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Chapter 26: Lumbosacral Decompression and Foraminotomy 229

Surgical Approach determined the safe corridors for pedicle screw placement for
The L7–S1 foraminotomy has been described using a lateral lumbosacral stabilization [67]. To date, there are no long‐term
approach, a transiliac approach, and an endoscopic‐assisted clinical studies that conclusively demonstrate an advantage of
approach [56,57,59]. The lateral approach can be performed bilat- stabilization techniques over dorsal decompression and forami-
erally, combined with a dorsal laminectomy or partial dorsal lami- notomy alone.
nectomy and is performed using the same patient positioning and Dorsal distraction/stabilization has been advocated in order to
initial approach as the dorsal laminectomy [56]. Once the superfi- increase the opening of the intervertebral foramina, essentially
cial fascia has been incised, dissection continues about midway decompressing the L7 nerve roots and correcting any preexisting
between the spinous processes and the ilial wing. A combination of instability. Following dorsal laminectomy or partial dorsal lami-
blunt and sharp dissection is used to separate the multifidus and nectomy, distraction is achieved using a laminectomy spreader
sacrocaudalis muscles, exposing the transverse process and [6] and any of the previously mentioned stabilization options. If
intervertebral foramen. The quadratus lumborum and longissimus screw fixation of the facetal joints is employed, the screws should
muscles are then partially elevated with periosteal elevators to be placed in the approximate center of the facetal joint and
allow exposure of the transverse process and pedicle of L7. The directed at a 30–45° angle from the sagittal plane to prevent
L7–S1 foramen can only be accessed from a dorsal‐oblique injury to the lumbosacral trunk and entry into the sacroiliac joint
approach because of the ilial wing. The foraminotomy is initiated [61–63]. Stabilization can also be achieved by inserting pins or
using a high‐speed drill and extended with fine burs or Kerrison screws into the body of L7 and the sacral wings and then embed-
rongeurs [56]. ding the pin ends or screw heads in PMMA to act as an internal
The transiliac approach to the L7 foramen involves a dorsal fixator [64,65]. Fusion of the joints is promoted by the removal of
approach to the wing of the ilium followed by the creation of an the articular cartilage prior to fixation and placing an autogenous
18 mm window through the iliac wing using a surgical drill. cancellous or commercially available bone graft. Pedicle screw
Through this approach, endoscopic exploration of the L7 nerve fixation is achieved with four pedicle screws, two each in L7 and
root, the intervertebral foramen, and the IVD can be performed S1, much like the screw and rod fixation described for the spacer
[57]. This technique was performed on cadavers and has not yet screw technique (Figure 26.12) [60,66–69]. Surgical techniques
been reported in clinical patients with follow‐up [56]. including dorsal laminectomy and lumbosacral stabilization
An alternative technique described in normal dogs involves the using pins or screws and PMMA have also been employed to
use of a modified mini‐dorsal laminectomy with endoscopic‐ treat DLSS in cats with good results [70,71].
assisted foraminotomy. CT follow‐up demonstrated that it is possi-
ble to enlarge the foramen using this approach, and that although it Variation
decreased in size by the 12th postoperative week it remained larger A more novel approach to distraction/fusion involves distracting
than preoperatively. Further clinical research is necessary to deter- the lumbosacral space with a permanent intervertebral device. A
mine if this technique can effectively treat dogs with DLSS and threaded titanium intervertebral spacer is placed into the L7–S1
foraminal stenosis [59]. intervertebral space following dorsal laminectomy, annulectomy
and discectomy [68,69] and is stabilized with a 2.7‐mm screw
Distraction and Stabilization/Fusion placed dorsoventrally from the vertebral body of S1, through a slot
Instability and subluxation are considered by some as integral to the in the spacer screw, and into the vertebral body of L7. The L7–S1
pathological processes that result in DLSS [60,61]. In contrast, oth- region can be further stabilized by using threaded pins and PMMA
ers report the process is associated with abnormal motion rather or 4.5‐mm pedicle screws placed bilaterally into the base of the
than true instability [10,11]. Partial discectomy or facetectomy may transverse processes of L7 and the alar wings of the sacrum. The
further exacerbate any existing instability [58,60,61]. Results of one screws are then connected by two rods with spherical stopper ends
study suggest that recurrence of clinical signs in dogs with DLSS abutting slotted polyhedral screw fixation clamps (Figures 26.12
following successful surgical decompression is associated with and 26.13) [68,69].
ongoing instability. In‐vitro testing of lumbosacral spines taken
from normal dogs revealed that while dorsal laminectomy does not
result in a significant loss of stiffness in the dorsoventral plane, the
addition of discectomy caused a significant decrease in stiffness in Postoperative Management
ventroflexion [58]. Combined facetectomy and dorsal laminectomy Depending on the procedure (degree of laminectomy and whether
decreased stiffness in both dorsiflexion and ventroflexion and com- distraction/stabilization procedures were performed), a 4–8 week
bined dorsal laminectomy, discectomy and facetectomy resulted in period of rest is recommended following surgery. Following this, a
a significantly less stable lumbosacral unit than any of the other gradual return to activity is recommended over a 4–6 week period.
combinations [58]. This period may need to be longer for working dogs. Rehabilitation
Some authors recommend stabilization following lumbosacral including swimming and underwater treadmill may also help
decompression. Stabilization techniques include the placement recovery. It is very important that any rehabilitation program be
of screws through the L7–S1 facetal joints with bone graft for designed by the surgeon and a qualified animal physiotherapist
fusion, the use of pins or screws and polymethylmethacrylate working in tandem [1,7].
(PMMA), and the use of pedicle screw–rod constructs designed
for applications in the human spine [61–66]. A biomechanical
study of canine lumbosacral spinal segments that were stabilized Postoperative Outcomes
with pedicle screw–rod fixation following dorsal laminectomy A summary of the recent studies reporting on outcome in dogs
and discectomy found that the pedicle screw–rod construct with DLSS is presented in Table 26.1. Following surgery, dogs
effectively stabilized the lumbosacral spine [60]. Another study with DLSS have good overall prognosis for improvement;