Ulnar nerve: Origin, course, branches and innervation

Ulnar nerve comes from the medial cord of the brachial plexus (C8-T1)
The ulnar nerve is one of the three main nerves in your arm. It travels from your neck down into your hand, and can be constricted in several places along the way, such as beneath the collarbone or at the wrist. The most common place for compression of the nerve is behind the inside part of the elbow.

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
Ulnar Nerve

Dr Rohit Bhaskar, Physio
Dr Rohit Bhaskar, Physio Dr. Rohit Bhaskar, Physio is Founder of Bhaskar Health and Physiotherapy and is also a consulting physiotherapist. He completed his Graduation in Physiotherapy from Uttar Pradesh University of Medical Sciences. His clinical interests are in Chest Physiotherapy, stroke rehab, parkinson’s and head injury rehab. Bhaskar Health is dedicated to readers, doctors, physiotherapists, nurses, paramedics, pharmacists and other healthcare professionals. Bhaskar Health audience is the reason I feel so passionate about this project, so thanks for reading and sharing Bhaskar Health.

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