Atlantoaxial Rotatory Subluxation

The atlas rotates on the axis and then fails to return to neutral. Proposed mechanisms include the lateral mass capsule and synovium becoming caught or swollen, the facet articulation effectively "over-riding" or jamming, and muscle splinting that maintains the abnormal position. Once locked, the joint behaves like a fixed deformity rather than a transient spasm.

In Grisel syndrome, infection or inflammation in the pharynx, retropharyngeal space, or after ENT surgery spreads to the upper cervical region. The classic explanation is drainage via the pharyngovertebral (periodontoidal) venous plexus, causing local hyperaemia, ligamentous laxity and decalcification around the C1-C2 joint, which lets the atlas slip and lock. This is why Grisel cases carry the worst prognosis - the soft tissues are abnormally lax and diagnosis is often delayed.

Compared with adults, children have more horizontal (less locked) facet joints, greater ligamentous laxity, a relatively large head, and incompletely ossified bony stabilisers. These features allow a larger physiological range of C1-C2 rotation and make the joint easier to lock with minor force or inflammation.

Fielding-Hawkins classification - the traditional, anatomy/displacement-based system, graded on the degree of anterior atlantodental shift:

Pang classification - based on 3-position dynamic CT motion analysis, grading how "stuck" the C1-C2 joint is rather than just the static shift:

Chronicity grading (Pang) - a crucial prognostic axis independent of type:

The combination matters most: the worst subgroup is chronic Type I, the best is acute Type III. This is the single strongest argument for early diagnosis and early reduction.

Step 1 - Plain radiographs (screening):

• Open-mouth (odontoid) view: the lateral mass that has rotated forward looks wider and closer to the dens, while the contralateral mass looks narrower and further - the asymmetric "wink" appearance. Asymmetry of the dens-lateral mass spaces raises suspicion.
• Lateral view: may show the assimilated posterior arch of C1 and an increased atlantodental interval if there is anterior shift.
• Plain films are suggestive, not confirmatory - positioning the twisted neck reproducibly is difficult and a normal film does not exclude AARS.

Step 2 - CT, ideally dynamic (3-position):

• The diagnostic test of choice. A static CT demonstrates the rotational malalignment of C1 on C2.
• A dynamic CT (neutral, then maximal active rotation to each side) shows the relationship is FIXED and does not correct - this both confirms AARF and grades it (Pang).

Step 3 - MRI (selective):

• Indicated if there are neurological signs, to assess the cord and space available for cord, and to evaluate soft-tissue/inflammatory change in Grisel syndrome. MRI also helps exclude a posterior fossa or cord tumour in atypical torticollis.

Why dynamic, not just static: A single CT can show rotation that is actually within physiological range if the head happened to be turned. The 3-position protocol asks the patient to actively rotate maximally each way. In a normal child the C1-C2 relationship changes predictably; in AARF the atlas and axis stay locked together and the pathological rotation persists.

According to PubMed, Pang's normative and prospective studies established this dynamic protocol as the means to both diagnose and grade AARF by plotting the C1-C2 motion curve against a normal template [Pang 2010; Pang and Li 2005].

According to PubMed, both the Fielding-Hawkins type and the measured C1-C2 rotation degree correlated significantly with recovery time in a paediatric series [Spinnato 2020].

Non-operative care (the default for most cases):

• Analgesia and muscle relaxants to break the splinting cycle.
• Soft collar and activity rest for very acute, low-grade cases.
• Traction (halter for lower-grade; skeletal calipers for higher-grade or chronic) to reduce the locked joint gradually; monitor neurology throughout.
• Immobilisation after reduction (collar, SOMI brace, or halo) to maintain alignment while the soft tissues settle.
• In Grisel syndrome, add antibiotics for the underlying infection.

According to PubMed, in adult traumatic AARF, conservative management succeeded in the majority of acute cases but in only a minority of chronic cases [Zafarshamspour 2024]; in children, conservative treatment is effective in most, with delayed recovery concentrated in Grisel cases and higher-grade/larger-rotation deformities [Spinnato 2020; Pang and Li 2005].

When to operate:

• Irreducible deformity (cannot be reduced by traction).
• Recurrent subluxation after successful reduction (re-slips out of alignment).
• Chronic fixation (especially greater than 3 months), where reduction often fails or does not hold.
• Neurological compromise or significant cord-space narrowing.
• Ligamentous incompetence / unstable associated fractures (more relevant in adult trauma).

According to PubMed, in the adult systematic review, chronically diagnosed patients were far less likely to reduce conservatively and more often required surgery; surgery was advised for irreducible dislocations, ligamentous injury, unstable fractures and persistent pain [Zafarshamspour 2024].

Posterior C1-C2 fusion is the standard operation when surgery is required:

• Aim to reduce first (intra-operative or pre-operative traction) and fuse in the best achievable alignment.
• Goel-Harms construct (C1 lateral mass screws + C2 pedicle/pars screws connected by rods) is the modern workhorse - it permits intra-operative reduction and gives high fusion rates.
• Magerl transarticular screws are an alternative but require intact anatomy and a pre-set alignment, and carry vertebral artery risk.
• Wiring (Gallie/Brooks) is largely historical, with higher non-union and a need for rigid post-operative immobilisation.
• Autograft bone and intra-operative neuromonitoring are standard; pre-operative CT angiography helps plan around the vertebral artery.