Peripheral Nerves

Muscle innervation & Clinical Findings

Spinal Accessory N (CN XI)

• Muscle innervation: trap, SCM

• Clinical findings

  • Neck, shoulder, medial scapular pain

  • Decreased cervical lordosis

  • A downwardly rotated scapula

  • Lateral winging of scapula

Scapular N C5-6

• Muscle innervation: supraspinatus, infraspinatus

• Clinical findings:

  • Dull ache lateral shoulder

  • Atrophy / weakness supraspinatus & infraspinatus

  • Increased scapula elevation during arm elevation

Long Thoracic N

• Muscle innervation: serratus anterior

• Clinical findings:

  • Weak scapular protection

  • Weakness with upward rotation of scapula

  • Medial winging of medial scapula

Musculocutaneous N C5-6

• Muscle innervations: coracobrachialis, brachialis, biceps brachii

• Clinical findings:

  • Lateral arm sensory changes

  • Weakness / atrophy biceps, brachialis, coracobrachialis, diminished biceps reflex 

Axillary N

• Muscle innervation: deltoid, teres minor

• Clinical findings:

  • Axillary pain

  • Deltoid area paresthesia

  • Atrophy deltoid & teres minor

  • Elevation weakness

  • Anterior shoulder dislocation

Radial N 

• Muscle innervation: Abductor pollicis longus, brachioradialis, anything starting with extensors, anconeus, supinator, and triceps

  • “A BEAST”

  • Clinical findings

    • Triceps weakness

    • Extensor of forearm weakness

    • Web space sensory loss, dorsal hand / forearm sensory loss

    • Crutch use (radial groove of humerus)

    • Midshaft humeral fx

Median N

• Muscle innervation: pronator teres, pronator quadratus, all flexors

• Clinical findings:

  • Ape hand

  • opposition weakness

  • Weak grasp (radial side)

  • Radial deviation

  • Pronation weakness

Ulnar N

• Muscle innervation: MAFIA = medial 2 lumbricals, adductor poll, flexors ulnar, side, interossei, abduction for pinky finger

• Clinical findings:

  • Ulnar claw

  • Inability to

    • Extend PIP and DIP (lumbricals)

    • Abduct fingers (interossei)

    • Adduct thumb (AP)

  • Weakness with ulnar deviation (FCU)

  • Hypothenar wasting

  • Loss of sensation of 4 - 5 fingers 

Femoral N

• Muscle innervation: iliopsoas, sartorius, pectineus, quad femoris

• Clinical findings:

  • Knee buckling

  • Knee extension weakness

  • Anterior knee pain

  • Sensory loss medial aspect of leg below knee

  • Forward trunk lean during gait

Obturator N

• Muscle innervation: adductor longus / brevis, gracilis, adductor magnus, obturator externus

• Clinical findings:

  • Loss of ER and adduction

Superior Gluteal N

• Muscle innervation: glute med, glute min, TFL

• Clinical findings:

  • Trendelenburg gait

Inferior Gluteal N

• Muscle innervation: glute max

• Clinical findings:

  • Posterior trunk lean at initial contact 

Tibial N

• Muscle innervation: Gastroc, soleus, popliteus, tibialis posterior

  • PF

Common peroneal - Superficial peroneal

• Muscle innervation: fibularis longus, fibularis brevis

  • Eversion

Common peroneal - Deep peroneal

• Muscle innervation: Tibialis anterior, extensor digitorum longus, extensor hallucis longus 

  • DF