Spinal Disorders: Fundamentals of Diagnosis and Treatment Part 39 ppt

Atlantoaxial Pedicle Screw Fixation The 2nd cervical nerve is at risk when exposing the C1/2 joint An alternative to the transarticular screw fixation is a stabilization of the spine wit

a b

Figure 14 Landmarks for occipital screw insertion

aPosterior view.bAxial view

nar control for optimal screw placement The medial border of the C2 pedicle (2 – 5 mm axial diameter) should be palpated with a dissector or a nerve hook The screw is positioned as medially as possible to avoid injuries to the vertebral

artery, which lies immediately laterally The entry point for screw insertion is

about 3 mm cranial to the lower edge of the C2 inferior facet Usually, there is a small groove at the transition of the inferior facet to the lamina which serves as

a landmark for the entry point The drill is angled to aim at the arch of C1 in a strictly sagittal plane The screw should pass just below the posterior border of the C1/2 joint In some cases, the craniocaudal angulation can only be achieved Injuries to the spinal cord

or vertebral artery are rare

if the technique is applied

if the drill is significantly inclined Rather than dissecting all the posterior mus-cles, we prefer only to expose the spine from C1 to C3 and choose a percutaneous insertion of the drill usually at the level of C7–T1 with a tissue protector Injuries

to the vertebral artery or spinal cord are rare if the technique is performed prop-erly [22, 27].

Atlantoaxial Pedicle Screw Fixation

The 2nd cervical nerve

is at risk when exposing

the C1/2 joint

An alternative to the transarticular screw fixation is a stabilization of the spine with pedicle screws which are connected with rods [29, 64] (Fig 15d–g) The

screw entry point in C 2 is more lateral (4–5 mm) than the transarticular screw

trajectory The drill is directed 20° – 35° cranially and 15° – 20° medially The

entry point in C 1 is below the lamina and 2–3 mm lateral to the medial edge of

the C1, which can be palpated with a dissector The screw is aimed about 10° – 15° medially and 15° – 20° cranially Care has to be taken not to injure the C2 exiting nerve root (greater occipital nerve).

Anterior Atlantoaxial Transarticular Screw Fixation

A second alternative is an anterior transarticular screw fixation [59] The screw entry point is 5 mm below the C1/2 joint line in the groove formed by the basis of

53

Figure 15 Landmarks for upper cervical spine screw insertions

Posterior atlantoaxial transarticular screw fixation: aposterior view;blateral view;c axial view Atlantoaxial pedicle

screw fixation: dposterior view;elateral view;f axial view at C2 Anterior atlantoaxial transarticular screw fixation:

ganterior view;hlateral view;iaxial view

the dens and the lateral mass (Fig 15h–j) The screw trajectory is angled 25°

later-ally and cranilater-ally However, the exposure of the entry point is not easy because it

is far up in the cervical spine During exposure great care has to be taken not to

injure the:

) hypoglossus nerve

) superior laryngeal nerve

Lateral Mass Screw Fixation

There are two commonly used techniques for screw placement in the lateral mass

of the lower cervical spine The screw entry point according to Roy-Camille [50]

is in the center of the lateral mass and the trajectory is directed 10° outwards

rect-angular to the posterior cortex According to the Magerl technique, the screw’s

insertion point lies 2 mm medial and cranial to the facet center The screw

trajec-tory is parallel to the facet joints and angled 20° – 25° outwards (Fig 16a–c).

Magerl’s method exhibits longer screw lengths and is therefore biomechanically

a b c

Figure 16 Landmarks for lower cervical spine screw insertions

Lateral mass screw fixation: aposterior view;blateral view;c axial view Pedicle screw fixation: dposterior view;e lat-eral view;faxial view

superior to the Roy-Camille method [50] Some studies have reported that the Magerl method is less likely to damage the neurovascular structures [51].

Lower Cervical Spine Pedicle Screw Fixation

This screw insertion

technique is reserved

for the most experienced

spine surgeons

Pedicle screw fixation in the lower cervical spine is demanding and reserved for the most experienced spine surgeons [38] The risk potential of spinal cord and vertebral artery injury is high [70] The pedicle dimensions are not infrequently

smaller than the screw [36] Preoperative CT planning is recommended to rule

out anatomical anomalies Computer assisted surgery may reduce the rate of misplaced screws [35, 60] but does not compensate for lack of profound knowl-edge of the cervical anatomy and surgical experience [2] The technique

accord-ing to Abumi and Kaneda [1] chooses an entry point slightly lateral to the center

of the lateral mass and inferior to the facet joint line (Fig 16d–f) The cortical bone at the entry point is opened with a burr and the hole is enlarged to bury the

pedicle screw (3 – 4 mm) The screw trajectory is angled 25°–45° medially A thin

pedicle finder is used to dilate the pedicle under lateral image intensifier control Perforations can be detected with a fine pedicle probe (feeler) (Fig 17) In experi-enced hands, the complication rate is low [2, 38].

Thoracic Spine Pedicle Screw Fixation

Screw placement in the thoracic spine requires a detailed knowledge of the anat-omy of the thoracic spine However, it can be done with a high safety margin

Figure 17 Surgical instruments for screw hole preparations

aFine awl.bThin pedicle finder.cThick pedicle finder.dPedicle feeler

when the proper technique is applied [20] The pedicle morphology of the thoracic

and lumbar spine has been thoroughly investigated in several studies [49, 65 – 67,

73] The landmarks for screw insertion T2–T11 are below the rim of the inferior

facet Sometimes it is necessary to osteotomize the lateral inferior part of the facet

to clearly identify the base of the superior facet The entry point is at the lateral

bor-der The screw trajectory is angled 20° medially and 10° caudally When the

extrape-dicular technique [14] is used, the entry point is slightly more lateral and the angle

to the midline is higher (Fig 18a–c) (see Chapter 3 ) This inside-out-inside

tech-nique involves a reduced risk of injuring the medial border of the pedicle [14] The

entry point at T1 is slightly more medial and the screw trajectory is less angled to

the midline The entry point for the pedicle of T 12 is at the level of the mammillary

process, which is opened/removed with a rongeur (Fig 18d–f) The screw trajectory

is angled more medially similarly to the lumbar spine The screws for adult patients

usually have a diameter of 5 (lower thoracic spine) and 6 mm (lower thoracic spine)

and have a length of 30 – 35 mm at T1 and 45 – 55 mm at T12, respectively.

Our preferred technique (Fig 17) is to use a sharp fine awl to open the cortical

bone at the entry point This position is checked in the lateral plane using an image

intensifier A thin pedicle finder is used to probe the pedicle again under

fluoro-Check for potential perforations with a fine pedicle feeler

scopic guidance A fine pedicle feeler is entered into the pedicle hole to verify that

the cortical shell of the pedicle is intact particularly medially, inferiorly and

anteri-orly In the lower thoracic spine, a thicker pedicle finder is used to further widen

the pedicle In questionable cases, the screw is inserted somewhat deeper than the

base of the pedicle, which can be checked in the lateral view with an image

intensi-fier The screw is then removed and the medial pedicle wall is palpated with the

pedicle feeler When the medial wall is intact the screw can be reinserted.

Lumbar Spine Pedicle Screw Fixation

The pedicle morphology of the lumbar spine has been accurately described in

several studies [41, 49, 56, 62, 67, 74].

a b c

Figure 18 Landmarks for thoracic pedicle screw insertions

Thoracic pedicle fixation at the level of T6:aposterior view;blateral view;caxial view Note the alternative extrapedicu-lar screw position on the right side Thoracic pedicle fixation at the level of T12:dposterior view;elateral view;faxial view

Several techniques have been described We prefer a more lateral insertion point with a larger angulation to the midline, which is also biomechanically more sta-ble than a straight anterior screw insertion The pedicle entrance point is at the lateral border of the base of the superior articular process The same technique is used as described for the insertion of thoracic screws The screw trajectory is angled 20°–25° to the midline In the sagittal plan the screws take a course paral-lel to the upper vertebral endplates (Fig 19a–c).

A double sacral screw

fixation provides a strong

sacral anchorage

Knowledge of the size and anatomy of the pedicle is required, but also an under-standing of the topography of nerve and vascular structures in relation to the pedi-cle is indispensable for safe pedipedi-cle placement The nerve roots are located directly

at the medial-inferior border of the pedicle Screws should not penetrate the ante-rior cortex except in cases in which this is absolutely necessary to enhance the pull-out resistance The screws should not be in contact with an artery because pulsa-tion can cause vessel wall erosion and the formapulsa-tion of an aneurysm.

Sacral and Iliac Screw Fixation

The most frequent technique is screw placement in the first sacral pedicle located just below the L5/S1 facet angled medially 20° cranially toward the anterior cor-ner of the promontorium Another alternative is to insert the screws at a 30° – 45° lateral and cranial direction into the sacral alae (Fig 19d–g) Both screw

a b c

f

g

Figure 19 Landmarks for lumbosacral and iliac screw insertions

Lumbar pedicle screw fixation at the level of L4: aposterior view;blateral view;c axial view Sacral screw fixation

tech-niques (red convergent S1 screw, green divergent S1 screw, blue divergent S2 screw):dposterior view;elateral view;

faxial view at S1;g axial view at S2 Pelvic fixation in the iliac wing: hposterior view;ilateral view;jaxial view

tions can be combined to enhance the sacral fixation [6, 62, 74] The insertion

point for the S2 screw is in the middle between the first and second dorsal

foram-ina The screws should be directed 5° caudally and 30° laterally [6] The slightest

risk of injury is from placement of S1 pedicle screws Lateral screw placement

car-ries a risk of injury to the internal iliac vein or the lumbosacral plexus Anterior

cortical penetration of the S2 segment could cause injury of the bowel [44, 52].

In neuromuscular scoliosis, fixation to the pelvis is often required to treat pelvic

obliquity or because of insufficient screw purchase at the sacrum The original

technique was introduced by Allan and Ferguson as the so-called Galveston tech-nique with insertion of a contoured rod into the iliac wing [3] However, this

technique has the disadvantage of resulting in a painful loosening of the rod in

the iliac wing with time (“windshield wiper effect”) A modification is to use a

screw instead of the contoured rod for pelvic fixation, which results in an excel-lent bony purchase An even stronger fixation is the so-called MW sacropelvic fixation [5] (see Chapter 24 ) The pelvic screw fixation starts with decortication

of the posterior superior iliac spine with a Luer A pedicle finder is inserted and aimed 20°–40° laterally and caudally aiming at the iliac notch and superior to the acetabulum (Fig 19h–j) A pedicle feeler is used to check that the iliac cortical laminae have not been perforated Simultaneously the length is determined Usu-ally, 7 – 8 mm strong 80- to 100-mm-long screws can be inserted.

Recapitulation

Surgical planning. Preoperative planning and a

profound knowledge of the surgical anatomy are

the prerequisites to achieving the goals of surgery

and helping to avoid serious complications

Ana-tomical dissection studies are extremely valuable

and supplement in-depth study of textbooks on

surgical anatomy The surgeon must proactively

consider potential extensions of the approach and

must be familiar with this anatomy.

Surgical approaches. Image intensifier or

radio-graphic verification of the correct level is an

abso-lute must Wrong level surgery is one of the most

frequent complications The anteromedial

ap-proach to the cervical spine apap-proaches the

anteri-or column through anatomical planes Great care

must be taken to retract the carotid artery laterally

and not medially Particularly, the recurrent

laryn-geal and the superior larynlaryn-geal nerve are at risk

dur-ing this approach The posterior approach to the

cervical spine can be associated with heavy

bleed-ing For exposure of the craniocervical junction, the

muscle insertion at the spinous process of C2

should be detached with an osteoligamentous flap.

The vertebral artery is at risk when exposing C1 A

deleterious complication of thoracotomy is wrong

site surgery The neurovascular bundle below the

rib must be preserved to avoid painful neuralgias.

The parietal pleura should be closed whenever

pos-sible Correct placement of the chest tubes

mini-mizes postoperative pulmonary complications The

thoraco-phrenico-lumbotomy gives an excellent

exposure of the thoracolumbar junction but is

ma-jor surgery The dissection should start with the

ret-roperitoneal abdominal approach to minimize

peri-toneal tears Corresponding stay sutures at both sides of the diaphragma incision facilitate repair when closing the wound The thoracic duct is at risk when exposing the thoracolumbar junction but

dif-ficult to identify during preparation The anterolate-ral retroperitoneal approach to the lumbar spine

L5–L2 is easily possible even in obese patients A muscle splitting approach is recommended In males, the psoas muscle can cover the whole lateral aspect of the anterior column Rather than dissect-ing and retractdissect-ing the psoas posterolaterally, a

pso-as splitting approach is the preferred alternative for

discectomy and interbody fusion The anterior lum-bar retroperitoneal approach approaches the

spine through anatomical planes The liberation of the peritoneal sac requires a dissection of the poste-rior rectus sheath at the arcuate line When retract-ing the common iliac vein medially to expose the L4/5 disc space, the ascending lumbar vein must be controlled and ligated prior to vessel retraction The

posterior thoracolumbar approach results in

con-siderable collateral damage to the spinal muscles, which can be minimized by mini-access surgery and use of pinpointed retractors which are

intermittent-ly released The target level must be identified prior

to surgery to avoid unnecessary and extensive de-tachment of back muscles.

Landmarks for screw fixation Occipital screw fixa-tion must be accomplished in the midline between

the superior nuchal and inferior nuchal line where

the bone is thick enough to bury a screw Posterior transarticular atlantoaxial screw fixation puts the

vertebral artery at risk laterally and the spinal cord

medially Atlantoaxial pedicle screw fixation is an

Key Articles

These texthooks are recommended for a study of the surgical anatomy of the spine and

surgical approaches:

Bauer RF, Kerschbaumer F, Poisel S (ed) ( 1993) Atlas of spinal operations Thieme,

Stutt-gart

Nazarian S ( 2007) Surgical anatomy of the spine In: Aebi M, Arlet V, Webb J AOSPINE

manual: principles and techniques, vol 1 Thieme, Stuttgart, pp 131–239

Louis R ( 1983) Surgery of the spine Surgical anatomy and operative approaches.

Springer, Heidelberg

Watkins RG ( 2003) Surgical approaches to the spine Springer, Heidelberg

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