
stress risers,
P. Berjano et al, Eur. Spine Journal 2013

62. o restoration
a)of bone continuity
b)both in the posterior
and anterior column,
P. Berjano et al, Eur. Spine Journal 2013

63. o solid distal
foundation
with iliac
screws in
fusions
extending to
the sacrum,
o are
suggested to
increase the
chance of
success.
P. Berjano et al, Eur. Spine Journal 2013

64. • In future, design of
specific implants
for this pathology
can provide
o increased stability
and
o fusion rate.
P. Berjano et al, Eur. Spine Journal 2013