Indications

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  Any ulnar nerve motor or sensory deficits if there is a laceration along its course

  
  
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  Blunt trauma with complete paralysis and high-energy fracture or dislocation injuries

  
  
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  Closed injuries without signs of progressive reinnervation

  
  
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  A worsening neurological deficit under observation

  
  
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  Ulnar nerve injuries arising after internal fixation of forearm or elbow fractures

Contraindications

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  Transient ulnar nerve palsies after percutaneous pinning of supracondylar humeral fractures in children

  
  
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  Transient ulnar nerve palsies after elbow dislocations

Examination/Imaging

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  There may be a sensory deficit involving all or part of the ulnar nerve distribution, including the dorsoulnar carpus.

  
  
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  With a low ulnar nerve lesion there is often clawing of the ring and little fingers. This may not be present with a proximal ulnar nerve lesion due to paralysis of the profundus to these fingers.

  
  
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  One may see any or all of the following signs:

  
  
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  A positive Froment sign (flexion of the interphalangeal joint of the thumb with side pinch)

  
  
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  A positive Jeanne sign (hyperextension of the metacarpophalangeal joint of the thumb)

  
  
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  A positive Wartenberg sign (paradoxical abduction of the little finger by unopposed extensor tendon action due to a paralyzed third palmar interosseous nerve)

  
  
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  Extrinsic weakness may involve the flexor digitorum profundus (FDP) to the little finger and ring finger and the flexor carpi ulnaris (FCU) (the latter rarely occurs).

  
  
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  Test of sudomotor function is particularly useful in small children and noncommunicative patients. An absence of sweating in the little finger is strongly indicative of an ulnar nerve axonotmesis.

Relevant Anatomy

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  The ulnar nerve originates as the terminal branch of the medial cord of the brachial plexus with its main contribution being from the C8/T1 roots. The nerve travels medial to the axillary and the brachial artery and posterior to the basilic vein in the anterior compartment of the proximal upper arm.

  
  
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  It pierces the medial intermuscular septum midway along the upper arm and then runs in the posterior compartment along the medial head of the triceps together with the superior collateral ulnar artery. The ulnar nerve has no branches proximal to the elbow. Approximately 8 cm proximal to the medial epicondyle the nerve passes under the arcade of Struthers, a thin aponeurotic band extending from the medial head of the triceps to the medial intermuscular septum ( Fig. 12.1 ).

  
  
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  At the elbow, the nerve passes through the cubital tunnel, where the articular branch of the elbow is the first branch to leave the nerve behind the medial epicondyle. After the cubital tunnel, the nerve enters the flexor compartment of the forearm between the two heads of the flexor carpi ulnaris muscle, where it gives off motor branches to the two heads ( Fig. 12.1 ).

  
  
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  At the elbow, the ulnar nerve contains ~ 20 fascicles, including the motor branches to the forearm muscles. The motor fascicles to the FCU and the intrinsics are centrally located, whereas the sensory fibers are superficially located. The proximal motor branches to the FCU and FDP can often be traced for up to 6 cm prior to interfascicular connections.

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  In the flexor compartment, the ulnar nerve lies on the medial side of the FDP together with the ulnar artery underneath the FCU, which protects the nerve along most of the forearm. The nerve supplies the FDP via muscular branches, which it gives off a few centimeters below the elbow. Most commonly, the ulnar nerve supplies the ulnar two slips.

  
  
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  Midway to distal third along the forearm, the ulnar nerve may give off the “nerve of Henle,” containing sympathetic innervation to the ulnar artery or a palmar cutaneous branch, which is inconsistent and clinically less famous than its median counterpart. When present, the branch continues distally on the ulnar artery, pierces the antebrachial fascia, and provides sensory innervation to the ulnar part of the palm over the area of the pisiform ( Fig. 12.2 ).

  
  
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  Reaching the distal fourth of the forearm, the dorsal cutaneous branch of the ulnar nerve originates and pierces the antebrachial fascia at ~ 5 cm from the pisiform. The dorsal cutaneous branch then travels subcutaneously and crosses from volar to dorsal at the level of the ulnar head to provide sensation to the ulnar half of the dorsal hand.

  
  
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  At the level of the wrist, the ulnar nerve becomes superficial again, lying only slightly dorsal and radial to the tendon of the FCU muscle and ulnarly to the ulnar artery. It continues distally superficial to the flexor retinaculum through the Guyon canal to divide into the superficial terminal and deep motor branches ( Fig. 12.2 ).

  
  
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  The superficial terminal branch continues distally deep to the palmaris brevis muscle, which it innervates. It then divides into two palmar digital nerves: one to the ulnar half of the little finger and one (a common palmar digital nerve) to adjacent sides of the little and ring fingers.

  
  
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  The deep motor branch passes between the abductor digiti minimi and flexor digiti minimi muscles together with the deep branch of the ulnar artery. It pierces the opponens digiti minimi muscle before coming to lie deep to the flexor tendons together with the deep palmar arterial arch. It gives motor branches to the hypothenar muscles, the ulnar two (or more) lumbricals, all palmar and dorsal interossei, the adductor pollicis, and variably to the opponens pollicis and flexor pollicis brevis (the deep head) muscles. It also provides articular branches to the wrist and possibly to the carpus and carpometacarpal joints.

  
  
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  The ulnar nerve has 15 to 25 fascicles at the wrist. It can be clearly divided into a volar sensory component and a dorsal motor component.

  
  
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  The motor fascicles lie dorsal and slightly ulnarly to the sensory fascicles at the wrist level and usually maintain a dorsal relationship as one moves proximally. The motor component remains as a distinct entity up to 90 mm proximal to the styloid. At 50–85 mm proximal to the radial styloid, the dorsal sensory branch joins the other groups. At the level of the mid-forearm, 50 mm from the ulnar styloid, the motor fascicles lie dorsal to the sensory fascicles.

  
  
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  Four different communicating branches between the ulnar and the median nerve have been reported in the literature with varying prevalence. These are important to recognize to explain patients’ sometimes paradoxical complaints of sensory and motor loss.

  
  
  
  
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    In the Martin-Gruber anastomosis, the median nerve sends motor fibers from the main trunk or the anterior interosseous branch to the ulnar nerve in the forearm that will ultimately innervate the intrinsic hand muscles.

    
    
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    The Marinacci communication is a reverse situation, with an ulnar nerve contribution to the median nerve in the forearm, and it is less common.

    
    
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    In the hand, the Riche-Cannieu anastomosis occurs between the recurrent branch of the median nerve and the deep branch of the ulnar nerve.

    
    
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    A distal communicating branch between the common digital nerves that arise from the ulnar and median nerves in the palm is called the communicating branch of Berretini.