High Yield Overview

ODONTOID FRACTURES

Type II High Risk | Age Determines Treatment | Collar vs Fusion

60%Type II (most common)

40%Type II nonunion with collar

85%Type III union with collar

65Age threshold for surgery

ANDERSON-D'ALONZO CLASSIFICATION

Type I

PatternTip of dens avulsion

TreatmentCollar (stable, rare)

Type II

PatternWaist/base of dens

TreatmentHigh nonunion - surgery often

Type IIA

PatternType II + comminution

TreatmentPosterior fusion (no screw)

Type III

PatternInto body of C2

TreatmentCollar (good union rate)

Critical Must-Knows

Type II is most common (60%) and most problematic (40% nonunion with collar)
Type III heals well with collar - fracture into cancellous C2 body
Elderly Type II - consider primary posterior C1-C2 fusion (Harms/Magerl)
Anterior odontoid screw preserves rotation for acute displaced Type II (young)
Transverse ligament integrity determines stability

Examiner's Pearls

"
Type II is at watershed blood supply zone - high nonunion risk
"
Age over 65, displacement over 5mm, angulation over 10° = surgical factors
"
Harms technique (C1 lateral mass + C2 pedicle screws) is gold standard posterior
"
Anterior screw contraindicated in Type IIA, barrel chest, posterior oblique line

Clinical Imaging

Imaging Gallery

2-panel (A-B) Type III odontoid fracture: (A) lateral cervical X-ray showing anteriorly displaced and angulated dens fracture, (B) 3D CT reconstruction showing fracture extending into C2 body. — 2-panel (A-B) Type III odontoid fracture: (A) lateral cervical X-ray showing anteriorly displaced and angulated dens fracture, (B) 3D CT reconstructioCredit: Jung MH et al. - Korean J Neurotrauma via Open-i (NIH) - PMC4852614 (CC-BY 4.0)

Sagittal cervical CT showing distracted Type II odontoid fracture - fracture line through base of dens at junction with C2 body without extension into vertebral body. — Sagittal cervical CT showing distracted Type II odontoid fracture - fracture line through base of dens at junction with C2 body without extension intoCredit: Shatsky JB et al. - Case Rep Orthop via Open-i (NIH) - PMC4913000 (CC-BY 4.0)

3-panel (a-c) Type II odontoid fracture with multimodal imaging and treatment: (a) sagittal CT showing displaced fracture at dens base, (b) sagittal STIR MRI showing marrow edema and prevertebral hema — 3-panel (a-c) Type II odontoid fracture with multimodal imaging and treatment: (a) sagittal CT showing displaced fracture at dens base, (b) sagittal SCredit: O'Brien WT et al. - J Clin Imaging Sci via Open-i (NIH) - PMC4498315 (CC-BY 4.0)

Critical Odontoid Fracture Points

Type II - The Problematic One

Type II (waist) has 30-40% nonunion rate with collar. Watershed blood supply at dens base. Most controversial treatment decisions revolve around this type.

Type III - Good Prognosis

Type III extends into C2 body = cancellous bone with good blood supply. 85% union with rigid collar. Usually non-operative unless significant displacement.

Age Matters

Elderly (over 65) have higher nonunion with collar alone. Strong consideration for primary posterior C1-C2 fusion. Balance surgical risk vs nonunion morbidity.

Surgical Options

Anterior odontoid screw: Preserves C1-C2 rotation, for acute Type II. Posterior C1-C2 fusion (Harms): For nonunion, elderly, Type IIA. Sacrifices rotation.

At a Glance: Quick Decision Guide

Type	Pattern	Union Rate (Collar)	Treatment
Type I	Tip avulsion	95%+	Collar 6-8 weeks
Type II (young)	Waist/base	60%	Anterior screw or collar
Type II (elderly)	Waist/base	40-50%	Posterior C1-C2 fusion
Type IIA	Comminuted	Poor	Posterior fusion (no screw)
Type III	Into C2 body	85%+	Collar 10-12 weeks

Mnemonic

TIP-WAIST-BODYAnderson-D'Alonzo Types

Tip

Tip avulsion (alar ligament origin)

Waist

Base of dens - watershed zone (high nonunion)

III

Body

Extends into C2 body (good blood supply)

Memory Hook:TIP is rare, WAIST is problematic, BODY heals well!

Mnemonic

DOGSType II Surgical Factors

Displacement

Greater than 5mm displacement

Old age

Age over 65 years

Gap/angulation

Angulation over 10 degrees

Smoking/comminution

Smoker or Type IIA pattern

Memory Hook:If the patient has DOGS factors, consider surgery!

Mnemonic

BARRELAnterior Screw Contraindications

Barrel chest

Obese or kyphotic - cannot get trajectory

Angulation

Fracture angulated posteriorly

Reverse oblique

Posterior-superior to anterior-inferior line

Ruptured TAL

Transverse ligament incompetent

Elderly osteoporotic

Poor screw purchase

Late presentation

Chronic nonunion (over 6 weeks)

Memory Hook:BARREL chest or reverse oblique = no anterior screw!

Mnemonic

ADITransverse Ligament Assessment

Atlantodental interval

Distance from C1 anterior arch to dens

Distance measure

Under 3mm adult, under 5mm child normal

Instability

Over 3mm suggests TAL rupture

Memory Hook:ADI over 3mm = TAL is not okay!

Overview and Epidemiology

Bimodal Age Distribution

Odontoid fractures have a bimodal age distribution:

Young adults: High-energy trauma (MVA, sports)
Elderly: Low-energy falls, osteoporotic bone

In the elderly, odontoid fractures are the most common cervical fracture pattern. Treatment decisions must balance surgical risk against nonunion morbidity.

Mechanism

Young: High-energy - MVA, diving, sports
Elderly: Low-energy falls
Hyperflexion: Anterior displacement
Hyperextension: Posterior displacement
Rotational component: May be present

Associations

Head injury: Common with high-energy
Other C-spine fractures: 10-20%
Vertebral artery injury: Rare but assess
Thoracolumbar fractures: Check whole spine

Anatomy and Biomechanics

C2 (Axis) Anatomy

The C2 vertebra (axis) is unique:

Odontoid process (dens) projects superiorly into the ring of C1
Articulates with anterior arch of C1 (atlas)
Held by transverse ligament posteriorly
50% of cervical rotation occurs at C1-C2

Blood Supply

Watershed Blood Supply

The base of the dens (Type II level) is a watershed zone between:

Ascending arteries from C2 body (supply base)
Apical arcade and posterior descending (supply tip)

This explains the high nonunion rate in Type II fractures - poor blood supply at fracture site.

Blood Supply by Region

Region	Source	Implication
Dens tip	Apical arcade	Type I heals well
Dens base (waist)	Watershed zone	Type II high nonunion
C2 body	Vertebral body vessels	Type III good healing

Key Ligaments

Transverse Ligament (TAL)

Primary stabilizer of C1-C2
Holds dens against C1 anterior arch
Rupture = atlantoaxial instability
Check ADI on lateral X-ray/CT
ADI over 3mm = TAL injury

Alar Ligaments

Connect dens tip to occipital condyles
Limit axial rotation
Type I fractures = alar ligament avulsion
Check for occipitocervical instability

Rule of Thirds

Rule of Thirds at C1 Level

At the C1 level, the spinal canal is divided:

1/3 odontoid process
1/3 spinal cord
1/3 free space (CSF)

This "physiological reserve" explains why neurological injury is relatively rare in odontoid fractures despite significant displacement - there is room for the cord to escape.

Classification Systems

Anderson-D'Alonzo Classification (1974)

The standard classification for odontoid fractures:

Anderson-D'Alonzo Classification

Type	Location	Frequency	Stability	Treatment
Type I	Tip avulsion	5%	Stable	Collar 6-8 weeks
Type II	Base of dens	60%	Unstable	Collar vs surgery
Type IIA	Type II + comminution	Rare	Very unstable	Posterior fusion
Type III	Into C2 body	35%	Often stable	Collar 10-12 weeks

Classification Imaging Examples

Sagittal CT of Type II odontoid fracture — Sagittal cervical CT demonstrating a classic Type II odontoid fracture with distraction. The fracture line runs through the base of the dens (waist of the odontoid) at its junction with the C2 body, without extension into the vertebral body. Type II fractures occur at the watershed vascular zone and have the highest nonunion rate (up to 30% with collar alone), making surgical stabilization often necessary, especially in elderly patients.Credit: Shatsky JB et al., Case Rep Orthop - CC BY 4.0

Type III odontoid fracture on X-ray and 3D CT — Two-panel imaging of a Type III odontoid fracture. Panel A: Lateral cervical X-ray showing anteriorly displaced and angulated dens fracture (note NG tube indicating trauma patient). Panel B: 3D CT reconstruction (posterior view) demonstrating the fracture line extending into the C2 body, confirming Type III pattern. Type III fractures have better union rates (over 90%) with immobilization due to larger cancellous bone surface area and preserved blood supply.Credit: Jung MH et al., Korean J Neurotrauma - CC BY 4.0

Complete odontoid fracture case - CT, MRI, and surgical treatment — Three-panel comprehensive case of Type II odontoid fracture from diagnosis to treatment. Panel (a): Sagittal CT with white arrow indicating the fracture at the dens base. Panel (b): Sagittal STIR MRI showing high signal at the fracture site (bone marrow edema) and prevertebral hematoma - common in acute trauma. Panel (c): Lateral X-ray demonstrating healed fracture after anterior odontoid screw fixation. The anterior screw provides direct compression across the fracture site while preserving C1-C2 rotation.Credit: O'Brien WT et al., J Clin Imaging Sci - CC BY 4.0

Clinical Assessment

History

Mechanism: MVA vs fall (age-dependent)
Neck pain: Posterior or suboccipital
Neurological symptoms: Rare (cord has space)
Head injury: Common with high-energy
Previous neck problems: Degenerative disease

Examination

Immobilization: Maintain until cleared
Palpation: C2 spinous process tenderness
Neurology: Full cord and root exam
Vascular: Rarely affected
Other injuries: Full trauma survey

Neurological Injury is RARE

Despite significant displacement, neurological injury is uncommon (less than 10%) because of:

Large spinal canal at C1-C2 (rule of thirds)
Gradual displacement allows cord adaptation
If neuro deficit present, suspect cord injury - urgent decompression may be needed

Red Flags

High-Risk Features

Urgent features requiring immediate attention:

Neurological deficit (rare but urgent)
Rapidly progressive symptoms
Respiratory compromise (high cord injury)
Vascular symptoms (vertebral artery)
Polytrauma with hemodynamic instability

Investigations

Imaging Protocol

First LineCT Cervical Spine

CT is gold standard for diagnosis. Shows fracture type, displacement, angulation, and comminution. Sagittal reconstructions essential for fracture line orientation (Grauer classification).

Assess LigamentsMRI

MRI for transverse ligament and other soft tissue assessment. Required if ADI increased or instability suspected. Also shows cord edema if neurological concerns.

DynamicFlexion-Extension X-rays

Only when fracture healed or stability confirmed. Assess for atlantoaxial instability. Never in acute setting with unstable fracture.

Key Measurements

Radiographic Measurements

Measurement	Normal	Abnormal	Significance
Atlantodental interval (ADI)	Under 3mm (adult)	Over 3mm	TAL rupture
Displacement	0	Over 5mm	Surgical indication
Angulation	0	Over 10°	Surgical indication
Posterior ADI (PADI)	Over 13mm	Under 13mm	Cord compression risk

CT vs MRI

CT: Best for bony detail, fracture classification, surgical planning MRI: Required for TAL integrity, cord assessment, and if CT findings don't explain symptoms

Always get CT first - MRI alone may miss subtle fractures.

Management Algorithm

Collar/Halo Treatment

Type I:

Rigid collar for 6-8 weeks
Excellent union rate (95%+)
Check for occipitocervical instability (alar ligaments)

Type II (selected patients):

Rigid collar (Philadelphia, Miami J) or Halo
Best for: Young, minimal displacement (under 5mm), transverse line
Union rate 50-60% (lower in elderly)
Close follow-up with CT at 6 and 12 weeks

Type III:

Rigid collar for 10-12 weeks (longer due to larger fracture)
Excellent union rate (85%+)
Halo rarely needed

Collar vs Halo

Factor	Collar	Halo
Immobilization	Moderate	Best
Comfort	Better	Poor
Complications	Fewer	Pin infections, loosening
Elderly tolerance	Better	High complication rate
Union rate (Type II)	50-60%	60-70%

Halo in Elderly

Halo vest in elderly (over 65) has high complication rate (40%+) including:

Pin loosening, infection
Respiratory complications
Falls and further injury
Poor tolerance

In elderly with Type II, primary posterior fusion often preferred over Halo.

Surgical Technique

Patient Positioning

Anterior Odontoid Screw:

Supine on radiolucent table
Head extended (chin tuck to expose neck)
Shoulder roll
Arms at sides (or taped down)
C-arm access for AP and lateral

Posterior C1-C2 Fusion:

Prone on Jackson or Mayfield frame
Head neutral or slight flexion
Mayfield pins or Gardner-Wells tongs
Arms tucked
Fluoroscopy or navigation

Proper positioning is essential for safe screw placement and to prevent intraoperative complications.

Complications

Complications Overview

Complication	Incidence	Prevention	Management
Nonunion (Type II)	30-40% (collar)	Patient selection, surgery for high-risk	Posterior fusion
Malunion	Variable	Maintain reduction	Osteotomy if symptomatic
Vertebral artery injury	0.5-2%	Preoperative CT planning	Angiography, observation
Screw malposition	5-10%	Fluoroscopy/navigation	Revision if symptomatic
Dysphagia (anterior)	10-20%	Gentle retraction	Usually temporary
Pseudarthrosis (post fusion)	2-5%	Bone graft, rigid fixation	Revision fusion

Nonunion Management

Managing Type II Nonunion

Symptomatic Type II nonunion:

Confirm nonunion on CT (over 6 months, no bridging bone)
Assess instability with flexion-extension views
Check transverse ligament on MRI

Treatment:

Posterior C1-C2 fusion (Harms technique) is gold standard
Anterior screw rarely works for nonunion (fibrous tissue)
Consider occipitocervical fusion if C1 lateral mass compromised

Postoperative Care

Postoperative Protocol

Week 0-2Immobilization

Collar for all surgical patients. Wound care. DVT prophylaxis. Pain management.

Week 2-6Early Healing

Collar continues. X-rays at 2 and 6 weeks. Gentle ROM when comfortable. Physio for surrounding muscles.

Week 6-12Check CT

CT at 6 weeks to assess fusion/healing. If progressing, continue collar. If not, reassess plan.

Week 12+Wean Collar

If CT shows union/fusion, wean collar. Flexion-extension X-rays to confirm stability. Physio for ROM and strengthening.

Collar Duration by Treatment

Postoperative Collar Protocol

Treatment	Collar Duration	Follow-up
Anterior screw	6-8 weeks	CT at 6 weeks
Harms fusion	6-8 weeks	CT at 6 weeks for fusion
Wiring alone	8-12 weeks	May need Halo if unstable
Collar (non-op)	10-12 weeks (Type II/III)	CT at 6 and 12 weeks

Outcomes and Prognosis

Union Rates

Union Rates by Type and Treatment

Type	Collar	Halo	Surgery
Type I	95%+	N/A	N/A
Type II (young)	60%	70%	90-95%
Type II (elderly)	40-50%	50% (high complications)	90-95%
Type III	85%+	90%+	95%+

Mortality

Conservative (Collar)

Elderly Type II: 15-25% 1-year mortality
Nonunion contributes to mortality
Balance surgical risk vs nonunion morbidity
Function often limited with fibrous union

Surgical

Lower mortality in elderly (some studies)
Early mobilization reduces complications
Perioperative risk must be considered
Better long-term function if fusion achieved

Elderly Decision Making

The elderly Type II dilemma:

High nonunion with collar (40%)
High Halo complication rate (40%)
Surgical risk must be balanced

Recent evidence favors primary posterior fusion in fit elderly patients - better union, earlier mobilization, lower long-term mortality.

Evidence Base

Elderly Type II: Surgery vs Non-Op

Level II

Vaccaro AR et al • J Bone Joint Surg Am (2013)

Key Findings:

Retrospective review of 156 elderly patients with Type II. Surgical treatment associated with higher fusion rate (84% vs 56%) and lower mortality at 1 year (16% vs 28%).

Clinical Implication: Consider primary surgery in fit elderly patients with Type II - better union and survival outcomes.

Anterior Screw: Single vs Double

Level III

Dailey AT et al • Spine (2010)

Key Findings:

Meta-analysis showed no significant difference in fusion rates between single screw (88%) and double screw (91%) anterior fixation.

Clinical Implication: Single screw is technically easier and equally effective - double screw not required.

Halo Complications in Elderly

Level III

Tashjian RZ et al • Spine (2006)

Key Findings:

In patients over 75, Halo vest associated with 42% major complication rate and 26% mortality. Risk increases with age and comorbidities.

Clinical Implication: Avoid Halo in elderly if possible - high complication rate. Consider primary surgical fusion.

Transverse Ligament Integrity and Stability

Level IV

Dickman CA et al • J Neurosurg (1991)

Key Findings:

Type II TAL injuries (ligament disruption or avulsion from C1) heal poorly and result in atlantoaxial instability requiring surgery.

Clinical Implication: MRI assessment of TAL is essential for treatment planning. TAL disruption = surgical stabilization.

Nonunion Risk Factors

Level III

Lennarson PJ et al • Spine (2006)

Key Findings:

Risk factors for Type II nonunion: age over 50, displacement over 4mm, posterior displacement, delay to treatment, smoking.

Clinical Implication: Multiple risk factors = consider primary surgery rather than conservative trial.

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOCritical

Elderly Type II Odontoid Fracture

EXAMINER

"78-year-old male fell at home. CT shows Type II odontoid fracture with 6mm posterior displacement. Neurologically intact. Past history of COPD and diabetes. How do you manage?"

EXCEPTIONAL ANSWER

This is a high-risk Type II odontoid fracture in an elderly patient with multiple poor prognostic factors: age over 65, displacement over 5mm, and comorbidities. My concern is the high nonunion rate (40-50%) with conservative management. I would first assess his overall fitness for surgery, consulting with medical team for COPD and diabetes optimization. Conservative options include rigid collar or Halo, but Halo has 40%+ complication rate in this age group. Given the displacement and age, I would recommend primary posterior C1-C2 fusion using the Harms technique (C1 lateral mass, C2 pedicle screws), which has 90-95% fusion rate. This allows early mobilization and reduces the morbidity of prolonged collar/Halo use. I would need a preoperative CT to assess C2 pedicle dimensions and vertebral artery anatomy. Postoperatively, a collar for 6-8 weeks with CT at 6 weeks to assess fusion.

KEY POINTS TO SCORE

High-risk Type II: age over 65, displacement over 5mm

Halo poorly tolerated in elderly (40% complications)

Primary posterior fusion (Harms) preferred in fit elderly

Need CT for pedicle dimensions and VA anatomy

Collar 6-8 weeks postop, CT at 6 weeks

COMMON TRAPS

✗Recommending Halo in elderly (high complication rate)

✗Collar alone with multiple risk factors

✗Not checking preoperative CT for screw planning

✗Anterior screw in displaced posterior fracture

LIKELY FOLLOW-UPS

"What if C2 pedicle is under 4mm width?"

"How would you manage if he couldn't have surgery?"

"What are risks of posterior fusion in this patient?"

VIVA SCENARIOStandard

Young Type II - Anterior Screw Candidate

EXAMINER

"25-year-old male, MVA, Type II odontoid fracture, 4mm anterior displacement, transverse fracture line on CT. No TAL injury on MRI. Would you consider anterior screw fixation?"

EXCEPTIONAL ANSWER

This patient is an excellent candidate for anterior odontoid screw fixation. The ideal indications are met: acute Type II, transverse fracture line (or anterior oblique), intact transverse ligament, young age, and anterior displacement (not posterior). Before proceeding, I would check for contraindications (BARREL): barrel chest, angulation posteriorly, reverse oblique line, ruptured TAL, elderly/osteoporotic, or late presentation. None appear to be present. The advantage of anterior screw is preservation of C1-C2 rotation (50% of cervical rotation). Technique involves anterior Smith-Robinson approach, C-arm guidance, and placement of a cannulated lag screw across the fracture into the dens apex. Single screw is sufficient (no benefit from double). Postoperatively, collar for 6-8 weeks with CT at 6 weeks to confirm union. Expected fusion rate is 90%+.

KEY POINTS TO SCORE

Ideal anterior screw candidate: acute, transverse line, intact TAL, young

BARREL contraindications must be excluded

Preserves C1-C2 rotation (major advantage)

Single screw as effective as double

90%+ fusion rate

COMMON TRAPS

✗Using anterior screw for reverse oblique fracture

✗Not checking TAL on MRI

✗Posterior fusion in ideal anterior screw candidate (unnecessary loss of rotation)

LIKELY FOLLOW-UPS

"What if the fracture line was posterior oblique?"

"How would you know if screw position is adequate?"

"What to do if nonunion occurs?"

VIVA SCENARIOChallenging

Type II Nonunion

EXAMINER

"65-year-old female was treated with collar for Type II odontoid fracture 4 months ago. CT shows persistent fracture line with no bridging bone. She has ongoing neck pain. How do you assess and manage?"

EXCEPTIONAL ANSWER

This appears to be a Type II nonunion, which is unfortunately common (30-40% rate). I need to confirm the diagnosis and assess stability. My workup would include: new CT to confirm nonunion (no bridging bone, fracture line still visible), MRI to reassess TAL integrity and look for any cord changes, and flexion-extension X-rays (with care) to assess dynamic instability. If she is symptomatic with confirmed nonunion and instability, surgery is indicated. The preferred approach is posterior C1-C2 fusion using the Harms technique. Anterior screw is unlikely to work for nonunion because of fibrous tissue at fracture site preventing compression. I would check C2 pedicle dimensions on CT before surgery. Postoperative collar for 6-8 weeks, CT at 6 weeks for fusion assessment. Expected fusion rate with posterior fusion is 90-95%.

KEY POINTS TO SCORE

30-40% nonunion rate with conservative Type II treatment

CT to confirm nonunion, MRI for TAL

Flexion-extension to assess instability

Posterior C1-C2 fusion is gold standard for nonunion

Anterior screw rarely works for nonunion

COMMON TRAPS

✗Trying anterior screw for nonunion

✗Continuing collar without investigating

✗Not assessing TAL integrity

✗Forgoing surgery in symptomatic patient

LIKELY FOLLOW-UPS

"What if TAL is also ruptured?"

"What if C2 pedicles are too narrow for screws?"

"What fusion rate do you expect?"

MCQ Practice Points

Classification Question

Q: Which odontoid fracture type has the highest nonunion rate?

A: Type II - fracture through the waist/base of the dens. This is at the watershed blood supply zone, leading to 30-40% nonunion with collar treatment. Type I and III have much higher union rates.

Anatomy Question

Q: What percentage of cervical rotation occurs at C1-C2?

A: 50% - This is why anterior odontoid screw fixation (which preserves the joint) is preferred over posterior fusion (which sacrifices rotation) when feasible.

Surgical Question

Q: What is a contraindication to anterior odontoid screw fixation?

A: Reverse oblique (posterior-superior to anterior-inferior) fracture line - The screw would distract rather than compress the fracture. Other contraindications: barrel chest, TAL rupture, elderly with osteoporosis, chronic nonunion.

Imaging Question

Q: What ADI measurement suggests transverse ligament injury in an adult?

A: Greater than 3mm - Normal ADI in adults is under 3mm. In children, up to 5mm may be normal. Increased ADI indicates TAL incompetence and atlantoaxial instability.

Treatment Question

Q: Why is Halo vest avoided in elderly patients with odontoid fractures?

A: High complication rate (40%+) - Including pin loosening, pin infection, respiratory complications, falls, and death. In elderly with Type II, primary posterior C1-C2 fusion often preferred.

Evidence Question

Q: What is the fusion rate difference between single and double anterior odontoid screws?

A: No significant difference - Meta-analysis shows similar fusion rates (~90%). Single screw is technically easier and sufficient.

Australian Context

Referral Patterns

Major trauma center referral for all odontoid fractures
Spinal surgery subspecialist management
MRI access may require transfer to tertiary center
Elderly falls pathway - screen for cervical fractures

Key Points for Australian Practice

Aging population means increasing incidence of elderly odontoid fractures
Early decision-making regarding surgery in elderly reduces morbidity
Access to MRI and spinal surgery varies by region
Telehealth/video consultation available for remote areas

ODONTOID FRACTURES

High-Yield Exam Summary

Classification

•Type I: Tip (rare, stable, collar)
•Type II: Waist (60%, 40% nonunion, controversial)
•Type IIA: Comminuted Type II (posterior fusion)
•Type III: Into C2 body (85% union with collar)

Key Numbers

•ADI over 3mm = TAL injury (adult)
•Displacement over 5mm = surgical factor
•Angulation over 10° = surgical factor
•Age over 65 = increased nonunion risk
•50% cervical rotation at C1-C2

Anterior Screw Contraindications (BARREL)

•B: Barrel chest
•A: Angulation posteriorly
•R: Reverse oblique fracture
•R: Ruptured TAL
•E: Elderly/osteoporotic
•L: Late presentation

Treatment by Type

•Type I: Collar 6-8 weeks
•Type II (young): Collar vs anterior screw
•Type II (elderly): Posterior fusion (Harms)
•Type IIA: Posterior fusion (no screw)
•Type III: Collar 10-12 weeks

Surgical Options

•Anterior screw: Preserves rotation, for ideal Type II
•Harms (C1-C2): Gold standard posterior, sacrifices rotation
•Magerl: Transarticular, higher VA risk
•Wiring: If screws not possible

Type

Pattern

Union Rate (Collar)

Treatment

Type I

Tip avulsion

95%+

Collar 6-8 weeks

Type II (young)

Waist/base

60%

Anterior screw or collar

Type II (elderly)

Waist/base

40-50%

Posterior C1-C2 fusion

Type IIA

Comminuted

Poor

Posterior fusion (no screw)

Type III

Into C2 body

85%+

Collar 10-12 weeks

Region

Source

Implication

Dens tip

Apical arcade

Type I heals well

Dens base (waist)

Watershed zone

Type II high nonunion

C2 body

Vertebral body vessels

Type III good healing

Type

Location

Frequency

Stability

Treatment

Type I

Tip avulsion

Stable

Collar 6-8 weeks

Type II

Base of dens

60%

Unstable

Collar vs surgery

Type IIA

Type II + comminution

Rare

Very unstable

Posterior fusion

Type III

Into C2 body

35%

Often stable

Collar 10-12 weeks

Measurement

Normal

Abnormal

Significance

Atlantodental interval (ADI)

Under 3mm (adult)

Over 3mm

TAL rupture

Displacement

Over 5mm

Surgical indication

Angulation

Over 10°

Surgical indication

Posterior ADI (PADI)

Over 13mm

Under 13mm

Cord compression risk

Factor

Collar

Halo

Immobilization

Moderate

Best

Comfort

Better

Poor

Complications

Fewer

Pin infections, loosening

Elderly tolerance

Better

High complication rate

Union rate (Type II)

50-60%

60-70%

Patient Positioning

Anterior Odontoid Screw:

Supine on radiolucent table
Head extended (chin tuck to expose neck)
Shoulder roll
Arms at sides (or taped down)
C-arm access for AP and lateral

Posterior C1-C2 Fusion:

Prone on Jackson or Mayfield frame
Head neutral or slight flexion
Mayfield pins or Gardner-Wells tongs
Arms tucked
Fluoroscopy or navigation

Proper positioning is essential for safe screw placement and to prevent intraoperative complications.

Complication

Incidence

Prevention

Management

Nonunion (Type II)

30-40% (collar)

Patient selection, surgery for high-risk

Posterior fusion

Malunion

Variable

Maintain reduction

Osteotomy if symptomatic

Vertebral artery injury

0.5-2%

Preoperative CT planning

Angiography, observation

Screw malposition

5-10%

Fluoroscopy/navigation

Revision if symptomatic

Dysphagia (anterior)

10-20%

Gentle retraction

Usually temporary

Pseudarthrosis (post fusion)

2-5%

Bone graft, rigid fixation

Revision fusion

Treatment

Collar Duration

Follow-up

Anterior screw

6-8 weeks

CT at 6 weeks

Harms fusion

6-8 weeks

CT at 6 weeks for fusion

Wiring alone

8-12 weeks

May need Halo if unstable

Collar (non-op)

10-12 weeks (Type II/III)

CT at 6 and 12 weeks

Type

Collar

Halo

Surgery

Type I

95%+

N/A

Type II (young)

60%

70%

90-95%

Type II (elderly)

40-50%

50% (high complications)

90-95%

Type III

85%+

90%+

95%+

Subtype	Fracture Line	Stability	Best Treatment
IIA	Transverse, minimal displacement	More stable	Collar likely OK
IIB	Anterior-superior to posterior-inferior	Unstable	Anterior screw ideal
IIC	Posterior-superior to anterior-inferior (reverse oblique)	Very unstable	Posterior fusion (screw won't work)

Approach	Technique	Indication	Advantage
Anterior Screw	Odontoid screw fixation	Acute Type II (no contraindications)	Preserves C1-C2 rotation
Harms (C1-C2)	C1 lat mass + C2 pedicle/pars screws	Type II elderly, nonunion, IIA	High fusion rate
Magerl (C1-C2)	Transarticular screws	C1-C2 instability	Rigid fixation
C1-C2 Wiring	Brooks/Gallie	If screws not possible	Simple technique

Technique	Fusion Rate	VA Risk	Key Factor
Harms	95-98%	Low	Requires C2 pedicle width over 4mm
Magerl	95-100%	Higher	Need safe trajectory on CT
Wiring	80-85%	Minimal	Less rigid, may need Halo

Subtype	Fracture Line	Stability	Best Treatment
IIA	Transverse, minimal displacement	More stable	Collar likely OK
IIB	Anterior-superior to posterior-inferior	Unstable	Anterior screw ideal
IIC	Posterior-superior to anterior-inferior (reverse oblique)	Very unstable	Posterior fusion (screw won't work)

Approach	Technique	Indication	Advantage
Anterior Screw	Odontoid screw fixation	Acute Type II (no contraindications)	Preserves C1-C2 rotation
Harms (C1-C2)	C1 lat mass + C2 pedicle/pars screws	Type II elderly, nonunion, IIA	High fusion rate
Magerl (C1-C2)	Transarticular screws	C1-C2 instability	Rigid fixation
C1-C2 Wiring	Brooks/Gallie	If screws not possible	Simple technique

Type	Displacement	Mechanism
Oblique anterior	Anterior dens displacement	Hyperflexion
Oblique posterior	Posterior dens displacement	Hyperextension
Horizontal	Minimal displacement	Variable

Odontoid Fractures

Odontoid Fractures

ODONTOID FRACTURES

ANDERSON-D'ALONZO CLASSIFICATION

Critical Must-Knows

Examiner's Pearls

Clinical Imaging

Imaging Gallery

Critical Odontoid Fracture Points

Type II - The Problematic One

Type III - Good Prognosis

Age Matters

Surgical Options

At a Glance: Quick Decision Guide

TIP-WAIST-BODYAnderson-D'Alonzo Types

DOGSType II Surgical Factors

BARRELAnterior Screw Contraindications

ADITransverse Ligament Assessment

Overview and Epidemiology

Mechanism

Associations

Anatomy and Biomechanics

C2 (Axis) Anatomy

Blood Supply

Watershed Blood Supply

Blood Supply by Region

Key Ligaments

Transverse Ligament (TAL)

Alar Ligaments

Rule of Thirds

Classification Systems

Anderson-D'Alonzo Classification (1974)

Anderson-D'Alonzo Classification

Grauer Modification (2005)

Grauer Type II Subclassification

Roy-Camille Classification

Roy-Camille Classification

Classification Imaging Examples

Clinical Assessment

History

Examination

Neurological Injury is RARE

Red Flags

Investigations

Imaging Protocol

Key Measurements

Radiographic Measurements

Management Algorithm

Collar/Halo Treatment

Collar vs Halo

Halo in Elderly

Surgical Options

Surgical Approaches

Anterior Odontoid Screw

Posterior C1-C2 Fusion

Posterior Technique Comparison

Surgical Technique

Patient Positioning

Anterior Odontoid Screw Technique

Surgical Steps

Harms C1-C2 Fusion Technique

Surgical Steps

Vertebral Artery Protection

Complications

Complications Overview

Nonunion Management

Postoperative Care

Postoperative Protocol

Collar Duration by Treatment

Postoperative Collar Protocol

Outcomes and Prognosis

Union Rates

Union Rates by Type and Treatment

Mortality

Conservative (Collar)

Surgical

Evidence Base

Elderly Type II: Surgery vs Non-Op

Anterior Screw: Single vs Double

Halo Complications in Elderly