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Introduction
  •  A fracture of the dens of the axis (C2)
  • Epidemiology
    • incidence
      • most common fracture of the axis
      • account for 10-15% of all cervical fractures
    • demographics
      • occur in bimodal fashion in elderly and young patients
        • elderly
          • commonoften missed, and caused by simple falls
          • associated with increased morbidity and mortality compared to younger patients with this injury 
        • young patients
          • result from blunt trauma to head leading to cervical hyperflexion or hyperextension
  • Pathophysiology
    • mechanism
      • displacement may be anterior (hyperflexion) or posterior (hyperextension)
        • anterior displacement
          • is associated with transverse ligament failure and atlanto-axial instability
        • posterior displacement
          • caused by direct impact from the anterior arch of atlas during hyperextension
    • biomechanics
      • a fracture through the base of the odontoid process severely compromises the stability of the upper cervical spine.
  • Associated conditions
    • Os odontoideum  
      • appears like a type II odontoid fx on xray
      • previously thought to be due to failure of fusion at the base of the odontoid
      • evidence now suggests it may represent the residuals of an old traumatic process
      • treatment is observation
Anatomy
  • Axis Osteology
    • axis has odontoid process (dens) and body
    • embryology
      • develops from five ossification centers  
      • subdental (basilar) synchondrosis is an initial cartilagenous junction between the dens and vertebral body that does not fuse until ~6 years of age  
      • the secondary ossification center appears at ~ age 3 and fuses to the dens at ~ age 12 
  • Axis Kinematics
    • CI-C2 (atlantoaxial) articulation
      • is a diarthrodal joint that provides 
        • 50 (of 100) degrees of cervical rotation 
        • 10 (of 110) degrees of flexion/extension 
        • 0 (of 68) degrees of lateral bend 
    • C2-3 joint
      • participates in subaxial (C2-C7) cervical motion which provides
        • 50 (of 100) degrees of rotation
        • 50 (of 110) degrees of flexion/extension
        • 60 (of 68) degrees of lateral bend
  • Occipital-C1-C2 ligamentous stability 
    • provided by the odontoid process and its supporting ligaments
      • transverse ligament  
        • limits anterior translation of the atlas
      • apical ligaments
        •  limit rotation of the upper cervical spine
      • alar ligaments
        • limit rotation of the upper cervical spine
  • Blood Supply
    • a vascular watershed exists between the apex and the base of the odontoid   
      • apex is supplied by branches of internal carotid artery
      • base is supplied from branches of vertebral artery
      • the limited blood supply in this watershed area is thought to affect healing of type II odontoid fractures.
Classification
  •  Anderson and D'Alonzo Classification  
Anderson and D'Alonzo Classification
Type I  Oblique avulsion fx of tip of odontoid. Due to avulsion of alar ligament. Although rare, atlantooccipital instability should be ruled out with flexion and extension films.
  
Type II  Fx through waist (high nonunion rate due to interruption of blood supply).
  
 
Type III  Fx extends into cancellous body of C2 and involves a variable portion of the C1-C2 joint.
  
 
Presentation
  • Symptoms
    • neck pain worse with motion
    • dysphagia may be present when associated with a large retropharyngeal hematoma
  • Physical exam
    • myelopathy
      • very rare due to large cross section area of spinal canal at this level
Imaging
  • Radiographs
    • required views
      • AP, lateral, open-mouth odontoid view of cervical spine
    • optional views
      • flexion-extension radiographs are important to diagnose occipitocervical instability in Type I fractures and Os odontoideum
        • instability defined as
          • atlanto-dens-interval (ADI) > 10mm 
          • < 13mm space available for cord (SAC)
    • findings
      • fx pattern best seen on open-mouth odontoid  
  • CT
    • study of choice for fracture delineation and to assess stability of fracture pattern
  • CT angiogram
    • required to determine location of vertebral artery prior to posterior instrumentation procedures 
  • MRI
    • indicated if neurologic symptoms present  
Treatment

Treatment Overview
Os Odontoideum Observation
Type I  Cervical Orthosis
Type II Young Halo if no risk factors for nonunion
Surgery if risk factors for nonunion
Type II Elderly Cervical Orthosis if not surgical candidates
Surgery if surgical candidates
Type III  Cervical Orthosis
  • Nonoperative
    • observation alone
      • indications
        • Os odontoideum
          • assuming no neurologic symptoms or instability
    • hard cervical orthosis for 6-12 weeks   
      • indications
        • Type I 
        • Type II in elderly who are not surgical candidates 
          • union is unlikely, however a fibrous union should provide sufficient stability except in the case of major trauma
        • Type III fractures   
          • no evidence to support Halo over hard collar
    • halo vest immobilization for 6-12 weeks 
      • indications
        • Type II young patient with no risk factors for nonunion
      • contraindications
        • elderly patients
          • do not tolerate halo (may lead to aspiration, pneumonia, and death)
  • Operative
    • posterior C1-C2 fusion 
      • indications
        • Type II fractures with risk factors for nonunion
        • Type II/III fracture nonunions 
        • Os odontoideum with neurologic deficits or instability
    • anterior odontoid osteosynthesis
      • indications
        • Type II fractures with risk factors for nonunion AND
          • acceptable alignment and minimal displacement
          • oblique fracture pattern perpendicular to screw trajectory
          • patient body habitus must allow proper screw trajectory
      • outcomes
        • associated with higher failure rates than posterior C1-2 fusion
    • transoral odontoidectomy
      • indications
        • severe posterior displacement of dens with spinal cord compression and neurologic deficits
Surgical Techniques
  • Halo immobilization 
    • in children and adults 
  • C1-C2 posterior fusion techniques
    • approach
      • posterior midline cervical approach
    • stabilization technique
      • sublaminar wiring techniques (Gallie or Brooks)
        • require postoperative halo immobilization and rarely used
      • posterior C1-C2 transarticular screws construct  
        • contraindicated in patients with an aberrant vertebral artery 
      • posterior C1 lateral mass screw and C2 pedicle screw construct  
        • modern screw constructs do not require postoperative halo immobilization
    • outcomes
      • C1-C2 fusion will lead to 50% loss of neck motion
  • Anterior odontoid screw osteosynthesis  
    • approach
      • anterior approach to cervical spine 
    • technique
      • single screw adequate
    • pros & cons
      • associated with higher failure rate than posterior C1-2 fusion
      • advantage is preservation of atlantoaxial motion
  • Transoral odontoidectomy post
    • technique
      • usually combined with posterior stabilization procedure
Complications
  • Nonunion
    • increased risk in Type II fractures due to poor blood supply
    • risk factors for nonunion include  
      • > 6 mm displacement (>50% nonunion rate)
      • age > 50 years
      • fx comminution
      • angulations > 10 degrees
      • delay in treatment
 

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Questions (8)

(OBQ12.65) A 45-year old male is involved in a motor vehicle accident and presents to the emergency room with complaints of neck pain. Physical exam shows he is an ASIA E. An open-mouth cervical radiograph is shown in Figure A. A sagittal CT scan is shown in Figure B. A CT axial angiogram is shown in Figure C. Which of the following treatment options is contraindicated in this patient. Review Topic

QID:4425
FIGURES:
1

Anterior screw osteosynthesis with single cannulated screw

13%

(407/3242)

2

Halo immobilization

15%

(486/3242)

3

Anterior screw osteosynthesis with two cannulated screws

10%

(324/3242)

4

C1-C2 transarticular screws

48%

(1560/3242)

5

Posterior C1-C2 wiring with autograft

14%

(438/3242)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

The clinical presentation is consistent with an odontoid fracture with an aberrant vertebral artery on the left. C1-C2 transarticular screws are an absolute contraindication in this scenario.

The vertebral artery is an important consideration when performing posterior cervical spine surgery. Injury to this artery can lead to stroke and death. Normally the vertebral artery travels superiorly in the transverse foramen of C6 to C2. At C2 the artery deviates laterally to the pass through the transverse foramen of C1 and then wraps medially on the superior surface of the posterior arch of C1 before ascending into the foramen magnum. Anomalous variants of the vertebral arery may be present in up to 30% of individuals, and may be intraosseous or extraosseous. Intraosseous variants may be injured during posterior cervical stabilization techniques. In patients with an aberrant vertebral artery, C1-C2 transarticular screws are contraindicated due to the risk of injury to the aberrant vertebral artery.

Patel et al. performed a literature review to investigate the optimal surgical treatment for unstable type II odontoid fractures in skeletally mature individuals. They found there is no moderate or high quality literature on the surgical management of acute type II odontoid fractures, and that there is no comparative data to objectively compare an anterior vs. posterior approach. They report that in equivocally indicated instances, anterior or posterior treatment can both be safely used with good outcome.

Wright et al. performed a retrospective study to look at the incidence of vertebral arery injury and subsequent neurological deficit in patients where C1-C2 trans-articular screws are placed. They found of 2492 C1-2 transarticular screws in 1318 patients, thirty-one patients (2.4%) had known vertebral artery injuries and an additional 23 patients (1.7%) were suspected of having injuries. Of the patients with known or suspected vertebral artery injuries, 2 (3.7%) of the 54 patients exhibited subsequent neurological deficits and one (1.9%) died from a bilateral VA injury.

Figure A is an open-mouth odontoid radiograph that shows a type 2 odontoid fracture. Figure B is a sagittal CT that shows a Type 2 odontoid fracture. Figure C is a CT angiogram that shows an anomalous vertebral artery on the left, with the absence of a normal vertebral foramen. Illustration A shows the anatomy of a normal vertebral artery and its relative position to a C1-C2 transarticular screw. Illustration B shows an anomalous extra-osseous vertebral artery. Illustration C shows a CT scan of an anomalous intra-osseous vertebral artery.

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(OBQ12.103) A young boy is involved in a motor vehicle accident and presents with neck pain. A CT scan is performed and is negative for fractures. Based on the presence of the ossification center shown in Figure A, what is the most likely age bracket of this patient. Review Topic

QID:4463
FIGURES:
1

< 1 years of age

0%

(6/2257)

2

1-3 years of age

7%

(151/2257)

3

3-6 years of age

35%

(783/2257)

4

8-10 years of age

47%

(1068/2257)

5

> 12 years of age

10%

(231/2257)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

The CT scan shows a fused basilar synchondrosis with a C2 secondary ossification center that is not yet fused. Therefore the patient is most likely 8-10 years of age.

The axis (C2) develops from five ossification centers. These include the body, two neural arches, the odontoid, and a secondary ossification center. The subdental (basilar) synchondrosis is an initial cartilagenous junction between the dens and vertebral body that does not fuse until ~6 years of age. The secondary ossification center appears around age 3 and fuses with the odontoid at around 12 years of age.

Vanderhave et al. review cervical spine trauma in children. They emphasize that children are particularly susceptible to substantial destabilizing cervical injuries and must be treated with a high degree of caution.

Figure A shows a coronal CT scan of the cervical spine. The basilar synchondrosis is fused and the neural arch, body, and odontoid are a single structure. The secondary ossification center at the tip of the odontoid has not yet fused. Illustration A shows the labeled version of Figure A. Illustration B shows the 5 ossification centers of the odontoid.

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(OBQ12.116) A 67-year-old male smoker was involved in a motor vehicle accident and presents with neck pain. On initial presentation his neurologic exam was intact. Injury films are shown in Figure A and B. The patient was evaluated and surgical treatment was recommended. The patient left the hospital against medical advice. Seven months later he returns with continued neck pain. His current neurologic exam shows no deficits. A current CT scan and MRI is performed and shown in Figure C and D. What is the most appropriate treatment at this time? Review Topic

QID:4476
FIGURES:
1

Physical therapy and NSAIDS

15%

(437/2911)

2

Hard Cervical Orthosis

3%

(73/2911)

3

Halo Immobilization

2%

(51/2911)

4

Anterior screw osteosynthesis

7%

(213/2911)

5

Posterior C1-C2 fusion

73%

(2117/2911)

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

The clinical presentation is consistent with a Type 2 odontoid fracture with a resulting nonunion due to inappropriate treatment. At this time a posterior C1-C2 fusion is the most appropriate treatment.

Type-2 odontoid fractures are at increased risk of nonunion due to poor blood supply at the junction between the dens and odontoid body. Therefore, in patients with risk factors for nonunion, surgical treatment is recommended. In patients that develop a symptomatic nonunion, a posterior C1-C2 fusion is the most appropriate treatment.

Tashjian et al. looked at the effect of treating patients > 65 years-of-age in a halo immobilization. In their study of 78 patients, 24 (31%) patients died during their hospital stay. Forty-two percent of the patients treated with a halo vest died compared with 20% in the non-halo vest treatment group. Major complications occurred in 66% of halo vest patients compared with 36% of non-HV patients. They recommend against halo immobilization in patients great than 65 years of age.

Patel et al. performed a literature review and investigated the optimal indications and methods of surgical treatment for unstable type II odontoid fractures in skeletally mature patients. They report there is no moderate or high quality literature on the optimal surgical management of acute type II odontoid fractures. They recommend in equivocally indicated instances, anterior or posterior treatment can both be done safely with good results.

Koivikko et al. looked at the risk factors for nonunion in Type-2 odontoid fractures treated with halo immobilization. They found nonunion correlated with a fracture gap (> 1 mm), posterior displacement (> 5 mm), delayed start of treatment (> 4 days) and posterior redisplacement (> 2 mm).

Figure A and B show a Type 2 odontoid fracture. Figure C is a CT scan showing a pseudoarthrosis of a Type 2 odontoid fracture. Figure D is an MRI showing an odontoid fracture pseudoarthrosis with no significant compression on the spinal cord. Illustration A identifies the odontoid (yellow) and anterior arch of C1 (green) on the lateral radiograph in the case of a Type-2 odontoid fracture. The posterior position of the anterior arch of C1 relative to the anterior cortex of C2 helps identify the Type-2 Odontoid fracture. In a normal individual the orange line should be continuous.

Incorrect Answers:
Answer 1: Physical therapy and NSAIDS would not be appropriate in a symptomatic Type-2 odontoid fracture pseudoarthorsis.
Answer 2: A hard cervical orthosis would not be appropriate in a symptomatic Type-2 odontoid fracture pseudoarthorsis.
Answer 3: Halo immobilization is not indicated in the setting of an odontoid fracture psuedoarthrosis and should be avoided in patients greater than 65 years of age.
Answer 4: Anterior screw osteosynthesis is not indicated in the setting of pseudoarthrosis, especially if the fracture is not aligned.

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(OBQ11.263) In Figures A-E, which of the following fracture patterns is at greatest risk for nonunion with nonoperative treatment? Review Topic

QID:3686
FIGURES:
1

Figure A

1%

(18/1671)

2

Figure B

58%

(966/1671)

3

Figure C

2%

(33/1671)

4

Figure D

17%

(284/1671)

5

Figure E

22%

(367/1671)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

Figure B shows a Type 2 Odontoid fracture with posterior displacement and angulation. This fracture pattern is at increased risk of nonunion compared with the other fracture patterns shown.

Type 2 odontoid fractures are fractures which occur through the waist of the odontoid process. These fractures are at risk for nonunion due to the watershed blood supply at this location. Increased fracture displacement, posterior displacement, and increased angulation are all risk factors for nonunion.

The Anderson and D'Alanzo classification is the most commonly used classification for odontoid fractures. Type 1 are tip fractures generally managed with cervical orthosis. Type 2 are waist fractures that can be managed with halo or operative intervention. Type 3 are fractures which extend into the C2 body and can be managed with halo, cervical orthosis, or surgery.

Koivikko et al. retrospectively reviewed the charts of 69 patients treated for a type 2 odontoid fracture with halo immobilization. They found nonunion did correlate with a fracture gap (> 1 mm), posterior displacement (> 5 mm), delayed start of treatment (> 4 days) and posterior redisplacement (> 2 mm).

Illustration A shows the location of a Type 2 odontoid fracture. Illustration B shows a Type 3 odontoid fracture. Notice how a type 3 fracture involved the body of C2 and extends into the facets.

Incorrect Answers:
Answer 1/Figure A: Type 2 Odontoid fracture with slight posterior angulation
Answer 3/Figure C: Type 3 Odontoid fracture with slight anterior displacement
Answer 4/Figure D: Type 3 Odontoid fracture with distraction but no angulation or anterior/posterior displacement
Answer 5/Figure E: Type 2 Odontoid fracture with anterior displacement

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(OBQ10.130) In patients who are neurologically intact, all of the following cervical spine injuries can be appropriately managed with external immobilization in a rigid cervical orthosis EXCEPT Review Topic

QID:3223
FIGURES:
1

Figure A

1%

(13/2536)

2

Figure B

1%

(32/2536)

3

Figure C

4%

(108/2536)

4

Figure D

5%

(115/2536)

5

Figure E

89%

(2259/2536)

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

A burst fracture of C1, also known as a Jefferson fracture, with associated transverse ligament disruption is shown in Figure E. Jefferson fractures can be appropriately managed with a cervical orthosis or halo device if the transverse ligament is intact. If there is combined lateral mass displacement >7 mm (8.1 mm with standard x-ray magnification), this indicates an injury to the transverse ligament, and the fracture pattern is unstable. This unstable fracture should be managed with traction followed by a transition to a halo device or C1-C2 fusion. C1 posterior arch fractures (Figure A), Type 1 odontoid fractures (Figure B), Type 3 odontoid fractures (Figure C), and Type 1 Hangman's fractures of C2 that have minimal displacement and angulation (Figure D) can be appropriately mangaged in an external cervical orthosis.

The review articles by Julien and Maak both state that Type I and III odontoid fractures are stable injuries and can be treated nonoperatively with immobilization, but note that there is poor evidence to clearly define the best treatment for Type 2 odontoid fractures (halo, rigid collar, anterior C2 screw, or posterior C1-C2 fusion). Management of Type III odontoid fractures is also debated however, and Miller's Review states halo immobilization is appropriate while AAOS Comprehensive Orthopaedic Review states that external cervical orthosis immobilization is appropriate.


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(OBQ10.185) In elderly patients with type II odontoid fractures, which of the following treatment modalities has the highest morbidity and mortality? Review Topic

QID:3278
1

Hard cervical collar

2%

(28/1555)

2

Anterior screw osteosynthesis

6%

(101/1555)

3

Halo vest immobilzation

81%

(1262/1555)

4

Posterior cervical stabilization

3%

(54/1555)

5

Soft cervical orthosis

7%

(102/1555)

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

Elderly individuals with odontoid fractures experience greater rates of morbidity and mortality than younger patients with this injury. Treatment with a halo vest (HV) has been associated with increased complications in the elderly patient population, and does not allow for immediate mobilization.

Tashjian et al reviewed a series of odontoid fractures (Type II, III, and combined patterns) in elderly patients to evaluate for predictors of in-hospital morbidity and mortality. In those pt's treated with a HV, 42% died compared with 20% in the non-HV group. Major complications occurred in 66% of HV patients compared with 36% of non-HV patients.

Smith et al looked at operative versus nonoperative treatment of isolated type II odontoid fractures in patients aged 80 years and more without neurologic deficit. They reviewed the records of 223 consecutive C2 fx's and concluded that Type II odontoid fractures in the octogenarian population are associated with substantial morbidity and mortality, irrespective of management method.


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(OBQ08.78) A 37-year-old male was involved in a motorcycle accident. He is neurologically intact. A coronal and sagittal CT scan is shown in Figure A. What is the most appropriate management? Review Topic

QID:464
FIGURES:
1

Posterior C1-C2 fusion

4%

(60/1424)

2

Anterior odontoid screw fixation

21%

(303/1424)

3

Transoral anterior odontoid resection

0%

(3/1424)

4

Cervical immobilization for 6-8 week in an external orthosis

73%

(1035/1424)

5

Treatment in a soft cervical orthosis for two weeks followed by range of motion exercises

1%

(18/1424)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

The clinical presentation is consistent with at Type III odontoid fracture. Cervical immobilization in a hard external orthosis is the most appropriate treatment.

The Anderson and D'Alonzo classification system breaks odontoid fractures into 3 types. Type I is an oblique avulsion fracture of the apical ligament. Type II occurs in the watershed area at the junction with the body of the axis. Type III fractures extend into the cancellous body of C2 and involves a variable portion of the C1-C2 joint. While the management of Type II fractures remains controversial due to high non-union rates, the literature supports that Type III fracture can be treated with immobilization in a hard cervical collar or halo vest. This is due to improved healing potential from a larger surface area of cancellous bone and a better blood supply than Type II fractures.

Julien et al performed a Medline meta-analysis (1966-1999) of 96 Level 3 articles. For Type I and III fractures, they found "sufficient evidence to establish a practice guideline, suggesting that cervical immobilization for 6 to 8 weeks is appropriate management". For Type II fractures the evidence is less clear, and analysis suggests that both operative and nonoperative management remain treatment options. They recommend additional randomized trials be performed to determine the best management of Type II fractures.

Nourbakhsh et al performed a Pubmed meta-analysis looking at fusion rates for Type II fractures treated with external immobilization (halo vest or collar) or surgery (posterior C1-2 fusion or anterior screw fixation). They identified risk factors associated with nonunion which support surgical treatment. In patients with Type II fracture who are older, have posterior displacement, or displacement of > 4-6 mm, they recommend operative management. In younger patients (age <45-55 years) with anterior displacement of the fracture, conservative management is as effective as surgery.

Incorrect Answers:
Answer 1: Posterior C1-C2 fusion is the most commonly performed operation for treatment of Type II odontoid fractures.
Answer 2: Anterior odontoid screw fixation is a surgical option in Type II fractures with an oblique fracture pattern that is perpendicular to the path of the screw.
Answer 3: Transoral anterior odontoid resection is rarely required in the treatment of odontoid fractures and is only indicated when there is posterior displacement of the dens leading to spinal cord compression, that can not be reduced by closed methods.
Answer 5: Treatment in a soft cervical collar is indicated in Type I odontoid fractures in all age populations.


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(OBQ06.263) A 36-year-old male falls while intoxicated two weeks ago and has had persistent neck pain ever since. For unclear reasons he did not seek medical attention. He now reports persistent neck pain, but denies symptoms in his upper and lower extremities. On physical exam he has Grade 5 motor strength in his upper and lower extremities, normal reflexes, and his sensory exam is normal. A CT scan is shown in Figure A. All of the following place this patient at an increased risk of nonunion EXCEPT: Review Topic

QID:274
FIGURES:
1

Fracture gap of 2 mm

3%

(60/2243)

2

Posterior displacement of > 5mm

2%

(35/2243)

3

Delay in treatment of 2 weeks

3%

(69/2243)

4

Age < 40 years

90%

(2026/2243)

5

Posterior angulation

2%

(45/2243)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

The clinical presentation is consistent with a Type II odontoid fracture. All of the listed variables are risk factors for nonunion in Type II odontoid fractures, EXCEPT for age < 40 years.

Koivikko et al looked at risk factors for nonunion in patients with Type II odontoid fractures. They found nonunion correlated with a fracture gap (> 1 mm), posterior displacement (> 5 mm), delayed start of treatment (> 4 days) and further posterior displacement after application of a halo vest (> 2 mm). They concluded that patients presenting with these risk factors are unlikely to achieve bony union by treatment in a halo vest.


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