Odontoid Fractures: Surgical Management by Fusion

Joel Finkelstein, M.D., FRCSC
Section Head, Orthopaedic Sunnybrook Spine Programme
Sunnybrook Health Sciences Centre, University of Toronto
Toronto, ON

Approximately fifty percent of axial rotation of the cervical spine occurs at the C1-C2 articulation. Instability at this level occurs most commonly as a result of fractures of the odontoid or bursting injuries of the atlas with disruption of the transverse ligament. The goal in the treatment is 1) to reestablish the normal anatomic relationships at the level or the ring of C1 and 2) to maintain them either through osteosynthesis of the dens or through a solid fusion of C1 and C2. The theoretical advantage of osteosynthesis of the dens is to maintain this motion. However, due to scarring of the transverse ligament related to the injury itself and with anything less than anatomical alignment of the odontoid process, there may be loss of C1-C2 motion despite one's best efforts. Inability to achieve anatomical alignment also precludes direct fixation of the dens. This technique is also contraindicated in patients with osteoporosis, nonunion, os odontoideum or thoracic kyphosis. The role of fusion for odontoid fractures is well established and a number of techniques are available to achieve the goals of treatment in a safe and effective manner.

 The mechanism of injury may be from forces causing extreme flexion, extension or rotation. Fractures of the odontoid can be difficult to identify in the osteopenic skeleton of geriatric patients. In the majority of cases, fractures can be identified on either the lateral cervical spine radiograph or open-mouth odontoid view. CT scan with sagittal and coronal reformations are useful for a better understanding of the fracture pattern and for surgical planning.

Classification of odontoid fractures is based on the level of the fracture. The system of Anderson and D'Alonzo is most widely used. This classification has the greatest clinical applicability and prognostic implications1.

Type I
Type I injuries represent an avulsion fracture of the alar ligament from the dens. The importance of this injury is its potential association with an atlantooccipital dissociation. In the absence of this, conservative treatment is indicated.

Type II
Type II injuries are the most common odontoid fractures. These are transverse or oblique fractures through the waist of the odontoid. This fracture occurs in the cortical bone caudad to the trasverse ligament and above the cancellous body of the axis. Displacement can be either anterior or posterior.

Type II fractures have the highest incidence of non-union. Various factors contribute to the poor prognosis associated with these injuries. These are unstable injuries and it is believed the fracture causes damage to the vascularity of the dens. The remaining dens is hard cortical bone with a small surface area for healing. Other factors have been suggested that may affect union. These include initial displacement of more than five millimeters, angulation greater than ten degrees, posterior displacement and comminution, age greater than 40 years, delay in diagnosis and smoking. The Type II fracture that cannot be reduced anatomically or maintained in a halo requires fusion.

Type III
Type III injuries are fractures into the body of the axis and usually have a well vascularized broad cancellous surface area. Treatment is generally with a hard collar or a halo orthosis.

C1-C2 Fusion Options:

1) Wiring Techniques
Gallie or Brooks fusion techniques utilize a sublaminar C1 wire with either C2 spinous process or C2 laminar wire. Tricortical iliac crest bone graft is placed on the C1 arch and over the C2 lamina and maintained by the wire. These are less commonly used today as they are less biomechanically stable and do not control lateral bending, axial rotation nor anteroposterior translation compared to the newer Magerl or Harms techniques2. Wiring techniques cannot be used in patients with posterior arch fractures of C1 and require the use of postoperative halo-vest immobilization.

2) C1-C2 Fusion Using Magerl Transarticular Screws3
The preoperative plan initially involves determining the feasibility of passing a screw across the C1-C2 joint safely without injury to the vertebral artery or the spinal canal. CT axial and sagittal reconstruction views are invaluable in visualizing the path of the vertebral artery and measuring the relationship between the artery, the canal and the joint (Figure 1). The danger to the vertebral artery lies in the C2 body as it ascends from a more medial position laterally. If the location is initially too medial, the pathway takes it very close to the C1-C2 joint and there may be little room for a screw to pass. The decision to pass a unilateral screw or to defer to another technique will depend on the location of the vertebral artery. A further technical issue with this procedure mandates that C1 be reduced fully on C2 or the vertebral artery is again at risk of injury. The technique can be supplemented with a Gallie wiring technique for added stability. Cancellous bone graft is placed into the C1-C2 facet joint after decorticating the posterior portion of the joint. Postoperatively, a hard collar is worn for six weeks.

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Figure 1a,b: Lateral and open mouth odontoid view of a patient undergoing C1-C2 fusion by the Magerl technique.

 

 

 

 

 

 

 

 

 

 

3) Atlantoaxial Fusion Using C1 Lateral Mass and C2 Pedicle Fixation, (Harms Technique)4
This technique can be used preferentially, or as an alternative to the Magerl technique where the vertebral artery precludes safe passage of a C1-C2 transarticular screw. Polyaxial screws and rods connect the lateral masses of C1 to the pedicles of C2. This technique is biomechanically equivalent to the Magerl technique. The location of the C1 lateral mass is anterior to the overhang of the C1 posterior arch and the screw head must sit proud to allow connection to the rod. Entry point is the midpoint of the lateral mass directed straight anteriorly to the anterior arch of C1. The C2 pedicle is cannulated and its orientation is 20 degrees cephalad to the transverse plane and 30 degrees medial to the sagittal plane. The safest technique for cannulating the C2 pedicle is by direct exposure and palpation of the superior and medial edges of the pedicle. A lateral fluoroscopic image can help to determine the proper cephalad angulation. Cancellous bone graft is placed into the C1-C2 facet joint after decorticating the posterior portion of the joint. Postoperatively, a hard collar is worn for six weeks (Figure 2).

finkelstein2ab.jpg
Figure 2a,b: AP and lateral radiograph following fixation using the Harm’s technique, (lateral mass C1 screws and C2 pedicle screws.



















4) C2 Intralaminar Fixation5
Bilateral crossing C2 laminar screws can be used as an alternative to C2 pedicle fixation. This technique has the advantage of having less risk to the vertebral artery and may be advantageous if there is difficulty with pedicle fixation. As described by Harms, the C1 fixation is as above. This technique is not as biomechanically rigid as the Magerl or Harms procedures but early case series report satisfactory results.

In summary, understanding of the anatomy and appropriate preoperative planning is mandatory for safe execution of any of the fusion techniques described above for C1-C2 instability. With the numerous tools now available in the surgeon's armamentarium, when surgery is required, fusion can be performed safely with good clinical outcome.

References

  1. Anderson L.D., D'Alonzo R.T. Fractures of the odontoid process of the axis. J Bone Joint Surg 1974; 56A: 1663-74.
  2. Grob D., Crisco J.J., Panjabi M.M., Wang P. Dvorak J. Biomechanical evaluation of four different posterior atlantoaxial fixation techniques. Spine 1992;17: 480-90
  3. Jeanneret B., Magerl F. Primary posterior fusion C1-2 in odontoid fractures: indications, technique and results of transarticular screw fixation. J Spinal Diord 1992; 5: 464-75.
  4. Harms J., Melcher R.P. Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine 2001; 26: 2467-71.
  5. Wright N.M. Posterior C2 fixation using bilateral, crossing C2 laminar screws: case series and technical note. J Spinal Disord Tech. 2004; 17: 158-62

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