Brachial Plexus Flashcards

Question

Musculocutaneous Nerve

Answer 1

**Origin:** (C5/C6/C7) Lateral cord of the brachial plexus **Sensory supply:** Lateral forearm **Motor supply:** Anterior compartment of the arm: Biceps (flexes elbow, supinates forearm) Brachialis (flexes elbow) Coracobrachialis (adducts shoulder, flexes elbow) **Clinical significance** Musculocutaneous nerve injuries are rare, but result in very weak elbow flexion and weak forearm supination which can be very disabling. **_CLINICAL FEATURES OF MUSCULOCUTANEOUS NERVE PALSY_** **SENSORY LOSS** numbness over lateral forearm **MOTOR DEFICIT** paralysis of anterior compartment of arm – very weak elbow flexion and weak forearm supination absent biceps reflex **DEFORMITY** wasting of anterior compartment of arm elbow usually held in extension with forearm pronated

Answer 2

**Origin:** (C5/C6) Posterior cord of the brachial plexus **Sensory supply**: “Sergeant’s patch” over the lower deltoid **Motor supply** Deltoid (abducts, flexes and extends shoulder) Teres minor (stabilises and externally rotates shoulder) **Clinical significance** The axillary nerve may be injured by shoulder dislocations or proximal humeral fractures, resulting in numbness over the sergeant’s patch and profound weakness of shoulder abduction from 15-90°. Other examination findings include deltoid wasting and weakness of shoulder flexion, extension and external rotation. **COMMON INJURIES** fracture of surgical neck of humerus stab wounds to posterior shoulder anterior shoulder dislocation pressure of crutches on armpits (“crutch palsy”) **_CLINICAL FEATURES OF AXILLARY NERVE PALSY_** **SENSORY LOSS** numbness over “sergeant’s patch” **MOTOR DEFICIT** paralysis of deltoid – very weak shoulder abduction from 15-90°; weak shoulder flexion and extension paralysis of teres minor – weak shoulder external rotation **DEFORMITY** wasting of deltoid muscle, making the bones of the shoulder joint very prominent and obvious shoulder may appear adducted and internally rotated

Answer 3

**Origin:** (C5/C6/C7/C8/T1) Posterior cord of the brachial plexus **Sensory supply** Posterior arm and forearm Lateral ⅔ of the dorsum of the hand Proximal dorsal aspect of lateral 3½ fingers **Motor supply** The radial nerve supplies the posterior compartment of the arm, which contains triceps (extends and adducts shoulder, extends elbow). It also supplies the entirety of the posterior compartment of the forearm. This consists of: Brachioradialis (flexes elbow) Anconeus (extends elbow, stabilises elbow joint) Supinator (supinates forearm) Extensor carpi radialis longus and brevis (extend and abduct wrist) Extensor carpi ulnaris (extend and adduct wrist) Extensor digitorum Extensor pollicis longus and brevis Extensor indicis Extensor digiti minimi Abductor pollicis longus (abducts thumb) **Clinical significance** Radial nerve injuries are commonly due to compression, for example by leaning or lying on the arm for extended periods, excessively tight plaster casts or prolonged tourniquet use. It can also be damaged by fractures of the humerus or radius, or by stab wounds. Radial nerve injury results in loss of innervation to the muscles of the posterior compartments of the arm and forearm. This manifests as numbness in the radial nerve distribution and a “wrist drop” deformity with very weak extension of the elbow, wrist and fingers. **COMMON INJURIES** fractures of proximal humerus, shaft of humerus or radius stab wounds to antecubital fossa, forearm or wrist this includes blood tests and venflons! pressure of crutches on armpits (“crutch palsy“) the patient falling asleep with arm hanging over the back of a chair, classically whilst drunk (“Saturday night palsy“) somebody else falling asleep with their head lying on the patient’s arm (“honeymoon palsy“) excessively tight plaster casts, wristbands or handcuffs prolonged tourniquet use on upper arm, for example during orthopaedic or plastics procedures

Answer 4

(C5/C6/C7/C8/T1) **Origin** Lateral and medial cords of the brachial plexus **Sensory supply** Thenar eminence, the lateral ⅔ of the palm of the hand Palmar aspect of lateral 3½ fingers Dorsal fingertips of lateral 3½ fingers **Motor supply** All muscles of the anterior compartment of forearm EXCEPT flexor carpi ulnaris and the medial two parts of flexor digitorum profundus. The median nerve, therefore, supplies pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, the lateral two parts of flexor digitorum profundus, flexor pollicis longus and pronator quadratus. These forearm muscles flex the wrist, the proximal interphalangeal joints of all four fingers and the distal interphalangeal joints of the index and middle fingers. They also pronate the forearm and abduct the wrist. The median nerve also supplies the LOAF muscles of the hand: The lateral two lumbricals Opponens pollicis Abductor pollicis brevis Flexor pollicis brevis The lumbricals flex the MCPJs and extend the IPJs of the index and middle finger. The muscles of the thenar eminence flex, abduct and oppose the thumb. **Clinical significance** The median nerve is most commonly damaged by compression within the carpal tunnel at the wrist, resulting in numbness of the median nerve distribution to the hand, wasting of the thenar eminence, weak grip strength and a “hand of benediction” deformity due to an inability to flex the index or middle fingers. It can also be injured by supracondylar fractures of the humerus and stab wounds or lacerations to the forearm or wrist.

Answer 5

**Origin**: (C8/T1) Medial cord of the brachial plexus **Sensory supply** Hypothenar eminence Medial ⅓ of the palm of the hand Palmar aspect of the lateral 1½ fingers Medial ⅓ of the dorsum of the hand Dorsal aspect of the medial 1½ fingers **Motor supply** The ulnar nerve supplies just two muscles in the anterior compartment of the forearm Flexor carpi ulnaris, which flexes and adducts the wrist The medial two parts of flexor digitorum profundus, which flex the distal interphalangeal joints (DIPJs) of the ring and little fingers. It also supplies all of the intrinsic muscles of the hand EXCEPT the LOAF muscles supplied by the median nerve. These can be remembered as the HILA muscles: Hypothenar eminence Interossei Medial two lumbricals Adductor pollicis The hypothenar eminence consists of opponens digiti minimi, flexor digiti minimi brevis and abductor digiti minimi, which oppose, flex and abduct the little finger respectively. The palmar interossei adduct the fingers, whilst the dorsal interossei abduct them. The medial two lumbricals flex the MCPJs and extend the IPJs of the ring and little fingers. Adductor pollicis adducts the thumb – it is worth noting that this muscle does not form part of the thenar eminence and actually lies deep beneath it as a separate structure. **Clinical significance** The ulnar nerve may be injured by supracondylar fractures of the humerus, medial epicondylar fractures, stab wounds to the forearm or wrist, or compression at either the cubital tunnel in the elbow or Guyon’s canal in the wrist. This results in numbness in the ulnar distribution to the hand, wasting of the hypothenar eminence and intrinsic muscles of the hand, a “claw hand” deformity due to an inability to extend the ring and little fingers, and weak finger abduction and adduction.

Brachial Plexus Flashcards

(30 cards)