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19 Cervical Distraction and Stabilization

Bianca Hettlich

Introduction Anatomical Considerations
Cervical distraction and stabilization has become increasingly Cervical vertebral anatomy is challenging for rigid fixation, with
popular for the treatment of cervical spondylomyelopathy (CSM). limited compact bone stock and proximity of important neurovas-
The goal of surgery is to eliminate motion at the affected vertebral cular structures (Figure 19.1). Dorsal approaches for stabilization of
articulation, thereby decreasing tissue responses secondary to the cervical vertebral column in large dogs are uncommon. The
instability such as ligamentous or annular hypertrophy as well as vertebral body offers the most bone for fixation and is easily
articular facet proliferation. Distraction of the intervertebral disc approached via a standard ventral approach. However, even this
space is beneficial for traction‐responsive lesions such as soft tissue part of the vertebra offers on average only 6–12 mm in bone depth
compression by thickened dorsal longitudinal ligament or ligamen- in most large dogs until the vertebral canal is breached. The verte-
tum flavum. While distraction per se may not lead to improvement bral body is hourglass shaped and therefore the greatest bone depth
of bony compression by facet proliferation, the use of a disc spacer is near the vertebral endplate and the thinnest portion over the
in a neutral or slightly distracted position is beneficial for load shar- mid‐body. Intervertebral disc orientation is oblique in a craniodor-
ing between the affected vertebrae, thereby improving implant lon- sal to caudoventral direction; therefore most bone will be purchased
gevity. Interbody fusion is desired to provide long‐term stability if implants are directed parallel to the endplates. The presence of the
and prevent implant failure. sternum and the limited exposure of the caudal cervical vertebral
column can make implant placement parallel to the endplate in C6
and C7 quite challenging. The transverse processes offer additional
Preoperative Planning fixation sites; however, bone is quite thin and care must be taken to
Well‐positioned orthogonal radiographs of the cervical vertebral avoid the transverse foramen (present C1–C6). Advancing implants
column are obtained to gain a general idea of vertebral body and through the ventral aspect of the vertebral body in a laterodorsal
disc space dimensions. For plate fixation, radiographs help deter- direction toward the pedicle would provide increased bone pur-
mine plate size and length and probable screw location. Computed chase and also bicortical fixation. However, the pedicle is very nar-
tomography provides excellent bony detail and is considered the row and pedicle width is not uniform throughout the span of a
most useful modality for preoperative planning of vertebral column cervical vertebra, thus making it challenging to be engaged with a
stabilization. Vertebral body dimensions, in particular height, pin or screw.
should be determined via CT to assist with selection of screw
lengths. If an intervertebral spacer is used, endplate height and Implant Selection
width, and disc space depth need to be calculated to obtain an Evidence in the veterinary literature confirms that bicortical
appropriately sized spacer. Disc space dimensions should be implant placement in the cervical vertebral bodies is associated
obtained from unaffected sites (if available) to determine “normal” with a high risk of injury to important neurovascular structures
dimensions. While MRI is considered the gold‐standard imaging such as spinal cord, nerve roots, or vertebral vasculature (i.e.,
modality for spinal cord evaluation and invaluable for overall vertebral artery in transverse foramen) [1]. Therefore, bicortical
assessment of disease, the osseous detail it provides can be challeng- vertebral body implants are not recommended for cervical fixation.
ing for preoperative planning. Despite less bone purchase and concern for implant stiffness,

Current Techniques in Canine and Feline Neurosurgery, First Edition. Edited by Andy Shores and Brigitte A. Brisson.
© 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/shores/neurosurgery

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