Download - Nerve Conduction Studies- Lower Leg
LUMBAR PLEXUS
Formed by the
ANTERIOR RAMI of
L1-4.
Anterior rami join to
form OBTURATOR N.
Posterior divisions of
the rami join to form
FEMORAL N.
OTHER NERVES
Other nerves include-
LATERAL
CUTANEOUS NERVE
OF THIGH (pure
sensory).
ILIOHYPOGASTRIC N
ILIOINGUINAL N
GENITOFEMORAL N
LUMBAR PLEXOPATHY
Abrupt onset pain in
anterior aspect of thigh.
Muscle wasting and
weakness in 2-3
weeks.
Absent knee reflexes.
Tender femoral N
Positive femoral stretch
sign
Clinical features Signs
Sensory symptoms are partial and seen in 1/3rd
patients.
NCV shows normal nerves- femoral, peroneal, suraland saphenous N.
May show reduced amplitude.
EMG may show changes of denervation andrenervation.
Recovery may be spontaneous over months-years.
FEMORAL NFrom dorsal portion of anterior rami of L2-L4
Mixed Nerve
Normal femoral conduction velocity – 70.0 ± 5.5 m/S
FEMORAL NERVE
In intraabdominal
course, supplies the
iliopsoas muscle.
Divides to anterior and
posterior division after
crossing Inguinal
ligament.
FEMORAL NERVE
Medial cut N
Supplies medial thigh
Intermediate cut N
Supplies anterior thigh
Supply to Pectineus
and Sartorius
Supplies
Knee and hip joint
Quadriceps musc.
Terminates as
Saphenous N
Anterior Division Posterior Division
FEMORAL NEUROPATHY
Causes
Weakness of Quadri.
Wasting of Quadri.
Loss of knee reflexes
Sensory loss in medial
aspect of thigh and leg
Causes
Diabetes mellitus
Intrapelvic collection
Pelvic surgery
Hip arthroplasty
Tumor of vertebra
Cannulation of Femoral
vein/artery
Inguinal lig
compression in
lithotomy
Renal transplant
ELECTROPHYSIOLOGY
Surface recording
electrode: belly of
vastus medialis
Reference electrode
prox to patella.
Stimulating electrode:
lateral to femoral artery.
NCV
Slowing of conduction velocity
Small CMAP amplitude.
Conduction block (if compressed at inguinal lig)
Saphenous vein can be used to evaluate sensory loss.
Normal femoral conduction velocity – 70.0 ± 5.5
m/S
SAPHENOUS NERVE
Largest and longest pure sensory
branch of Femoral N .
Supplies skin over medial aspect of
leg and foot.
Normal Saphenous conduction velocity- 49.03 ± 3.36 m/s.
SNAP Amplitude- 3.54 ± 1.52 µV
SAPHENOUS N
Arises from posterior
division of Femoral N
Becomes superficial
just above medial
condyle
Continues down to
head of 1st metatarsal
SAPHENOUS NEUROPATHY
Uncommon
Follows
Laceration injuries
Entrapment in subsartorial canal
Surgery for varicose veins
Causes sensory impairment in medial aspect of
knee, leg and foot.
SAPHENOUS NERVE CONDUCTION
Stimulate 1 cm above
inferior border of
patella between gracilis
and sartorius.
Recording electrode-
15 cm distal on medial
border of tibia.
Stimulate between
medial head of
gastrocnemius and
tibia, 12- 14 cm
proximal to med
malleolus
Recording electrode is
placed anterior to
medial malleolus
Normal Saphenous conduction velocity- 49.03 ± 3.36 m/s.
SNAP Amplitude- 3.54 ± 1.52 µV
LATERAL FEMORAL
CUTANEOUS NERVE
OF THIGH
L2-3.
Sensory supply to
Anterolateral aspect of
thigh.
Latency and Amplitude of SNAP
above Inguinal Lig- 2.8±0.4ms
and 6±1.5 µV
MERALGIA PARESTHETICA
Entrapment of the
nerve at Inguinal tunnel
Seat belts
Obesity
Unknown
Proximal lesions
Psoas abscess
Retroperitoneal tumor
Post op scarring
Pain & paresthesia over
lateral surface of thigh.
Symptoms increase on
standing and prolonged
walking.
Sensory loss is in area
smaller than supplied by
the nerve
NCV- abnormal conduction in Lat Cut N of Thigh
EMG- normal study of paraspinal, iliopsoas, quadriceps.
NERVE CONDUCTION-
LAT CUT N OF THIGH
Surface Electrode- 17-
20 cm distal to Ant
Supr Iliac Spine
(ASIS).
Reference electrode- 3
cm distal to surface
electrode.
Antidromic stimulation
above inguinal
ligament 1 cm medial
to ASIS
Latency and Amplitude of SNAP above Inguinal Lig- 2.8±0.4ms
and 6±1.5 µV
SACRAL PLEXUS
Branches
Sup Gluteal N(L4-S1)
Gluteus medius
Gluteus minimus
Tensor facsia lata
Inf Gluteal N(L5-S1)
Gluteux maximus
Sciatic N (L4-S3)
SACRAL PLEXOPATHY
Abrupt onset pain in
posteror aspect of the
thigh and buttocks.
Weakness of knee
flexor
Absent reflexes.
Sciatic N tenderness
Positive SLR test.
SCIATIC NERVE
L4-S3
Comes out of sciatic notch
Supplies all hamstrings (medial trunk) except short head of biceps femoris
All muscles distal to knee
Normal Sciatic N Conduction
velocity- 52.75±4.66 m/s
SCIATIC NEUROPATHY
Causes include-
Trauma
Fracture/disloc of hip joint
Injection
Puncture wound
Muscle scarring
Vasculitis
Compression Anesthesia
Coma
Lymphoma & tumours
Symptoms
Involvement of hamstrings
Involvement of muscles below knee
Variable sensory loss.
Needs motor conduction studies of
Peroneal N
Post Tibial N
Sural N
Sup Peroneal N
EMG
SCIATIC N CONDUCTION
Difficult d/t deep location.
Surface Electrode on distal peroneal innervated muscle egabd hallucius
Stimulation-
Just below gluteal fold
Medial trunk- apex of popliteal fossa
Lateral trunk- head of fibula
NCV
EMG
Helps differentiate the condition and levels
Denervation in paraspinal muscle + normal sural snap
s/o L5/S1 radiculopathy
Involvement of gluteal muscles- involvement prior to
sciatic notch
Peroneal neuropathy v/s sciatic neuropathy-
Lat trunk- short head of biceps
Med trunk- hamstrings and other tibial supp muscles
Normal Sciatic N Conduction velocity- 52.75±4.66 m/s
COURSE & BRANCHES
Branches-
Lat Cut N of Calf
Supplying anterior,
lateral and posterior
surface of leg
Superficial Peroneal N
Also supplies lateral and
dorsal portion of leg and
dorsum of foot.
Deep Peroneal N
COMMON PERONEAL NEUROPATHY
Occurs due to
compression around
head of fibula.
In sleep/coma
Anesthesia
Plaster/tight bandage
Cross legging
Fracture of fibula
Callus/cyst/lipoma
Vasculitis
Leprosy
Weakness of
Dorsiflexion of foot and
toes
Eversion of foot
Cause foot drop and
slapping gait
Sensory loss
In distribution of
superficial peroneal N
or lat cut N of calf,
depending on level of
lesion
ELECTROPHYSIOLOGY
Evaluation by conduction study of
Different segments of common peroneal nerve
Superficial peroneal nerve
EMG of peroneal nerve innervated muscles.
Sural conduction and EMG of short head of biceps
differentiate from sciatic neuropathy
PERONEAL NERVE
CONDUCTION
Surface recording- ext
digi brev
Stimulation –
2cm distal to fibular
neck,
At fibular neck
5-8cm above fibular
neck
Conduction velocity
Below knee segment-
48.3±3.9ms
Above knee segment-
52±6.2ms
Latency on ankle stimulation
3.77±0.86ms
Distal CMAP amplitude
5.1±2.3mV
SUPERFICIAL PERONEAL
NERVE CONDUCTION
Active electrodeJust above junction of lateral third of a line connecting the malleoli.
Reference electrode3cm distal to active electrode.
Stimulation10-15cm proximal to upper edge of lateral malleolus anterior to peroneus longus
Normal peroneal nerve conduction velocity-49±3.4ms and amplitude of SNAP 3.5±1.5µV
In peroneal neuropathy conduction block and
reduction in motor nerve conduction velocity >10ms
across head of fibula localizes the lesion at this site.
In common peroneal neuropathy muscles supplied
by the deep branch are frequently/severely
affected.
Common peroneal nerve and lateral trunk of sciatic
nerve- EMG of short head of biceps are useful
SURAL NERVE
S1 and S2
Medial derived from Tibial N
Lateral derived from Peroneal N
Pure sensory N
Sural N conduction velocity- 50.9±5.4 m/s, amplitude of SNAP 18±10.5µV
SURAL NEUROPATHY
Uncommon
Part of generalised neuropathies
Compression
Baker’s cyst
Against hard object
Tendon sheath ganglia
Scar tissue
# 5th metatarsal
Presents with
Numbness and paresthesia in supplied region
Low conduction velocity and amplitude in NCV
SURAL
Leg should be relaxed
and in lateral position.
Surface Electrode-
between lateral malleolus
and tendoachilles.
Stimulated 10-16 cm
proximal to recording
electrode, distal to lower
border of gastrocnemius
at the junction of middle
and lower third of leg.
Sural N conduction velocity- 50.9±5.4 m/s, amplitude of SNAP 18±10.5µV
TIBIAL NEUROPATHY
Damage at popliteal
fossa uncommon.
Causes-
Baker’s cyst
Nerve sheath ganglia
Popliteal A Aneurysm
Leprosy
Weakness of
plantar flexors
Invertors
Intrinsic foot muscles
Sensory loss in sole
TARSAL TUNNEL SYNDROME
Rare picture
Pain and paresthesia
of sole
Weakness of intrinsic
foot muscles (rare)
Causes
Ill-fitting footwear
Tight plaster cast
Post traumatic fibrosis
Tenosynovitis
RA
Hypothyroidism
Idiopathic
ELECTROPHYSIOLOGY
Needs tibial N conduction, medial and lateral plantar N conduction, EMG.
Tibial N conduction-
Surface recording-abductor hallucis/abductor digitiquinti below and ant to navicular tuberosity.
Stimulation behind and proximal to medial malleolus/in poplitealfossa.
Motor conduction of medial and lateral plantar N
Recording electrode (M)- abductor hallucis (belly)
Recording electrode (L)-abductor digiti quinti
Nerve stimulation- behind and above medial malleolus
Sensory conduction of
medial and lateral
plantar nerves:
Stimulation- 1st and 5th
toes- M and L
respectively.
Recording electrode-
just below medial
malleolus.
In Tarsal Tunnel Syndrome
Conduction block and latency prolongation across tarsal
tunnel
Accurate localisation by inching technique (1cm)-abrupt
prolongation in latency.
Normal conduction velocity of Tibial N-48.3±4.5ms
Motor conduction
Latency for medial plantar nerve-3.8±0.5ms
Latency for lateral plantar nerve-3.9±0.5ms
Sensory conduction for
Latency for medial plantar nerve-2.4±0.2ms, 3.2±0.3ms,
4±0.2ms (10,14 and 18 cm segment).
Latency for lateral plantar nerve-3.2±0.3ms,4±0.3ms (14
and 18 cm segment).