Subaxial cervical anterior and posterior fixation techniques

1. Subaxial Cervical Fixation
Techniques
Mohamed Mohi Eldin, MD,
Professor of Neurosurgery,
Faculty of Medicine,
Cairo University,
Egypt.

2. Before placement of any implant, a
some questions should be answered
1. Is implant indicated?
2. Is a rigid or dynamic implant optimal?
3. Is deformity reduction, correction, or
prevention required?
4. Which system is ideal for
– obtaining fusion and
– preventing subsidence?

3. Subaxial Cervical Fixation Techniques
• Ventral stablization
• Posterior stabilization
• Combined (360)
stabilization

4. Anterior Fixation Techniques
First introduced (1955) by Smith & Robinson
Then popularized by Cloward
1. Anterior distraction (resisting compression),
2. Anterior compression (tension band),
3. Anterior cantilever beam fixation.

5. Anterior Distraction implants
1. Interbody struts:
– Bone,
– Cages,
– Acrylic, or
– Metal implants
2. Screw-plate construct:
– Fixed-moment arm,
– Non-fixed-moment arm,
– Applied-moment arm, or
– dynamic mode.

6. Interbody implants
• Bone Graft
– Autograft
– Allograft
• Cages (Graft substitutes)
– Carbon fiber reinforced
polymers
– Polyetheretherketone
(PEEK)
– Acrylic
– Titanium

7. Cage design evolution
1. Threaded (Screw cages)
2. Non-threaded
– Box-shaped
– Vertical ring designs
– Anterior plating

8. Anterior Compression (Tension Band)
Fixation
• +/- interbody struts
• Allows the application of
compression using a
screw-rod construct,
thereby
• enabling preloading of
bone graft, increasing
bone healing.

9. Anterior screw-plate construct
• Plates Types:
1. Nonconstrained Plates:
First-generation
2. Constrained (rigid) Plates
Second-generation (static)
2. Semiconstrained (semirigid)
Third-generation (dynamic)

10. First-Generation Plates
• Bohler (1967) first use
• Orozco and Houet (1970s):
– One-third tubular plate
– ‘H’ and ‘HH’ plates
• Herrmann (1975)
• Caspar‘trapezoidal’ plate
(1980)
• First anterior cervical plates
were unlocked and required
bicortical purchase.

11. First-Generation Plates
(abandoned nonrigid)
• Motion at screw-plate interface.
• Compressive forces (higher chance of fusion)
• Both unicortical and bicortical screws
• High rate of screw backout and breakage.
H-Plates

12. Second-Generation Plates
(Constrained-rigid plates)
• Screw convergence
• Ventral distraction fixation in
neutral position.
• Usually with interbody graft
• In extension, resist distraction
(tension-band)
Orion
Plate

13. Third-Generation Plates
(Dynamic semi-constrained)
• Prevent stress shielding
• Allow subsidence
• Mechanisms of dynamism :
1. screw toggling
2. Allowance of axial settling
Codman
Plate
ABC plate

14. Screw Toggling
(permission of axial subsidence)
• Rounded screw head/cup configuration
allows the screw to rotate in the
sagittal plane with respect to the plate
as subsidence occurs.

16. Allowance of axial settling
• The screws allowed to
slide along the long axis
of the plate for a limited
distance
• Allow subsidence while
minimizing the risk of
screw cutout.

17. Subsidence (settling)
• Loss of disc height following surgery
• Due to
1. Bone Graft remodeling and resorption (normal, complex
biological process) before being replaced by new living bone
2. Graft collapse, and
3. Pistoning of the graft.

18. Stress shielding
• Bone heals best under
compression (Wolfe’s
law).
• Stress shielding is
defined as ‘an implant
induced reduction of
bone healing, enhancing
stresses leading to
osteoporosis, or
nonunion’

19. Multilevel Fixation
• The caudal end of the construct is
the most likely to fail (longer
moment arm and increased forces)
– screw loosening or
– hardware failure
• This can be decreased by
1. maximizing screw purchase at
caudal end
2. dynamic fixation
3. good bone-grafting techniques
4. Postoperative immobilization (rigid
collar in the first few months)

20. Advantages of Anterior Cervical Plates
• Enhancing solid fusion
• Resisting kyphosis
• Reduce external bracing
• Mobilization of adjacent
segments
• Reduce risk of graft
extrusion
• Reduce rate of nonunion.

21. Disadvantages of
Anterior Cervical Plates
• Increased cost
• Special instruments and
training
• Plate-specific complications:
– screw loosening or fracture,
– infection,
– neural injury

22. Posterior Cervical Fixation Techniques
1. Wiring: (Historical)
– Sublaminar
– Facet
– Interspinous
2. Laminar screw fixation,
3. Lateral Mass:
– Plate
– Rod
4. Pedicle Screws

23. Interspinous Wiring
• Intact posterior
elements
• Restore posterior
tension band
• After soft tissue injury
• Augment other
anterior or posterior
fixation techniques

24. Rogers’ interspinous wiring
• Burr hole at the base of the upper and lower
spinous processes.
• Stainless steel or titanium wire or cable through
the burr holes in a figure eight pattern.
• Wire is tightened using a Tensioner.

25. Abdu’s triple-wiring
• As the Rogers’ technique.
• 2nd wire through upper burr hole and looped around upper spinous
process.
• 3rd wire through lower burr hole and looped around the lower
spinous process.
• These two wires are passed through two autologous bone graft
struts, lateral to spinous processes.
• Wires are tightened under tension

26. SUBLAMINAR WIRING
Cables are generally safer than wires

27. SUBLAMINAR WIRING
• Pros:
– Simple
– Safe
– Large surface area for fusion
• Cons:
– Wire breakage or cutout
– Not suitable if posterior elements deficient
– Poor fixation in axial load & rotation

28. SUBLAMINAR WIRING
Almost never used in the subaxial spine
because the spinal canal is smaller compared to
the spinal canal at the C1/C2 levels.
Specially in patients with degenerative or
congenital cervical stenosis.

29. Facet Wires
• Facet could easily get broken

30. Facet-Spinous Process Wiring
• Not secure & facet could easily get broken

31. Posterior cervical wiring
Complications (rare)
• Wire pullout
• Injury (cord or spinal nerves)
• Over-tightening (avulsion
fractures).
• Loss of fixation (poor bone
quality)
• Inadequate postoperative
immobilization.
• Nonunion, malunion
• Hardware failure
• Infection

32. Posterior cervical screw fixation
1. Laminar screw,
2. Lateral Mass
Screw:
– Plate
– Rod
3. Pedicle Screws

33. LAMINAR SCREWS
(Translaminar screw fixation)
• Uncommon in subaxial spine
• C7 has larger laminar size
– high unilateral screw placement success
rate:
• 100% for 3.5 mm screw,
• 92% for 4.0 mm screw
– moderate bilateral screw placement
success rate
• 90% for 3.5 mm,
• 68.8% for 4.0 mm.
• At C3-C6, success rates much lower.

34. Utilized in only selected cases
• Deficient lateral masses
• Failure to place a lateral mass screw
• Requires intact posterior elements, specifically
intact laminae

35. Complications of laminar screw
• laminar cortical breach:
– medial cortex (thecal and cord injury)
• Violation of the facet joint
• Screw loosening
• hardware failure

36. Lateral mass screw fixation
widely considered the mainstay technique for
posterior fixation of the subaxial spine
With high fusion rates, (85-100%)

37. LATERAL MASS SCREW FIXATION
• Restore posterior column tension band
• Rotational & axial stability
• Greater stability in lateral bending
• Applicable C3 to C7 levels
• No need for intact lamina

38. LATERAL MASS SCREW
(Anatomical Factors)
• Size
• Orientation
• Bone Quality
• Vertebral Artery
• Nerve Root

39. The relation between the lateral mass
and the VA
• At the C7 level, the VA is
more laterally located.
Thus, at C7 the direction
should be calculated
carefully.

40. Lateral Mass Screws

43. Cervical Pedicle Screws
• To correct deformity esp.
Kyphosis
• More risky
• Needs very lateral
dissection to allow for 45
degrees angulation
• Higher resistance to pullout
than lateral mass screws.

44. CERVICAL PEDICLE SCREWS
• Pedicular width 3.5–6.5 mm,
• Pedicular height is 5–8 mm
• Pedicular angulation decreases
from 50 degrees medially at
the C5 to 11 degrees medially
at the T5 in the transverse
plane.
• The pedicle angulation in the
sagittal plane is 3–5 degrees
downward with reference to
the lower endplate of C7.

45. C7 Pedicle Screw
• C7 lateral mass is often inadequate (average
thickness is about 9 mm)
• A pedicle screw at C7 is preferable.

46. C7 Pedicle Screw
• A small laminotomy
(paplate pedicle)
• Entry point at junction of two
lines:
– Vertical line (middle of C6–7 facet joint)
– Horizontal line 1 mm under middle of
C7 transverse process.
• Direction
– 30–35 degrees medially
– 5 degrees downward (reference to C7
lower endplate)
• Screw:
– length 20- to 22-mm
– diameter 3.5-mm

49. Medial Pedicle Wall Breach
(spinal canal violation)

50. Lateral Pedicle Wall Breach
(transverse foramen penetration)

51. Cervical Pedicle Screws

52. In certain cases with anterior column
failure
• CPS may be an option

53. 360 Stabilization
• Provides very strong
construct in severe
cervical instability

54. Posterior column + Anterior column
Disruption
• An anterior standalone bone graft will not be
sufficient for fixation…. WHY ?
– Graft extrusion,
– Kyphotic deformity
– Significant risk of neural injury.
• To avoid dislocation and graft extrusion :
1. Anterior plating
2. Supplemental posterior fixation,
3. Rigid external orthosis (halo vest)

55. As a rule
Any stand-alone posterior
fixation technique, is
insufficient to restore
stability in cases involving
the anterior and/or middle
columns.