Evoked Potential

Selective Dorsal Rhizotomy

Judi Berry, CNIM

History
reduces spasticity and rigidity in cerebral palsy patients
cp is motor deficiency 
harrington
loss of descending inhibition causing spasticity
forrestor and assoc. did human trials by sectioning several sensory nerve roots
modified technique to preserve function
can affect walking, bladder, bowel function where sensory input is vital
only guy for 50 years
gross and assoc. partial rhizotomies which were non-selective
79 fasano, first intraoperative findings w/ emg, neurophysiologist for first time
using 1Hz probe then increased to 50 Hz, noticed three different things
1. some showed normal with low but increased show change; simultaneous activation
2. lack of inhibition of reflex arc, after discharge responses were seen
3. 

simultaneous activation
simultaneous activation at unexpected levels
simultaneous activation at unexpected sides/contralaeral levels

they would then section each rootlet down

effective procedure, 98% improvement!

Peacock Types

types vary; decremental, squared, decremental scquared, incremental squared, miltiphasic, clonic, irregular and sustaine

Park and Phillips grades system, 0 - 4, with +'s 2 + starting to get into abnormal, 3 and 4 are 

diagram shows ventral horn synaps for motor root (ventral and the dorsal nerve root tracts that input posteriorly

want to leave one rootlet intact at each level

Current Trends

Patient Type

must have adequate strength in trunk and legs
support weight on feet
hold posture agains gravity
make appropriate movments to walk or crawl
motivation and ability to cooperate with therapy; communicate with therapist

not considered
history of meningitis, congenital brain infection, hydrocephalus, head trauma, familial disease, severe scoliosis

overwhelming popluation is between 2-5, patients gestitational age, 84% were born between 25 and 38 weeks, most are preterm born

Anesthesia

Monitoring methods

prone, EMG wires, can do lobster tail to expose all nerve root, minimally invasive technique is new, need to separate motor and sensory roots from each other, less than a microvolt to a threshold of about 3mA

surgeon use peacock probes, two microelectrodes to disect out nerve root, also use to stimulate, they may not fit into the adaptoer

anode 

1st stimulate entire root and record overall response type and section into 3-8 rootlets

2nd establish threshold with stimulation of 1 sec duration and not responding channels
*threshold is 200 uV

3rd switch to 50 Hz pulse train with 1s duration at the determined threshold level without significant delay. 

eseentially dorsiflexing their feet, it will result in their feet moving back and forth, the clonic movement is 

Anesthetize

Propfol will give false readings by anesthetizing the cord, no or low propofol and gas as low as possible, TIVA, test the ankle conus, most of them will have it and can see if they have it pre operatively and then maintain that level of clonus

EMG filter settings of 30 - 1000 with time base 

keep warm saline close at hand, will calm the free running activity, effective for cauda equina

length of the stumulation window, 2 second sweep, 200 uS pre stimulus and 800 uS post stimulus

have a second person to make recordings, will have to make 96 recordings, have a clip board and a pen, which rootlet, type of rresponse, wheter or not that root was cut

clonus will start to disappear, will see the muscles relaxing, immediate indications that the surgery is effective, set yourself at the foot f the bed with a plastic sheet
This 5-year-old boy is undergoing a selective dorsal rhizotomy for relief of spastic diplegia secondary to cerebral palsy. He was a 26 week preemie and has had a VP shunt with 3 revisions. He has sustained clonus bilaterally, drags his right toe and is unable to swing his legs in phase. He circumducts his feet, but does not scissor as much. In order to determine which individual rootlets to section, the adaptation of the monosynaptic spinal H-reflex to rapid stimulation was assessed intraoperatively.
07:30 - Sterile needle electrodes were inserted bilaterally into the following muscles: iliopsoas (L1-2), quadriceps (L2-4), adductor (L2-4), tibialis anterior (L4-5), hamstring (L5-S2), gastrocnemius (S1), intrinsic toe flexors (S2), and external anal sphincter (S2-4). After surgical exposure of the cauda equina, the segmental levels were identified by electrical stimulation and sensory vs. motor roots determined by the low electrical threshold of the motor roots. Individual sensory rootlets were then stimulated separately, first with single pulses to determine the threshold for the response, then with a 50 Hz train for one second.  Normal rootlets were identified by a decrementing or squared EMG response to the train.  In contrast, abnormal rootlets exhibited either: 1) an incrementing response during the train; 2) multiphasic or clonic patterns of the response during the train; 3) sustained EMG discharges after the train; and/or 4) spread of the reflex contraction to muscles innervated from other segmental levels or from the contralateral side.  These observations were discussed with the surgeon to guide the selection of rootlets to be transected.  Rootlets showing significant anal sphincter responses were always preserved. The total number of rootlets tested vs. sectioned in this patient were:


    L Side    Sectioned    Tested    R Side    Sectioned    Tested
    L2    1    3    1 (30%)    2            
    L3    0    4    1    3            
    L4    0    4    1.5    3
    L5    4    7    3 (60%)    4
    S1    2    4    1    2
    S2    -    -    -    -
            Total    7    22    7.5    14


    Total for both sides:  Sectioned    14.5     Tested        36

Cerebral Palsy, loss of descending inhibition, leading to hyperactive reflex arcs
Identify motor roots by lower threshold
Separate sensory roots into several "rootlets", test with high frequency train
  • normal rootlets have decrementing response: leave
  • abnormal rootlets may increment, spread to other segmental levels or even to the other side: section
  • Anesthesia: no paralysis, stimulation is painful, may require more agent (isofluarne, desflurane, sevoflurane, etc.) to counteract
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