The ulnar nerve can be tested through a variety of motor and sensory assessments, primarily focusing on the muscles it innervates in the hand and forearm.
Motor Testing of the Ulnar Nerve
The ulnar nerve's motor function is crucial for hand dexterity and strength. Here's how to assess it:
Forearm Flexion
The ulnar nerve innervates the flexor carpi ulnaris (FCU) muscle, which is responsible for wrist flexion and ulnar deviation.
- How to test: Ask the patient to flex their wrist towards the pinky side (ulnar deviation).
- Expected Result: Strong and symmetrical flexion and ulnar deviation. Weakness suggests ulnar nerve dysfunction in the forearm.
Finger Flexion
The ulnar nerve also innervates the flexor digitorum profundus (FDP) to the ring and little fingers.
-
How to test:
- Instruct the patient to bend their little finger. This assesses the FDP and helps differentiate from the flexor digitorum superficialis (FDS).
- While the FDS is also involved in finger flexion the ulnar nerve's role is primarily in the deep flexors of the ring and little finger.
-
Expected Result: A strong ability to bend the little finger individually. Weakness may indicate ulnar nerve impairment affecting those specific flexor muscles in the forearm.
Hand Intrinsic Muscles
The ulnar nerve innervates most of the hand's intrinsic muscles, including:
-
Hypothenar muscles: Muscles of the pinky side of the palm.
-
Interossei muscles: Muscles between the metacarpals that are involved in finger abduction and adduction.
-
Adductor Pollicis: The muscle that pulls the thumb inwards.
-
How to test:
- Ask the patient to abduct the little finger away from the other fingers.
- Test the ability to perform a strong lateral pinch (key grip) using the thumb and index finger.
- Ask the patient to cross their fingers.
-
Expected Result: Strong and coordinated movements. Weakness or atrophy may indicate ulnar nerve issues within the hand.
Sensory Testing of the Ulnar Nerve
Sensory testing can be performed by assessing light touch and pinprick sensation in the ulnar nerve’s dermatomal distribution, typically:
- Dorsal and Palmar Aspects of the Little Finger: Primarily the little finger, and the ulnar (pinky) side of the ring finger.
- Ulnar side of the Hand and Wrist: Along the hypothenar eminence on the palm.
Example of testing methods:
-
Using a cotton swab or pin prick, lightly stimulate the testing area and ask the patient if they can feel the sensation and if it feels the same bilaterally.
-
Expected Results: Normal sensation throughout the distribution area. Changes in sensation suggest nerve damage or compression.
Summarized testing using the referenced video
- FCU: Flexor Carpi Ulnaris - Testing strength of wrist flexion towards the little finger side.
- Finger Flexion: Testing the flexor digitorum profundus muscle (FDP).
- Hypothenar Muscles: Testing abduction of the little finger away from the other fingers.
- Interossei Muscles: Testing the ability to cross the fingers or hold a piece of paper between the fingers.
- Adductor Pollicis: Testing lateral pinch strength (thumb to index finger)
