The Risks of Spinal Deformity Surgery: Occurrence of New Neurologic Deficits

In the blog post from December 17^th, 2018 the operative
risks which are common to all surgical procedures done under general anesthesia
were presented.  This post will focus on
the one of the risks unique to spinal deformity surgery: New neurologic deficits.  This includes paralysis, leg/arm weakness,
sensory changes, bowel and bladder incontinence, etc…these are some of the bad
things that worry patients, families and surgeons the most.  In 99% of surgeries one main goal is to
preserve the patients’ neurologic function that they had before surgery and 1%
of the time we are aiming to improve neurologic function (for patients who have
problems for which surgery on the spine is being performed).

In 2019, optimal monitoring of spinal cord function during
surgery, in the U.S., is to continually assess the motor and sensory tracts of the
spinal cord. (3)  This is accomplished
with:

1.
Sensory tracts: SSEPs or Somatosensory evoked
potentials

2.
Motor tracts

a.
DNEPs or Descending Neurogenic evoked potentials

b.
TcMEPs or Transcranial Motor evoked potentials

There are three noteworthy studies in the area of new neurologic
deficits during spinal deformity surgery:

#1: In the largest series of spinal surgeries
published to date, Hamilton et al published on 108,419 surgeries (all ages)
from the Scoliosis Research Society Morbidity and Mortality database.  There were 1064 new neurologic deficits
(1.0%) which were comprised of 662 nerve root deficits, 74 cauda equina
deficits and 293 spinal cord deficits, and 35 unknown.  This study reported revision surgery had a
41% higher new neurologic deficit rate than primary surgeries (1.25% vs. 0.89%)
and pediatric patients were 59% higher than adults for new neurologic deficit
(1.32% vs. 0.83%).

Recovery Rates                                none      partial   complete

               Nerve
root                         4.7%      46.8%    47.1%

               Cauda
equina                    9.6%      45.2%    45.2%

#2: From our institution Washington University in St.
Louis (Shriners Hospital for Children, St. Louis Children’s Hospital and
Barnes-Jewish Hospital), Raynor et al, reported the largest single-center
experience with new neurologic deficits after spinal surgery, 12,375 surgeries
(all ages) over a 25-year time span.
Neuromonitoring alerts occurred in 3.1% of surgeries and in 93% of those
events the corrective interventions during surgery led to data recovery and no
new neurologic deficits.  Only 0.12% of
all patients had a permanent new neurologic deficit after surgery.

#3: In another study from our center, Thuet et al
reported on the largest single-center study on neuromonitoring of pediatric
patients (<18 years of age) published to date.   Of the 3436 pediatric patients, there were
74 (2.2%) neuromonitoring alerts for which intraoperative corrective
interventions improved 92% to baseline data and function.  Only 6 (0.17%) patients had a new neurologic
deficit.

One important finding of this study is neuromonitoring,
using sensory and motor tract analysis, is able to predict final neurologic
outcome in 99.8% of surgeries. 

In addition, it is important to remember intraoperative
alerts happen, and most are not foreseen or predictable.  In this study intraoperative neuromonitoring
events occurred once every 42 cases and permanent neurologic deficit every 573
cases.  Hence it is important an action
plan is ready to go at all times if a neuromonitoring alert occurs in surgery.

Take-home thoughts about spinal deformity surgery (without
vertebral column resections):

1.
Intraoperative neuromonitoring alerts occur in
2.2%-3.6% of cases. (1, 5, 8)

2.
Intraoperative corrective interventions decrease
new neurologic deficit rate by 86-92%. (1, 8)

3.
Permanent new neurologic deficits occur in 0.12-0.3%
of cases. (1, 5, 6, 8)

4.
New neurologic deficits are more likely in
revision surgery (vs. primary) and pediatric patients (vs. adults). (4, 6, 7)

5.
Intraoperative neuromonitoring can predict long-term
neurological outcome in 99.8% of cases. (8)

6.
Optimal intraoperative neuromonitoring involves
assessing the sensory and motor parts of the spinal cord.

7.
Rates of new neurologic deficit vary by type of
spinal deformity: congenital 2.2%, neuromuscular 1.1%, and idiopathic 0.8%. (7)

1.
Buckwalter JA, Yaszay B, Ilgenfritz RM, Bastrom
TP, Newton PO.  Analysis of
intraoperative neuromonitoring events during spinal corrective surgery for
idiopathic scoliosis.  Spine Deformity
2013;1:434-8

2.
Cho SK, Lenke LG, Bolon SM, Pahys JM, Cho W,
Kang MM, Zebala LP, Koester LA.  Can
intraoperative spinal cord monitoring reliable help prevent paraplegia during
posterior vertebral column resection surgery?
Spine Deformity 2015;3:73-81

3.
Fehlings MG, Brodke DS, Norvell DC, Dettori
JR.  The evidence for intraoperative
neurophysiological monitoring in spine surgery.
Does it make a difference?  Spine
2010;35:s37-46

4.
Hamilton DK, Smith JS, Sansur CA, et al.  Rates of new neurological deficit associated
with spine surgery based on 108,419 procedures.
Spine 2011;36:1218-28

5.
Leong JJ, Curtis M, Carter E, Cowan J, Lehovsky
J.  Risk of Neurological Injuries in
Spinal Deformity Surgery.  Spine
2016;41:1022-7

6.
Raynor BL, Bright JD, Lenke LG, et al.  Significant change or loss of intraoperative
monitoring data.  Spine 2013;38:E10-8

7.
Reames DL, Smith JS, Fu K, et al.  Complications in the surgical management of
19,360 cases of pediatric scoliosis: a review of the Scoliosis Research Society
Morbidity and Mortality database.  Spine
2011;36:1484-91

8.
Thuet ED, Winscher JC, Padberg AM, et al.  Validity and Reliability of Intraoperative
Monitoring in Pediatric Spinal Deformity Surgery.  Spine 2010;35:1880-6