Unilateral vs Bilateral | MRI Before Reduction Debate | Urgent Decompression for SCI
- Bilateral dislocation = translation more than 50% = complete SCI in 50%
- Unilateral dislocation = translation approximately 25% = root injury common
- MRI before reduction if neurologically intact and available within 4 hours
- Closed reduction safe with prior MRI or awake monitored reduction
- Posterior approach preferred for reduction, anterior for discectomy if needed
- “25% translation suggests unilateral, 50%+ suggests bilateral
- “Awake closed reduction allows real-time neurological monitoring
- “Disc herniation in 40% - this is the MRI debate crux
- “Posterior approach allows direct facet manipulation and reduction
Clinical Imaging
Imaging Atlas
25% translation = unilateral facet dislocation. More than 50% translation = bilateral. On lateral X-ray, count vertebral body widths of displacement.
Disc herniation in 40% of facet dislocations. Pre-reduction MRI preferred if neurologically intact and available quickly. If incomplete SCI, don't delay reduction for MRI.
Awake closed reduction with traction is safe with real-time monitoring. Open posterior reduction for failed closed or when MRI shows disc. Never blind closed reduction without imaging or monitoring.
Incomplete SCI = urgent reduction within 24 hours. Complete SCI = less urgent but still reduce. Root injury = painful, distressing but allows time for workup.
| Scenario | MRI Needed? | Reduction Method | Key Pearl |
|---|---|---|---|
| Bilateral + complete SCI (ASIA A) | Not mandatory before reduction | Closed or open reduction | Prognosis already poor - prioritize reduction |
| Bilateral + incomplete SCI | If delays less than 4h, otherwise proceed | Urgent reduction (closed or open) | STASCIS: less than 24h decompression improves outcomes |
| Bilateral + neurologically intact | Yes - before reduction | Close monitoring, may need anterior first | If disc herniation, anterior discectomy first |
| Unilateral + root injury | Yes - allows full workup | Posterior open or closed awake | Not as urgent - allows complete planning |
| Unilateral + intact | Yes - before reduction | Elective reduction | Disc in 40% - MRI valuable |
25-50Translation Rule
Hook:25% is UNI-lateral (one facet), 50% is BI-lateral (two facets) - divide by 2!
DISCMRI Decision
Hook:DISC reminds you why MRI matters - 40% have disc herniation that affects reduction strategy!
ACOReduction Methods
Hook:ACO - Awake Closed is OK, but need Open if it fails!
FLEXPosterior Reduction Steps
Hook:FLEX the neck to unlock, then extend to reduce - counterintuitive but correct!
Overview and Epidemiology
Cervical facet dislocations represent a spectrum of high-energy injuries ranging from unilateral perched facets to bilateral locked facets with complete spinal cord injury.
Types of facet dislocation:
- Unilateral perched facet: Facet tip-to-tip, not fully dislocated
- Unilateral locked facet: Complete dislocation, facet jumped
- Bilateral perched facets: Both facets subluxed but not locked
- Bilateral locked facets: Severe instability, high SCI rate
Mechanism:
- Flexion-distraction is the primary mechanism
- Rotational component produces unilateral injury
- Pure flexion-distraction produces bilateral injury
- Associated with high-energy trauma (MVA, diving)
On lateral X-ray: 25% anterior translation of vertebral body suggests unilateral dislocation. More than 50% translation indicates bilateral dislocation. This is a quick screening tool before CT.
Anatomy and Biomechanics
Facet joint anatomy:
- Orientation approximately 45 degrees to horizontal
- Superior articular process faces posterolaterally
- Inferior articular process faces anteromedially
- Joint capsule is the primary restraint to flexion
Why facets dislocate:
- Flexion force overpowers facet capsule
- Superior facets slide superiorly and anteriorly
- Once past inferior facet, they become "locked"
- Capsule rupture allows abnormal translation
40% of facet dislocations have associated disc herniation. This is why pre-reduction MRI is important in neurologically intact patients - reduction may push herniated disc into the spinal cord.
Stability assessment:
- Facet dislocations are 3-column injuries
- Posterior tension band is destroyed
- DLC is always disrupted
- These are unstable injuries requiring surgical stabilization
| Feature | Unilateral | Bilateral |
|---|---|---|
| Translation | Approximately 25% | More than 50% |
| Rotation | Present | Minimal |
| Cord injury rate | 30% | 50-75% |
| Root injury | Common (same level) | Less common |
| Reduction difficulty | Moderate | High |
| Mechanism | Flexion + rotation | Pure flexion-distraction |
Neurological considerations:
- Unilateral: Root compression at level of dislocation (e.g., C6-7 dislocation = C7 root)
- Bilateral: Cord compression - complete SCI in up to 50%
- Incomplete SCI has better prognosis than complete
- Root injury generally recovers well
Classification
Practical Classification
| Type | Definition | Key Features |
|---|---|---|
| Unilateral perched | Facet tip-to-tip | Rotation, approximately 25% translation |
| Unilateral locked | Facet jumped completely | More rotation, root symptoms common |
| Bilateral perched | Both facets subluxed | Less than 50% translation, unstable |
| Bilateral locked | Both facets jumped | More than 50% translation, high SCI rate |
| With fracture | Facet fracture-dislocation | May affect reduction strategy |
Perched: Facet tips are sitting on each other (tip-to-tip). Locked: Superior facet has jumped past and is sitting anterior to inferior facet.
Perched may reduce more easily; locked often requires open reduction.
Clinical Assessment
History:
- Mechanism (MVA, diving, fall)
- Any transient neurological symptoms
- Neck pain and location
- Current neurological symptoms
Physical examination:
- Head position: May be rotated toward side of unilateral dislocation
- Neck: Swelling, bruising, deformity
- Torticollis: Classic for unilateral facet dislocation
- Complete spine: Log-roll examination
- Motor: Individual myotome testing
- Sensory: Dermatomal testing and perianal
- Reflexes: Deep tendon reflexes, Babinski
- Sacral sparing: Critical for prognosis (ASIA B vs A)
ASIA grading is essential:
- A: Complete (no motor/sensory below level)
- B: Sensory incomplete (sensory but no motor)
- C: Motor incomplete (motor less than half muscles grade 3+)
- D: Motor incomplete (at least half muscles grade 3+)
- E: Normal
Complete examination with sacral sparing check differentiates complete from sensory incomplete.
Specific findings in facet dislocation:
- Unilateral: Torticollis (chin rotated away from side of dislocation), C-spine tenderness, possible radiculopathy
- Bilateral: Severe pain, often holds head with hands, quadriplegia or quadriparesis if SCI
Differential Diagnosis
The painful, deformed, post-traumatic cervical spine has several mimics. Distinguishing them changes urgency and approach.
| Diagnosis | Distinguishing Features | Key Discriminator |
|---|---|---|
| Unilateral facet dislocation | Approx 25% translation, rotation, torticollis, same-level radiculopathy | Rotation with translation under 50% |
| Bilateral facet dislocation | More than 50% translation, high SCI rate, severe instability | Translation more than 50% without rotation |
| Facet fracture-subluxation | Fractured superior/inferior articular process, may be reducible without lock | Fracture line on CT through the facet |
| Hyperflexion sprain (DLC injury, no lock) | Widened interspinous distance, focal kyphosis, no jumped facet | Facets reduced/perched, ligamentous only |
| Burst/teardrop fracture | Anterior column comminution, retropulsion, axial-flexion mechanism | Vertebral body fracture dominates, facets congruent |
| Atlantoaxial rotatory subluxation | Upper cervical, fixed torticollis, paediatric/atraumatic | C1-C2 level, abnormal odontoid relationship |
| Ankylosing spondylitis fracture | Fused spine, trivial trauma, highly unstable transverse fracture | Bamboo spine, fracture through ankylosed segment |
Investigations
Imaging Algorithm
First-line imaging. Shows facet relationship (perched, locked), associated fractures, translation percentage. 3D reconstructions helpful for surgical planning.
Critical for disc assessment. Shows disc herniation (40% of cases), cord contusion, ligamentous injury. Influences reduction strategy.
Vertebral artery assessment. Injury in 20-40% of facet dislocations. Particularly important C1-C3.
Confirm reduction. Assess for iatrogenic fracture, hardware position if immediate fixation.
CT interpretation:
Key findings to document:
- Facet relationship: Normal, perched, locked
- Translation: Percentage of vertebral body width
- Rotation: Asymmetry of spinous processes, facets
- Associated fractures: Facet, vertebral body, lamina
- Canal compromise: Percentage occlusion
On CT axial images, the naked facet sign shows an "empty" facet joint with the superior articular process displaced anteriorly. This confirms jumped facet.
MRI decision tree:
| Neurological Status | Get MRI Before Reduction? | Rationale |
|---|---|---|
| Neurologically intact | Yes (if less than 4h delay) | Disc in 40%, affects strategy |
| Root injury only | Yes (if less than 4h delay) | Allows complete planning |
| Incomplete SCI | If delay less than 4h, otherwise proceed | Time critical for outcomes |
| Complete SCI (ASIA A) | Not mandatory | Prognosis already poor, prioritize reduction |
| Unconscious/cannot examine | Yes | Cannot do awake reduction anyway |
Management
Pre-Reduction MRI: The Controversy
The question: Should MRI be obtained before attempting closed reduction?
Arguments FOR pre-reduction MRI:
- 40% have disc herniation that may worsen with reduction
- Disc may be pushed into cord during reduction
- Allows complete surgical planning
- Identifies cord injury for prognostication
Arguments AGAINST waiting for MRI:
- Delays reduction (time is cord)
- STASCIS shows early decompression improves outcomes
- Awake reduction with monitoring is safe
- Closed reduction under anesthesia with MRI already done is safe
Practical approach:
- Neurologically intact: MRI before reduction (if available within 4 hours)
- Incomplete SCI: MRI if doesn't delay reduction more than 4 hours
- Complete SCI: MRI not mandatory before reduction
- If no MRI available: Awake closed reduction with continuous neurological monitoring is acceptable
If MRI shows disc herniation: Many surgeons prefer anterior discectomy first before reduction. This removes the disc that could be pushed into the canal, followed by posterior reduction and fusion (or anterior-posterior approach).
Surgical Technique
- Neurological worsening: 1-5% (higher with reduction)
- Failure of reduction: May need different approach
- Hardware failure: 5-10%
- Non-union: 5%
- Adjacent segment disease: Long-term risk
- Need for second approach: If instability persists
- Neuromonitoring: SSEPs and MEPs essential
- Mayfield and positioning: Prone setup
- Lateral mass screws: Appropriate sizes
- Reduction instruments: Cobb elevator, Penfield, lamina spreader
- Fluoroscopy: Confirm reduction and hardware
- Anterior set backup: If combined approach needed
Complications
| Complication | Incidence | Prevention/Management |
|---|---|---|
| Neurological worsening | 1-5% | Neuromonitoring, careful reduction, pre-reduction MRI |
| Failed reduction | 5-10% | May need open or combined approach |
| Hardware failure | 5-10% | Adequate fixation length, consider combined approach |
| Non-union | 5-10% | Bone graft, smoking cessation, stable fixation |
| Vertebral artery injury | Less than 1% | Pre-op CTA, careful screw placement |
| Adjacent segment disease | 10-20% at 10 years | Limit fusion levels |
| Loss of reduction | 5% | Adequate fixation, compliance with collar |
Neurological worsening:
- Most feared complication
- Risk factors: disc herniation not addressed, forced reduction, over-distraction
- Prevention: pre-reduction MRI, neuromonitoring, gentle technique
Failed closed reduction:
- Occurs in 10-30% of closed attempts
- Usually indicates severely locked facets or interposed bone/disc
- Proceed to open reduction
Postoperative Care
Rehabilitation Timeline
- ICU if SCI
- Neurological checks every 4 hours
- Drain if used (remove 24-48h)
- DVT prophylaxis
- Mobilize with collar
- X-ray to confirm alignment
- Begin SCI rehabilitation if applicable
- Wound check
- Continue collar
- Progressive mobilization
- X-ray at 6 weeks
- Physio for conditioning
- CT to assess fusion
- Consider collar removal if fused
- Increase activity
- Return to work planning
Collar protocol:
- Hard collar (Miami J or similar) for 6-12 weeks post-surgery
- Earlier weaning if solid fusion evident and stable construct
- Longer if osteoporosis or concern about fixation
Outcomes and Prognosis
Neurological outcomes:
- Complete SCI (ASIA A): Poor neurological prognosis, focus on stability and rehabilitation
- Incomplete SCI: Significant potential for improvement, especially with early decompression
- Root injury: Generally good recovery over 6-12 months
Sacral sparing (any perianal sensation or voluntary anal contraction) converts ASIA A to B and dramatically improves prognosis. Always check carefully.
Factors affecting outcome:
- Initial neurological status (ASIA grade)
- Time to reduction/decompression
- Quality of reduction
- Associated injuries (head, chest)
- Patient factors (age, comorbidities)
Evidence Base
STASCIS: Surgical Timing in Acute Spinal Cord Injury
- Prospective multicentre cohort of 313 adults with acute cervical SCI (182 early, 131 late)
- 19.8% of early-surgery patients improved ≥2 AIS grades at 6 months vs 8.8% in the late group (OR 2.57, 95% CI 1.11–5.97)
- Adjusted odds of ≥2 grade AIS improvement 2.8x higher with early surgery
- Complication rates similar (24.2% early vs 30.5% late, p=0.21) - early decompression is safe and feasible
SLIC: Subaxial Cervical Spine Injury Classification and Severity Scale
- Scores three domains: injury morphology, disco-ligamentous complex (DLC), and neurological status
- Distraction morphology = 3 points; rotation/translation = 4 points; DLC disrupted = 2 points
- Facet dislocation is a distraction/translation injury that almost always scores in the operative range
- Score of 4 or more favours surgery; 3 or less favours non-operative care; raters agreed with the algorithm in 93.3% of cases
Exam Viva Scenarios
Practise clinical reasoning and management decisions out loud
“A 32-year-old man presents after a diving accident. He has bilateral C5-6 locked facet dislocation on CT with ASIA C incomplete quadriplegia. How do you manage this patient?”
“A 45-year-old woman has a unilateral C6-7 locked facet dislocation after a car accident. She has C7 radiculopathy with weakness of her triceps and finger extensors. She is neurologically otherwise intact. Walk me through your management.”
“You have attempted awake closed reduction for bilateral C5-6 locked facets. Despite 70 lbs of traction, the facets remain locked. The patient has incomplete SCI (ASIA C). What do you do now?”
MCQ Practice Points
Q: On lateral cervical X-ray, what percentage translation suggests bilateral facet dislocation? A: More than 50% translation indicates bilateral dislocation. Approximately 25% suggests unilateral.
Q: What percentage of facet dislocations have associated disc herniation on MRI? A: 40% - this is the main argument for pre-reduction MRI in neurologically intact patients.
Q: What is the maximum traction weight for a C5-6 facet dislocation? A: Approximately 10 lbs per level above injury. For C5-6: 5 levels x 10 = 50 lbs (some allow up to 70-80 briefly).
Q: When reducing a locked facet operatively, should you flex or extend the neck? A: Flex first to unlock the facets (opens the joint), then extend to complete reduction.
Q: A C6-7 facet dislocation will compress which nerve root? A: C7 root - cervical roots exit above their numbered vertebra, so the C7 root exits at C6-7.
Q: What differentiates ASIA A from ASIA B? A: Sacral sparing - any perianal sensation or voluntary anal contraction converts complete (A) to sensory incomplete (B).
Guidelines, Registries & Global Practice
Global epidemiology. Cervical facet dislocations are high-energy injuries of the subaxial spine, most often at C5-6 and C6-7, typically from road traffic collisions, falls and diving. They sit within the broader burden of traumatic spinal cord injury: in the STASCIS cohort the majority of subaxial dislocation/translation injuries presented with complete or incomplete cord injury, and early decompression (less than 24h) more than doubled the odds of a ≥2-grade AIS improvement at 6 months (Fehlings 2012, PMID 22384132). Bilateral locked facets carry the highest cord-injury risk; unilateral injuries more often produce a same-level radiculopathy.
| Body / Region | Recommendation | Evidence Level |
|---|---|---|
| AOSpine / AANS-CNS (international) | Offer decompression ≤24h for adult acute SCI regardless of level; consider early surgery in central cord syndrome (Fehlings 2017, PMID 29164024) | GRADE: conditional, low quality |
| AANS/CNS (USA) | Early closed reduction recommended for awake, examinable patients with cervical fracture-dislocation; reduction safe without prior MRI in this group (Grant 1999, PMID 10413120) | Level III option |
| Spine Trauma Study Group (SLIC) | Subaxial injuries scoring 4 or more should be considered operative; facet dislocations score in the operative range (Vaccaro 2007, PMID 17906580) | Validated classification |
| NICE / BOA (UK) | Major trauma networks: immobilise, transfer to a spinal-capable centre, MRI before reduction in the neurologically intact, urgent surgery for evolving deficit | Consensus / guideline |
Practice variation. The pre-reduction MRI question is the main genuine divergence. North American practice (AANS/CNS, supported by Grant 1999) favours immediate awake closed reduction in alert, examinable patients with significant deficit, accepting that reduction can displace disc material but rarely worsens neurology. Many UK/European units prefer MRI before reduction in the neurologically intact, citing the rise in disc herniation after reduction (Vaccaro 1999, PMID 10382247). The shared ground: in incomplete SCI, do not let MRI delay decompression beyond the ≤24h window (Badhiwala 2021, PMID 33357514). In limited-resource settings without rapid MRI or neuromonitoring, awake closed traction reduction with serial neurological checks remains the pragmatic standard.
Registry note. There is no implant joint registry for cervical trauma equivalent to the arthroplasty registries (NJR, AJRR, AOANJRR); evidence is driven by prospective cohorts and pooled analyses such as STASCIS and the Badhiwala 2021 individual-patient pooled analysis rather than registry data.
- Major trauma centres with 24/7 spinal surgery and neuromonitoring
- Early transfer of SCI to a specialised spinal unit
- Coordinated pre-hospital retrieval and spinal immobilisation
- MAP support (target 85-90 mmHg) to limit secondary cord injury
- Pre-reduction MRI in the intact: routine (UK/Europe) vs selective (North America)
- Awake closed reduction availability depends on MRI/monitoring access
- ≤24h decompression target is universal for incomplete SCI
- Anterior-first when disc herniation present is widely accepted
Critical documentation:
- Baseline neurological exam before any intervention
- ASIA grade at presentation
- Imaging interpretation and timing of MRI
- Decision-making rationale for reduction approach
- Informed consent including neurological worsening risk
Common issues:
- Failure to document baseline neurology
- Delayed recognition of facet dislocation
- Neurological deterioration during reduction without documented monitoring
Classification
- Unilateral: approximately 25% translation, single locked facet
- Bilateral: more than 50% translation, both facets locked
- Perched: tip-to-tip, may reduce easier
- Locked: jumped completely, often needs open reduction
MRI Decision
- 40% have disc herniation - key reason for MRI
- Neurologically intact: MRI before reduction (if less than 4h delay)
- Incomplete SCI: MRI if doesn't delay more than 4h
- Complete SCI: don't delay reduction for MRI
Reduction Methods
- Awake closed: safe with continuous neuro monitoring
- Open posterior: direct facet access, preferred for failed closed
- Weight max: approximately 10 lbs per level above injury
- Flex to unlock, extend to reduce
Approach Selection
- Posterior: direct facet reduction, lateral mass screws
- Anterior: if disc herniation needs removal first
- Combined: disc herniation + facet dislocation
- Posterior first if facet dislocation + disc (then anterior)
Complications
- Neurological worsening: 1-5%
- Failed reduction: 10-30% of closed attempts
- Hardware failure: 5-10%
- Always use neuromonitoring during reduction