Pathophysiology of Peripheral Nerve LesionsPart 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 occasion-ally 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 non-penetrating 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