American Academy of PM&R October 1-4, 2015 C.R. Sridhara MD

Workshop- W302Obtaining Reliable Sensory Responses in the Lower Extremities

Obtaining Reliable Sensory Responses in the Lower Extremities

OBJECTIVES

1) Understand the anatomy of the sensory nerves in the lower limbs

2) Learn the contribution of the sensory nerve evaluation to theelectrodiagnostic study including the ones less commonly studied

3) Perform sensory studies on a subject to include superficial peroneal, sural, saphenous, plantar nerves

4) Learn techniques to minimize “noise” in order to achieve optimal results

5) Interpret the sensory findings in the context of the entire electrodiagnostic study to provide prognosis and recommendations for management

Medial Dorsal Cutaneous (disc electrodes)

A: On Medial dorsal cutaneous nerve, plantar flex and invert foot passively, find nerve at level of malleoli. The nerve extends to the first web space. If cannot palpate, can try halfway between extensor hallucis longus tendon and lateral malleolus.

R: 4 cm distal.

G: lateral ankle

Stim: 14 cm to the anterolateral leg ½ way between the tibial crest and posterior middle of the leg or posterior to the line that extends from the recording electrode to the fibular head

Sural (disc electrodes)

A: On sural nerve, posterior and inferior angle of the lateral malleolus.

R: 4 cm distal to active electrode along the lateral border of the foot over the dorsal surface.

G: lateral leg just proximal to the active electrode

Stim: 14 cm proximally in posterior leg 1 cm lateral to midline.

Point of Caution: Position the patient in lateral decubitus position facing away from the examiner

Saphenous (disc electrodes)

A: 4 cm above reference electrode along the saphenous nerve in the medial distal leg

R: Anterior edge of the medial malleolus

G: Medial leg just proximal to the active electrode

Stim: 14 cm proximal to active electrode 1 cm posterior to the tibia

Point of Caution: Nerve always accompanies the saphenous vein

Deep Peroneal (disc electrodes)

A: Interspace between the 1st and 2nd toes

R: 4 cm distally on the 2nd toe

G: Lateral to the active electrode on the foot

Stim: 12 cm proximal to the active electrode and lateral to the extensor hallucis longus tendon

Point of Caution: Use a cotton ball on the active electrode under the tape to keep the contact better

Lateral Femoral Cutaneous (sensory needle recording and stimulating electrodes)

A: 14 cm distal to the anterior superior iliac spine along line to lateral patella. (Find the point at which a low stimulus produces sensation in the distribution of the lateral femoral cutaneous nerve for the area of recording).

R: 4 cm distal to active electrode in the thigh on line to lateral patella

G: Anterior thigh close to the active electrode

Stim cathode: One fingerbreadth medial to anterior superior iliac spine along the inguinal ligament

Stim anode: Just proximal to anode

Point of Caution: Use the bar electrode as the anode to have the ability to rotate it as necessary around the cathode to decrease the shock artifact.

Medial Calcaneal Nerve (disc electrodes)

A: 1/3rd distance from apex of the heel to the mid point between tuberosity of the navicle and tip of medial malleolus

R: Apex of the heel

G: Medial heel

Stim: Tibial nerve 10 cm proximal to the active electrode

Point of Caution:

Medial Plantar Nerve (disc electrodes)

A: Tibial nerve just proximal to flexor retinaculum

R: 4 cm proximal to the active electrode

G: Dorsum of the foot between stimulator and active electrode

Stim: 14 cm distal to the active electrode between 1st and 2nd metacarpal. Measure 10 cm in a straight line to the plantar foot and 4cm along the medial foot

Point of Caution: Will need high stimulation to obtain the response

Lateral Plantar Nerve (disc electrodes)

A: Tibial nerve just proximal to flexor retinaculum

R: 4 cm proximal to the active electrode

G: Dorsum of the foot between stimulator and active electrode

Stim: 14 cm distal to the active electrode between 4th and 5th metacarpal. Measure 14 cm in a straight line to the lateral plantar foot

Point of Caution: Will need high stimulation to obtain the response

Posterior Femoral Cutaneous Nerve (disc electrodes)

A: Posterior thigh 6 cm proximal to the mid popliteal region

R: 4cm distal to the active electrode

G: Posterior thigh just proximal to the active electrode

Stim: 12 cm proximal to the recording electrode on a line connecting the active recording electrode with the ischial tuberosity in the groove between the medial and lateral hamstring muscles

Point of Caution: Palpate the posterior thigh while patient is slightly flexing the knee to confirm the intermuscular groove. Complete relaxation of thigh is important to obtain the response

TIPS for Sensory conduction Studies

-Press lightly with stimulator for sensory studies; keep fingers on patient.

-Always keep the other hand over the ground electrode

-Do not cross wires or let them hang off the examination table.

-Rotate the stimulator to decrease shock artifact.

-Always use electrode gel on the electrodes with each change of the electrode position.

-Clean the skin with alcohol and may need skin abrading under all electrodes to decrease the shock artifact, especially in the lower limb sensory studies.

-Slide the stimulator in the anterior posterior plane to find appropriate point of stimulation in the leg nerves

Normal Values:

Nerve

/ SNAP uV
Peak to peak / DSL ms
Onset / CV m/s / Distance cm
Medial Dorsal Cutaneous
Age adjusted / <50 = 8
50-70 = 5
>70 = Present / <30 = 3.3
31-50 = 3.5
51-70 = 3.6
>71 = 3.9 / <30 = 42
31-50 = 40
51-70 = 39
>71 = 36 / 14
Sural
Age adjusted / <30 = 8
31-50 = 7
51-70 = 5
>71 = Present / <30 = 3.2
31-50 = 3.6
51-70 = 3.9
>71 = 4.0 / <30 = 43
31-50 = 39
51-70 = 36
>71 = 35 / 14

Saphenous

/ Range 1-15 / Range 2.1- 3.8 / Range 37-66 / 14
Deep Peroneal / 3.4 ± 1.2 / 2.9 ± 0.4 / 42.0 ± 5.0 / 12
Lateral Femoral Cutaneous / Range 10-25 / 2.6 ± 0.2 / Range 42-65 / 14
Posterior Femoral Cutaneous / 6.5 ± 1.5 / 2.8 ± 0.2 ?Peak / 38-50? / 12
Medial Plantar / >10 / 3.2 ± 0.3 / 14
Lateral Plantar / >8 / 3.1 ± 0.3 / 14
Medial Calcaneal / 8 / 2.3 / 10

Butler ET, Johnson EW, Kaye AZ: Normal conduction velocity of the lateral femoral cutaneous nerve. Arch Phys Med Rehabil: 1974; 55: 31-32

Del Toro DR, Park TA, Mandel JD, Wertsch JJ: Development of a nerve conduction study technique for the medial calcaneal nerve. Muscle Nerve: 1992; 15: 1194-

DiBenedetto M: Sensory nerve conduction studies in the lower extremities. Arch Phys Med Rehab, 1970; 51:253-258

Dumitru D, Nelson MR: Posterior femoral cutaneous nerve conduction. Arch Phys Med Rehabil: 1990; 71: 979-982

Izzo KL, Sridhara CR, Rosenholtz H, Lemont H: Sensory nerve conduction studies of the branches of the superficial peroneal nerve. Arch Phys Med Rehabil: 1981;62: 24-27

Lee HJ, Bach JR, DeLisa JA: Deep peroneal nerve: Standardization in nerve conduction study. Am J Phys Med Rehabil: 1990; 69: 202-204

Saeed MA, Gatens PF: Compound nerve action potentials of the medial and lateral plantar nerves through the tarsal tunnel. Arch Phys Med Rehabil: 1982; 63: 304-307

Wainapel SF, Kim DJ, Ebel A: Conduction study of the saphenous nerve in healthy subjects. Arch Phys Med Rehabil: 1978: 59; 316-319

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