What is the ulnar nerve and where does it originate?

The ulnar nerve is a major nerve of the upper limb. It originates from the medial cord of the brachial plexus with a root value of C8 and T1 (and C7 contributes to the flexor carpi ulnaris).

What muscles does the ulnar nerve innervate in the forearm and hand?

In the forearm, it innervates the flexor carpi ulnaris (FCU) and medial half of the flexor digitorum profundus (FDP). In the hand, its deep branch supplies hypothenar muscles, interossei (3 palmar and 4 dorsal), adductor pollicis, deep head of flexor pollicis brevis (often), and 3rd and 4th lumbricals.

What causes a 'claw hand' and how does it differ with ulnar nerve injury?

Claw hand results from ulnar nerve injury, causing hyperextension at the metacarpophalangeal joints and flexion at the interphalangeal joints, primarily in the ring and little fingers. It is more pronounced with injury at the wrist because the FDP remains intact, retaining distal interphalangeal flexion.

What are the key differences between ulnar nerve injury at the elbow versus the wrist?

Injury at the elbow (e.g., cubital tunnel syndrome) affects all ulnar-innervated muscles, leading to claw hand and loss of thumb adduction. Injury at the wrist (e.g., Guyon’s canal syndrome) spares the forearm muscles, resulting in a more pronounced claw hand with intact FDP function.

What is Froment's sign and what does it indicate?

Froment's sign is a clinical test where the thumb flexes at the interphalangeal joint when attempting to hold a paper. It indicates paralysis of the adductor pollicis muscle due to ulnar nerve injury, as the flexor pollicis longus compensates.

Why is the ulnar nerve called the 'funny bone' and the 'musician's nerve'?

It is called the funny bone because striking the medial elbow causes tingling along its sensory distribution. It is nicknamed the musician’s nerve because it controls fine intrinsic hand movements essential for activities like playing piano.

What sensory areas does the ulnar nerve supply?

The ulnar nerve provides sensation to skin over the hypothenar eminence (via palmar cutaneous branch), medial dorsum of the hand and medial 1½ fingers (via dorsal cutaneous branch), and palmar aspect of medial 1½ digits (via superficial branch).

Ulnar Nerve Anatomy – Course & Claw Hand

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