This document discusses the history and evolution of spine instrumentation. It describes various instrumentation techniques for the cervical, thoracic, and lumbar spine, including Harrington rods, Luque rods, Cotrel-Dubousset systems, pedicle screws, and lateral mass screws. Key developments include the introduction of segmental fixation, hooks and wires, pedicle screws, and dynamic stabilization systems. Placement techniques are outlined for lateral mass screws, pedicle screws, and laminar hooks.

1. Spine Instrumentation –
Cervical/Thorasic/Lumbar
Dr. Sairamakrishnan S

2. History of spine instrumentation
• The use of internal fixation as a tool for both stabilization and
correction of deformity was a major advance in modern spine
surgery.
• A thorough knowledge of the evolution of spinal instrumentation
should yield a better understanding of both present and future
developments.

3. DORSAL THORACOLUMBAR
INSTRUMENTATION
• In 1975, the Harrington rod represented the state of the art in spinal
instrumentation.
• Originally developed by Paul Harrington for the correction of spinal
deformities.
• The use of a distraction system provided excellent correction of
coronal plane deformities.
• Use of distraction as the sole correction tool resulted in the loss of
normal sagittal plane alignment. (flat back syndrome)
• Hook dislodgement and rod breakage also proved to be troublesome
complications.

4. • In addition, casting or bracing was generally required in the
postoperative period, which proved to be difficult or impractical in
some patients

5. • Eduardo Luque advanced a major concept in the mid1970s that
quietly pushed forward the future direction of spinal instrumentation:
segmental spinal fixation.
• Luque popularized the use of a 3/16-inch steel rod secured at each
spinal level with sublaminar wires.
• Luque reasoned that increasing the number of fixation points along a
construct would reduce the force placed upon each individual point
and obviate the need for a postoperative cast or brace.
• It increased the potential corrective power of instrumentation,
reduced the potential for construct failure, and resulted in improved
fusion rates

7. • Some users of Harrington rod instrumentation adopted Sublaminar
wires - “Tex-Mex” operation.
• Complications of Sublaminar wires
• Neurological injury
• Cut through
• Difficult to revise
• In response to these concerns, Drummond and colleagues developed
a method for segmental fixation using a button-wire implant passed
through the base of the spinous process

8. • Though it does not provide as strong fixation as sublaminar wires it
avoids, however, passing anything into the spinal canal and thus
reduces the risk of direct neurologic injury.
• Hence the name “chicken-Luque” procedure.

9. • The Cotrel Dubousset (CD) system was introduced in 1986 using a
1/4-inch rough-surfaced rod.
• The multiple-hook design applied the principles of segmental fixation
without the need for sublaminar wires.
• This proved a powerful force in the correction of scoliosis.
• Cross-linking the two parallel rods together provided further stability.
• Had difficulty in revision due to the inability to remove the hooks
without destroying the locking mechanism.
• Since then multiple systems with variation in locking has been
developed.

10. • A major advance provided by these spinal systems was the
exploitation of the pedicle as a site for segmental fixation.
• This innovation is generally credited to Roy-Camille of Paris
• Advantages of pedicle screws
• biomechanically superior
• can be placed into the sacrum
• they can be placed even after a laminectomy
• can be positioned without entering the spinal canal.

11. • screw-plate vs screw-rod
• Most surgeons were ultimately attracted to rods because their use
provides greater flexibility, reduces encroachment upon the adjacent
facet joints, and leaves more surface area for fusion

12. • There has been an interest in developing dynamic stabilization
systems for degenerative diseases.
• They have been approved as an adjunct to fussion
• Interspinous devices that increase the intervertebral space have also
been developed to treat a myriad of degenerative conditions. The
primary indication is mild or moderate neurogenic claudication from
spinal stenosis

13. VENTRAL THORACOLUMBAR
INSTRUMENTATION
• Dwyer developed a ventral system for internal fixation using screws
connected by a cable.
• The Zielke device connected transvertebral screws with a threaded
rod and nuts and was more rigid than the Dwyer cables. This added
both strength and the capacity for incremental correction and
derotation, permitting a more powerful correction.
• The ventral Kostuik-Harrington instrumentation was an adaptation of
short Harrington rods to achieve short-segment ventral fixation.

14. • Ryan introduced a plate secured by a rostral and caudal bolt inserted
through the vertebral body - offered less resistance to rotation.
• The Yuan I-Plate was an alternative design that consisted of a 3.5-mm
stainless steel plate secured with transvertebral screws allowed for
the placement of three screws at each vertebral level.

15. DORSAL CERVICAL INSTRUMENTATION
• Earliest methods to provide internal fixation for dorsal cervical fusions
involved the use of spinous process wiring.
• The Brooks and Gallie techniques use sublaminar wires to compress
an autologous bone graft.
• Halifax clamps are a pair of upgoing and downgoing sublaminar hooks
tightened together with a screw that is then secured in position with
a locking mechanism.

16. • Magerl introduced transarticular screw placement for internal fixation
of C1-2.

17. • Lateral mass plate fixation with screws was introduced by Roy-Camille
and associates.
• The first technique for screw placement was modified by Magerl and
Seeman, Anderson and colleagues and An and colleagues.
• Lateral mass screw-rod fixation systems were designed to use 3.5-mm
and 4-mm diameter lateral mass screws with polyaxial head designs
attached to titanium rods for improved ability to connect fixation
points.

18. VENTRAL CERVICAL INSTRUMENTATION
• First system was developed by Bohler in the mid1960s
• Potential for screw backout was recognized as a possible cause of
serious complications
• Earlier systems consisted of simple plates with slots or holes but
without any locking devices. Constraint of the screws depended on
obtaining bicortical purchase and “blocking” backout by screw
angulation.
• This led to the development of the Cervical Spine Locking Plates.

19. • The CSLP used a titanium expansion screw that secured the screw
head to the plate and, thus, allowed for unicortical purchase without
the risk of screw backout.
• Although this plate was widely used and had good reported surgical
results, some surgeons felt that the system was too rigid and shielded
the graft from stress, thereby promoting a significant rate of
pseudarthrosis.
• Ventral fixation of odontoid fractures can be achieved with the
placement of one or multiple screws.

21. Lateral Mass Fixation (C3-6)

24. Entry point
• The screw entry point is found
slightly superomedial to the
intersection of these lines.

25. Opening of the cortex
• Penetrate the cortex with a thin burr
or an awl.

26. Medio-lateral angulation
• The drill trajectory should be aimed
25 degrees laterally to avoid the
vertebral artery which is located
directly anterior to the entry point.

27. Cranio-caudal angulation
• To identify the cranio-caudal
angulation, a Penfield elevator is
inserted in the facet joint which will
be included in the fusion.
• The drill trajectory is then then
parallel to this elevator, avoiding
compromise of the facet joints.

28. Monocortical vs Bicortical
• Utilizing 14 mm screws will be safer but only
monocortical purchase can be achieved.
• A longer screw providing bicortical purchase will
result in a more stable construct. However, the
screw tip should not extend too far beyond the
second cortex as it may compromise the nerve
root.

29. Drilling
• If a monocortical screw is planned,
the drill is set for a 14mm screw
hole.
• For bicortical screw the drill bit is
advanced only for a short distance,
then pulled back before advancing
again. This maneuver is repeated
until the second cortex can be felt
and crossed.

30. Screw insertion
• A screw of appropriate diameter (3.5 mm) and length is carefully
inserted into the same created trajectory.

31. Cervical pedicle screws
• Pedicle screws offer three-column fixation and have greater pullout
strength than lateral mass screws
• The small mid-cervical pedicles and the proximity of the cord,
vertebral arteries, and nerve roots limit enthusiasm for routine use of
pedicle screw fixation.
• Most frequently, C3-6 pedicle screw placement is recommended for
posterior-only corrections of markedly unstable three-column injuries
or for maintenance of correction after cervical osteotomy or
postlaminectomy kyphosis

32. • Standard entry point is 3 mm below the superior facet joint.
• The drill is angled 45 degrees medially and advanced in a vertical line
parallel to the endplate.
• Alternatively, Abumi recommended removal of the lateral mass with a
high-speed bur to provide a direct view of the pedicle introitus.

33. • Due to the low margin of error
superior laminotomy is
recomended

34. Entry points
• The starting point is just below
the facet joint at the half way
point between the medial and
lateral margins of the lateral
mass.

35. Opening of the cortex
• Open the superficial cortex of
the entry point with a burr.

36. Medio-lateral angulation
• Depending on the exact
location of the starting point,
the angle is around 45°.
• Angulation decreases
somewhat as you progress
cranial to caudally,
approaching 50° at C3 and 40°
at C6.

37. • A trajectory roughly
perpendicular to the axis of the
posterior elements is required.
• This trajectory can be fine
tuned by palpating the inferior
and superior margins of the
pedicle through the laminotomy.

38. Screw incertion

39. Anterior Subaxial Cervical Fixation
FIRST-GENERATION PLATES
• Allowed motion at the screw-plate interface and as
such were considered nonrigid implants
• graft exposed to greater compressive forces thereby
promoting fusion

40. SECOND-GENERATION PLATES
• The second-generation plates were
rigid implants that were best utilized in
trauma
• They also reduce the need for
postoperative immobilization
• However, they may stress shield the
bone graft and result in either implant
failure or a pseudoarthrosis

42. THIRD-GENERATION PLATES
• The third-generation plates improved on the original Caspar plate
design by preventing screw backout while allowing for some motion
at the screw-plate interface, thereby enabling load sharing between
the bone graft and the implant
• Two subtypes: (1) rotational and (2) translational.
• The rotational dynamic plates allow screws to rotate or toggle at the
screw-plate interface
• Translational dynamic plates allow for axial translation and rotation of
the plate

44. HARRINGTON DISTRACTION FIXATION

46. Pedicle screw

47. • Screw charecteristics
• Diameter- 4.5mm to 7mm
• Length – 30mm to 55mm
• Self-tapping and non tapping screws
• Monoaxial and polyaxial screws

48. • The transverse width of the pedicle is the limiting factor in terms of
screw size
• The strength or resistance to bending and breaking of a screw is
proportional to the third power of its minor diameter.
• The pullout resistance of a screw is related to the amount of bone
that can be incorporated between the threads of the screw. The
distance between the threads (pitch), major diameter, and thread
shape all influence the pullout resistance of a screw

50. Pedicle screw entry techniques
• Intersection technique
• Pars intraarticularis technique
• Mamillary process technique

51. • Although the midline of the transverse process corresponds to the
location of the pedicle at L4, this relationship does vary at different
lumbar levels.
• Above L4, the midline of the transverse process is rostral to the
pedicle, and at L5, it is an average of 1.5 mm caudal to the pedicle

53. • Pars intaarticularis technique relies on the easy identification of pars
and the lateral border of the lamina.
• Since pars intraarticularis is the junction between the pedicle and the
lamina the entry point is directy over the posterior aspect of the
pedicle.

54. • The mamillary process technique uses the mamillary process which is
a small prominence at the base of the transverse process.
• This entry point is the most lateral entry point of all the techniques.
• It provides the most medio-lateral angulation.

55. Thoracic entry points
• The transverse process is rostral to the pedicle in the upper thoracic
spine and caudal to the pedicle in the lower thoracic spine. The
crossover occurs at T6-7.
• Hence entry point with relation to the transverse process varies based
on the level.

56. • The entry point of the pedicle
screw for the lower thoracic
segments is defined after
determining the intersection of
the mid portion of the facet
joint and the superior edge of
the transverse process. The
specific entry point will be just
lateral and caudal to this
intersection.
• The entry point tends to be
more cephalad as you move
to more proximal thoracic
levels.

58. Sacral pedicle screw
• Entry point is superior and lateral to the S1 foramen just inferior to the
inferior articular process of the L5 vertebra.
• The trajectory should aim for the sacral promontory.
• Bicortical purchase increases the strength of the fixation
• Unicortical - 1
• Bicortical/S1 endplate purchase - 1.5
• Tricortical purchase – 2
Advantage of Pedicle Screw Placement Into the Sacral Promontory (Tricortical Purchase) on
Lumbosacral Fixation - Kato, Minor et al, Journal of Spinal Disorders and Techniques,
10.1097/BSD.0b013e31828ffc70

60. • Insertion techniques - freehand, fluoroscopy-based, and frameless
stereotaxy systems.
• The screw entrance site is decorticated with a drill or rongeur
• The pedicle is probed with a blunt-tipped pin or small curet.
• Intraoperative radiographs are used to check pin placement.
• Holes are tapped with successively larger taps until a desired
diameter is reached
• The walls of the pedicle should be palpated from within after each
tap to verify the integrity of the cortical bone.

61. • Screws should be placed with as much lateral-to-medial angulation as
possible so as to maximize the beneficial effects of triangulation on
screw pullout.
• No significant advantage is gained by penetration of the ventral cortex

62. Entry point
• Open the superficial cortex of
the entry point with a burr or a
rongeur.

63. Cranial-caudal angulation
• A pedicle probe is used to
navigate down the isthmus of
the pedicle into the vertebral
body. The appropriate
trajectory of the pedicle probe
in the cranial caudal direction
occurs by aiming to be parallel
to the superior endplate

64. Medio-lateral inclination
• The medio-lateral inclination will
depend on the location up to 45°
in L5 or 0° in T5.
• The main goal is to avoid medial
penetration of the spinal canal
superficially and lateral or anterior
penetration of the vertebral body
cortex at the depth of insertion.
• Ideally, the two screws should
converge but stay entirely within
the cortex of the pedicles and
body.

65. Probing
• Once the pedicle track has
been created, it is important to
confirm a complete
intraosseous trajectory by
pedicle and body palpation
using a pedicle sounding
device.
• At any point in the process,
radiographic confirmation can
be obtained.

66. Screw insertion
• A screw of appropriate diameter
and length is carefully inserted
into the same created
trajectory.

67. Entry point T1 to T3
• The entry point lies just below
the rim of the upper facet joint,
3 mm lateral to the center of the
joint near the superior border of
the transverse process.

68. Opening the cortex
• Open the superficial cortex of
the entry point with a burr or
an awl.

69. Medio lateral angulation
• Their transverse angulation
ranges from 30° at the level of
T1, to 15° at the level of T3.

70. Cranial-caudal angulation
Anatomic trajectory Subchondral/straightforward
trajectory

71. Screw placement

72. The cortical bone trajectory
• Described by Santoni as an alternative for osteoporotic patients due
to higher amount of interface between screw and cortical bone
• This technique requires a more medial entry point and cephalad-
lateral trajectory
• The starting point is in the inferior pars.
• The CBT will require shorter screws

74. Grading System Used for the Assessment of
Screw Placement Proposed by Abul-Kasim

77. Laminar Hook Insertion

78. • Preoperative imaging studies are useful for determining the adequacy
of the spinal canal for sublaminar hook placement.
• laminotomies are performed, removing the caudal portion of the
lamina above and the rostral portion of the lamina below the level of
hook application.
• Once a hook is placed, it should be compressed against its lamina to
prevent migration into the spinal canal

79. Pedicle Hooks

80. • Thoracic pedicle hooks are placed between the superior and inferior
articulating surfaces of the facet.
• The caudal portion of the inferior articular process is removed by
using a drill or osteotome.

81. Cross-Fixation
• Cross-fixation increases the stability of a construct by preventing
rotation or translation.
• Screw pullout resistance is also markedly improved with the use of
rigid cross-links combined with toeing in of the screws

82. Interbody Cages
• A cage should ideally have a hollow region of sufficient size to allow
packing of bone graft or bone graft substitute.
• It should be structurally sound so that it can withstand the great
forces applied to it in the immediate postoperative period and allow
immediate patient mobilization.
• It should have a modulus of elasticity that is close to that of vertebral
bone to optimize fusion and avoid subsidence.
• It should have ridges or teeth to resist migration or retropulsion into
the retroperitoneal space or the spinal canal.

83. • Serrations on the top and bottom surfaces of the cage may improve
fixation strength and diminish motion at the cagebone interface
• It should be radiolucent to allow visualization of fusion on
radiographs and may have radiopaque markers to localize the precise
location of the implants on intraoperative and postoperative
radiographs.
• If inserted from a dorsal approach (TLIF or PLIF), it should be tapered,
with a bullet-shaped tip to allow easier initial insertion into the disc
space with minimal trauma to the adjacent thecal sac and nerve
roots. This is especially beneficial when introducing the graft into
narrowed disc spaces for distractive purposes.

84. • The stiffness of a cage has been found to influence fusion rates.
• Ideally, a cage would have a modulus of elasticity that is similar to
that of vertebral bone, which would optimize the load transfer
between the cage and the adjacent vertebral bodies and reduce the
effects of stress shielding on the graft material.
• Carbon fiber cages have a modulus of elasticity closer to that of
cortical bone,34 while metal and titanium cages exceed the stiffness
of the vertebral bone.

85. • The modulus of elasticity of stainless steel and titanium implants is
200 and 110 GPa, respectively, compared with that of vertebral
trabecular and cortical bone, which is 2.1 and 2.4 GPa, respectively.
• Titanium cages also have the disadvantage of incomplete
radiographic assessment of the fusion mass.
• Furthermore, owing to the mismatch of modulus of elasticity of
titanium and vertebral bone, the stiffness of titanium cages may
cause subsidence into the vertebral end plates

86. • To create a more suitable modulus bone-cage-bone transition, PEEK
cages have been developed and are routinely used as interbody
devices.
• PEEK is a semicrystalline aromatic polymer that is radiolucent and can
be formed into any shape.
• Radiopaque markers are routinely incorporated into the borders of
the cage so that the surgeon can precisely localize the implant on
radiographs.

87. • Despite a more biologic modulus of elasticity of PEEK as compared to
metal, there is some biomechanical evidence showing lower primary
fixation and initial stability of PEEK cages compared to titanium cages
of equal dimensions.
• But they provide same clinical outcomes when augmented with
posterior instrumentation.

88. • Some studies have evaluated the fusion rate and its relationship to
cage stiffness, evaluating a poly-L-lactide (PLLA) cage versus a
titanium cage.
• An in vitro study showed that PLLA cages were mechanically sufficient
directly after implantation
• After 6 months, increased interbody fusion was seen with the PLLA
cages.
Smit TH, Müller R, Dijkvan M, et al. Changes in bone architecture during spinal fusion: three years
follow-up and the role of cage stiffness. Spine (Phila Pa 1976). 2003;28:1802-1809.

89. • One of the goals of lumbar interbody fusion is to increase/ restore
disc space height and maintain segmental lordosis.
• Increasing disc space height is relatively easy to accomplish in the
prone or supine patient intraoperatively and is usually maintained on
short-term follow-up.
• However, over time, settling of the cage into the vertebral end plates
can occur. If significant subsidence occurs, it can lead to segmental
loss of lordosis and loss of anterior column support.

90. • These changes may result in an unfavorable biomechanical
environment contributing to pseudarthrosis and possibly compression
of the neural elements.
• The causes of subsidence are multifactorial and may be due to any
combination of improper graft selection, poor bone quality,
insufficient bony healing, lack of supplemental open or percutaneous
fixation, and overexuberant end-plate preparation.

96. Cervical cages
• Reduces the need for bone graft harvesting and reduces donor site
morbidity.
• Promotes osteointegration and provides adequate resistance to
compressive forces.
• They are zero profile devices and do not warrant removal during
revision surgeries.
• Latest generation cages can be used as standalone systems in cervical
fussion.