Fractures of the odontoid proces of the axis (C2)
ANATOMY OF THE SPINE
The human spine is formed by individual vertebrae and connective tissue discs in between. The vertebrae form the spinal canal. There are seven cervical, twelve thoracic, and five lumbar vertebrae. The intervertebral discs are the link between the individual vertebral bodies.
Normal anatomy of the spine. Longitudinal section and cross sections through the cervical, thoracic and lumbar spine.
The little joints that link the vertebrae together are known as facet joints. They help to stabilize the spine and, together with the intervertebral discs, allow a certain degree of mobility of the spinal cord. The spinal canal should be wide enough to allow nerve roots to float freely in cerebrospinal fluid.
The front border of the spinal canal is built by the vertebral bodies and intervertebral discs, the side by the intervertebral joints (facets) and back by the ligamentum flavum (yellow band) and vertebral arches. Discs consist of an outer fibrous ring (annulus fibrosus), which surrounds an inner gel-like center (nucleus pulposus).
The spinal cord and nerve roots lie within the spinal canal. The spinal cord extends downwards approx. to the 1st lumbar vertebra. Below, only nerve roots are present in the spinal canal. At the level of the intervertebral disc the nerve roots pass through the neural root foramina to exit the spinal canal. The spinal cord and nerve roots conduct electric-like signals from the skin and joints to the brain, and process of movement is initiated from the brain to the muscles.
The connection between the head and the spine is the atlanto-occipital joint. It consists of the condyles of the occipital bone and the upper joint surfaces of the 1st cervical vertebra. The 1st cervical vertebra is called the atlas. The atlas is connected to the 2nd cervical vertebra (axis) below as well.
Fractures of the odontoid process of the 2nd cervical vertebrae most frequently due to trauma. Spinal tumors or other diseases can also cause fractures of the odontoid.The Anderson and D'Alonzo classification is used to assess the severity of the fracture:
Type I Fracture of odontoid tip. Due to a possible avulsion of alar ligament. Atlantooccipital instability should be ruled out with flexion/extension Radiographs.
Type II Fracture through the odontoid waist. Due to interruption of blood supply high nonunion rate.
Type III Fracture extends into the C2 vertebral body and may involve the C1-C2 joint.
Grauer Classification of Type II fractures:
Type IIa Nondisplaced/minimally displaced and no comminution.
Type IIb Displaced fracture. Fracture from anterosuperior to posteroinferior.
Type IIc Displaced fracture. Fracture from anteroinferior to posterosuperior or comminution.
Risk factors for nonunion are ≥6mm displacement, angulations >10°, age >50 y, odontoid comminution, treatment delay, smoker.
In 25-40% of cases with odonthotid fracture, death occurres instantly. Most survivors are usually without symptoms.
CAUSE OF SYMPTOMS
Acute compression of the cervical spinal cord
Cervical vertebral fracture
SYMPTOMS AND SIGNS
Total or partial paralysis of the hands and feet
Insensitivity from the neck down
Pain and stiffness in the neck
THE DIAGNOSIS IS BASED ON Medical history Clinical exam Computer tomography
additionally you may have to do: Magnetic resonance imaging (MRI)
The treatment may be non-surgical or surgical.
Non-surgical treatment may include
Type I and Type II in elderly (>50y) patients who are not surgical candidates and Type III fractures - stiff collar for 6-12 weeks
Type II in young patients (<50y) with no risk factors for nonunion - halo vest for 6-12 weeks.
WHEN SHOULD AN OPERATION BE PERFORMED?
Anterior odontoid osteosynthesis should be considered in case of:
Type II fracture with risk factors for nonunion and suitable fragment alignment alowing screw placement.
Posterior C1-C2 fusion should be considered in case of:
Type II fractures with risk factors for nonunion not suitable for anterior screw,
Chronic Type II/III fractures with nonunion
Os odontoideum with neurologic deficits or instability
Transoral odontoidectomy should be considered in case of:
Severe posterior displacement of dens with spinal cord compression and neurologic deficits.
WHAT IS THE GOAL OF SURGERY?
To restore the protective function of the spine
HOW IS SURGERY PERFORMED?
Anterior odontoid osteosynthesis
Posterior C1-C2 fusion
Transoral odontoid resection
WHICH OTHER DISEASES SHOULD BE EXCLUDED (DIFFERENTIAL DIAGNOSIS)? Other fractures of the spine Osteoporosis Pathologic vertebral fracture