Unusual NCS Flashcards
Superficial peroneal sensory study is a _____ study to which nerve root?
pure sensory
L5
Helpful with diagnosis of where pathology is in _____
footdrop
could be from lumbosacral plexus injury, peroneal motor nerve injury, sciatic nerve injury (lateral devision) or from L5 radiculopathy
Why is the superficial peroneal nerve not compressed in tarsal tunnel?
passes superior to tarsal tunnel.
What is the anatomy of the peroneal nerve (superficial branch)
branch off the common peroneal just below the fibular head. It goes into the lateral leg and innervates (motor wise) the peroneus longus and peroneus brevis It pierces the deep fascia in the lower part of the leg and comes back superficial. It crosses above the extensor retinaculum at the ankle. The superficial peroneal sensory nerve would be normal in anterior tarsal tunnel syndrome. When it pierces through the distal fascia, it branches into two peripheral branches: medial dorsal cutaneous nerve and the intermediate dorsal cutaneous nerve. Those two branches innervate sensation to the entire dorsal aspect of the foot except for the first web space (deep peroneal nerve).
How do you set up for superficial peroneal sensory study
bimalleolar line. You feel for the edge of the tibia and to the lateral malleolus you go halfway along that line. You go 3 cm proximal to the bimalleolar line. Lateral malleolus, and the edge of the tibia (bimalleolar line), go 3 cm proximal and place the active electrode. The reference is 4 cm distal to that. Put the ground on the leg, measure back 14 cm from the active electrode (sensory study), and palpate the shaft of the fibula, and stimulate anterior over the shaft of the fibula. We’re basically picking up over the intermediate dorsal cutaneous nerve when we do that.
The superficial peroneal sensory nerve is absent bilaterally in ____% of people
2
people > ____ yoa may not have findings for superficial peroneal and sural nerves
65, due to age; small nerves
femoral nerve motor study is used for femoral neuropathy which can be caused by which two major things
femoral art line with hematoma after
pelvic cancer with radiation to the area
loss of femoral nerve would cause which sensory loss?
loss of sensation down medial leg/foot (saphenous nerve is terminal extension of the femoral nerve)
how do you set up for femoral motor nerve test?
do the test with a monopolar needle pickup. Put the needle into the vastus medialis obliquis (VMO). Put reference over superior patella. Stimulate along the ilioinguinal ligament. Feel for femoral artery (NAVEL). Stimulate over nerve both above and below the ilioinguinal ligament (3 cm above and 3 cm below)
-do normal leg first
-if conduction block
-Stimulate below ilioinguinal ligament – should be normal.
-Stimulate above ilioinguinal ligament, it should be abnormal
-pickup with monopolar needle. Can use it to find conduction block (greater than 50% reduction in amplitude) because you don’t move the pickup (monopolar needle). You can compare amplitudes along the femoral nerve on the side you’re testing. You can’t compare amplitudes from one leg to the other (because you will have moved the needle and can’t be sure you’re the same depth from the nerve).
Can confuse femoral nerve injury with ______.
how do you tell the difference
-can confuse femoral nerve injury with diabetic amyotrophy (lumbar polyradiculopathy affecting L2-4 roots)
-In diabetic amyotrophy, both the adductors and femoral nerve affected.
-In femoral nerve entrapment – only the femoral nerve affected.
*reminder: adductor magnus is dual innervated with obturator and sciatic component
NCS for lateral femoral cutaneous nerve?
-NCS: Feel for ASIS, go 1 cm midline to that, and stimulate. Go distal 14 cm, put pickup surface electrode on the lateral thigh, with reference 4 cm distal to that
-side to side comparison
-most efficacious way to identify this pathology: [TQ] Somatosensory Evoked Potentials
-Can also diagnose with a diagnostic block to see if it improves
most efficacious way to diagnose lateral femoral cutaneous nerve pathology?
somatosensory evoked potentials
How do you perform the saphenous sensory study?
what is it the terminal extension of?
-terminal extension of the femoral nerve
-medial leg and medial foot
-feel for medial malleolus, and the tibialis anterior tendon, go ½ way between the two and put the pickup. Put the reference 4 cm distal. Stimulate 14 cm proxima (sensory study). Feel for the medial edge of the tibia and stimulate right under the medial edge of the tibia. The nerve is very deep there, so you have to turn up the duration and intensity (painful)
_____ is also known as backpackers palsy or ruck sac palsy
spinal accessory nerve
The spinal accessory nerve has 2 components:
-The spinal accessory nerve has 2 components.
- Accessory (bulbar) component
-special visceral efferent fibers and those are rising from the nucleus ambiguous located in the medulla. (bulbar – come off brainstem) They join the spinal portion of the nerve near the jugular foramen.
-Accessory special visceral afferent fibers separate from the spinal portion near the jugular foramen and unit from the fibers of Cranial nerve 10 and go to the muscles of the pharanx. They don’t make it out to the SCM or the trapezius.
- Spinal component
-Consists of the first 5 cervical segments and they ascend within the spinal canal and enter the cranium through the foramen magnum and then join with the bulbar fibers to exit out the jugular foramen and innervate the - Sternocleidomastoid muscle
- trapezius muscle.
-You can also see that there is a branch at C2 that exits out the foramen and merges with the spinal accessory nerve under the SCM. It moves towards the trapezius and sort of makes a plexus and then there’s some more innervation from the spinal nerves (some people say it includes C2, C3, C4 some people say it even includes C5 [controversy]). (almost dual innervated as it meets up with the C2-4). There are really two areas where they come out of the foramen and form a plexus that’s right under the trapezius muscle. One major component from C2 and then some other ones from C3, C4, C5 into this plexus
-The primary innervation is through the main spinal accessory nerve, but part of the lower trapezius get some of the fibers from C3 and C4. You could have an injury at different places and have some function of the trapezius. If you have a C2 injury that goes the major component of the trapezius muscle, you may have that upper and middle trapezius out, but there might still be some function of the lower trapezius depending on where the injury is.
Why might the lower trap be okay with spinal accessory nerve involvement?
if intracranial lesion, lower trap receives more c fibers than from accessory so may have atrophy of upper and middle but not lower.
If the trapezius is no longer working, what kind of scapular winging will you have
lateral winging on trap activation.
if the serratus anterior is out, will have what kind of winging?
medial winging.
What are the three locations of pathology for spinal accessory nerve?
- intracranial (meningioma or acoustic neuroma)
- intraspinal - canal (also bulbar [pertaining to the medulla oblongata] lesions) problems, syringomyelia, tumors, intracranial mass like meningioma and acoustic neuroma
-usually SCM and trapezius affected - peripheral injury (SCM will be spared) secondary to something like radical neck dissection (sacrificed in posterior dissection)
(blunt trauma) radial neck dissection (head and neck cancer), lymph node biopsy. (blunt trauma) Stretch injury ie. If force on top of shoulder which depressed their shoulder can injure the spinal accessory nerve. Radiation, carotid enderaterectomy, coronary arty bypass grafts (when they do sternotomy).
-usually only trapezius affected (Can’t shrug shoulder), but SCM spared
