General Editor: Luiz Vialle

Authors: Ronald Lehman, Daniel Riew, Klaus Schnake

Occipitocervical trauma - ATLAS, Type IV Occipitocervical fusion

back to Spine overview

Glossary

1 Introduction top

enlarge

Type IIIb injuries with a ruptured the transverse atlantal ligament requires surgical treatment.

The following points are generally considered as criteria for cervical instability:

  • > than 7mm overhang C1-C2 (total right or left)
  • > 45° axial rotation C1-C2 on one side
  • > 3mm C1-C2 translation at the AADI
  • < 13 mm Posterior atlanto dental interval
  • Transverse ligament injury

2 Occipital fixation top

enlarge

Occipital plate

There are several plate systems available for the occiput (examples shown on the left). Their application is based on the same principles and to illustrate these concepts, we will show the use of plate placed in the midline which allows for modularity and rotation when connecting to the rods.

 


enlarge

If plates are not available, wiring techniques may also be used. These will not be described in detail here.


enlarge

Plate placement

Independently of the plate system used, its placement should be close to but still caudal to the external occipital protuberance (EOP).

Placement of the plate at the EOP will increase the risk of erosion of the skin.

A too caudal position may compromise the foramen magnum.

 


enlarge

Screw placement

The thickest part of the cranium is the dense ridge which runs vertically in line with the internal occipital crest.

The thickness of this crest is 11.5-15 mm in males and 10-12 mm in females, and provides the best bone stock for screw purchase.

As you move laterally this crest becomes thinner and around 7-8 laterally to the midline, the bone thins out to a thickness of only 5-6 mm.


enlarge

Another landmark with thicker bone is the superior nuchal line which runs horizontally.


enlarge

An occipital condyle screw may provide added stability in cases where additional occipital or skull fixation is needed (skull fracture).

3 Plate application top

enlarge

Preparation of plating site

The occiput bone is dissected up to the external EOP and laterally as far as needed to accommodate the plate.


enlarge

Landmarks

The following landmarks are identified;

  • EOP
  • Superior nuchal line
  • Caudal aspect of the occiput (foramen magnum)

enlarge

Neurological deficit

In cases of neurologic deficit or when decompression is indicated, the posterior arch of C1 is now removed. 


enlarge

The midline of the posterior aspect of the skull which is in line with the EOP is identified.

The plate is placed centered in the midline on the posterior aspect of the occiput. This allows for optimal placement, sizing and shape of the plate.


enlarge

Once the optimal plate is chosen, the location of the central cranial screw entry point is marked with the plate in place.


enlarge

The drill guide is set to 8 mm (female) or 10 mm (male) and the central cranial screw hole drilled.


enlarge

The screw hole is palpated to verify that the anterior cortex is still intact.


enlarge

If intact, additional drilling in 2 mm increments is performed until the anterior cortex is penetrated.


enlarge

A screw of appropriate length is inserted through the plate into the predrilled hole.


enlarge

After insertion of the first screw, there is enough flexibility in the system to allow for adjustments. Ensure the plate is flush with the skull and that it is level.


enlarge

The remaining screws are then inserted with the same drill technique as for the first screw ensuring bicortical purchase in the order 2-5.

However, care is taken during drilling of the lateral holes (2 and 3) as the bone will be thinner than in the midline (4 and 5).


enlarge

When additional occipital or skull fixation is needed, an occipital condyle screw is now inserted.

4 Cervical screw fixation top

enlarge

C1 fixation

For C1 fixation, C1 lateral mass screws can be used.


enlarge

C2 fixation

For C2 fixation the following options are available:

A consideration is given to use pedicle or interlaminar screws when doing an occiput to C2 fusion as oftentimes the starting point for the pars screws may compromise the facet joint.

5 Alignment in the occipital cervical region top

If there is a preoperative X-ray available the surgeon can use this as a guide to properly align the occipito cervical junction during fusion. Ideally proper alignment allows for horizontal gaze.

6 Rod contouring top

enlarge

When the correct alignment is verified, rods are temporarily placed.

Some systems have the advantage of rod with a ball point which allows for easier placement and contour of the occipito cervical region (which can be relatively difficult when bending straight rods to the proper contour). If these rod-screw systems are not available a standard rod can be bent.

7 Decortication top

enlarge

Prior to final placement of the rods, decortication of lamina facets, and posterior aspects of the skull is performed.


enlarge

When using intralaminar screw fixation at C2, care must be taken not to decorticate deeply which might compromise screw fixation.

8 Fusion top

enlarge

Rod insertion

The rods are inserted.


enlarge

Bone grafting

There are several options for bone grafting material including:

  • Autograft (iliac crest cancellous bone)
  • Allograft (cortico cancellous or cortical onlay graft).
  • Local bone
  • Various biomaterials

Bone grafting material is placed against the decorticated dorsal elements of the spine.


enlarge

Transverse rod connectors may be used to enhance axial stability and help hold cortical-onlay graft in place. 

v1.0 2016.12.01