Keywords
atlanto-occipital luxation - dog - cervical vertebrae trauma - closed reduction
Introduction
A 12-year-old, 33 kg, female spayed crossbred dog presented 2 hours after being hit
by a car. On physical examination, the dog had multiple superficial bleeding wounds
over the left side of the head. Bilateral epistaxis was present and harsh lung sounds
referred from the upper respiratory tract were heard across both lung fields. The
dog was able to stand with support but not ambulate. On neurological exam, there were
multiple neurological deficits; clinical signs are summarized in [Table 1]. The initial findings were indicative of a brain stem lesion. There was no previous
history of major illness.
Table 1
Neurological assessment of the dog from presentation before closed reduction, through
to discharge
|
Neurological reflexes
|
Pre-reduction
|
1-day post-reduction
|
2-days post-reduction
|
|
Mentation
|
Dull/depressed
|
Quiet, responsive
|
Bright, responsive
|
|
Head tilt
|
Present, right sided
|
None
|
None
|
|
Pupillary light—direct
|
Reduced, bilateral
|
Present, bilateral
|
Present, bilateral
|
|
Pupillary light—consensual
|
Reduced, bilateral
|
Present, bilateral
|
Present, bilateral
|
|
Pupil size
|
Symmetrical, normal
|
Symmetrical, normal
|
Symmetrical, normal
|
|
Palpebral
|
Absent, bilateral
|
Present, bilateral
|
Present, bilateral
|
|
Menace
|
Absent, bilateral
|
Present, bilateral
|
Present, bilateral
|
|
Gag
|
Not assessed
|
Present
|
Present
|
|
Forelimb proprioception
|
Present
|
Present
|
Present
|
|
Hindlimb proprioception
|
Absent, bilateral
|
Absent, bilateral
|
Present, bilateral
|
|
Withdrawal
|
Present
|
Present
|
Present
|
|
Gait
|
Non-ambulatory tetraparesis
|
Ambulatory paraparesis
|
Ambulatory mild ataxia
|
Case Description
Baseline blood tests were performed and within normal limits. Following stabilization,
the dog was sedated with fentanyl (Biomed, Auckland, New Zealand) at 5 µg/kg intravenously
(IV) for a computed tomography (CT) of the head and neck. The CT was performed (Somatom
go.Up 64-slice CT Scanner, Siemens Healthineers, Erlangen, Germany), with the patient
positioned in sternal recumbency. Iodinated contrast (Omnipaque 300 mg/mL, GE Healthcare
Limited, Auckland, New Zealand) was hand-injected IV at a dosage of 600 mg/kg. The
images were taken at the following settings: slice thickness, 1 mm; pitch, 0.35; rotation
duration, 1.0 second tube voltage, 130 kV and soft and sharp algorithms. Reformatted
dorsal and sagittal images were then acquired.
An atlanto-occipital luxation (AOL) was identified ([Fig. 1]).[1] The cranial articular processes of the atlas were displaced toward the left, relative
to the occipital condyles. The cranial articular processes of the atlas were rostrally
displaced and interlocked with the occipital condyles in a luxated position. The luxation
was such that there was a persistent rotary displacement locking the head tilted as
seen on physical exam. A small periarticular fracture fragment was noted attached
to the right cranial articular process of the atlas. This was suspected to be a periarticular
fracture shard from the right occipital condyle. A small fracture fragment was identified
and associated with the left transverse process of C1 at the cranial margin that did
not alter its integrity. No other fractures of the occiput or atlas were present.
The brain stem was deformed most notably on the right and ventral aspect at the site
of luxation. Conforming radiopaque material of ∼50 Hounsfield units was seen surrounding
the brain stem at the site of luxation that was most consistent with haemorrhage.
The atlantoaxial junction appeared normal. The calvarium was intact with no signs
of intracalvarial haemorrhage or increased intracranial pressure identified.
Fig. 1 Cross-sectional computed tomographic images (slice interval 1.0 mm) using bone reconstruction
algorithm of the dog before closed reduction. The green arrows indicate the occipital
condyles and the blue arrows show the atlas. (A) Axial view of atlanto-occipital luxation (AOL). The red arrow shows the external
sagittal crest. (B) Dorsal view of AOL. Sagittal view of right (C) and left (D) sides of the AOL.
There was a comminuted displaced fracture of the left orbit with large bony fragments
compressed into the caudal aspect of the left nasal cavity. There was increased fluid
opacity within the left orbit thought to be due to haemorrhage and oedema. Mild exophthalmos
was seen with the globe intact. A conforming soft tissue opaque material considered
consistent with fluid, was seen within the left nasal cavity and the left sphenopalatine
sinus. The lateral wall of the left sphenopalatine sinus had a bony fragment compressed
axially into its centre, resulting in a large communication between the sinus and
the retrobulbar tissues. The olfactory region of the frontal bone was intact. Non-displaced
parasagittal fractures were also found through the right mandibular fossa. A similar
parasagittal fracture through the left mandibular fossa of the temporal bone was identified
that is mildly displaced. The retroarticular process was also fractured and mildly
displaced. A soft tissue opacity was seen within the left bulla and associated external
ear canal. A complete, mildly displaced fracture of the sagittal ridge of the calvarium
was seen with gas-like opacity compatible with emphysema surrounding the bony fragment.
Mildly displaced fractures associated with both zygomatic arches were found, which
were worse on the left side ([Fig. 2]). No abnormalities were detected in the thorax or abdomen.
Fig. 2 Three-dimensional reconstructions of the dog's skull in left and right lateral views,
illustrating multiple fractures.
Prior to closed reduction, anaesthesia was induced. The dog was maintained on a fentanyl
constant rate infusion at 3 µg/kg IV then given a bolus of fentanyl at 5 µg/kg IV
and alfaxalone (Jurox, Rutherford, Australia) IV to effect to achieve anaesthetic
induction, then intubated with an endotracheal tube and maintained with isoflurane
in oxygen.
The AO luxation was treated by closed reduction. The procedure was performed on the
CT table to allow for imaging as needed. The dog was positioned in sternal recumbency.
A harness was placed onto the dog and secured caudally to the end of the CT table
with a ratchet strap. Securing the head was complicated by the zygomatic fractures
and lack of undamaged attachment points on the skull. Therefore, a custom harness
was designed with strapping tape to attach to the maxillary canine teeth. A second
ratchet strap connected this tape harness to a stationary pole beyond the CT gantry.
Tightening of the cranial ratchet strap allowed for carefully controlled tension to
be applied to allow a slow distraction of the occipital condyles from the interlocked
cranial articular facets of the atlas. This set-up is illustrated in [Fig. 3]. Careful distraction force was applied using the cranial ratchet straps to distract
the head from the body, parallel to the plane of the cervical spine. An assistant
manually stabilized the atlas. Once the head was cranially distracted to allow clearance
of the occipital condyles from the interlocked atlas, then the head was flexed slightly
to the left and carefully rotated clockwise to lift the right occipital condyle over
the rim of the articular fovea, thus reducing the atlanto-occipital joint. The occipital
condyle was reduced back into apposition with the cranial articular fovea with a slight
pop felt. ([Figs. 4] and [5]). This process is shown in [Video 1].
Fig. 3 Photographs demonstrating the positioning and securing of the patient for the closed
reduction, with the craniocaudal view on the left and the caudocranial view on the
right.
Fig. 4 Cross-sectional computed tomographic images (slice interval 1.0 mm) using bone reconstruction
algorithm of the dog after successful closed reduction of the atlanto-occipital luxation
(AOL). The foramen magnum now aligns with the vertebral canal. (A) Axial view of AO joint. The occipital condyles now sit within the cranial articular
fovea of the atlas (B) Coronal view of AO joint. Sagittal view of right (C) and left (D) sides of the AO joint.
Fig. 5 Three-dimensional reconstructions of the atlanto-occipital luxation pre- and post-reduction
(left and right respectively), as seen from the ventral aspect.
Video 1
Actual closed reduction procedure.
Confirmation of the AO joint reduction was achieved by a repeat CT scan as seen in
[Fig. 4]. Post-reduction palpation and gentle motion of the craniovertebral junction suggested
normal position and function of the articulation of the AO joint.
Recovery from anaesthesia was uneventful, with neurological status improving by the
next day ([Table 1]). After 2 days of cage rest, the dog was ambulatory and discharged from hospital.
The owners were advised to use a harness for restricted activity and short walks.
Four weeks after the closed reduction, the dog presented in the clinic for re-examination
and was found to be neurologically normal. The dog was ambulatory, bright and responsive.
The owners reported that the dog was clinically normal at home. [Video 2] shows the dog walking well when it presented for a revisit 4 weeks after discharge.
Video 2
The dog walking well when it presented for a revisit 4 weeks after discharge.
Discussion
Traumatic luxations of the AO joint are rarely reported in the veterinary literature.
A review of publications found 11 cases (nine canines, one feline and one alpaca)
of AOL that survived treatment.[2]
[3]
[4]
[5]
[6]
[7] Out of those cases, five dogs were treated surgically[7] and the remaining animals were managed conservatively.[2]
[3]
[4]
[5]
[6] This condition is reported to have a high mortality rate in people,[1]
[8] so is possible that this injury in dogs is more common than reported with animals
perhaps not surviving long enough to be diagnosed with AOL.
Atlanto-occipital luxations in humans occur mainly as ligamentous injuries due to
high-speed trauma such as motor vehicle accidents or falls from heights.[1]
[8] There are different subtypes of AOLs in people,[9]
[10] including atlanto-occipital rotatory luxation (AORL).[10] The AORL is best diagnosed by CT imaging, showing the rotation of both occipital
condyles in relation to the atlas.[10] This description appears to fit best with the displacement seen on CT in the dog
of this report. Given the low number of cases reported, no subclassification system
exists in the veterinary literature, and no detailed description of the type of dislocation
is available in the previous reports.
The AORL in humans has been noted to carry a better clinical outcome than non-rotatory
AOL.[5]
[11] Treatment in such cases typically involves either surgical reduction and stabilization
or stabilization with bracing and splinting. Subclassification for AOLs in dogs may
also be appropriate as there may be prognostic and treatment implications as in people;
however, more data would be needed to confirm this.
Survival after closed reduction in traumatic AOL has been reported in three dogs,
one cat and one alpaca.[2]
[4]
[5]
[6] All three dogs had a bilateral dislocation of the occipital condyles, and one of
them had an avulsion fracture between the atlas and occiput but without displacement.[2] In each of these cases, closed reduction was performed by applying traction to the
AO joint and by reducing the luxation by rotation force. Sufficient stability seems
to be achieved long-term by the formation of fibrous scar tissue as healing response
to injury of the ligaments around the AO joint.[5]
[12]
This case report highlights the importance of CT imaging in the diagnosis of AOL as
well as CT as a guiding imaging tool for conservative treatment. The spatial orientation
of the luxation and the degree of overriding displacement was readily recognized and
destabilizing articular fractures could be excluded. With the CT results, the degree
of fractures of the caudal skull could be clearly identified so that a stable bony
distraction column could be precisely planned. Using the ratchet straps aided in distraction,
which improved control during closed reduction. With greater control and understanding
of the situation, the CT images substantially improved 3-dimensional orientation,
and thus the closed reduction was achieved relatively quickly. An immediate post-reposition
scan confirmed successful reduction. Immediately rescanning with CT allowed confirmation
of successful reduction.
This report shows that closed reduction is a viable option to successfully treat AOL
in the dog. Being non-invasive, the described method is relatively quick and avoids
additional injury to the surrounding soft tissue structures, as compared to surgical
reduction.
