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Origin
  • Ulnar nerve comes from the medial cord of the brachial plexus (C8-T1)                                            
Course
  • Arm
    • lies posteromedial to brachial artery in anterior compartment of upper 1/2 arm
    • pierces medial IM septum at the arcade of Struthers ~ 8cm from medial epicondyle and lies medial to the triceps   
      • the arcade of Struthers is an aponeurotic band extending from the medial IM septum to the medial head of the triceps 
  • Elbow
    • runs behind medial epicondyle with superior ulnar collateral artery  
    • Cubital tunnel  
      • roof - Osbourne’s ligament proximally (extension of deep forearm fascia between heads of FCU) and FCU aponeurosis distally  
      • floor - posterior and transverse bands of MCL and elbow joint capsule
    • sends small sensory branch to elbow that can be sacrificed
  • Forearm
    • enters forearm between 2 heads (humeral and ulnar heads) of FCU 
    • runs between FCU and FDP
  • Wrist
    • the ulnar nerve and artery pass superficial to the transverse carpal ligament 
    • bifurcates into sensory and deep motor branches in Guyon's canal    
      • roof - volar carpal ligament
      • floor - transverse carpal ligament, hypothenar muscles
      • ulnar border - pisiform and pisohamate ligament, abductor digiti minimi muscle belly
      • radial border - hook of hamate
Innervation
  • Motor Innervation 
    • forearm
      • FCU
      • FDP ring and small
    • thenar
      • adductor pollicis
      • deep head of flexor pollicis brevis (FPB)
    • fingers
      • interossei (dorsal & palmar)
      • 3rd & 4th lumbricals 
    • hypothenar muscles
      • abductor digiti minimi
      • opponens digiti minimi
      • flexor digiti minimi
  • Sensory Innervation
    • sensory branches of ulnar nerve
      • dorsal cutaneous branch
      • palmar cutaneous branch
      • superficial terminal branches
Clinical Conditions
  •  Cubital Tunnel Syndrome  
    • sites of compression (proximal to distal)
      • medial intermuscular septum
        • most proximal site, 8cm proximal to medial epicondyle
      • Arcade of Struthers 
      • medial epicondyle (osteophytes)
      • cubital tunnel retinaculum (Osborne's ligament)
        • anconeus epitrochlearis muscle replaces Osborne's ligament in 11% of population, causing static compression 
      • aponeurosis of the two heads of the FCU (arcuate ligament)
        • often continuous with Osbourne's ligament
      • deep flexor/pronator aponeurosis 
        • most distal site, 4 cm distal to medial epicondyle
    • elbow flexion reduce cubital tunnel volume because  
      • FCU aponeurosis tenses
      • Osborne's ligament becomes taught
      • MCL bulges into cubital tunnel
    • the internal anatomy of the ulnar nerve explains the predominance of hand symptoms in cubital tunnel syndrome 
      • 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
      • causes
        • ganglia most common cause (from triquetrohamate joint, 30-50%)
        • other causes include mass, trauma (fracture of distal radius or ulna, hook of hamate), muscle anomaly, ulnar artery aneurysm or thrombosis
      • compression sites  
        • Zone 1: proximal to bifurcation, both motor & sensory symptoms
          • caused by hook of hamate fracture and ganglia 
        • Zone 2:  deep motor branch, motor symptoms only
          • caused by hook of hamate fracture and ganglia 
        • Zone 3:  superficial sensory branch, sensory symptoms only
          • caused by ulnar artery aneurysm or thrombosis

Ulnar Nerve

 
 

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