Monday, March 4, 2019

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

In the blog post from December 17th, 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%
               Spinal cord                         10.6%    43%       45.7%
#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

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