General Editor: Luiz Vialle

Authors: Ronald Lehman, Daniel Riew, Klaus Schnake

Occipitocervical trauma - Odontoid, AAIII Odontoid screw fixation

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Glossary

Authors: Ronald Lehman, Daniel Riew, Klaus Schnake

1 Introduction top

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Screw options

For this procedure either one or two screws can be used.

Two screws provide higher rotational stability. A one screw technique is generally sufficient for younger patients with good bone quality.

Measurement of the odontoid diameter will determine whether one or two screws are technically feasible.

A lag screw technique should not be used in osteoporotic bone due to the possibility of screw perforation.

In osteoporotic bone the following options can be utilized:

Specialized kits for anterior odontoid screw fixation are available, however we will here describe the use of standard implants to show the principles.

This procedure is contraindicated for fractures running from anterior caudal to posterior cranial.


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Imaging

Two image intensifiers are necessary to identify the odontoid process in the true AP and true lateral projections. Using just one image intensifier is not recommended due to the high risk of failure.

2 Reduction top

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It is essential for the success of this procedure that the fracture is anatomically reduced prior to the surgical access.

Reduction can be performed:

  1. using halo traction preoperatively.
  2. intraoperatively placing the head in an extended position.
  3. intraoperatively using Mayfield clamp or a similar tool.
  4. by pushing directly on the anteriorly displaced C1/2 segment through the mouth with the index finger in the case of a persistent anterior displacement.

3 Preparation top

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The patient is placed supine. The head is placed in the extended position to reduce the fracture and to facilitate the insertion of the screws.

4 Approach top

An anteromedial approach is used. Right handed surgeons should access through the patients right side and vice versa.


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The placement of the incision is determined by placing a long K-wire along the side of the neck in the intended direction of the screw and viewing on the image intensifier. The transverse incision can then be made in the neck where the K-wire is likely to exit the skin (in most cases at the C4/5 level).


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To better visualize the screw entry point, two Hohmann retractors or specially curved radiolucent retractors are inserted on either side of the odontoid (dens) to expose the body of the axis.

5 Option 1: Conventional screw insertion top

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Screw entry point

The screw point is located in anterior part of the inferior C2 endplate. To access the entry point, the drill sleeve is placed on the C2-C3 disk. In osteoporosis entry point can be chosen in the C2/3 disk.


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Trajectory

In the sagittal plane, the screw should be angled slightly posteriorly in order to exit at the posterior half of the odontoid’s tip (bicortical).


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In the frontal plane, the screw should be angled a few degrees toward the midline. A second drill is inserted in the same manner.


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Drilling

The screw holes are drilled using a 2.5 mm drill bit.

It is absolutely essential that tissue protectors are used when drilling and tapping to avoid damaging vital structures.

The oscillating attachment should be used to avoid soft-tissue damage.


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If fully threaded screws are used, one drill bit is removed and the entire hole in the distal fragment is overdrilled with a 3.5 mm drill bit.

If double treaded screws are used, overdrilling is not necessary.


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It is essential to leave one drill bit in order to maintain reduction and "loose the drill hole".


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Screw insertion

The depth of the hole to the tip of the odontoid is measured, tapped, and a 3.5 mm cortex screw of the appropriate length inserted.


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The second screw is inserted applying the same technique.

6 Option 2: Cannulated screw insertion top

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Using lateral image intensifier control, a 20 cm long, 1.2 mm K-wire is inserted in a sagittal direction on both sides following the same entry point and trajectory as the screws above.


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The length of the K-wire in the bone is measured with the special ruler, indicating the length of screw required, typically 38-42 mm.


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In order to allow the self-drilling screw to start entering the bone in the near cortex, the cortex is perforated with the special cannulated countersink.


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Odontoid-type cannulated screws with the appropriate length are inserted.

During insertion of the cannulated screw, it is essential to observe this procedure on the lateral image intensifier to ensure that the K-wire does not advance superiorly.

7 Option 3: Single screw insertion top

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The screw point is located in the midline of the inferior C2 endplate. To access the entry point, the drill sleeve is placed on the C2-C3 disk. In osteoporosis entry point can be chosen in the C2/3 disk.


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In the sagittal plane, the screw should be angled slightly posteriorly in order to exit at the posterior half of the odontoid’s tip (bicortical).


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Using lateral image intensifier control, a 20 cm long, 1.2 mm K-wire is inserted.


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The length of the K-wire in the bone is measured with the special ruler, indicating the length of screw required, typically 38-42 mm.


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In order to allow the self-drilling screw to start entering the bone in the near cortex, the cortex is perforated with the special cannulated countersink.


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The odontoid-type cannulated screw with the appropriate length is inserted.

During insertion of the cannulated screw, it is essential to observe this procedure on the lateral image intensifier to ensure that the K-wire does not advance superiorly.


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The K-wire is removed.

v1.0 2016.12.01