Ulnar Nerve Injury

HPI:  Middle age male who presents after falling at work. His medial forearm stroke a metal bucket just distal to his elbow and resulted in a large laceration.

PE: Patient is unable to flex at the DIP of digit 4 and 5. He is unable to cross the second and third fingers or adduct his fingers. He has decreased sensation over the medial aspect of the 4th and 5th digit.  Suspected ulnar nerve laceration. 

Anatomy: Derives from the medial portion of the brachial plexus (C8-T1). It lies posteromedial to the brachial artery in the upper arm and traverses behind the medial epicondyle.  The ulnar nerve runs along on the ulnar aspect of the wrist along with the ulnar artery. It passes through Guyon’s canal where it bifurcates into sensory and deep motor branches.  

Innervation:
-   Motor:

• Flexor carpi ulnaris and Flexor digitorum profundus for the 4th and 5th digits.
• Adductor pollicis and deep head of flexor pollicis brevis
• Interossei and 3rd and 4th lumbricals. 
• Abductor digiti minimi, opponens digiti minimi, flexor digiti minimi. 
  

-    Sensory:

•  Dorsal and palmar cutaneous branches as well as Superficial terminal branches. 
  

Clinical conditions:

•  Distal humerus fracture
  
•  External compression at the medial epicondyle
  
•  Prolonged elbow flexion. 
  
•  Medial epicondylitis (Golfer’s elbow)
  
•  Compression in Guyon’s canal (spares 4th and 5th digit flexion)
  
•  Propulsion of a wheelchair
  
•  Fractures of the hook of the hamate
  

Treatment: Forearm exploration with transected nerve repair.

Pearls:

•  Evaluate flexion at the DIP of the 4th and 5th digits. 
  
•  Inablity to adduct the fingers. Crossing the 2nd and 3rd digit is maximum adduction. If unable to do this secondary to pain, can adduct 2nd and 3rd digit in “scissoring” motion against examiners fingers between the medial aspect of 2nd digit and lateral aspect of 3rd digit.  
  
•  Decreased sensation at the lateral 4th and entire 5th digit. 
  
•  Compression in Guyon’s canal will exhibit decreased sensation and inability to adduct the fingers. Flexion of 4th and 5th digit is spared.