NEURAL INJURY DURING SPINE SURGERY THE ROLE OF INTRAOPERATIVE NEUROMONITORING IN SPINE SURGERY Shane Burch MD ASSISTANT PROFESSOR SURGERY DEPT OF ORTHOPEDICS UCSF

Hamilton, D. K., J. S. Smith, et al. (2011). "Rates of New Neurological Deficit Associated with Spine Surgery Based on 108,419 Procedures: A Report of the Scoliosis Research Society Morbidity and Mortality Committee." Spine (Phila Pa 1976).

•

Spinal Cord Injury

•

Nerve root injury more frequent than spinal cord injury •

2.9% adult spinal deformity surgery (Pateder, Spine 2005)

•

Buchowski (Spine 2007) •

n=108, 11.1% root injury

•

SSEPs, NMEPs, EMG

•

None detected

Hamilton, D. K., J. S. Smith, et al. (2011). "Rates of New Neurological Deficit Associated with Spine Surgery Based on 108,419 Procedures: A Report of the Scoliosis Research Society Morbidity and Mortality Committee." Spine (Phila Pa 1976).

UTILITY OF NEUROMONITORING

MECHANISMS OF INJURY •

•

Degenerative (without manipulation) •

Direct

•

Indirect

• Diagnosis

Deformity (with manipulation) •

•

Direct •

Instrumentation

•

Decompression / dural tear

•

cautery

Buchowski, J. M., K. H. Bridwell, et al. (2007). "Neurologic complications of lumbar pedicle subtraction osteotomy: a 10-year assessment." Spine (Phila Pa 1976) 32(20): 2245-2252.

• Prediction

Indirect •

Spinal manipulation

•

hypotension

• Intra-operative

MODALITIES Wake-up test SSEPs • Posterior tib. nerve to scalp • Examine the continuity of the dorsal columns • EMGs • Free run • Direct - Stimulus applied to the nerve root • CMAP • TcMEPs • Stimulus applied to the scalp • CMAP in different muscle groups • Direct Spinal Cord Stimulation

• •

/ Prevention

Surgical Response

ALARM CRITERIA •

Threshold CMAP • Measured Voltage increase to obtain baseline amplitude •

•

Amplitude CMAP • Measured drop in amplitude from baseline •

• •

>50%

Latency

UNKNOWNS •

•

CMAP •

Amplitude?

•

Latency vs AUC?

Change during injury •

BACKGROUND •

Lieberman, J. A., R. Lyon, et al. (2008). "The efficacy of motor evoked potentials in fixed sagittal imbalance deformity correction surgery." Spine 33(13): E414-24.

•

Hsu, B., A. K. Cree, et al. (2008). "Transcranial motor-evoked potentials combined with response recording through compound muscle action potential as the sole modality of spinal cord monitoring in spinal deformity surgery." Spine 33(10): 1100-6.

•

Kelleher, M. O., G. Tan, et al. (2008). "Predictive value of intraoperative neurophysiological monitoring during cervical spine surgery: a prospective analysis of 1055 consecutive patients." J Neurosurg Spine 8(3): 215-21.

Stepwise vs linear?

•

Root Dominance

•

Hemodynamics / Ca2+

•

Anesthetics

CASE EXAMPLE ALIF

• 62 Y

FEMALE

• SCOLIOSIS • ALIF

MECHANISM OF INJURY

CASE EXAMPLE

• 81 Y • 45

FEMALE

DEGREE SCOLIOSIS

• BACK AND •2

LEG PAIN

STAGE APPROACH

• TRANSPSOAS

/ PSF

CLINICAL TRANSLATION: TLIF sensitivity and specificity of TcMEPs to detect and predict isolated nerve root injury.

METHOD

• Determine

• Transforaminal

• Primary TLIF

at levels L4-5, L5S1: 42 L4/5 and 37 L5/S1

lumber interbody fusion (TLIF) at L4/5, L5/S1

level.

• Average

age 59.2 yrs- 29 Male, 50 Female

• Retrospective

chart review of 79 patients undergoing TLIF • Multi-myotomal

• NASS

2009

METHOD • Warning

criteria >80% drop in MEP amplitude In at least one myotome during sustained retraction of L4/L5 nerve root During diskectomy/ insertion of cage.

• Nerve

root damage = sustained changes on examination at hospital departure

• EMG

MEP

warning criteria= >5s tonic EMG activity

RESULTS

CLINICAL TLIF

RESULTS

% drop from baseline

Nerve Root Retraction

0%

20%

40%

•7

patients had threshold EMG activity

•2

of 5 deficits accurately predicted on EMG

•3

false negative results produced

X

60% X

X

80%

X

X 100%

120% 1.00

2.00

3.00

4.00

5.00

6.00

• Multimyotomal

Minutes of Retraction

HOW DID WE MISS NERVE INJURIES? • false

MEP 100% sensitive and 83% specific to isolated nerve root injury

VARIABILITY IN TCMEP

negatives

• IOM • surgeon • tech

Figure 1. Average total frequency of TcMEP by diagnosis.

Figure 2. Average frequency of TcMEP in non-critical and critical junctures of surgery by diagnosis.

FALSE POSITIVE / NEGATIVES tcMEPs • Trial to trial variability ~ 5%-10% • Hemodynamic fade – hypotension • Frequency of testing • SSEPs • Injury to ventral cord • EMG • Lesion proximal to stimulus • Missed tonic EMG

IMPORTANT FOR TRANSPSOAS APPROACHES

•

HEAD POINT OF INJURY

UNKNOWNS •

•

CMAP •

Amplitude?

•

Latency vs AUC?

Change ge during injury •

Stepwise vs linear? ar??

•

Root Dominance Root D

•

Hemodynamics / Ca2+

•

Anesthetics

FOOT

PURPOSE • To

develop an animal model

• To

monitor TcMEPS changes during nerve root injury: compression vs retraction

• To

compare tcMEPs changes to EMGs for nerve root injury: compression vs retraction

ANIMAL MODEL

ANIMAL MODEL •

• No

reliable large animal model

• Anesthetic

issue

• Team: anesthesiologist

/ neurophysiologist / surgeon •

Porcine model •

Lumbar nerves similar to humans

•

Overcome thickness of the calvarium

•

Anesthetic regimen

•

Venous plexus

Mapping of the nerve roots

REDUCTION IN TCMEP AFTER NERVE ROOT LIGATION (% BASELINE TCMEP)














     




   
 

     


     


   
 



     
 

    


    
 

      
 

   

  
 



  
 

  


 

     
 

     


  
 



      
    
  

   
 

     
 

    






    


 

      
 

      


    


 


EFFECT OF RETRACTION FORCE OF TCMEP AMPLITUDE IN THE TIBIALIS ANTERIOR tcMEP AMPLITUDE % BASELINE

2N 4N 1N

10.00

7.50

0.83

5.00 0.55 2.50 0.28 0 2N 0

4N 0

0

1

2

3

4

5

6

7

8

9

1N

2N

4N

1N

10

2N

4N 20

1N

% BASELINE EMG THRESHOLD L5 NERVE ROOT

1.10

EFFECT OF RETRACTION FORCE ON EMG THRESHOLD OF L5 NERVE ROOT 2N 4N 1N

10 11 12 13 14 15 16 17 18 19 20

TIME (MIN)

TIME (MIN)

WHAT ABOUT COMPRESSION INJURIES?

1N, 2N Compression vs. 1N, 2N, 4N Retraction 1.4

1.2

2N v 1N COMPRESSION (Ligation subtracted)

100.00%

80.00% Mean 2N compression 60.00%

Mean 1N Compression Power (Mean 2N compression)

40.00%

Power (Mean 1N Compression)

% BASELINE AMPLITUDE TcMEP

% BASELINE AMPLITUDE TcMEP

120.00%

1

0.8

0.6 y = -0.0585x + 1.0226 R² = 0.9656

0.4

20.00%

0.2

0.00% 0

1

2

3

4

5

6

7

8

9

y = 0.8339x-0.498 R² = 0.9148

10

TIME (MINS)

0 0

1

2

3

4

5

6

7

8

9

10

TIME (MIN)

CLINICAL TLIF

DISCUSSION

% drop from baseline

Nerve Root Retraction

0%

• Curvilinear

change in TcMEPs following sustained retraction and compression – stretch injury has a much slower change

20%

40%

X

60%

• The

X

rate of change proportional to force and predictable

X

80%

X

X

• The

100%

120% 1.00

2.00

3.00

4.00

5.00

Minutes of Retraction

6.00

recovery of TcMEPs and NRT is inversely proportional to force

• NRT

and TcMEPs are correlated and proportional in both comporession and retraction

MODEL

ALGORITHM

*+,-.%+/%0-&01!2&3+4%!4,%2+*50-113+4% '#!"

• Short

acting relaxant for exposure

'!!"

&!"

MAP

• Frequent

tcMEPs

• TIVA !"#$%&#'()%

Zone of Recovery

• Maintain

• Bight

,-./01234"'" %!"

,-./01234"#" ,-./01234"("

• Dual

block

modality testing • Education

$!"

• EMG

/ tcMEP

• SSEP

/ tcMEP

#!"

!" !"

'"

#"

("

$"

)"

%"

*"

&"

+"

'!"

''"

'#"

CHANGE IN PRACTICE

• TcMEPS

may predict nerve root injury – application to patient set-up – application in indirect (stretch injury)

• Frequent

motors during retraction OR spinal manipulation

• Development

of automated algorithms and retractors to detect early changes

THANK YOU