hints about spine instrumentation and deformity correction

Pedicle screws in spine deformity
By
Amer Alkot Mostafa
Lecturer of Orthopedic and Spine
Surgery
Al-Azhar University Assiut

Scoliosis Scoliosis Scoliosis Scoliosis Scoliosis Scoliosis

IOLS
-History of scoliosis management
-Surgeries for scoliosis deformity
-Options for spine instrumentations
-history of pedicle screws
-Principle for pedicle screws
-Advantages of pedicle screws
-Complications of pedicle screws

Spine deformity is a big dilemma dating many decades before
-Among pharaohs of the 18th and 19th dynasty 3 kings
had spine deformity.
-Amenhotep (Amenophis) II,
-Ramses II (The Great), and
-Merenptah ( his son ).
Imhotep is the first
known surgeon

-In the ancient world medicine
was not distinguished from
religion and mysticism
-Ancient works of philosophy,
religion, myths, and fairy tales
dating back as far as
3500 BC invoke images of
people with spinal deformity.
The boxing boys
fresco … Room
1600 BC

-Greeks also reported
deformity in statues
and described it in
scientific bases
-Hippocrates describes the
normal curves of the
spine in details
Alexander the
great with neck
deformity

-He classified the vertebrae into three groups.
1-the vertebrae lying above the clavicle
2-the thoracic vertebrae
3-the 5 vertebrae between the chest and the pelvis.
-Hippocrates introduced the terms kyphosis and
scoliosis and wrote in depth about diagnosis and
treatment of both.

-kyphosis → when the spine moves backward.
-lordosis → when it moves forward.
-Scoliosis → when it moves to the side.
-Succussion → when there is no deformity but the
vertebrae had slipped.
Galen described 4 deformities

According to Hippocrates and Galen deformity is
caused by
-Tuberculous nodes in the lung
-Trauma due to a fall on hips or shoulders,
-aging
-painful conditions

-Hippocrates recommended diet and extension of the
spine for the treatment of scoliosis.
-Manipulation was widely practiced by Hippocrates.
-He invented devices based on
-Extension.
-Axial traction.
-Three points compression.

Hippocratic ladder
Hippocratic board
Hippocratic bench
Hippocratic devices

-Ancient Arabian doctors had also
their contribution in the field of
spine deformity
-Famous example is the work of
Avicenna (980-1037)
However most of his work
was lost or stolen
Avicenna (Ibn-Cina)

-First true surgery was done by Guerin in 1839
-Percutaneous myotomies of the praspinal muscle
on the concave side
-Followed by long periods of immobilization
-Some success was obtained
-In 1891, Hadra attempted wiring of the spinous
processes in a patient with kyphosis due to Pott’s
disease .

-In 1911 Hibbs advocated non instrumented fusion for
a deformed spine.
-This procedure initially provided Stabilization but
-relied on the use of casts for long time
-did not provide deformity correction.
-Trials for instrumentations appeared at the beginning
of 1900 after discovery of antibiotics.

-Fritz Lange in the early 1900s, was one of the first
physicians to use foreign materials such as silk or
metal to support the spine
-He used steel splint in the spine
-4mm steel wires on each side of the spinous P,
-Inserted under the muscles and
-Fixed by silver wires .
-Caused infection and irritation by its sharp edges.

-In 1908, he used a tin coated wire
-5mm thick and 10 cm long
-Knobs on either end to reduce irritation
-Fixed to the spinous processes using silk.
-Patient kept in plaster jacket for 6 weeks then slowly
mobilized.
-He concluded that instrumentation lead to rapid
fusion than non-instrumentation.

-The goal of surgery at this time was halting the
progression of deformity
-Harrington system, since 1962 remained the state of
the art technique for scoliosis correction for a decade
and a half.
-It was primarily designed to apply distraction to the
spine.
-50-60% of curve correction could be achieved using
these rods and the results considered excellent.

-This system marked the beginning of the great era of
scoliosis surgery .
the major pitfalls of the system:
1. Limited amount of correction
2. Iatrogenic flatback
3. Does not address rotational deformity
4. Lamina fracture if excessive forces are applied
5. Inadequate rib cage correction
6. Post operative immobilization required

-In 1973, Edwardo Luque introduced the principle of
segmental fixation.
-This procedure involved multiple points of fixation by
sublaminar wires to create a more rigid option
-The goal was to reduce the need for external
immobilization.
-it involved steel sublaminar wires at various levels
over prebent rods .
-This technique improved sagittal balance, but many
neurological complications was noticed

-Hybrid system was done and called (tex-mix)
-The great break-through in deformity surgery was
the appearance of pedicle screws
-Another advancement was the development of
crosslinking devices that provide additional stability
-The TSRH system was the first to utilize cross-links
(Texas Scottish Right Hospital, 1983).

Pedicle Screws
-History
-Advantages
-Principle and biomechanics
-Method of pedicle screws insertion
-Disadvantages
-All pedicle screw ( high density low dnsity)
-Pedicle screws in pediatric deformity

History
-Boucher and king in1943 had found that it is
applicable to use facet screws to immobilize spine till
the graft is taken
-Later on Boucher described the first principles of
pedicle screws in spine
-The actual era of the pedicle screw began when Roy-
Camille (1970) reported the use of a screw-plate
device for spinal fractures.

-The development of rod-screw systems made
contouring easier, and encouraged the use of pedicle
screws in the treatment of scoliosis.
-After these advances pedicle screw instrumentations
became the ‘state-of-the-art’ for spinal disorders
including deformity
-In 1995 pedicle screws have been FDA approved for
spondylolisthesis only.

Advantages of pedicle screws
-Offers an enhanced three-dimensional deformity
correction
-Preserve motion segments by reducing the number
of fused levels
-They can rigidly stabilize both the ventral and dorsal
aspects of the spine.
-Can be used after laminectomy or spinal osteotomy
-Unlike sublaminar wires do not violate the vertebral
canal.

-Increase fusion rate markedly with less incidence of
psudoarthrosis
-Provide the strongest point of attachment of the
vertebra, and allows forces to be applied to the spine
without failure of the bone metal interface.

-Every screw has a head, shaft, and threaded portion
-The minor diameter of the screw is that of its core
-The major diameter of the screw is the threaded part
-Mechanical bending force is a function of the
core diameters
-Change in core diameter significantly changes the
bending strength of screws
-Two fold increase in core diameter causes eight
folds increase in bending strength

The pullout strength of screws depend on
-Screw bone interface
-Quality of bone
-Screw length
-Outer diameter of the screw

insertion technique
Since the introduction of original insertion technique
by Suk many other technique were published
-Funneling
-Mini laminotomy
-C-arm guided……etc
-the spine is exposed traditionally with subperiosteal
dissection

-The entry point for the targeted pedicle is identified
-Entry point is decorticate by a burr or rongeure
-Some surgeons prefer to do facetectomy before
pedicle screw insertion
-The pedicle finder is used to determine the proper
direction of the pedicle
-At the UIV and LIV no extreme medial or lateral
trajectory is needed however in the apex extreme
lateral or medial direction is needed

-Marker may be used and proper position is ensured
by c-arm
-Screw dimeter is ideal to be 80% of the pedicle width
-The pedicle may tolerate a screw size 115% of pedicle
size
-As regard screw length the pedicle alone provides 60-
80% of the screw purchase and the body provide the
remaining 40-20%

-The ideal screw length should penetrate 70% of the
vertebral body
-The screws should never exceed 5mm of the anterior
vertebral wall
-Extra pedicular approach may be utilized in difficult
insertion or in hypoplastic pedicles
- Extra pedicular screws may be used on the concavity

-Pedicle screws in the thoracic spine were not widely
used because of the fear of neurological injury
-despite the superior biomechanical advantages of
pedicle screws over other forms of spinal
instrumentation it maybe hazardous.
-The incidence of misplaced thoracic pedicle screws
ranges from 1.5-25%.
-The incidence of screw-related neurological
complication is 0.9%.

Complications of pedicle screws
-Loss of curve correction.
at the end of follow-up this ranges from (1 - 5.4)%.
-Screw malposition
This varies from (1.2 – 20)%.
-Dural Lesion
durotomy is about 0.35% per screw all was on the
concavity of the dorsal curve.

-Neurologic complications
transient neuropraxia---to--- complete paraplegia
-May be due to
-Screw malposition
-Vascular issues due to cord ischemia,
-Pedicle fractures,
-Hematoma,…..etc

-Vascular complications
Although injury to the IVC, Aorta, Azygos v and iliac
vessels were reported special concern was given for
the aorta in most literatures
-Highest risk of injuring the aorta at T10, T4, T11, and
T9 in right thoracic idiopathic scoliosis.
-Preoperative evaluation of the position of the aorta
to the thoracic spine significantly important for safe
pedicle screw placement.

-pulmonary complications
-pneumothorax
-hemothoax
-infection
-mostly superficial due to long time surgery
-loosening
-septic due to deep infection
-aseptic loosening (less common)

Pedicle Screws In EOS
Pedicle screws in EOS has a special concern as regard
-Small size of the pedicle
-Change in the canal morphology
-Pedicle screws are more superior than hooks or
sublaminar wires as regard stability and ability
to withstand distraction force

however to be inserted in the body it needs to pass
the NCC which is an active growth plate that fuse at
the age of 4-7 years
In his study on procine model Yazici found that
unilateral pedicle screws significantly alter
pedicle/hemi-canal growth compared to controls
with no instrumentation

-Ruf and Harms showed that pedicle screw could be
used in 2 years-old child without negative effects on
vertebral growth
-El-Sharkawi and Alkot in a study on 21 patient with
EOS found no evidence of canal stenosis at the
pedicle screws level level
-Most author accept this principle and pedicle screws
are used widely for EOS patient as proximal or distal
foundation points

Take home message
Pedicle screws are safe, effective, anchoring points for
spine deformity surgery in older or very young
patients

hints about spine instrumentation and deformity correction

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