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220 Section III: Spinal Procedures

Figure 25.13 Transarticular screws have been placed across the large L7–S1
articular facets. Prior to instrumentation the articular cartilage would be
debrided and a bone graft placed to encourage arthrodesis. Note that the
ideal screw orientation for maximal purchase is 45° in the craniodorsal to
caudoventral plane and 30° in the dorsomedial to ventrolateral plane.
Figure 25.14 Two String of Pearls™ (SOP) plates have been applied to the
dorsal surface of L7–S1 with one screw of each plate engaging L7 and S1.
Insertion landmarks and angles are the same as for pin fixation.

into the canal, they serve an important role as a baseline evaluation If implant placement is appropriate, and bony alignment and
tool for long‐term follow‐up [12]. Postoperative CT is performed to apposition are acceptable, postoperative complications are most
determine the actual position of implants in relation to the vertebral often due to implant failure or infection. Implant loosening and
canal and length of screw or pin penetration past the trans‐cortex. failure may be due to inappropriately sized or placed fixation,
Accuracy of CT in determining canal violation is excellent, allowing poor bone‐holding properties, or excess patient mobility after
prompt identification of inappropriately placed pins or screws (i.e., surgery. Catastrophic implant failure is usually due to poor deci­
violating the canal or intervertebral foramen, or insufficient bone sion‐making regarding type and size of fixation. Infection is less
purchase due to lateralization of implant). While it is uncommon to likely due to intraoperative contamination but more to hematog­
replace mildly malpositioned implants once identified on CT, the enous spread of bacteria. Appropriate perioperative antimicro­
knowledge gained is beneficial for future stabilization procedures. bials should be administered to decrease risk of contamination
Stainless steel implants, which are to date the most commonly used, from the skin. Providing a course of therapeutic antimicrobials
create prohibitive artifacts on MRI, eliminating this modality for after a clean surgery is controversial and should be decided on a
postoperative evaluation of the instrumented site. case‐by‐case basis.
Seroma formation can occur despite meticulous dead‐space clo­
sure. Warm compresses and time are usually sufficient to resolve
Complications these and repeated aspiration should be avoided due to the risk of
Because of the proximity of important neurovascular structures and iatrogenic contamination. Because of the resection of lumbar muscu­
the anatomical restrictions of the vertebral column, iatrogenic lature and possible muscle atrophy around the PMMA fixation of
injury to spinal cord, nerve roots, vascular supply, and interverte­ thoracolumbar injuries, the PMMA can often be palpated and may be
bral discs are possible. Thorough and precise preoperative planning displeasing to owners who should be educated about this possibility.
with proper translation at the surgical table should decrease the Appropriate stabilization of vertebral column injuries should
potential for catastrophic complications. Postoperative imaging, lead to fracture healing and stable fibrosis of luxations. Long‐term
while not preventing iatrogenic damage, is a valuable tool for subse­ complications may include stable nonunion, malalignment, granu­
quent surgeries as it provides immediate feedback about what went loma formation, and chronic pain from low subclinical implant
well and not so well during a recent procedure. loosening or infection. When stability is deemed appropriate,