# Cervical Facet Dislocation

> Cervical facet dislocation for NEET-PG Orthopaedics: unilateral and bilateral locking, Allen-Ferguson mechanisms, MRI before reduction and tong traction.

- Canonical URL: https://prepelephant.com/topics/neet-pg/orthopaedics/cervical-facet-dislocation
- Exam / course: NEET-PG · Subject: Orthopaedics
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Rockwood and Green's Fractures in Adults; Campbell's Operative Orthopaedics; Maheshwari Essential Orthopaedics
- How to cite: "Cervical Facet Dislocation", PrepElephant, https://prepelephant.com/topics/neet-pg/orthopaedics/cervical-facet-dislocation

## Direct answer

A cervical facet dislocation is a flexion-type injury in which the inferior articular process of one vertebra locks onto the facet below, most often at C5 on C6. Unilateral locking displaces the body by about a quarter of its diameter, while bilateral locking produces about half displacement and a higher cord risk. MRI is advised before closed reduction with skull tongs wherever it will not delay reduction, because a disc can be pushed into the canal.

## What you must remember

- **Mechanism:** unilateral locking is flexion with rotation (distractive flexion stage 2 in Allen-Ferguson terms), and bilateral locking is distractive flexion stage 3, with the articular process driven over the facet below.
- **Unilateral locking:** about 25 percent anterolisthesis on the lateral film, often with a rotated posture; neurology is usually preserved, though incomplete injury is possible.
- **Bilateral locking:** about 50 percent displacement, a complete instability with greater cord risk, and the lateral film shows loss of normal alignment.
- **Allen-Ferguson:** a mechanism-based system (compressive flexion, vertical compression, distractive flexion, lateral flexion, compressive extension and distractive extension) that predicts the injury pattern and stability.
- **Imaging:** a lateral radiograph shows alignment, CT defines facet and fracture anatomy, and MRI before reduction excludes disc herniation, although obtunded patients need it most and an awake patient with a deficit should not have reduction delayed.
- **Reduction:** closed reduction with Gardner-Wells or Crutchfield tongs and incremental weight, under neurological monitoring, often succeeds in an awake patient who can cooperate.
- **Definitive care:** posterior fusion after reduction is usual, while anterior discectomy and fusion suits a herniated disc or a failed closed reduction.

## Unilateral and bilateral locking side by side

Both injuries share a mechanism, but the degree of displacement and ligament damage separates them. The table gives the working differences a candidate should carry into an exam answer.

| Feature | Unilateral | Bilateral |
|---|---|---|
| Displacement on lateral film | About 25 percent | About 50 percent |
| Ligament injury | Partial, one facet | Complete, both facets |
| Cord injury risk | Lower | Higher |
| Reduction | Closed, under monitoring | Closed, after MRI and monitoring |
| Definitive care | Posterior fusion usually | Posterior fusion after reduction |

The more complete the ligament disruption, the less predictable a closed reduction becomes, so a bilateral injury with changing neurology is treated as an emergency. Reduction is staged, with neurological checks and repeat imaging at each increment of traction.

In an exam answer, state the displacement figure and the cord risk together, because those two facts drive both the reduction method and the choice of fixation.

## Where the exam tries to catch you

Facet injuries reward careful sequencing more than a memorised drug or device.

- **Trap:** applying traction in an obtunded patient or one needing surgery without an MRI — **Correct:** image the disc first, because a fragment can be pushed into the canal; an awake, cooperative patient may be reduced early with serial neurological checks.
- **Trap:** treating unilateral and bilateral dislocation as the same injury — **Correct:** unilateral is about 25 percent displacement with partial ligament damage, while bilateral is about 50 percent with complete disruption.
- **Trap:** choosing an anterior approach for every dislocation — **Correct:** posterior fusion is usual, with the anterior route reserved for disc herniation or failed reduction.

## Frequently asked questions

### What is the typical level of a cervical facet dislocation?

The C5 on C6 level is the most common site, reflecting the mid-cervical flexion mechanism. Lower cervical levels, including C6 on C7, are the next most frequent.

### What is the Allen-Ferguson classification used for?

The Allen-Ferguson system classifies subaxial cervical injuries by mechanism, such as distractive flexion (facet dislocation) or compressive extension, which then predicts the pattern of bony and ligamentous damage. Knowing the mechanism helps anticipate instability and the risks of reduction.

### Why is MRI done before closed reduction of a facet dislocation?

MRI shows a herniated disc or ligamentous injury that traction could displace into the spinal canal. Scanning first lowers the risk of worsening the cord injury, and it is essential in obtunded patients, though practice differs for awake patients.

### How is a facet dislocation reduced in a conscious patient?

Gradual skull tong traction, using Gardner-Wells or Crutchfield tongs with incrementally added weight, is applied while neurological checks are repeated at each step. Reduction is often achieved in awake patients who can report symptoms as they occur.

### Which surgery stabilises a reduced cervical facet dislocation?

Posterior cervical fusion with instrumentation is the usual definitive stabilisation. Anterior discectomy and fusion is chosen when a disc herniation prevents safe reduction or the anterior column needs decompression.