Makindo Medical Notes

✋ Although the 4th & 5th digits are held in the clawed position when the ulnar nerve is injured at the wrist, a high lesion (above elbow) paralyses the long flexors → loss of this sign. This is called the ulnar paradox 🧩.

🩻 Anatomy of the Ulnar Nerve

• Origin: medial cord of brachial plexus (C8, T1).
• Course:
  • Descends medial arm → passes posterior to medial epicondyle (“funny bone”).
  • Runs between flexor carpi ulnaris & FDP in forearm.
  • Enters hand via Guyon’s canal near pisiform.

The ulnar nerve is a major nerve of the upper limb, originating from the brachial plexus (C8–T1). It supplies key forearm flexors and most intrinsic hand muscles, as well as sensation to the medial 1½ fingers.

🌿 Branches

• Forearm muscular: flexor carpi ulnaris, medial half of FDP.
• Hand muscular: hypothenar muscles, interossei, medial 2 lumbricals, adductor pollicis.
• Sensory:
  • Dorsal cutaneous branch → dorsum medial 1½ fingers.
  • Palmar cutaneous branch → palmar medial 1½ fingers.

⚙️ Functions

• Motor: finger ab/adduction (interossei), grip & pinch strength, wrist flexion (FCU), DIP flexion of 4th & 5th (FDP).
• Sensory: medial hand + medial 1½ digits (palmar & dorsal).

🚨 Clinical Relevance

• Ulnar nerve entrapment:
  • Elbow → cubital tunnel syndrome.
  • Wrist → Guyon’s canal syndrome.
  • Symptoms: paraesthesia in medial 1½ digits, weak grip, hand intrinsic wasting.
• Ulnar nerve injury:
  • High lesion (elbow/humerus): FCU + FDP (digits 4–5) + intrinsic hand weakness → less obvious clawing (ulnar paradox).
  • Low lesion (wrist): long flexors intact, intrinsic weakness → claw hand deformity of digits 4–5.
  • Froment’s sign: thumb IP flexes (FPL via median nerve) when trying to pinch a paper due to weak adductor pollicis (ulnar).
• Claw hand deformity:
  • Hyperextension of MCP + flexion of IP joints (digits 4–5).
  • Caused by unopposed extensor digitorum + FDP action.

🧪 Investigations

• Clinical exam: interossei (finger ab/adduction), Froment’s sign, sensory testing.
• Nerve conduction studies / EMG.
• MRI/US if structural entrapment suspected.

💊 Management

• Conservative: activity modification, splints, physio, NSAIDs.
• Neuropathic pain management if required.
• Surgical decompression (cubital tunnel release, Guyon’s canal release) for persistent/severe cases.

📚 Summary

🔑 The ulnar nerve (C8–T1) supplies most intrinsic hand muscles and sensation to the medial 1½ digits. 👉 Low lesion → classic claw hand. 👉 High lesion → less clawing (ulnar paradox). 👉 Froment’s sign = key clinical test for adductor pollicis weakness.