Discussion
Diseases affecting the atlanto-occipital joint have been rarely
documented in the horse and their diagnosis can be a considerable
challenge. Craniovertebral junction (CVJ) trauma is a difficult clinical
condition. Being a highly mobile functional unit at the junction of the
skull and the vertebral column, traumatic events in this area may
produce devastating neurological complications and death. Additionally,
many of the CVJ traumatic injuries can be left undiagnosed or even raise
difficult treatment dilemmas .
In human literature it is considered that the combination of clinical
and radiographic examination when indicated (using the National
emergency X-Radiography Utilization study criteria) is inadequate for
fracture detection of the cervical spine following blunt trauma compared
to CT imaging .
Again in human literature, when comparing radiography to CT imaging the
lateral view radiograph alone had only a 73% sensitivity (95% CI,
50–89%) and 92% specificity (95% CI, 87–95%) for cervical spine
abnormalities compared with MDCT findings. The addition of other
radiographic views did not change the sensitivity of radiography but
rather marginally decreased its specificity to 91% (95% CI, 86–94%).
Although radiographic examination of the entire cervical vertebral
column had been performed at the time of initial onset of clinical
signs, the fracture had not been identified. Retrospective review of the
radiographic examination allowed identification of the ventrally located
linear osseous fragment, however definitive diagnosis of the extent of
the atlas and occiput fractures was not possible, nor was the
identification of any compression of the spinal cord.
Definitive diagnosis was achieved by CT myelography of the cervical
vertebral column, performed under general anaesthesia. This allowed
detailed analysis of the fracture configuration and visualisation of
extradural compression caused by soft tissue swelling associated with
the atlanto-occiptal fracture site. In addition, general anaesthesia
allowed CT imaging of the entire cervical spine providing the ability to
rule out the presence of injury in the rest of the neck. Magnetic
resonance imaging would have theoretically allowed improved soft tissue
assessment and more accurate determination of the nature of the soft
tissue material within the vertebral canal however the practical
application of Magnetic Resonance Imaging for imaging the neck in the
live horse is limited due to patient size and practical application. CT
imaging was chosen due to availability of the imaging modality. Whilst
general anaesthesia was an increased risk to the patient, this was
considered justifiable in order to determine a diagnosis.
General anaesthesia is not always possible if horses are displaying
severe neurological signs or for economical reasons. Practical
application of CT imaging a neurological case under standing sedation is
based upon level of neurological deficits and risk assessment would be
performed on a case by case basis due to the increased difficulties of
positioning a neurological patient for standing sedation. In
neurological patients, initial treatment and monitoring has been
performed prior to anaesthestic in order to reduce risk to the patient
during recovery. In this case, general anaesthesia allowed positive
myelogram acquisition and also to assess the entirety of the neck
however standing CT could be performed for lesion monitoring once the
primary diagnosis had been made.
Considered treatment options for this case included (1) conservative
management, (2) fracture fixation, (3) dorsal hemilaminectomy or (4)
local infiltration of steroids into the cerebrospinal fluid and left
atlanto-occipital joint.
Continued conservative management was considered inappropriate by the
owner due to ongoing clinical signs, pain and neurological deficits
displayed by the patient. Both clinician and owner felt interventional
therapy was justified.
Option (2) fracture fixation was considered. Atlantoaxial arthrodesis is
described in humans and is a technically difficult and invasive
procedure. Internal fixation of a fractured axis in an adult horse has
been successfully performed but fixation of an atlas has not been
described in the horse. Given the comminuted conformation and chronic
nature of the fracture site, it was considered this would be challenging
surgery with a high risk recovery for the patient from general
anaesthesia.
Option (3) dorsal hemilaminectomy in order to release the pressure
within the spinal column and improve ataxia. Nixon and Stashak (1988)
have described successful laminectomy for relief of compression caused
by atlantoaxial subluxation in four horses. Two horses recovered fully,
one horse had residual grade 1 neurologic deficits and the fourth horse
was euthanised due to limb fracture 6 weeks after surgery. Laminectomy
and hemilaminectomy has been reported as a successful treatment for
relieving spinal compression in dogs. In canines this procedure is
commonly associated with postoperative neurological deterioration (.
Given the increased risk to the patient this option was not chosen.
Finally, option (4) infiltration of corticosteroids into the
cerebrospinal fluid and left atlantooccipital joint medication.
Intra-thecal steroid use is widespread for a variety of reasons in
humans but to the authors knowledge, has not been reported in equines.
Personal communication with colleagues had suggested positive response
to intrathecal corticosteroids following traumatic spinal injury in
equines. It was thought this could be successfully performed in the
standing patient using the technique described by and therefore
eliminate any further anaesthetic risk for the patient. Medication of
both the atlantoccipital joint and the cerebrospinal fluid was performed
sequentially under the same sedation, therefore it is not possible to
definitively determine which of these procedures provided a greater
contribution to improvement in the clinical signs.
The technique for medication of the cerebrospinal fluid and the
atlanto-occiptal joint was performed under ultrasound guidance. This
technique was a quick procedure to undertake and repeatable without side
effect. However, this case report describes only one case whereby no
adverse side effects were found following subarachnoid space injection
of corticosteroids under standing sedation. A larger number of cases is
required in order to ascertain the safety of this procedure.
This case report describes a fracture to the atlanto-occiptial joint
which had been refractory to conservative management and presented with
chronic remodelling of the fracture site. Local medication of the
atlanto-occiptal joint and cerebrospinal fluid resulted in significant
improvement in ataxia and clinical signs almost immediately post
treatment.