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226 Section III: Spinal Procedures

A B

C D

Figure 26.4 MRI of a dog with DLSS. (A) Transverse and (B) sagittal images with the pelvic limbs extended causing dorsiflexion of the lumbosacral space.
(C) Transverse and (D) sagittal images taken with the pelvic limbs pulled forward. Note the dramatic difference in the bulge of the disc and compression of
the nerves of the cauda equina, illustrating the dynamic nature of the lesion. Source: Courtesy of Dr. Laurent Guiot.

decompression. Intervertebral stabilization techniques may also be One of the most important anatomical features for adequate
performed in cases with preexisting instability or those where post- decompression of the lumbosacral disc space is that the L7 nerve
operative instability is a concern. For some dogs foraminotomy root arises just cranial to the intervertebral foramen (Figure 26.5)
alone may be recommended. and travels through a lateral recess prior to exiting the foramen.
Adequate decompression of the nerve root through the limited
Surgical Anatomy approach offered by a dorsal laminectomy may not be possible
It is crucial that the anatomy of the lumbosacral region be well (Figure 26.6) [2]. A partial or complete facetectomy, which carries a
understood to maximize the effectiveness of surgery and to prevent risk of destabilizing the lumbosacral space, or foraminotomy may
complications. therefore be required [2].
The spinal cord ends in the caudal half of L6 and the cranial half of
L7 in the majority of large‐breed dogs, though it may extend more Dorsal Laminectomy
caudally in some small‐breed dogs [50]. The cauda equina arises Patient Preparation and Positioning
from the conus medullaris and is composed of the L6, L7, S1–S3 and The dog is positioned in sternal recumbency with the pelvic limbs
Cd1–Cd5 nerve roots. It is bordered dorsally by the interarcuate liga- either drawn forward or in a neutral frog‐leg position. The pubis
ment and laminae of L7 and S1, ventrally by the dorsal longitudinal can be supported with a sandbag or rolled towel to further open the
ligament, IVD and vertebral bodies of L7 and S1, and laterally by the intervertebral space for decompressive surgery.
vertebral foramina and pedicles of L7 and S1. The connection
between L7 and S1 is formed by the facetal joints and the IVD [12]. Surgical Technique
This articulation is further stabilized by the dorsal and ventral longi- The landmarks for surgical approach include the wings of the ilium
tudinal ligaments, interarcuate ligament, the interspinous ligament, and the spinous process of L6. The spinous process of L7 is short
and the surrounding spinal musculature and fascia. and can be difficult to palpate. A midline skin incision is made from