Abstract
Peripheral nerve entrapments can be due to such causes as constrictions through soft-tissue structures, space-occupying lesions, and external compressive forces. They typically present with a characteristic sensory and/or motor pattern. Nerve conduction studies may help in classifying the extent and location of the disorder. MRI and ultrasound, which are gaining in popularity, can help delineate the cause and guide localized treatment. Treatment may include medications, rest, biomechanical interventions, hydrodissection, and release procedures.
Key Concepts
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Peripheral nerve injuries due to mechanical constriction or deformation
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Pathophysiology is most often ischemic due to capillary hypoperfusion resulting from the constrictive force.
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May be due to tight anatomic passageways, space-occupying masses, external compressive forces, trauma, and inflammation
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May produce sensory and/or motor symptoms with atrophy
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Pattern of involvement is typically focal and mononeuritic
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Seddon classification of nerve injuries (mild to severe)
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Neurapraxia: demyelination of axon sheath
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Axonotmesis: axonal disruption with intact epineurium
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Neurotmesis: complete disruption
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Conditions
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Median nerve
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Sites of compression: bicipital aponeurosis in antecubital fossa, between two heads of pronator teres (pronator syndrome), origin of flexor digitorum superficialis (FDS), carpal tunnel in wrist
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Pronator syndrome
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Proximal, ventral forearm pain and paresthesias of radial 3.5 digits
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Tinel’s sign at proximal forearm, pain with resisted pronation and/or FDS of third finger
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Anterior interosseous syndrome
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No sensory symptoms, purely motor
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May have proximal, volar forearm pain
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Abnormal pinch (OK) sign d/t weakened flexor pollicis longus (FPL) and flexor digitorum profundus (FDP) of second and third fingers
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Carpal tunnel syndrome
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Paresthesias in radial 3.5 digits
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Positive Tinel and Phalen signs at wrist
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Weakness in thumb abduction, grip, or pinch
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Radial nerve
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Sites of compression: radial tunnel between heads of supinator, arcade of Frohse
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Radial tunnel syndrome/posterior interosseous nerve syndrome (PIN)
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Aching pain in supinator and extensor tendon group 3 to 5 cm distal to lateral epicondyle
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Weakness upon metacarpophalangeal extension and of extensor carpi ulnaris (PIN)
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Ulnar nerve
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Sites of compression: cubital tunnel at the posteromedial elbow, arcade of Struthers, Guyon’s canal in wrist
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Cubital tunnel syndrome
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Aching pain at medial elbow
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Paresthesias of ulnar 1.5 digits
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Weakness of dorsal interosseous and abductor digiti minimi muscles
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Lateral antebrachial cutaneous nerve
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Site of compression: lateral free margin of bicipital aponeurosis
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Terminal sensory branch of musculocutaneous nerve
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Supplies sensation over radial half of forearm
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Femoral nerve
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Sites of compression: inguinal ligament, lumbar plexus due to mass
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Sensory over anteromedial thigh and leg
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Weakness of quadriceps muscle and knee jerk reflex
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Saphenous nerve
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Site of compression: exit point of subsartorial fascia in medial distal thigh
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Branch of femoral nerve
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Purely sensory: knee and lower leg medially
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Lateral femoral cutaneous nerve (meralgia paresthetica)
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Site of compression: near attachment of inguinal ligament to anterior superior iliac spine
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Paresthesias over anterolateral thigh
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Peroneal nerve
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Sites of compression: fibular head, anterior tarsal tunnel at ankle
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Divides into deep peroneal nerve (DPN) and superficial peroneal nerve (SPN) branches near fibular neck
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Deep: paresthesias of first web space, weakness to ankle/toe dorsiflexion
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Superficial: paresthesias of lateral distal leg and dorsum of foot, weakness to eversion
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Posterior tibial nerve
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Sites of compression: popliteal fossa due to mass, posterior tarsal tunnel behind medial malleolus (tarsal tunnel syndrome)
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Proximal lesion: calf pain, plantar flexion weakness
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Distal lesion: heel and plantar foot paresthesias
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Interdigital neuroma (Morton neuroma)
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Site of compression: metatarsal heads
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Pain radiating into toes
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Sural nerve
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Site of compression: distal lateral leg
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Sensory over lateral foot and heel
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