Pathophysiology of
Peripheral Nerve Lesions
Part 3: Lower Extremity
Entrapment Syndromes
David A. Lake, PT, PhD
Department of Physical Therapy
Armstrong Atlantic State University
Savannah, GA
Obturator Nerve
• Obturator Nerve
Anatomy
– Arises from anterior
division of L2-4 spinal
nerves
– Passes along the medial
edge of the psoas and
over the sacroiliac joint
– Passes through the
obturator canal (foramen)
to enter the medial thigh
Obturator Nerve
• Obturator Nerve Entrapment
results from:
– Abdominal tumors
– Endometriosis
– Obturator hernias
– Abdominal trauma & surgery
• Symptoms
– Pain along medial thigh
Obturator Nerve
• Symptoms of Obturator
neuropathy reported by patient
include:
– Pain along medial thigh - “obturator
neuralgia” common
– Numbness along medial thigh also
common
– Occassionally report gait
abnormalities
– Rarely do patients report weakness
Obturator Nerve
• Neurologic findings of Obturator
damage include:
– Weakness in thigh adduction
– Circumduction of thigh when
walking
– Occassionally wide stance
– Positive EMG signs of denervation in
adductor muscles
Femoral Nerve
• Anatomy of the
Femoral nerve
– Posterior division of
L2-L4 spinal nerves
– Passes over and
innervates the psoas
and iliacus
– Passes under the
inguinal ligament to
enter the anterior
thigh
Femoral Nerve
• Injury most
commonly occurs in
one of two places
– In the retroperitoneal
space
– Under the inguinal
ligament
• Less commonly as a
stretch injury from
hip hyperextension
Femoral Nerve
• Injury in the retroperitoneal space
– Most common secondary to
abdominal surgery and
retroperitoneal hematomas
– Estimated that in up to 7.5% of
hysterectomies there is femoral
nerve damage
Femoral Nerve
• Injury under the inguinal ligament
– Most common secondary to nerve
compression during lithotomy
positioning
– Estimated that femoral nerve damage
occurs in up to 2.3% of total hip
surgeries particularly in complicated
revisions
– Less common from inguinal hematomas
resulting from femoral vessel
catheterization
Femoral Nerve
• Symptoms of nerve injury reported by
patients
– Most commonly unilateral but can be
bilateral after lithotomy
– Weakness in quadriceps femoris muscles
– Knee buckling on weightbearing
– Easy loss of balance and falling
– Numbness on anteromedial thigh & leg
– Pain usually only with retroperitoneal
hematomas
Femoral Nerve
• Diagnosis of femoral nerve injury
– Weakness of quads with diminished or
eliminated patellar tendon reflex
– Thigh adduction and ankle dorsiflexion
strength is normal
– MR & CT for presumed space occupying
lesion
– NCV studies of CMAP of femoral nerve
and SNAP of saphenous nerve show 
amplitudes and conduction velocities
– Spontaneous activity and  recruitment
of MUAPs of quadriceps femoris
Femoral Nerve
• Terminology note:
– Saphenous nerve is the sensory branch of
the femoral nerve
– NCV - nerve conduction velocity but also
includes amplitude in of the compound
action potentials from surface recordings
– CMAP - compound motor action potentials
– SNAP - sensory nerve action potentials
– MUAPs - motor unit action potentials
recorded with needle electrodes in the
muscle
Saphenous Nerve
• Anatomy of Saphenous
Nerve:
– Saphenous nerve branches
from the femoral nerve in
the groin and travels
distally though the
subsartorial (Hunter’s or
adductor) canal
– Becomes subcutaneous
medial to the patella to
innervate skin over anterior
patella
– Continues along medial leg
Saphenous Nerve
• Anatomy of
Saphenous Nerve:
– Saphenous nerve
terminal branches
innervate the skin of:
• The medial knee
• The medial leg
down to the medial
malleolus
• A small area of the
medial arch of the
foot
Saphenous Nerve
• Neuropathies of Saphenous nerve
occur:
– Occasionally through entrapment as it
exits the subsartorial canal next to the
pes anserine bursa as a result of
bursitis or other narrowing of the canal
– Most commonly the result of damage
with:
• Varicose vein surgery
• Removal of the saphenous vein for
coronary artery bypass grafting
• Arthroscopic surgery of the knee
Saphenous Nerve
• Primary symptoms of nerve
damage reported by patients
include:
– Paresthesia, hyperthesias and pain
along the medial leg
– Knee pain is also common and if
only the infrapatellar branch is
damaged , there may only be
anterior knee numbness
Saphenous Nerve
• Diagnosis is done with the
following findings:
–  SNAP of saphenous nerve
– No weakness in quadriceps femoris
muscles
– Normal EMG findings in quadriceps
femoris, hip adductors and iliacus
– Occasionally + Tinel sign over
subsartorial canal
Lateral Femoral
Cutaneous Nerve
• Anatomy of the Lateral
Femoral Cutaneous Nerve
(LFCN):
– Arises from L2 & L3
– Passes through abdomen
over iliacus
– Emerges under inguinal
ligament next to anterior
superior iliac spine
– Penetrates fascia lata to
ramify over lateral thigh
Lateral Femoral
Cutaneous Nerve
• Neuropathy of the LFCN:
– Termed Meralgia Paresthetica and most
commonly due to compression under
the inguinal ligament
– Contributing factors can include:
•
•
•
•
•
Pregnancy
Obesity
Wearing a heavy tool belt or very tight belt
Automobile accident restrained by seatbelt
Chronic leaning against object such as
gymnastic bars
Lateral Femoral
Cutaneous Nerve
• Symptoms patients report
with LFCN neuropathy:
– Pain (burning), numbness,
paresthesia or occasionally hyperesthesia along
the lateral thigh - where a
pants pocket is
– Sometimes worse with
standing, walking, running,
turning in bed
– May improve with hip
flexion
Lateral Femoral
Cutaneous Nerve
• Diagnosis of LFCN neuropathy:
– History of precipitating factor
– Pattern of pain, numbness,
paresthesias along lateral thigh
–  SNAP amplitude and conduction
velocity
– Lack of quadriceps or adductor
weakness or sensory loss over
femoral or obturator distributions
Lateral Femoral
Cutaneous Nerve
• Some evidence for physical
therapy intervention effectiveness
from case study:
– Thermal US & mobilization to
inguinal ligament followed by icepack
– 3 treatments/week for 3 weeks
reduced pain from 6/10 to 2/10
– Lasted until patient started running
again
– Subsequent treatments reduced pain
again
Sciatic Nerve
• Anatomy of Sciatic Nerve
– Arises from L5, S1 & S2
– Composed of lateral
division, the common
peroneal nerve, and the
medial division, the tibial
nerve, in a common
sheath
– Leaves the pelvis through
the greater sciatic notch
– Rise just inferior to the
piriformis to run deep to
the gluteus maximus
Sciatic Nerve
• Anatomy of Sciatic Nerve
– However in 10-30% of subjects, either all or
part of the sciatic nerve penetrates the
piriformis muscle (b or d in picture)
Sciatic Nerve
• Neuropathies of the
Sciatic Nerve can
result from:
– Entrapment by the
piriformis
– Posterior dislocation of
the hip joint
– Acetabular fracture,
repair of femoral neck
fracture or hip
arthoplasty
Sciatic Nerve
• Neuropathies of the Sciatic
Nerve can result from:
– Prolonged compression of
the buttock or posterior thigh
– Inappropriately administered
intramuscular injection in the
buttock
– Small vessel disease
blocking vessel to nerve
Sciatic Nerve
• Symptoms reported by patients with
Sciatic Neuropathies include:
– Loss of muscle strength of all muscles
below the knee and the hamstrings and
adductor magnus
– Paresthesias, numbness or pain in all
areas below the knee except the medial
leg area served by the saphenous nerve
Sciatic Nerve
• In partial injury common peroneal
nerve more vulnerable because
• fewer axons than tibial nerve
• more exposed to traction injury being
tightly secured at fibular head and
sciatic notch.
Sciatic Nerve
• Differential diagnosis of
sciatic neuropathy
– Easy from distribution of
motor and sensory loss
– Foot drop
– NCV & EMG studies to
confirm diagnosis
– Differentiate from L5 & S1
radiculopathy by pattern
of muscle impairment and
sensory loss
Sciatic Nerve
• Differential diagnosis of
sciatic neuropathy
– Motor L4-L5 loss is hip
extensor/knee flexor
weakness
– Motor L5 loss is foot drop
& no heal walking and
weakness in toe extension
– Motor S1 loss is lack of
plantar flexion & toe
walking
Common Peroneal
Nerve
• Anatomy of the
Common Peroneal
Nerve
– Splits from the Tibial
Nerve at some point
before the popliteal
fossa
– The lateral cutaneous
nerve of the calf and the
lateral sural nerve arise
in the popliteal fossa
Common Peroneal
Nerve
• Anatomy of the
Common Peroneal
Nerve
– It curves lateral around
the neck of the fibula
through the “fibular
tunnel” made by the
fibula and tendon of
the peroneus longus
– It then splits into the
deep and superficial
peroneal nerves
Common Peroneal
Nerve
• Peroneal Nerve
Neuropathies
– Most common site of
injury is the fibular
neck where it can
suffer different forms
of injury including:
• Traction
• Compression
• Other forms of
trauma
Common Peroneal
Nerve
• Peroneal Nerve Neuropathies
– Compression
• Lying on with pressure on fibular head (coma,
anesthesia)
• Pressure wrapping around knee including: casts,
AFOs, compression stockings, & pneumatic splints
• Recent loss of weight and loss of fat padding around
the fibular head added risk
Common Peroneal
Nerve
• Peroneal Nerve Neuropathies
– Traction
• Prolonged squating such as crop
harvesting, yoga meditation and exercises
• Lithotomy positioning for prolonged
periods such as in childbirth
• Ankle sprains
– Trauma
• Blunt trauma as well as open wounds
• Fibular fractures or dislocations
• Surgical procedures such as arthroscopic
or open knee procedures
Common Peroneal
Nerve
• Peroneal Nerve Neuropathies
– Other factors
• Diabetics and others with
polyneuropathies are particularly prone
to injury at this point
• Prolonged (> 30 min) cold applied to the
knee has been shown to produce
irreversible injury to the common
peroneal nerve at this point as well
Common Peroneal
Nerve
• Symptoms of Peroneal Nerve
Neuropathies include:
– Complete or partial footdrop
– Paresthesias or numbness on the
anterio-lateral leg & dorsum of the
foot
– Mild, deep “boring” pain around the
lateral leg and knee may be reported
Common Peroneal
Nerve
• Diagnosis of Peroneal Nerve
Neuropathies include:
– History generally is related to a sudden
onset with a single episode of trauma or
compression
– 3-fold higher incidence in males
– Generally unilateral (approx 10% bilateral)
– Weakness in ankle dorsiflexion & toe
extension with retention of ankle plantar
flexion, inversion, toe flexion and ankle
eversion
Common Peroneal
Nerve
• Diagnosis of Peroneal Nerve
Neuropathies include:
– Normal quadriceps and plantar flexor
reflexes (patellar & achilles tendon
reflexes)
– NCV studies involve CMAP from tibialis
anterior and extensor digitorum brevis,
SNAP from sensory component and
spontaneous activity and  MUAP
recruitment
Common Peroneal
Nerve
• Differential Diagnosis of Peroneal
Nerve Neuropathies require:
– Distinguish from flail foot - peripheral
neuropathy has just weakness while flail
foot is total incoordination of all
movements
– Distinguish from upper motoneuronal
injury (head injury or stroke) - normal
plantar flexor and knee extension reflexes
in neuropathy but changed in upper
motoneuronal disorders
– Distinguish from sciatic mononeuropathy
Tibial Nerve
• Anatomy of the Tibial
Nerve:
– Originates primarily from
L4-S2 after formation in the
posterior thigh it continues
along the midline
posteriorly through the
popliteal fossa
– In the popliteal fossa it
gives off the medial sural
cutaneous nerve and motor
branches to the popliteus,
plantaris, gastrocnemius &
soleus
Tibial Nerve
• Anatomy of the Tibial Nerve:
– The tibial nerve then runs
beneath the fibrous arch of the
soleus and at this point is
commonly referred to as the
posterior tibial nerve
– Innervates tibialis posterior,
flexor digitorum longus & flexor
hallucis longus as it runs with
these muscles
– Exits the leg through the tarsal
tunnel inferior to the medial
malleolus
Tibial Nerve
• Anatomy of the Tibial Nerve:
– Tarsal tunnel has osseous
base and roof is the flexor
retinaculum
– Exits the tarsal tunnel & gives
off the medial calcaneal nerve.
– But the medial calcaneal nerve
often branches proximal to the
tarsal tunnel
– It splits into the medial and
lateral plantar nerves
Tibial Nerve
• Anatomy of the Tibial Nerve:
– The medial and lateral plantar
nerves enter the foot through
the fascial origin of the
abductor hallicus longus
which is referred to as the
abductor tunnel
Tibial Nerve
• Tibial Neuropathies:
– Damage in or around the popliteal fossa
– Damage in the tarsal tunnel (tarsal
tunnel syndrome)
Tibial Nerve
• Tibial Neuropathies:
– The popliteal fossa is the most common
site of tibial nerve injury (48% in a recent
study) followed by distal to it - mostly in
the tarsal tunnel (27%) and then
proximal to it (25%)
– Most common etiology is trauma (56%)
followed by ischemia (19%) &
neoplasms (17%)
– Lesions proximal to the popliteal fossa
most commonly from cast compression
or blunt trauma
Tibial Nerve
• Tibial Neuropathies:
– Popliteal lesions of the tibial nerve occur
mostly from penetrating and nonpenetrating trauma, tibial dislocations
during knee injury and only very rarely
following surgical procedures
– Tibial nerve lesions distal to the popliteal
fossa are primarily the result of tibial
fractures, posterior compartment
syndrome, and entrapment in the
tendinous arch of the soleus or in fibrous
bands between heads of gastrocnemius
Tibial Nerve
• Tibial Neuropathies:
– Most common cause of tarsal tunnel
syndrome injury is secondary to trauma
• Displaced fracture of distal tibia
• Fracture of tarsal bones
• Fracture of the calcaneous
• Medial ankle sprains
• Tenosynovitis of tendons in tarsal tunnel
(tibialis posterior, flexor hallucis longus,
flexor digitorum longus
• Perineurial fibrosis secondary to trauma
Tibial Nerve
• Tibial Neuropathies:
– Other non-traumatic causes of tarsal
tunnel syndrome
• Space occupying lesions such as
tumors, ganglia
• Foot deformities such as varus heel
with pronated forefoot or valgus heel
with abducted forefoot (pes planus)
• Rarely but seen with patients with
diabetes and inflammatory arthritis
Tibial Nerve
• Symptoms:
– Sensory disturbances in the distribution
of the sural, medial & lateral plantar and
medial calcaneal nerves - posteromedial
leg (calf), lateral ankle, on the lateral
aspect, sole and heel of the foot
– If damage proximal to popliteal fossa
weakness in ankle plantar flexion and
inversion and toe flexion
– Weakness of knee flexion may be seen if
denervation of gastrocnemius
Tibial Nerve
• Symptoms:
– Baker’s cysts in the popliteal fossa may
also affect the common peroneal nerve
– Entrapment as the tibial nerve passes
through the fibrous arch of the soleus
produces severe pain and tenderness in
the popliteal fossa and upper calf (soleus)
made worse by weight-bearing & passive
dorsiflexion of the ankle
– Entrapment in the tarsal tunnel foot
paresthesias, pain and numbness are
most prominent symptoms
Tibial Nerve
• Diagnosis:
– History of tibial nerve symptoms with
symptoms most unique to tibial nerve
being:
• Hypersensitivity of the foot initially or after
nerve repair
• Insensitivity of the foot with axonal loss and
foot ulcerations
– Imaging studies can show some
obstructions and diagnosis fractures
– EMGs, SNAPs, CMAPs and H-reflex
testing