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Chapter 26: Lumbosacral Decompression and Foraminotomy 227

Figure 26.5 This dissected anatomical specimen shows the relationship of Figure 26.7 Intraoperative image showing the initial steps for standard dor-
the L7 nerve root (black arrows) to the intervertebral disc (hypodermic nee- sal laminectomy. The borders of the laminectomy have been burred using a
dle). The spinous process of L7 (asterisk), median crest of the sacrum high‐speed drill. The spinous process of L6 is cranial to the laminectomy
(arrowhead), sacral wing (cross), and cut edge of the ilial wing (yellow (asterisk), the remnant of the spinous process of L7 (circled star) is visible
arrow) facilitate orientation. Source: Courtesy of Dr. Laurent Guiot. within the laminectomy, and the sacral crest is also visible (yellow arrow-
head). Source: Courtesy of Dr. Laurent Guiot.

Figure 26.6 A skeletal specimen of the L7 vertebral body showing the lateral
recess through which the L7 nerve root exits the spine (yellow arrowhead),
vertebral endplate (asterisk), vertebral foramen, and facetal joint (black Figure 26.8 Intraoperative image of a dorsal laminectomy showing the thin
arrow). layer of inner cortical bone being carefully peeled away with an iris spatula
providing access to the spinal canal. Source: Courtesy of Dr. B. Brisson.
the spinous process of L5 to the caudal median eminence of the
sacrum. The subcutaneous fat and superficial fascia are incised laminectomy continues in the red cancellous bone layer until the
along the midline to expose the deep gluteal and caudal fascia. The white inner cortical bone is reached. At this point the ligamentum
fascia is incised around each of the spinal processes. This allows for flavum is resected, exposing the epidural fat of the lumbosacral
the elevation of the multifidus lumborum muscles (L6) and the sac- space. When removing the ligamentum flavum it is important the
rocaudalis dorsal medialis epaxial muscles (L7) from the spinous dissection does not extend deeper than the remaining bony lamina
processes and along the midline in between the processes. Soft tis- to avoid damage to the cauda equina [7]. The inner cortical bone is
sue elevation is continued laterally to expose the L6–L7 and L7–S1 then thinned with the burr until it can be peeled using elevators and
articular processes, and the median sacral crests caudally forceps or removed with Kerrison rongeurs (Figure 26.8) to expose
[51,52]. The fascia between the spinous processes can be very thick the cauda equina (Figure 26.9).
and difficult to elevate. The spinous processes of L7 and S1 are The S1 nerve root is visible through this approach and runs lat-
removed with double‐action rongeurs. The dorsal laminectomy is eral to the dural sac. In contrast, the L7 nerve root is located more
performed using a high‐speed surgical drill including at least the laterally and runs through the lateral recess prior to emerging from
caudal half of L7 and most of the sacrum. The lateral extent of the the foramen; this allows only a portion of the L7 nerve root to be
laminectomy is generally the caudal facets of L7 and the cranial fac- visualized through this approach. The laminectomy site can be
ets of S1 (Figure 26.7). Once through the outer cortical bone, the enlarged to the medial limit of the facetal joint capsule [51,52] and