Ulnar nerve

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 4^th & 5^th 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