Ulnar Nerve

OVERVIEW
Key Points:

• Assess for both extrinsic and intrinsic median innervated muscles:

• Extrinsic muscles provide wrist flexion and small, ring +/- long finger distal interphalangeal joint flexion.
• Intrinsic muscles provide most of the fine motor movements of the fingers including finger abduction and adduction (including first dorsal interosseous muscle function which is critical to pinch), small finger abduction/opposition/flexion, also provides lumbrical function to the small and ring fingers. Can provide some innervation to some of the thenar musculature.

• Sensory examination includes testing the dorsal cutneous nerve, ulnar-specific digital cutaneous nerves (palmar aspect of the small finger and ulnar half of the ring finger), and the palmar ulnar nerve branch territories.

• Originates from roots: C8, T1.

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EXAMINATION

• Physical examination of the ulnar nerve includes both motor and sensory examination.
• Ulnar nerve function is particularly important in that it contributes to the following ulnar nerve only innervated motor functions: intrinsic function of the hand, which allows for fine motor activity, coordination of finger motion and pinch strength. It provides flexion to the small and ring fingers. It provides sensation to critical areas of the hand–the resting surface of the hand or ulnar border of the small finger.
• The ulnar nerve also contributes to pinch and grip strength.

Detailed Examination Links:

Proximal Extrinsic Motor Branches (Ulnar Nerve)

Flexor Carpi Ulnaris

Flexor Digitorum Profundus (Ulnar half to small, ring +/- long finger)

Distal Intrinsic Motor Branch (Superficial Ulnar Nerve Branch)

Palmaris Brevis (which cannot be examined)

Distal Intrinsic Motor Branches (Deep Ulnar Nerve Branch)

Abductor Digiti Minimi

Flexor Digiti Minimi

Opponens Digiti Minimi

3rd and 4th Lumbricals (to small and ring fingers)

Palmar and Dorsal Interosseous Muscles

Adductor Pollicis

Flexor Pollicis Brevis (Deep Head)

Sensory Branches

Dorsal Branch of the Ulnar Nerve

Common and Proper Digital Nerves (Superficial Branch) (to volar small and ulnar half of ring finger)

Palmar Branch of the Ulnar Nerve

Articular Branches to the Elbow Joint and Carpal and Metacarpo-phalangeal Joints.

Summarized Examination:

• Ulnar deviation wrist flexion””palpate the flexor carpi ulnaris
• Finger flexion””ask the patient to flex at the at the distal interphalangeal joint of the small and fing fingers (tests ulnar-innervated flexor digitorum profundus).
• Finger metacarpal phalangeal joint flexion and interphalangeal joint extension of the small and ring fingers (tests for ulnar-innervated lumbrical function).
• Finger abduction and adduction to test interosseous muscle function–a quick test asks the patient to `cross the fingers”™.
• Small finger movement””ask the patient to flex the metacarpalphalangeal joint of the small finger (to assess flexor digiti mimimi), abduct, and oppose small finger. Also ask the patient to pinch a piece of paper between the thumb and index finger–those with weakness of the ulnar nerve will exhibit compensatory flexion of the thumb interphalangeal joint as they use flexor pollicis longus to gain pinch strength instead (Froment”™s sign).
• Sensation to the volar small finger.

Pathological Findings:
Known sites of ulnar nerve compression or entrapment:

• Arm/Elbow:

• At the arcade of Struthers–thick fascia that extends from the medial head of the tricps to the intermuscular septum (between the triceps and biceps muscles) that can compress the underlying nerve (especially after transposition).
• At a large and bulging medial head of the triceps muscle.
• At an anomalous epitrochleoanconeus muscle just at the proximal elbow level.
• The major compressive site is at the cubital tunnel–the fascial covering that overlies the ulnar nerve as it travels from superficial (at the elbow) to deep (just distal to the elbow) as it enters the flexor carpi ulnaris.
• Osborne”™s band–thickened fascia that runs between the two heads of the flexor carpi ulnaris muscle and can compress the underlying nerve as it enters and dives under this muscle.

• Wrist/Proximal hand:

• At thickened antebrachial fascia just proximal to the wrist crease.
• At Guyon”™s canal: the space at the wrist through which passes the ulnar artery, veins and the ulnar nerve.
• At the leading edge of the hypothenar muscles (this fibrous edge can compress the underlying deep motor branch of the ulnar nerve)
• At anomalous muscles in this area, such as an accessory slip of the palmaris longus, can also cause compression.

Clinical Relevance:

• The ulnar nerve is critical to normal upper extremity function.
• Isolated ulnar nerve injury is most debilitating for the loss of coordinated hand/finger activity, hand strength and ability to perform fine motor activity as well as the loss of sensation to the ulnar border of the hand.
• Initially, ulnar nerve injury findings can be relatively subtle–patients note frustrating dysfunction–but with resulting atrophy and clawing the changes become more obvious to the observer. Clawing is noted to be more severe in distal (versus proximal) ulnar nerve injury patterns because of the greater imbalance between extrinsic and intrinsic motor function.
• In proximal ulnar nerve injury patterns, when the denervation time permits (3 to 6 months or less is ideal), restoration of intrinsic muscle function and prevention of clawing is critical and can be accomplished through median to ulnar nerve transfer procedures. Tendon transfers can also be used to restore small and ring finger flexion. In chronic injuries, various anticlaw procedures can be done but these perform poorly in the severely stiff or chronic pain type patient. Nerve transfer to restore the vital sensation to the ulnar border of the hand can be restored irrespective of time since injury since sensory nerve injuries are not time sensitive.
• Restoration of ulnar innervated loss of function associated with lower or complete brachial plexus injury is challenging indeed and the ability to restore complete normal hand function remains elusive in adults.
• Direct ulnar nerve injury in the arm is often due to penetrating injury at the posterior elbow; at the wrist it is commonly associated with injury to the ulnar artery as these two structures travel close together.
• The ulnar nerve is commonly noted for its susceptibility to compression neuropathy, particularly at the elbow. Examination of compressive neuropathy includes all of the above mentioned techniques to examine motor and sensory dysfunction as well as the performance of provocative maneuvers at known sites of compression (see above).

Relevant Anatomy:
Innervation:

• Roots: C8, T1.
• Nerve: Ulnar nerve.
• Muscles Innervated: Flexor carpi ulnaris, flexor digitorum profundus (ulnar ½), palmaris brevis, abductor digiti minimi, flexor digiti minimi, opponens digiti minimi, 3rd and 4th lumbricals, palmar and dorsal interosseous muscles, adductor pollicis, flexor pollicis brevis (deep head).
• Innervation Route:

Muscles
• C7, C8, T1 â†’ ulnar nerve â†’ flexor carpi ulnaris branch.
• C8, T1 â†’ ulnar nerve â†’ flexor digitorum profundus III, IV branches.
• C8, T1 â†’ ulnar nerve â†’ superficial branch â†’ palmaris brevis.
• C8, T1 â†’ ulnar nerve â†’ deep motor branch â†’ abductor digiti minimi branch.
• C8, T1 â†’ ulnar nerve â†’ deep motor branch â†’ flexor digiti minimi.
• C8, T1 â†’ ulnar nerve â†’ deep motor branch â†’ opponens digiti minimi.
• C8, T1 â†’ ulnar nerve â†’ deep motor branch â†’ 3rd and 4th lumbricals.
• C8, T1 â†’ ulnar nerve â†’ deep motor branch â†’ palmar and dorsal interosseous.
• C8, T1 â†’ ulnar nerve â†’ deep motor branch â†’ adductor pollicis.
• C8, T1 â†’ ulnar nerve â†’ deep motor branch â†’ flexor pollicis brevis (deep head).

Sensation
• C8 â†’ ulnar nerve â†’ dorsal cutaneous branch of ulnar nerve.
• C8 â†’ ulnar nerve â†’ palmar cutaneous branch of ulnar nerve.
• C8 â†’ ulnar nerve â†’ superficial branch â†’ digital cutaneous branches of ulnar nerve.