Ulnar Nerve Claw Hand (Main en Griffe)

Definition

Anatomy of the Ulnar Nerve

Origin & Course

Muscles Supplied

• Flexor carpi ulnaris (FCU)
• Medial half of flexor digitorum profundus (FDP) — ring & little fingers

• Hypothenar muscles: Abductor digiti minimi, Flexor digiti minimi, Opponens digiti minimi
• All 4 dorsal interossei
• All 3 palmar interossei
• Medial 2 lumbricals (3rd & 4th)
• Adductor pollicis
• Deep head of flexor pollicis brevis

Pathophysiology of Claw Deformity

Normal finger mechanics (lumbrical action):

• Lumbricals and interossei flex the MCP joints and extend the IP joints via the lateral bands of the extensor expansion.
• This "intrinsic plus" posture allows smooth, coordinated finger movement.

After ulnar nerve palsy:

Why Clawing is More Pronounced in Ring & Little Fingers?

• Index and middle fingers receive their lumbricals from the median nerve (1st and 2nd lumbricals), which are intact.
• Ring and little fingers receive lumbricals from the ulnar nerve (3rd and 4th lumbricals), which are paralyzed.
• Therefore clawing is confined to 4th and 5th digits in isolated ulnar palsy.

High vs. Low Ulnar Nerve Lesion — Paradoxical Claw

Ulnar paradox: High lesions produce less clawing than low lesions, because FDP paralysis reduces the deforming force at the IP joints.

Clinical Tests

1. Bouvier's Test (Finochietto-Bouvier)

• Examiner passively blocks MCP hyperextension (holds MCPs in slight flexion)
• Patient attempts to extend fingers
• Positive (correctable): IP joints extend fully → intrinsic tendons and extensor expansion are intact → surgical correction by MCP blocking procedure will work
• Negative (non-correctable): IP joints fail to extend despite MCP correction → lateral bands or capsular contracture present → tendon transfer alone is insufficient

2. Card Test (Froment's sign variant)

• Patient asked to hold a card between ring and little fingers
• Loss of 4th palmar interosseous (adduction) → cannot hold card

3. Froment's Sign

• Patient grips a paper between thumb and index finger
• With adductor pollicis palsy, FPL compensates → thumb IP flexes to maintain grip

4. Jeanne's Sign

• MCP hyperextension of thumb during pinch grip (due to adductor pollicis + 1st dorsal interosseous weakness)

5. Wartenberg's Sign

• Little finger remains abducted at rest (unopposed extensor digiti minimi, palmar interosseous paralyzed)

Sensory Loss Pattern

• Palmar: Little finger + medial half of ring finger
• Dorsal: Medial 1.5 fingers (only in high lesions — dorsal cutaneous branch exits ~5 cm proximal to wrist)
• Hypothenar eminence: Yes (palmar cutaneous branch of ulnar nerve)

Motor Loss Summary Mnemonic: "LOAF vs Rest"

• Median = LOAF (Lumbricals 1&2, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis superficial head)
• Ulnar = everything else in the hand (all interossei, lumbricals 3&4, hypothenar, adductor pollicis, FPB deep head)

Causes of Ulnar Nerve Injury

Surgical Correction (Brief)

• Static procedures: Zancolli capsulodesis (MCP volar plate tightening) — blocks hyperextension
• Dynamic procedures (tendon transfers):
  • ECRL/ECRB extension with FDS (Bunnel/Stiles-Bunnel)
  • FDS lasso procedure (Zancolli lasso)
  • EIP/EDM transfers through interosseous membrane

Key Points for 10-mark Answer

1. Ulnar nerve = C8, T1; most vulnerable at medial epicondyle
2. Supplies medial 2 lumbricals and ALL interossei → "intrinsic muscles of ring & little fingers"
3. Clawing = MCP hyperextension (EDC unopposed) + IP flexion (FDP/FDS unopposed)
4. Only ring & little fingers clawed (median supplies 1st & 2nd lumbricals for index & middle)
5. Ulnar paradox — high lesion claws less than low lesion
6. Bouvier's test differentiates correctable vs non-correctable claw
7. Associated signs: Froment, Wartenberg, Jeanne's
8. Leprosy = most common cause worldwide (bilateral claw)
9. Guyon's canal anatomy is key for wrist-level lesion localization
10. Surgical correction targets MCP hyperextension — either static (capsulodesis) or dynamic (tendon transfer)