Type II High Risk | Age Determines Treatment | Collar vs Fusion
ANDERSON-D'ALONZO CLASSIFICATION
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
Clinical 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
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 |
TIP-WAIST-BODYAnderson-D'Alonzo Types
| I | Tip Tip avulsion (alar ligament origin) |
| II | Waist Base of dens - watershed zone (high nonunion) |
| III | Body Extends into C2 body (good blood supply) |
| I | Tip Tip avulsion (alar ligament origin) |
| II | Waist Base of dens - watershed zone (high nonunion) |
| III | Body Extends into C2 body (good blood supply) |
Hook:TIP is rare, WAIST is problematic, BODY heals well!
DOGSType II Surgical Factors
| D | Displacement Greater than 5mm displacement |
| O | Old age Age over 65 years |
| G | Gap/angulation Angulation over 10 degrees |
| S | Smoking/comminution Smoker or Type IIA pattern |
| D | Displacement Greater than 5mm displacement | G | Gap/angulation Angulation over 10 degrees |
| O | Old age Age over 65 years | S | Smoking/comminution Smoker or Type IIA pattern |
Hook:If the patient has DOGS factors, consider surgery!
BARRELAnterior Screw Contraindications
| B | Barrel chest Obese or kyphotic - cannot get trajectory |
| A | Angulation Fracture angulated posteriorly |
| R | Reverse oblique Posterior-superior to anterior-inferior line |
| R | Ruptured TAL Transverse ligament incompetent |
| E | Elderly osteoporotic Poor screw purchase |
| L | Late presentation Chronic nonunion (over 6 weeks) |
| B | Barrel chest Obese or kyphotic - cannot get trajectory | R | Reverse oblique Posterior-superior to anterior-inferior line | E | Elderly osteoporotic Poor screw purchase |
| A | Angulation Fracture angulated posteriorly | R | Ruptured TAL Transverse ligament incompetent | L | Late presentation Chronic nonunion (over 6 weeks) |
Hook:BARREL chest or reverse oblique = no anterior screw!
ADITransverse Ligament Assessment
| A | Atlantodental interval Distance from C1 anterior arch to dens |
| D | Distance measure Under 3mm adult, under 5mm child normal |
| I | Instability Over 3mm suggests TAL rupture |
| A | Atlantodental interval Distance from C1 anterior arch to dens |
| D | Distance measure Under 3mm adult, under 5mm child normal |
| I | Instability Over 3mm suggests TAL rupture |
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
Differential Diagnosis
The radiographic appearance of the dens can be deceptive. Several entities mimic or coexist with an acute odontoid fracture and must be actively distinguished, because the management differs substantially.
Differentiating Odontoid Fracture from Mimics
| Entity | Distinguishing Feature | Clue on Imaging | Pitfall |
|---|---|---|---|
| Acute Type II fracture | Sharp lucent line at dens base, soft-tissue swelling | Cortical disruption, prevertebral haematoma, marrow oedema on STIR | Best diagnostic standard |
| Os odontoideum | Smooth corticated ossicle, hypertrophied anterior C1 arch | Rounded margins, no oedema, often wide gap | Mistaken for acute nonunion - it is chronic |
| Persistent ossiculum terminale (Bergmann) | Small ossicle above a normal dens body | Above the level of the transverse ligament, stable | Usually incidental, not unstable |
| Mach effect / overlap artefact | Apparent lucency from overlapping arches or teeth | Disappears on a true open-mouth or CT view | False-positive fracture call on plain film |
| Atlantoaxial rotatory subluxation | Torticollis, asymmetric dens-lateral mass spacing | Dynamic CT shows fixed rotation | Coexists with trauma in children |
| Pathological / metastatic lesion | Lytic destruction, age-atypical pain | Bone destruction without clear trauma, marrow replacement on MRI | Low-energy fracture can be the first sign of malignancy |
Os Odontoideum is the Classic Trap
An os odontoideum has smooth corticated margins and no marrow oedema, indicating chronicity, whereas an acute fracture has sharp irregular edges and prevertebral soft-tissue swelling. Treating a chronic, well-compensated os odontoideum as an acute fracture - or vice versa - is a common examination error. Dynamic flexion-extension imaging (when safe) clarifies whether it is stable.
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
CT is gold standard for diagnosis. Shows fracture type, displacement, angulation, and comminution. Sagittal reconstructions essential for fracture line orientation (Grauer classification).
MRI for transverse ligament and other soft tissue assessment. Required if ADI increased or instability suspected. Also shows cord edema if neurological concerns.
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
Collar for all surgical patients. Wound care. DVT prophylaxis. Pain management.
Collar continues. X-rays at 2 and 6 weeks. Gentle ROM when comfortable. Physio for surrounding muscles.
CT at 6 weeks to assess fusion/healing. If progressing, continue collar. If not, reassess plan.
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
AOSpine GOF Mortality Study: Surgery vs Non-Op in the Elderly
- Retrospective multicentre cohort of 322 patients aged 65 or older with type II odontoid fracture (165 operative, 157 nonoperative). Nonoperative treatment carried higher 30-day mortality (adjusted HR 3.00, 95% CI 1.51-5.94) with a trend toward higher long-term mortality (HR 1.35, 95% CI 0.97-1.89). Overall 30-day mortality 14%, maximal follow-up mortality 44%.
AOSpine GOF Treatment Predictors
- Prospective multicentre cohort of 159 patients aged 65 or older with radiographically confirmed type II odontoid fracture. Independent predictors of treatment failure were older age (OR 1.08 per year), initial nonsurgical treatment (OR 3.09), male sex (OR 4.33) and baseline neurological comorbidity (OR 4.13). 12-month mortality 18.2%.
Nonunion Outcomes With Nonoperative Treatment
- Subgroup of the AOSpine GOF study (58 nonoperatively treated elderly type II fractures). 30% developed primary or secondary nonunion and 22% required delayed surgery, yet NDI and SF-36 outcomes did not differ by union status at 12 months.
Anterior Odontoid Screw Fixation (Landmark Series)
- 147 consecutive patients undergoing direct anterior odontoid screw fixation. Fusion rate 88% for recent fractures (6 months or less) but only 25% for remote fractures (18 months or more). Fusion was independent of patient age, sex and number of screws (one vs two); horizontal and posterior-oblique fracture lines fused better than anterior-oblique.
Age as a Risk Factor for Halo Failure
- Case-control study of 33 isolated type II dens fractures treated by halo immobilisation. Age over 50 years was a highly significant risk factor for nonunion (P = 0.002), with a 21-fold higher risk of halo failure. Sex, displacement amount and direction were not significant.
Transverse Atlantal Ligament Injury Classification
- Analysis of 39 transverse atlantal ligament injuries defined the Dickman classification: Type I (midsubstance disruption, n=16) cannot heal without internal fixation and needs early surgery; Type II (bony avulsion from the C1 tubercle, n=23) is initially treated in a rigid orthosis with a 74% success rate.
Harms Technique: Posterior C1-C2 Polyaxial Screw-Rod Fixation
- Original description of C1 lateral mass plus C2 pars/pedicle polyaxial screws connected by rods in 37 patients. Solid fusion was achieved in all patients with no vascular or neurological injury, and the technique allows intraoperative reduction without sacrificing the joint surfaces if temporary.
Exam Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
Elderly Type II Odontoid Fracture
"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?"
Young Type II - Anterior Screw Candidate
"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?"
Type II Nonunion
"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?"
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.
Guidelines, Registries & Global Practice
Global Epidemiology
- Most common cervical fracture in patients over 70 worldwide
- Incidence rising with ageing populations across high-income countries
- Type II predominates (about 60% of dens fractures)
- Low-energy falls in the elderly now outnumber high-energy injuries
- Up to 80% of geriatric cases are osteoporotic-bone fractures
Referral and Pathways
- Major trauma / spinal unit referral for all odontoid fractures
- CT first, MRI for ligament and cord assessment
- Elderly falls pathways should actively screen the C-spine
- Shared decision-making essential in frail elderly patients
Side-by-Side Society Guidance
Major Guideline Positions
| Body | Emphasis | Type II Elderly Stance |
|---|---|---|
| AANS/CNS (US) | Evidence-based management of dens fractures | Surgery recommended for displacement over 5mm or age over 50; halo or surgery both options |
| AO Spine / AO Foundation | Upper cervical injury classification, operative algorithms | Favours operative stabilisation in unstable type II, individualised in frail elderly |
| BOA / NICE (UK) | Spinal injury assessment and major trauma pathways | Multidisciplinary decision; nonoperative acceptable if surgery high-risk |
| EFORT / European consensus | Geriatric trauma, fragility-fracture care | Early mobilisation prioritised; stable nonunion an accepted goal if unfit |
Registry and Resource-Setting Notes
- No dedicated dens-fracture implant registry exists; outcome data derive from prospective cohorts such as the AOSpine North America Geriatric Odontoid Fracture (GOF) study rather than arthroplasty-style registries.
- High-resource settings: ready CT/MRI access, navigation or fluoroscopy for screw placement, and early posterior C1-C2 fixation in fit elderly.
- Limited-resource settings: reliance on plain radiographs and rigid collars, restricted MRI for ligament assessment, and a lower threshold for nonoperative management - making accurate stability assessment and falls prevention even more important.
Controversies and Areas of Uncertainty
Odontoid fracture management is one of the most genuinely contested areas in spinal trauma. A strong viva candidate can articulate where the evidence is soft and argue both sides.
Operative vs Nonoperative in the Elderly
The AOSpine GOF data suggest a 30-day survival advantage and higher fusion with surgery, but selection bias is unavoidable - fitter patients are offered surgery. No randomised trial has settled the question, and the competing systematic review found stable nonunion is an acceptable goal with under 5% needing revision.
Is Bony Union Even the Goal?
In frail elderly patients, stable fibrous nonunion may give equivalent function and pain to bony union. Chasing radiographic union with high-risk surgery or prolonged halo may add morbidity without functional benefit.
Anterior Screw vs Posterior Fusion
Anterior screw preserves rotation but fails in osteoporotic bone, reverse-oblique lines and chronic fractures. Posterior C1-C2 fusion is more reliable but sacrifices rotation. The trade-off (motion vs union reliability) is unresolved for the borderline young-elderly patient.
Collar vs Halo
Halo offers marginally better immobilisation but with high complication rates in the elderly. Many units have largely abandoned the halo in older patients, yet high-quality comparative data remain limited.
How to Frame Controversy in a Viva
State the principle first ("treatment is individualised because the evidence is observational, not randomised"), then give the balance (survival/fusion advantage of surgery vs selection bias and the acceptability of stable nonunion), and finish with a patient-specific plan. Examiners reward candidates who acknowledge uncertainty rather than dogmatically insisting on one answer.
ODONTOID FRACTURES
Clinical 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