Updated: 2/1/2020

Ulnar nerve

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https://upload.medbullets.com/topic/121976/images/ulnar_nerve.jpg
Origin of Ulnar Nerve
  • Ulnar nerve comes from the medial  cord of the brachial plexus (C8-T1)
Course of Ulnar Nerve
  • Lies posteromedial to brachial artery in anterior compartment of upper 1/2 arm
  • Pierces medial IM septa at the arcade of Struthers ~ 8cm from medial epicondyle and lies with triceps
  • Travels on back of medial epicondyle; vulnerable in fractures
    •  Runs with superior ulnar collateral artery
    • Cubital tunnel
      • roof - cubital tunnel retinaculum (medial epicondyle to olecranon) / osbourne’s fascia (extension of deep forearm fascia between heads of FCU)
      • floor - posterior and transverse bands of MCL
  •  Does send small sensory branch to elbow that can be sacrificed
  • Passes into forearm between 2 heads of flexor carpi ulnaris
  • Runs between FCU + FDP
  • At the wrist, the ulnar nerve and artery pass superficial to the flexor retinaculum
Motor Innervation of Ulnar Nerve
  • motor
    • forearm
      • flexor carpi ulnaris
      • flexor digitorum profundus III and IV
    • thenar
      • adductor pollicis 
      • deep head of flexor pollicis brevis (FPB)
    • fingers
      • dorsal interosseous (abduction) & palmar interosseous (adduction) 
      • 3rd & 4th lumbrical (1st & 2nd by median nerve)
    • digiti minimi
      • abductor digiti minimi
      • opponens digiti minimi
      • flexor digiti minimi
  • sensory branches of ulnar nerve
    • dorsal cutaneous branch
    • palmar cutaneous branch
    • superficial terminal branches
Clinical Conditions
  •  Cubital Tunnel Syndrome compression sites 
    • Arcade of Struthers (tunnel 8 cm proximal to medial epicondyle formed by fibrous connection between IM septum and medial head of triceps) 
    • medial intermuscular septum
    • medial epicondyle (osteophytes)
    • cubital tunnel retinaculum (taught with flexion)
      • often the retinaculum is consistent with Osborne’s ligament
    • aponeurosis of the two heads of the FCU (arcuate ligament) is often consistent with the retinaculum and osbournes ligament, however these fibers meet perpendicular to retinaculum/osbournes ligament
    • deep flexor/pronator aponeurosis (most distal site - approximately 4 cm distal to medial epicondyle)
    • The internal anatomy of the ulnar n can explain the predominance of hand sx from cubital tunnel syndrome – the fibers to FCU and FDP are central and hand intrinsic fibers are peripheral!
  • Ulnar tunnel syndrome: compression in Guyon’s Canal
    • no involvement of dorsal cutaneous nerve since it branches before canal
    • no involvement of  FDP of 4th & 5th and FCU
    • ganglia most common cause (from triquetrohamate joint, 32-48%)
    • other causes: other mass, trauma (Distal radius/ulna, hook of hamate), muscle anomaly, ulnar artery aneurysm
    • Zones of compression
      • Zone 1: proximal to bifurcation: hook of hamate fx & ganglia, motor & sensory findings
      • Zone 2:  deep motor branch; hook of hamate fx & ganglia, motor sx
      • Zone 3:  superficial sensory branch; ulnar artery thrombosis

Ulnar Nerve

 
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(M1.AN.17.4707) A 12-year-old boy presents to the emergency department with severe right elbow pain after falling off his bicycle. His mother says that he was otherwise healthy prior to the fall and does not take any medications. On physical exam he has pain over the medial side of his elbow and limited range of motion due to pain. Over his medial 1 and ½ fingers, he has loss of digit flexion and decreased sensation. Which of the nerves shown in Figure A is most likely to be affected in this patient? Tested Concept

QID: 108425
FIGURES:
1

A

6%

(13/230)

2

B

5%

(11/230)

3

C

15%

(34/230)

4

D

19%

(44/230)

5

E

52%

(120/230)

M 2 B

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