Overview

Odontoid fractures account for 5% to 15% of all cervical spine injuries and are seen more frequently in elderly patients. The Anderson and D’Alonzo system for odontoid fractures is widely used to classify these injuries ( Fig. 11-1 ). Distinctions are made between fractures at the tip of the odontoid (type I), the base of the odontoid (type II), and the body of the axis (type III). Each fracture type is associated with a particular pattern of healing and outcome. Type II fractures are the most common odontoid injury ; they are associated with high morbidity and mortality and may be physiologically prone to poor healing. They produce atlantoaxial instability, because the integrity of the atlantoaxial complex is compromised, and this enables abnormal movement that may result in compression of the cervical spinal cord and subsequent injury. Fractures across the base of the odontoid involve considerably less trabecular bone, which is the site of fracture repair, than the body of the axis and the odontoid process itself. Consequently, type II fractures have lower rates of healing and are treated differently from type I and type III fractures, most of which are managed effectively with nonsurgical bracing.

Anteroposterior and lateral views illustrate the Anderson and D’Alonzo classification of odontoid fractures.

Nonoperative management of type II odontoid fractures with immobilization in a rigid brace or halo-vest orthosis is associated with high mortality and significant failure rates, but several surgical options are available. Historically, posterior atlantoaxial fusion was performed using Gallie and Brooks wire fixation. Although this continues to be a viable alternative in children and in patients with contraindications to screw fixation because of vascular or bony anomalies, wire fixation is not adequate in most patients, because it provides poor biomechanical stiffness in flexion and extension, and it cannot counteract anteroposterior shear forces. Current posterior atlantoaxial screw-fixation techniques involve placing screws either across C1 and C2, such as C1–C2 transarticular screws, or into each vertebra separately, such as lateral mass screws placed in C1 and C2 that are connected with a rod. Posterior screw-fixation methods have excellent rates of bony fusion but are technically demanding and are very damaging to the muscles. Furthermore, fusion of the atlantoaxial complex, which provides the largest amount of rotation in the cervical spine, restricts this movement more than 50%.

Since its introduction in the early 1980s, anterior fixation of type II and some rostral type III odontoid fractures has gained popularity. In this procedure, a screw is placed from the base of the axis, across the fracture fragment, to the distal tip of the odontoid. This allows the fracture fragments to be realigned directly and allows the distal tip to be brought into approximation with the axis. Direct anterior screw fixation provides immediate atlantoaxial stability and theoretically preserves C1–C2 motion, because it avoids arthrodesis, keeping the C1–C2 joints intact. Either one or two screws have been used for fixation. Theoretically, the use of two screws provides increased stability by preventing rotation of the odontoid relative to the body of C2, and this may be the preferred technique in patients with poor bone quality. Despite this theoretical benefit, no difference in load-bearing strength, flexion-extension and rotational stiffness, or union rate has been demonstrated consistently in biomechanical or clinical studies.

Direct anterior screw fixation of type II and shallow type III odontoid fractures is an excellent motion-preserving operation in appropriate patients. When performed correctly, atlantoaxial stability is restored immediately, the likelihood of fracture healing is high, and patients maintain anatomic movement along the C1–C2 axis.

Indications

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  Type II fracture that courses obliquely from the anterosuperior to the posteroinferior portion of the dens ( Fig. 11-2 )

  
  

  
  

  
  

  

  
  

  
  

  Lateral view of C2 depicts a Grauer type IIB injury, which is ideal for anterior screw fixation.

  
  

Contraindications

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  An oblique fracture line from posterosuperior to anteroinferior that would parallel screw trajectory

  
  
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  Poor bone quality resulting from severe osteoporosis, comminution of the fracture, additional fractures of the body of C2, or type II fractures with severe angulation and/or displacement that cannot be completely reduced preoperatively

  
  
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  A barrel chest, short neck, subaxial cervical spondylosis, or severe thoracic kyphosis that would impede appropriate drill and screw placement

  
  
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  Severe spinal canal stenosis

  
  
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  Remote odontoid fractures or those with delayed diagnosis

  
  
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  Incompetent transverse atlantal ligament that results in atlantoaxial instability regardless of whether the odontoid process remains intact

  
  
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  Pathologic odontoid fractures

  
  
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  Difficulty in swallowing

Operative Technique