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Chapter 25: Vertebral Fracture and Luxation Repair 211

approaches allows familiarization of location and dimension of the In small‐breed dogs, reduction can sometimes be achieved with
canal in relation to implants at the opened site, they should only be thumb forceps alone.
performed if compression is deemed sufficiently significant.
Monocortical Screw and PMMA Fixation
The ventral aspect of the vertebral bodies is utilized for monocortical
Cervical Injuries screw fixation with PMMA. Since bone near the vertebral endplates
Cervical fractures or luxations generally require substantial force as has the largest dimensions, screw position should be as cranial or
the surrounding musculature provides relative protection during caudal in relation to the vertebral body as possible. Care must be
trauma. Unstable vertebral body fractures are the most common taken not to perforate the vertebral endplate and the screw should be
indication for cervical stabilization. oriented parallel to the caudoventral/craniodorsally angled disc
space. Medium‐ to large‐breed dogs can usually accommodate 3.5‐
Anatomical Considerations mm cortical screws, while 2.0‐mm or 2.7‐mm screws are more
The vertebral bodies offer the most substantial amount of bone and appropriate for smaller dogs and cats. The use of titanium screws
can easily be exposed via a ventral approach. Pedicle dimensions are allows for improved postoperative advanced imaging, especially
small and the presence of the transverse foramen, which houses the MRI. Nonself‐tapping screws are preferred to avoid inadvertent per­
vertebral artery, makes safe transpedicular implant passage chal­ foration of the transcortex into the vertebral canal. When drilling, a
lenging. Articular processes extend more laterally than dorsal and drill stop is advantageous to help prevent penetration into the verte­
are in close proximity to the exiting nerve roots via the interverte­ bral canal. Screw‐on drill stops (e.g., Positive Drill Stop by Animal
bral foramina. More challenging muscular coverage and the lack of Orthopedics) are positioned along the drill bit based on preoperative
easily palpable landmarks hinders lateral approaches. Dorsal access measurements of the height of the vertebral body. Alternatively, drill­
to the vertebral canal requires an approach through what is often­ ing can commence without a stop, relying on the change in drill bit
times massive dorsal cervical musculature with the potential for pressure to indicate penetration of the cis‐cortex into the narrow
increased postoperative morbidity. medullary space of the vertebral body. An appropriate size depth
gauge or blunt straight probe can be used to carefully determine
Positioning and Approach integrity of the trans‐cortex. Two to four screws can be placed into
Careful positioning of the anesthetized dog in dorsal recumbency each vertebral body as necessary depending on the size of the bone
with the cervical spine in relative extension helps with alignment and the degree of instability. Screw length must be sufficient to allow
and reduction of some fractures/luxations. A standard ventral mid­ about 10–15 mm of screw protruding that will be incorporated into
line or paramedian approach will provide access to the ventral the PMMA. If screws are placed parallel to one another near an end­
aspect of the vertebral column. For caudal cervical trauma, partial plate, they may be angled slightly toward the midline to prevent inter­
myotomy at the insertion of the sternocephalicus muscle from the ference of implants during drilling and placement of the second
sternum may provide a somewhat improved access. Bony land­ screw. Transverse processes offer an additional location for screw
marks for a ventral approach include the wings of C1, the increased placement (Figure 25.4). While these processes do not provide a large
spacing between the ventral processes of C2 and C3 compared with amount of bony purchase, bicortical screw placement is possible,
other vertebrae, the prominent transverse processes of C6, and the
first pair of ribs. Surgical stabilization generally requires instrumen­
tation of vertebrae adjacent to the site of trauma; therefore, the
approach often exposes most of the cervical vertebral bodies.

Implant Selection
Bicortical pin fixation with smooth or positive‐profile end‐threaded
fixation pins has long been the standard for cervical vertebral fixa­
tion. Unfortunately, it carries an unacceptably high risk of injury to
neurovascular structures as pins, even at recommended insertion
angles (30–40°) and landmarks (ventral midline), may violate the
vertebral canal, transverse foramen, or intervertebral foramen.
Therefore, bicortical cervical implants are no longer recommended.
Monocortical implants significantly decrease the risk of such injury.
While either cortical or cancellous screws can be utilized for mono­
cortical fixation, cortical screws may offer improved resistance to
shear forces due to their larger core diameter. Biomechanical stud­
ies are supporting the use of monocortical screw constructs in the
canine cervical spine [2,3].

Reduction
Gentle manipulation for reduction of the unstable cervical vertebral
column can be achieved in several ways. Point‐to‐point reduction Figure 25.4 Monocortical vertebral body and bicortical transverse process
screw fixation with PMMA in the cervical spine. Note how the transverse
forceps can be placed carefully around the mid‐vertebral body to process screws avoid the transverse foramen. Vertebral body screws can be
manipulate the vertebra. Screws or small positive‐profile end‐ placed anywhere along the ventral aspect to accommodate the injury,
threaded pins can used for manipulation if they are inserted in an affording a high degree of freedom in application. For fixation of two adja­
area that does not jeopardize bony purchase for surgical fixation. cent vertebrae, 20 g PMMA is usually sufficient.