Cervical pedicle screw placement [Neurosurgery Wiki]

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====== Cervical pedicle screw placement ======

see [[C1 pedicle screw placement]].

see [[C2 pedicle screw placement]].
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{{::cervical_pedicle_screw_placement.png?400|}}

see also [[Thoracic pedicle screw placement]]

see also [[Lumbar pedicle screw placement]].
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===== C3–6 fixation =====

==== Lateral mass screws ====

{{::cervical_lateral_mass_screw_placement.png?600|}}

Generally applicable to C3–6. The lateral masses of the thoracic spine are usually too small and not strong enough for these screws. C7 is a transitional level, and lateral mass screws may sometimes be used. 

Occasionally even T1 may be amenable.

Technique:

A number of methods have been promulgated with various screw entry points and trajectories.

Comparing 3 techniques there was a lower risk of nerve injury with the following:

1. ENTRY 1 mm medial to the midpoint of the [[lateral mass]].In the cranial-caudal direction, the midpoint is used. A Penfield 4 may be used to palpate the medial wall of the pars to help determine entry point and trajectory

2. TRAJ 30° laterally, 15° cephalad (editor’s note: for upper cervical levels more cephalad trajectory
is used, for caudal cervical levels 15° or less may be closer). To get the lateral angulation, the holes are best drilled from the contralateral side of the patient, holding the drill shaft almost up against the spinous processes (if they are still present).

a) SCREWS 3.5 mm diameter,14–16mm length (for C3–6)

b) rod size: 3.5 mm diameter rods are usually used, and can be placed as far caudally as T3 as long as there is not gross instability (below T3, 5.5 mm diameter rods are used either via transitional rods or with rod connectors, e.g. “domino” connector)

Spinous process wiring may be used with intact spinous processes to help secure the bone graft.

===== Transarticular screw fixation =====

An alternative to lateral mass fusion. First described in 1972 by Roy Camille. May be used alone or as an anchor point.

1. PROS:

a) screws cross 4 cortical surfaces for better purchase

b) compresses across the joint to promote fusion

c) useful at cervico-thoracic junction where trajectory preserves facet capsule

d) lower implant profile

2. CONS: cannot correct deformity

3. ENTRY midpoint of lateral mass

4. TRAJ perpendicular to joint, neutral to 5° lateral(to avoid VA and exiting root).

5. biomechanics: stability equivalent to lateral mass screws

6. clinical: 25 patients (81 screws), 71 anchor, 10 fixation, 3.5 years F/U: solid fusion, no
complications.

===== Translaminar cervical screw fixation =====

May be used in cervical or thoracic spine.

1. indications: salvage technique when anatomy precludes pedicle screws.

2. PROS:

a) avoids complications related to pedicle screws

b) no need for fluoroscopy (reduces radiation exposure)

3. CONS: requires intact posterior elements (cannot do with laminectomy)

4. ENTRYcontralateral spinolaminar junction (at base of spinous process)

5. TARGET junction of the transverse process and the superior facet contralateral to the entry point

6. SCREWS 3.5–4.5 mm ×26 mm polyaxial screw

7. biomechanics: no data

8. clinical: 7 patients (C-T fixation), 14 months F/U, no hardware complications. Inconsequential
ventral penetration in 5%.

===== C7 screws =====

C7 is a transitional level, and as a result either the lateral masses or the pedicles or both may be relatively small.

Screw fixation options:

1. pedicle screws: recommended especially when the C7 lateral mass is of inadequate size
for lateral mass screws.
Placement with fluoroscopy may be difficult due to shoulder artifact on lateral fluoro, and direct visualization of the medial wall of the pedicle may be required as in the thoracic spine

2. lateral mass screws:

a) ENTRY as for C3–6 

b) TRAJ compared to C3–6 screws, slightly less lateral at ≈ 15° and a little less cephalad at ≈ 10°
c) SCREWS3.5 mm diameter,14 mm length

d) biomechanics: lab studies indicate that C7 lateral mass screws are biomechanically equivalent
to C7 pedicle screws in constructs extending down to C7 

3. C7 transfacet screw:

a) PROS: reduced risk to spinal cord and nerve roots

b) CONS: disrupts C7-T1 facet capsule, so T1 must be included in fusion. short screws result in
low pullout strength �may be best used as an intermediate anchor point and not an construct
endpoint

c) ENTRY1–2 mm medial and superior to center of facet

d) TRAJ 30° inferiorly and 20°laterally, TARGET goal is bicortical purchase

e) SCREWS3.5mm diameter × 8–10mm polyaxial screws

f) biomechanics: equivalent to C7-T1 pedicle screws

g) clinical: 10 patients, long cervico-thoracic fixation, 6 months F/U, 3 patients with solid fusion.

===== Complications =====

Screw malposition varies from 0%–4% in the [[atlas]] and 0%–7% in the [[axis]]
((Harms J, Melcher RP. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine (Phila Pa 1976) 2001;26:2467–2471.))
((Ni B, Zhou F, Guo Q, Li S, Guo X, Xie N. Modified technique for C1-2 screw-rod fixation and fusion using autogenous bicortical iliac crest graft. Eur Spine J. 2012;21:156–164.))
((Stulik J, Vyskocil T, Sebesta P, Kryl J. Atlantoaxial fixation using the polyaxial screw-rod system. Eur Spine J. 2007;16:479–484)).

[[Posterior fusion of the atlas and axis by transarticular screw fixation]] or Magerl screws pose an additional risk of [[Iatrogenic vertebral artery injury]], neurological deficit or inadequate bony purchase.

Vertebral artery injury is one of the most dangerous complications of screw fixation and is usually due to incorrect cervical pedicle screw entry with vertebral artery injury. The incidence of iatrogenic vertebral artery injury is 1.3%–4% for Magerl fixation
((Neo M, Fujibayashi S, Miyata M, Takemoto M, Nakamura T. Vertebral artery injury during cervical spine surgery: a survey of more than 5600 operations. Spine (Phila Pa 1976) 2008;33:779–785.)).
Fortunately, the risk of neurological deficit is low (0.2%) 
((Wright NM, Lauryssen C. Vertebral artery injury in C1-2 transarticular screw fixation: results of a survey of the AANS/CNS section on disorders of the spine and peripheral nerves. American Association of Neurological Surgeons/Congress of Neurological Surgeons. J Neurosurg. 1998;88:634–640.)).
Mortality is greatly increased if both vertebral arteries are injured. Lateral deviation of screws can often lead to penetration of the foramen transversalis and subsequent vertebral artery injury
((Neo M, Sakamoto T, Fujibayashi S, Nakamura T. The clinical risk of vertebral artery injury from cervical pedicle screws inserted in degenerative vertebrae. Spine (Phila Pa 1976) 2005;30:2800–2805.)).
Current trends include the use of intraoperative CT and computer-assisted navigation systems to improve screw trajectory and reduce screw perforation 
((Ludwig SC, Kramer DL, Balderston RA, Vaccaro AR, Foley KF, Albert TJ. Placement of pedicle screws in the human cadaveric cervical spine: comparative accuracy of three techniques. Spine (Phila Pa 1976) 2000;25:1655–1667.))
((Richter M, Mattes T, Cakir B. Computer-assisted posterior instrumentation of the cervical and cervico-thoracic spine. Eur Spine J. 2004;13:50–59.)).
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Subaxial [[lateral mass screw]]s carry a risk of [[nerve root injury]] (1.3%) and [[lateral mass]] fracture ((Katonis P, Papadakis SA, Galanakos S, et al. Lateral mass screw complications: analysis of 1662 screws. J Spinal Disord Tech. 2011;24(7):415-420. doi:10.1097/BSD.0b013e3182024c06)).

Direct root injury during lateral mass screw insertion can be avoided with fluoroscopic control. Insertion under sagittal angulations of less than 15° may lead to impingement of the exiting nerve root by the protruding screw threads
((Katonis P, Papadakis SA, Galanakos S, et al. Lateral mass screw complications: analysis of 1662 screws. J Spinal Disord Tech. 2011;24(7):415-420. doi:10.1097/BSD.0b013e3182024c06)).
In axial trajectories greater than 30° lateral to the midline, lateral mass fracture (1.6%) or screw cut-out (1.3%) may occur 
((Katonis P, Papadakis SA, Galanakos S, et al. Lateral mass screw complications: analysis of 1662 screws. J Spinal Disord Tech. 2011;24(7):415-420. doi:10.1097/BSD.0b013e3182024c06)).
However, neurological harm is not common. Screws placed too medially can cause [[vertebral artery injury]].

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[[Occipitocervical fusion Complications]]