An evaluation of multimodal spinal cord monitoring in scoliosis
surgery: a single centre experience of 354 operations.
Authors
S Bhagat1, A Durst2, H Grover3, J Blake4, L Lutchman5, A S Rai6, R
Crawford7
Norfolk and Norwich University Hospital
Colney Lane
Norwich
Norfolk
NR4 7UY
al_durst@hotmail.com
1
Consultant Spinal Surgeon (Trauma & Orthopaedics), Ipswich Hospital
Specialty Registrar, Trauma & Orthopaedics, Peterborough City Hospital. Corresponding author. .
3
Clinical Physiologist (Neurophysiology), Norfolk & Norwich University Hospital
4
Consultant Neurophysiologist, Norfolk & Norwich University Hospital
5
Consultant Spinal Surgeon (Trauma & Orthopaedics), Norfolk & Norwich University Hospital
6
Consultant Spinal Surgeon (Trauma & Orthopaedics), Norfolk & Norwich University Hospital
7
Consultant Spinal Surgeon (Trauma & Orthopaedics), Norfolk & Norwich University Hospital
2
Description of Alert Cases (as summarised in Tables 5 and 6):
1 patient with neuromonitoring alert with new post-operative spinal cord deficit: (True
positive)
Patient 2: A 10 year old girl with Foetal Alcohol Syndrome presented with severe early onset curve
age 28 months treated with cast then growing rods. Age 10 underwent anterior release and posterior
correction with resultant paraplegia from T10 level. She had several periods of loss and subsequent
recovery of lower limb SSEPS and MEPs during the anterior release. The SSEPs and MEPs
recovered after the anterior release so the decision was made to proceed. She had normal neurology
immediately post-operatively however she developed paraplegia from T10 level overnight. Her postoperative MR scan showed evidence of a cord infarction from T5-T11 infarct suggesting vascular
occlusion.
4 patients with neuromonitoring alert with nerve root deficit: (True positives)
Patient 13: 51 year old man with hyperkyphosis due to ankylosing spondylitis underwent L2 posterior
subtraction osteotomy (PSO) and posterior kyphosis correction from T10-S1. He had loss of the
SSEPs and decreased MEPs bilaterally during the correction and rod contouring bilateral loss of
SSEPs and decrease MEPs occurred. A Decision was taken not to attempt further correction and
refrain from further instrumentation. He woke up with bilateral L2 and L3 weakness. 2 weeks later he
underwent further decompression at L2-3 and realignment of osteotomy. He had normal neurology at
final follow up.
Patient 14: A 55 year old woman with hyperkyphosis due to ankylosing spondylitis underwent PSO at
L3 and posterior correction of kyphosis with instrumentation from T6-S1. The SSEPs and MEPs were
lost immediately following correction, the reason for which was thought to be L3-4 compression after
closure of osteotomy. Responses recovered with reversal of the correction. The patient has
persistent weakness of grade 3 on left and grade 4 on right L4 myotomes.
Patient 21: A 54 year old lady with polio and residual bilateral lower limb weakness, underwent
removal of instrumentation and L3 osteotomy for a fatigue fracture at her distal rod fixation. During
the dissection she had bilateral reduction in her MEPs. Her SSEPs remained unchanged. Postoperatively she had suggestion of L3 nerve root impingement with intermittent right thigh pains and
paraesthesia. CT did not show any metalwork impingement, however nerve conduction studies
confirmed L3 nerve root compression. The patient has persistent intermittent L3 pain and
paraesthesia.
Patient 24: A 53 year old woman with severe degenerative scoliosis had significant single muscle
attenuation of the MEP from the left Tibilais Anterior muscle with EMG evidence of L5 screw pedicle
breach. She developed L5 radicular pain and underwent removal of pedicle screw at 9 months with
resultant pain relief but mild weakness.
9 patients with neuromonitoring alerts with transient post-operative neurological
deficit. (True positives)
Patient 4: A 14 year old girl with AIS who underwent anterior release as first stage of scoliosis
correction had unreliable MEPs to start with. She had repeated episodes of loss of lower limb SSEPs
during the procedure due to unknown reasons but changes were related to periods of hypotension
and recovered with increasing the blood pressure. The procedure was stopped and the wake up test
performed was normal. Whilst in recovery she developed bilateral lower limb weakness associated
with hypotension. The neurological deficit persisted for 5 weeks, but had fully recovered at the time of
final follow up at 5 months.
Patient 8: A 13 year old girl with AIS had complete unilateral loss of left MEPs and bilateral reduction
in SSEPs 5 minutes following posterior pedicle screw correction. The correction was undone,
metalwork was removed and procedure was abandoned. Patient awoke with transient altered
sensation in her left foot, which resolved over a few days. 12 days later procedure was completed
with intact monitoring and no resultant neurology.
Patient 11: A 14 year old girl with AIS who underwent posterior scoliosis correction with a pedicle
screw construct had a breach of the ligamentum flavum during the T10/11 facetectomy. There was
an immediate unilateral loss of right MEPs accompanied by a transient decrease of right cortical
SSEPs, The MEP change persisted and the procedure was abandoned. Post-operatively, she had no
sensory deficit in her lower limbs but had transient right leg weakness, brisk knee reflexes and
extensor plantar reflexes. An MRI showed no evidence of signal change in the spinal cord. A second
stage operation was planned 5 days later, however she had no recovery of motor potentials in the
right lower limb so the procedure was postponed by a further 14 days. When the operation was finally
performed 12 weeks later she had symmetrical SSEP and recordable, but asymmetrical MEPs
throughout. The operation completed without complication and post operatively she had normal
neurology.
Patient 12: A 13 year old girl with AIS who underwent a posterior scoliosis correction. She had loss of
her left MEPs and SSEPs during the correction of her deformity (de-rotation of screws on thoracic
apex), which initially recovered after metalwork removal. A second attempt at de-rotation was
uneventfully, however right-sided MEPs and SSEPs were lost while probing her right T3. Despite no
breach being identified, metalwork was removed and the procedure was abandoned. Postoperatively the patient had transient sensory deficit in her left lower limb. 12 days later the procedure
was completed with intact monitoring and normal neurology post operatively.
Patient 15: A 48 year old woman with hyperkyphosis due to ankylosing spondylitis and mobilizing with
crutches, underwent PSO at L3 and posterior thoracolumbar fixation. She had proximal fixation with
hooks at T3-4 and T6-7, with loss of MEPs and SSEPs after PSO. She had 40-50% recovery of
SSEPs after some time and only traces of MEP. CT scan carried out post-operatively suggested
possible breach of the pedicle screws. 9 days later her L4, L5 and S1 screws were replaced, with
medial wall breach identified. She had transient leg numbness, while her walking also improved from
her pre-operative function, only using one stick at follow up.
Patient 17: A 15 year old boy with congenital kyphosis (vertebral dysplasia) lost left then right MEPs
followed by reduced left SSEPs following anterior and posterior correction. The correction was
released at which time the MEPs recovered. The procedure was abandoned. He had transient loss
of sensation in his left foot, which fully recovered after a few days. Surgery was subsequently
completed 12 days later with intact monitoring and normal neurology for the patient.
Patient 19: A 17 year old boy with congenital kyphosis underwent posterior decompression and
attempted an excision of T7 hemi-vertebrae. He had partial excision of T7 from right side
uneventfully, but then during excision from the left side there were repeated periods of loss left MEPs
and SSEPs. The decision was taken not to attempt further decompression and to fix the deformity in
situ. Immediately post operatively he had left lower limb altered sensation, which recovered
overnight, and left lower limb weakness which subsequently recovered fully.
Patient 20: A 72 year old lady with degenerative scoliosis underwent revision deformity correction with
extension of instrumentation proximally from T14 to L5. During correction she had complete bilateral
loss of MEPs and bilateral reduction in SSEPs. . The correction was reversed and wake up test was
performed which was normal. The procedure was completed with further gradual incremental
correction. The patient had transient paraesthesia in both feet which resolved after a few days.
Patient 25: A 67 year old lady, revision posterior degenerative scoliosis correction with an L3 PSO.
During the osteotomy there was marked MEP and SSEP reduction in signals, but no change in fEMG.
The correction was reversed, however monitoring was non-recoverable. The patient had transient
right leg weakness that resolved after a few days.
9 patients with neuromonitoring alerts that responded to intervention, with no postoperative neurological deficit: (True positives)
Patient 1: A 7 year girl old with paraplegia and neuromuscular scoliosis secondary to cerebral palsy
underwent posterior correction from T4-L5. A clear sustained left MEP reduction indicating possible
L4-5 nerve root injury however as the patient had quadriplegia the nerve root injury was considered
insignificant. Post operatively her neurological status was unchanged.
Patient 3: A 7 year old girl with early onset scoliosis underwent growing rods correction surgery. She
had loss of MEPs following placement of proximal thoracic lamina hooks and distraction. Distraction
was released and lamina hooks were removed which led to recovery of MEPs. SSEPs remained
unchanged throughout. Post operatively her neurological status was normal.
Patient 5: A 12 year old girl with adolescent idiopathic scoliosis (AIS) and severe curve that
underwent posterior pedicle screw correction had loss of MEPs with no SSEP change. Following
reversal of correction, removal of metalwork, and normal wake up test, the MEPs returned however
were repeatedly lost again when reattempting correction. Decision was taken to abandon the
procedure. A week later she had anterior correction from T6-11 and further posterior correction 4
months later as a 3rd stage, both of which had normal monitoring and no neurological deficit.
Patient 6: A 15 year old girl with AIS who had previous correction from T10-L3 had worsening of
deformity proximally. She underwent further correction from T3-T11 and had loss of left MEP during
placement of thoracic pedicle screws. These were removed, tracks were probed and no breach was
found. Procedure was completed with normal SSEPs and right sided MEPs whereas left sided MEPs
were intermittently lost. Post operatively her patient’s neurological status was unchanged.
Patient 7: A 14 year old girl with AIS underwent posterior scoliosis correction with a pedicle screw
construct. She had loss of left MEPs following placement of K-wire for the T6 pedicle (apical) screw.
The decision was made not to use the T6 screw. MEPs returned to baseline levels and the procedure
was completed. Her SSEPs remained unchanged. Post operatively her neurological status was
unchanged.
Patient 10: A 12 year old girl with an Arnold Chiari type 1 malformation but no syrinx and scoliosis had
decreased left MEPs, but unchanged SSEPs, following correction, which was undone and the
metalwork removed, during which time the MEP’s recovered. Subsequently she was placed on the
halo traction and 2/52 later procedure was completed with intact monitoring and normal postoperative neurology.
Patient 22: A 74 year old lady with degenerative scoliosis underwent posterior deformity correction,
with instrumentation from T10 to L5. During L2 screw insertion, there was fracture of the pedicle and
she had single muscle MEP reduction in vastus medialis, indicating possible left L2-4 nerve root
injury. The screw was removed and MEPs eventually recovered. Her SSEPs remained unchanged.
Post operatively she had no new deficit
Patient 23: A 71 year old lady with degenerative scoliosis underwent posterior deformity correction,
with instrumentation from T10 to L5. During rod positioning, she had a bilateral 80% reduction in
SSEPs, which recovered when the rods were removed. There was no loss of the MEPs. The rods
were replaced and the correction was completed without any further reduction in SSEPs. Postoperatively she had no neurological deficit.
Patient 26: A 35 year old lady with a severe scoliosis and associated rib hump, which had progressed
from infancy, elected to have anterior and posterior releases with anterior fusion and stabilization from
T5 to T11. Preoperative MRI showed no cord or vertebral abnormalities. During rod contouring the
T5 vertebral body fractured and left sided MEPs were lost a minute later. The screw was removed
and monitoring returned to normal. Her SSEPs remained unchanged. Post operatively the patient
had no neurological deficit.
2 patients with neuromonitoring alerts that did not respond to intervention, with no
post-operative neurological deficit: (False positives)
Patient 9: A 13 year old girl underwent posterior correction of AIS with pedicle screws had single
muscle MEP reduction (right Tibialis Anterior muscle). A pedicle breach of the right L4 screw was
revised but the right MEP remained attenuated. Her SSEPs remained unchanged. The procedure
was completed without any neurological consequences
Patient 16: A 13 year old with Coffin Lowery syndrome and progressive thoracolumbar kyphosis
underwent posterior surgery with a plan to perform PSO had bilateral loss of MEPs and reduction in
SSEPs at 2.5 hours into the course of operation, which did not recover. He had decompression at
T11-12. The MEPs did not recover and so the decision was taken to cancel the osteotomy. He had
subsequent T12 PSO and correction at 4 months later with intact SSEP/ absent MEP monitoring and
no neurological sequelae although any subtle changes would be difficult to assess because of his
learning difficulties.
1 patient with absent monitoring from outset of surgery and new post-operative
spinal cord deficit (Excluded from sensitivity and specificity calculations)
Patient 18: A 2 year old girl with Camptomelic Dystrophy with severe T6 vertebral collapse with
severe kyphosis and cord compression, but no objective neurological deficit. A posterior in situ
application of rods to the angles of the ribs on either side of the deformity with no attempt at deformity
correction was performed. She had absent lower limb MEPs and SSEPs from the start of her
monitoring, before surgery commenced, but upper limb SSEPs and MEPs were present. Post
operatively she had complete paraplegia from T6 level. She was taken back to theatre on the same
day to have removal of implants, but this did not improve her neurology.
Because this patient does not fit with any of the above categories she has not been included in our
sensitivity and specificity calculations. However, due to her post-operative deficit we have included in
our series.