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The
Ulnar Nerve
Ulnar Nerve
We routinely record the sensory response from the fifth finger and the
dorsum of the hand. Record the motor response from the abductor digiti
minimi (ADM) and in ulnar neuropathies, from the first dorsal interosseous
(First DI) as well.
In the sensory study, place the active electrode over the middle of
the proximal phalanx of the fifth finger and the reference over the middle
of the intermediate phalanx. Choose a point ll cm.
proximal to the active electrode over the ulnar nerve at the wrist and
stimulate the ulnar nerve there lateral to the flexor carpi ulnaris tendon.
The ground electrode is placed between the stimulator's cathode and the
active electrode.
The sensory dorsal branch is studied with a bar electrode over the web
space between the fourth and fifth metacarpals. Stimulate the nerve at
a point 8 cm proximal to the active electrode between the ulnar and the
flexor carpi ulnaris tendon.
Do the motor studies with the active electrode placed over the belly
of the ADM and the reference over the fifth finger.
Stimulate the nerve at the wrist and above the elbow two fingerbreadths
above the medial epicondyle. Be especially careful to ensure
that the proximal and distal responses are similar in configuration and
that proximal amplitude drop does not exceed 2 mv.
In the ulnar neuropathy work-up, stimulate the nerve below the elbow
and at the axilla and Erb's point. As the fibers to the First DI and ADM
are already organized in different fascicles high in the nerve, a separate
study of the first DI using the same stimulation points is needed.
Stimulate the nerve below the elbow in the forearm just lateral to the
belly of the flexor carpi ulnaris muscle. At this level the ulnar nerve
is deep and requires a higher voltage and longer duration stimulus. Calculate
the conduction velocity between the stimulation points and the wrist.
The nerve is then stimulated at the axilla and Erb's point, and the
nerve's length is measured with the tape closely following its anatomy
and the arm abducted to 90 degrees.
Then do the same work-up for the First DI fibers.
Ulnar
Entrapment, Compression or Injury Sites
The ulnar nerve can be entrapped or injured in the hand or in the vicinity
of Guyon's canal; at the wrist where it is involved by injury; in the cubital
tunnel by a thickened flexor carpi ulnaris aponeurosis; at the elbow, most
common compression site; and in the thoracic outlet in compressions between
the first rib and the clavicle.
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