Page 157 - Zoo Animal Learning and Training

158 Section III: Spinal Procedures

Approach [1–3] in retraction with blunt self‐retaining retractors, such as Balfour
Two approaches are described for ventral slot, the median and the retractors. Weitlaner retractors can also be used, but Gelpi retrac-
paramedian approaches (Figure 17.2). A ventral midline skin tors should be avoided at this stage due to the risk of damaging the
incision is performed from the larynx to the manubrium of the ster- neurovascular structures. Moist towels or sponges should be placed
num. In the median approach, the paired sternocephalicus and underneath the retractors to protect the tissues. In the paramedian
sternohyoideus muscles are identified and both muscles are divided approach, after identification of the sternocephalicus and sternohy-
on the midline. The trachea is identified immediately under the oideus muscles, the right sternocephalicus muscle is separated from
sternohyoideus muscles. Digital and scissor dissection is used to the right sternohyoideus muscle (Figure 17.2). The sternohyoideus
expose and retract the trachea, recurrent laryngeal nerve, esopha- muscles are then retracted to the left with the trachea, esophagus,
gus, and left carotid sheath towards the left, while the right carotid and carotid sheath. This approach reduces the risk of hemorrhage
sheath is retracted to the right. Finger dissection is safest and most from the right caudal thyroid artery and protects the trachea, right
effective at this stage. Care should be exercised to avoid damage to recurrent laryngeal nerve, vagosympathetic nerves, and right
these structures, particularly the recurrent laryngeal nerve which carotid sheath, while offering increased exposure of the caudal
runs on the lateral side of the trachea. These structures can be held cervical vertebrae [4]. Retraction is maintained with blunt self‐
retaining retractors as described for the midline approach.
At this stage identification of the disc spaces for the ventral slot
A approach is very important. The main landmarks are the large
transverse processes of the C6 vertebra and the prominent ventral
process of C1 (Figure 17.2). These structures must be identified by
the surgeon and assistant to avoid approaching the wrong site. The
ventral tubercles of the vertebral bodies should be palpated.
The ventral tubercle of C5 lies on the midline in the cranial border
of the transverse processes of C6. The longus colli muscles are
attached to the ventral tubercles. It is important to identify the ven-
tral tubercles and the left and right transverse processes along the
ventral aspect of the spine before incising the longus colli muscles
along the intervertebral disc space to be approached. Importantly,
there is no intervertebral disc between C1 and C2.
Once the intervertebral disc space has been identified and
exposed, the tendinous insertions of the longus colli muscles are
sharply transected. Hemostasis with bipolar cautery is important at
this stage. Subperiosteal elevation of the longus colli muscle cranial
and caudal to the ventral tubercle and disc space follows and retrac-
B tion of the musculature is maintained using Gelpi retractors. The
Lone Star® Retractor System (Cooper Surgical, Trumbull, CT) is
useful in the caudal cervical region of deep‐chested dogs as an alter-
native to long curved Gelpi retractors. Achieving adequate retrac-
tion of the musculature at C6 may be difficult due to its long
ventrally positioned transverse process. Partial resection of the lon-
gus colli muscle at that location may facilitate visualization. Once
the musculature is retracted and hemostasis is achieved, the ventral
slot can begin.
The slot is created with a high‐speed pneumatic drill. Some sur-
geons prefer to remove the ventral tubercle with rongeurs and to
excise the annulus fibrosus with a #11 blade before drilling any
bone but these steps are not necessary. When performing the slot it
is important to stay on the midline and to minimize its size. Because
of the angulation of the cervical intervertebral discs, the slot should
begin in the cranial vertebral body. Ideally the slot should not
exceed one‐third of the length and width of the vertebral bodies
Figure 17.2 Approach to the ventral aspect of the cervical spine for a ventral (Figures 17.3 and 17.4) [5,6]. Drilling is performed through the
slot. (A) Observe the large ventrally positioned transverse processes of the outer cortex, cancellous bone, and intervertebral disc, until the
sixth cervical vertebra (arrows). Identification of C6 is important to allow inner cortex is identified. It is important to recognize the differ-
identification of the correct disc space. (B) Median approach is shown by ences in color and consistency of the cancellous and cortical bone
the dotted white lines over the sternohyoideus and sternocephalicus mus- respectively. Cancellous bone is red, dark and soft, while cortical
cles. Paramedian approach is illustrated by the dotted yellow lines. After a bone is white and hard. Irrigation and suction are essential for this
midline skin incision and identification of the sternocephalicus and sterno- procedure. Care should be exercised at this stage to thin the inner
hyoideus muscles, the right sternocephalicus muscle is separated from the
right sternohyoideus muscle in the paramedian approach. The sternohyoi- cortex along the cranial and caudal aspects of the slot. One should
deus muscles are then retracted to the left with the trachea, esophagus, and verify the thickness of the inner cortex regularly at this stage. The
carotid sheath. Source: Reproduced with the permission of The Ohio State cortex should be thinned to a point where a soft cortical shell
University. remains. Then, the dorsal annulus is grasped and the remaining