1. science
2. medicine
3. surgery

Multimodality Monitoring During Transpsoas Lateral
Access To the Spine – A Multicenter Study
Justin Silverstein, DHSc, CNIM
Neuro Protective Solutions, LLC
Spine Medical Services, PLLC
Long Island NY
Jon Block DC,CNIM
ION Intraoperative Neurophysiology, LLC
Walnut Creek, CA
NEUROMONITORING
Goal: To protect the main motor branches of
the lumbar plexus with an intraoperative
functional assessment.
• Motor branches to protect:
1.
Abdominal Innervation: Subcostal
(T12,last thoracic intercostal),
Illioinguinial & Illiohypogastric)
2.
Obturator Nerve
3.
Femoral Nerve
Most feared neurological
complication is damaging
the femoral nerve.
• There is risk of
FEMORAL NERVE injury
during these procedures
• This injury is NOT
RADICULAR in nature
but is a LUMBAR
PLEXOPATHY or
FEMORAL
NEUROPATHY
• Use of Triggered EMG
can only give proximity to
the nerve but CANNOT
assess the function of the
nerve
AHMADIAN, et al. (2012).
Spine 12: 755.
Femoral Nerve Anatomy
• Left lateral view of a left sided
specimen, made after dissection of
the psoas muscle (PS). The spinous
processes would be at the right side
of the image (not visible). Outlines
show the approximate locations of
the vertebral bodies, disc spaces
and pedicles. Transverse processes
(TP) are also outlined.
L3
TP
PS
Note the close proximity
of the L4-5 needle (at a
mid-disc location in
green) and the fully
formed trunk of the
femoral nerve.
Source:
Lumbar Plexus Anatomy within the Psoas
Muscle: Implications for the Transpsoas
Lateral Approach to the L4-L5 Disc
Timothy T. Davis, MD, Hyun W. Bae, MD, MAJ
James M. Mok, MD, MC, USA,
Alexandre Rasouli, MD, and Rick B. Delamarter, MD
L4
TP
Neuromonitoring Goals:
•
To provide a functional assessment of function throughout the procedure.
•
Detecting a reduction in neural function can provide an early alert to surgeons of
impending neurological damage so that immediate action can be taken to avoid
permanent damage.
•
The presence of evoked responses can provide the surgeon with the confidence to
continue the discectomy and arthrodesis placement, therefore reducing constraints on
retraction time.
“Multi-modal neuromonitoring” consists of
2 Types of Evoked Potentials
Saphenous
Somato-Sensory
Evoked Potentials
(SSEPs)
Motor Evoked
Potentials (MEPs)
Neurodiagn J. 55:1–10, 2015
© ASET, Missouri
Motor Evoked Potentials for Femoral Nerve Protection in
Transpsoas Lateral Access Surgery to the Spine
Jon Block, D.C., CNIM1; Justin W. Silverstein, DHSc, CNIM, R. EP T. R.NCS.T., CNCT,
Hieu T. Ball, M.D.4; Laurence E. Mermelstein, M.D.5; Hargovind S. DeWal, M.D.5;Rick
Madhok, M.D.6; Sushil K. Basra, M.D.5; Matthew J. Goldstein, M.D.7
1ION Intraoperative Neurophysiology, LLC Walnut Creek, California
2Neuro Protective Solutions, LLC Commack, New York
3Spine Medical Services, PLLC
Walnut Creek, California
4California Comprehensive Spine Institute, Inc.
San Ramon, California
5Long Island Spine Specialists, PC Commack, New York
6Neuroaxis Neurosurgical Associates, PC Kew Gardens, New York
7Orthopedic Associates of Manhasset, PC Great Neck, New York
ABSTRACT. Detecting potential intraoperative injuries to the femoral nerve should be the main goal of neuromonitoring of lateral lumber interbody fusion
(LLIF) procedures. We propose a theory and technique to utilize motorevoked potentials (MEPs) to protect the femoral nerve (a peripheral nerve), which is at
risk in LLIF procedures. MEPs have been advocated and widely used for monitoring spinal cord function during surgical correction of spinal deformity and
surgery of the cervical spine, but have had limited acceptance for use in lumbar procedures. This is due to the theoretical possibility that MEP recordings may
not be sensitive in detecting an injury to a single nerve root secondary to overlapping muscle innervation of adjacent root levels. However, in LLIF
procedures, the surgeon is more likely to encounter lumbar plexus elements, including peripheral nerves, than nerve roots. Within the substance of the psoas
muscle, the L2, L3, and L4 nerve roots combine to form the trunk of the femoral nerve. At the point where the nerve roots become the trunk of the femoral
nerve, there is no longer any alternative overlapping innervation to the quadriceps muscles. Insult to the fully formed femoral nerve, which completely blocks
conduction in motor axons, should theoretically abolish all MEP responses to the quadriceps muscles. On multiple occasions over the past year, our neuromonitoring groups have observed unilateral (surgical-side-only) femoral motor and/or sensory evoked potential intraoperative changes, many of which
resolved with a surgical intervention (i.e., prompt removal of surgical retraction).
Corresponding Author’s Email: wiredneuro@gmail.com
Received: September 16, 2014. Accepted for publication: November 21, 2014.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/utnj.
1
Preserving femoral nerve function: A review of
multimodality neuromonitoring in 97 transpsoas
J Silverstein, DHSc, CNIM, J Block, DC, CNIM, M Goldstein, MD, R Madhok, MD, S Basra, MD, L Mermelstein,
MD, H DeWal, MD, H Ball, MD & J Dowling. Being Presented at ISASS 2015 – San Diego
• A multi-center group of board certified neurophysiologists, fellowship trained orthopedic spine and
neurological surgeons performed and monitored 97 lateral transpsoas procedures over the course of one year.
• Saphenous SSEPs and Motor evoked potentials from the approach side quadriceps was performed
• 2 patients exhibited a loss of the approach side sSSEP concurrently with a loss of the quadriceps MEP
responses while the retractors were in place.
• With removal of the retractors, the responses from both modalities returned to baseline values and no new neurological deficits were
observed
• 1 patient exhibited a loss in the sSSEP with return to baseline after intervention (MEPs were not obtained at
baseline in this case).
• In 6 procedures, quadriceps MEPs were recorded at baseline and were lost following placement of the
retractors (with sSSEPs unobtainable at baseline in these cases)
• Removal of retractors showed a full return of MEPs to baseline in 5 patients with no new post-op neurological deficits noted.
• Patient 6 exhibited postoperative ipsilateral quadriceps palsy; however, this case was early on in our adoption
of the MEP technique and proper technique and interventional protocols were not yet in place.
• We also had one patient exhibit transient thigh paresthesia without intraoperative SSEP or MEP detection
• We report a sensitivity of 92% and a specificity of 100%, with a PPV of 100% and a NPV of 99%.
Case Study:
• Lateral L4-5 procedure with a concurrent loss of the surgical side
Sapehnous SSEPs and a loss of only the surgical side quadriceps MEPs.
• All other Posterior Tibial and the contralateral Saphenous SSEPs and all
other MEP responses were unchanged.
• Informed surgeon of loss of sensory and motor evoked potentials at the
time when the discectomy was complete, trial size was established and
he was preparing for the final implant.
• Surgeon hastened the insertion of the implant and removed the retraction
as soon as was possible.
• The lost Saphenous SSEP and MEPs quickly returned to baseline values.
L Quadriceps
R Quadriceps
MEPs
March 2015
Case Study:
Loss of Quadriceps MEPs & Saphenous
SSEPs during the discectomy in an L4-5
Trans-psoas Discectomy & Fusion
Post operative exam:
Knee extension reported as 3/5 strength down from 5/5 pre-operatively
Saphenous SSEPS
PTN SSEPS
Ipsilateral Saphenous
SSEPS
Ipsilateral
Waterfall
Contralateral
Waterfall
Motor Evoked Potentials: Ipsilateral Muscle Recordings
Vastus Medialis
Tibialis Anterior
Gastrocnemius
Adductor Hallucis
Motor Evoked Potentials: Ipsilateral Muscle Recordings
Vastus Medialis
Tibialis Anterior
Gastrocnemius
Adductor Hallucis
Jon Block, DC, CNIM & Justin Silverstein, MS, CNIM
Neurodiagnostic J. 54 (4) Dec 2014.
Motor Evoked Potentials for Femoral Nerve Protection in Transpsoas Lateral
Access Surgery to
the Spine
J Block, DC, CNIM, J Silverstein, DHSc, CNIM, H Ball, MD, L Mermelstein, MD, R
Madhok, MD, M Goldstein, MD, S Basra, MD, & H DeWal, MD
Neurodiagnostic J. 55(1): In press Mar 2015
3/19/2015
The Monitor- ASNM’s Monthly Newsletter
November 2014
Variable Results in Motor Mapping of the Lumbar Plexus:
A Comparison of 3 Different L2-L3 Far Lateral Lumbar Discectomy & Fusion Procedures
Justin Silverstein, MS, CNIM, Jon Block, DC, CNIM, Sushil Basra, MD
Spine Medical Services, PLLC, ION Intraoperative Neurophysiology, LLC, Long Island Spine Specialists, PC
There has been a major trend in surgery towards less invasive procedures performed through smaller surgical apertures. Smaller surgical openings are
associated with decreased visualization, and surgeons must rely more on intraoperative tools including fluoroscopic imaging and motor nerve mapping
techniques to assess their relative anatomical position and proximity to neural structures respectively. In retroperitoneal lateral lumbar interbody fusion
(LLIF) procedures, the surgeon must establish a safe surgical corridor to access the disc space by traversing through the substance of the psoas muscle
while avoiding damage to the lumbar plexus. Surgeons utilize Triggered EMG (T-EMG) using a monopolar electrical probe to detect the presence and
proximity of lumbar plexus elements in the surgical field. A detailed understanding of the functional anatomy of the lumbar plexus and an appreciation of
anatomical variants is essential to understanding how to effectively map the lumbar plexus. Anloague and Huijbregts (2009) describe a prevalence of
anatomical variation ranging between 8.8-47.1% in the individual nerves of the lumbar plexus with a mean prevalence of 20.1%.
No clear guidelines for muscle selection in LLIF procedures have been established. In this article, the authors describe their personal experience and
rationale for selection of essential muscle recordings for LLIF procedures at the L2-3 level. We present 3 separate L2-3 LLIF procedures that illustrate the
variability of lumbar plexus elements that may be encountered at the same surgical level in different patients. At the L2-L3 Level, we recommend the
following essential T-EMG muscle recordings to assist in the navigation of the lumbar plexus:
Abdominal Muscles: The major elements of the upper lumbar plexus include multiple nerves that innervate the abdominal muscles including the
Subcostal (T12), Illiohypogastric (T12, L1) and Illioinguinial (L1) nerves. Gaining access to the retroperitoneal space and traversing the abdominal wall
poses a risk of injury to these major nervous structures and abdominal wall paresis is an associated complication of the LLIF procedure. (Ahmadian,
Deukmedjian, Abel, Dakwar, & Uribe, 2013; Dakwar et al, 2011). The authors have often observed T-EMG responses from abdominal muscle recordings
that have been useful in alerting the surgeon of the presence of neural elements in the surgical field. (Figure 1).
Adductors:The Obturator nerve is formed by the L2, L3, & L4 roots and descends through the Psoas muscle to innervate the major muscle group for leg
adduction. Figure 2 illustrates an example where motor mapping at the L2-3 level resulted in T-EMG responses limited to the adductor muscle recording
channel suggesting proximity to the Obturator nerve.
Quadriceps:The femoral nerve (L2, L3, & L4) innervates the quadriceps muscles. Anterior thigh pain, paresthesia and diminished knee extension are
complications associated with a femoral nerve injury in LLIFs. (Ahmadian, Deukmedjian, Abel, Dakwar, & Uribe, 2013). We recommend using multiple
quadriceps muscle recordings (i.e. rectus femoris & vastus medialis). Figure 3 illustrates an example where motor mapping at the L2-3 level resulted in TEMG responses from multiple quadriceps muscles in addition to adductor muscle responses suggesting proximity to both the Femoral and Obturator
nerves.
Although more study is needed, the authors recommend the utilization of abdominal, adductor and quadriceps muscle recordings when mapping the
lumbar plexus in L2-3 LLIF procedures.
Conclusions:
•
•
Saphenous SSEPs can be recorded to detect
electrophysiological changes and prevent femoral
nerve injury during lumbar trans-psoas interbody
fusion.
Larger sampling size is underway to validate
whether addition of this technique offers increased
sensitivity and/or specificity, and helps to reduce the
risk of postoperative neurological deficits.
Limitations
•
These techniques requires the presence of a QUALIFIED
NEUROPHYSIOLOGY PROFESSIONAL for the establishment of baseline
potentials and to monitor the potentials in a continuous fashion.
•
The saphenous nerve SSEP was not able to be established at baseline
in 10% of the patients during our pilot study.
•
In our Second Study: Saphenous SSEP were not obtained in 6% (6/97)
of the patients and MEPs to the Quadriceps were not obtained in 6%
(6/97) of the patients
Closing Thoughts
Monitoring:
• SSEP
• Saphenous nerve SSEP - Monitors Femoral nerve function
• Continuous recordings provide valuable information about the functional integrity of the
femoral while the retractors are in place.
• This is especially important at the L3-4 and L4-5 Levels.
• Upper Extremity SSEPs should be monitored for potential
positional injuries and to assess the effects of anesthetics on
evoked potentials
• Other SSEPs can be used as controls, to assess global quada
equina function, to assess positional leg issues and nerve root
stretching caused by arthrodesis placement (Duncan et al,
2012)
• Posterior TIbial Nerve SSEP
• Deep Peroneal SSEP
Closing Thoughts
Monitoring:
• MEP
• MEPs SHOULD be used as complimentary information to
assess peripheral nerve function (i.e. femoral nerve and
obturator nerve).
• The utility of MEPs in detecting alterations in nerve root function is unclear
• MEP responses are recorded from the same muscles used for EMG
• Combined with Saphenous SSEPs, MEPs may provide redundant information regarding
femoral nerve function.
• MEPs are only beneficial if quad muscles are obtained.
• AHL muscle used as control to ensure MEPS are present.
• MEPs should be assessed periodically following final retractor placement, discectomy
and arthrodesis placement.
Thank you!
Intraoperative Neurophysiology
Jon Block DC,CNIM
www.smsneuro.com
ION Intraoperative Neurophysiology
951 Country Lane
Walnut Creek, CA 94596
jblockny@gmail.com
(678) 977-6666
www.npsneuro.com
Contact: Justin@smsneuro.com
Manual T-EMG Threshold Technique
Manually determining
motor threshold level
Stimulation intensity
manually controlled
Key Concept:
Motor Mapping must be differentiated from Monitoring Nerve Function
• The presence of a Triggered EMG response does not provide the surgeon
with evidence of functional continuity of plexus elements
Rationale: Even if a nerve is surgically transected, the distal segment of the nerve will
remain electrically excitable for approximately 24-48 hours until degeneration of the
distal segment takes effect.
Monitoring the function of the nerves of the lumbar plexus throughout the procedure
requires the utilization sensory and motor evoked potentials.
48 hours later