The Ulnar Nerve - A Physical Therapy Guide

Origin & Roots

• Spinal levels: C8, T1
• Arises from the medial cord of the brachial plexus
• Travels with the median nerve and axillary artery in the proximal arm

Course Through the Upper Limb

Arm

• No branches given off in the arm
• Pierces the medial intermuscular septum at the arcade of Struthers (~8 cm proximal to the medial epicondyle)
• Passes posterior to the medial epicondyle ("funny bone") through the ulnar groove
• Enters the cubital tunnel beneath the humeral-ulnar aponeurosis (arch of flexor carpi ulnaris)

Forearm

• Passes between the two heads of flexor carpi ulnaris (FCU)
• Travels between the FCU and flexor digitorum profundus (FDP)
• Lies medial to the ulnar artery in the distal two-thirds of the forearm
• Gives off two cutaneous branches distally:
  • Dorsal cutaneous branch (5-8 cm proximal to wrist): dorsal medial hand and dorsal ring/little fingers
  • Palmar cutaneous branch: proximal medial palm

Wrist & Hand (Guyon's Canal)

• Passes superficial to the flexor retinaculum, lateral to the pisiform
• Divides in Guyon's canal into:
  • Deep (motor) branch: curves around the hook of hamate, supplies hypothenar muscles, all interossei, medial two lumbricals, adductor pollicis, deep head of flexor pollicis brevis
  • Superficial (sensory) branch: sensory to little finger and medial half of ring finger

Motor Innervation Summary

Sensory Innervation

• Palmar: Little finger + medial half of ring finger (palmar surface)
• Dorsal: Dorsomedial hand, dorsal little finger and medial ring finger
• Proximal medial palm: palmar cutaneous branch (not through Guyon's canal)

Common Injury Sites & Clinical Features

1. Cubital Tunnel Syndrome (most common)

• Compression at the elbow - beneath the humeral-ulnar aponeurosis / ulnar groove
• Causes: prolonged elbow flexion, leaning on elbows, post-fracture cubitus valgus ("tardy ulnar palsy")
• Symptoms: numbness/tingling in ring and little fingers, weak grip/pinch, intrinsic muscle wasting
• PT note: the dorsal cutaneous and palmar cutaneous branches are spared when compression is at Guyon's canal (wrist), which helps localize the lesion

2. Guyon's Canal Syndrome (wrist)

• Compression between pisiform and hook of hamate
• Causes: cycling (handlebar pressure), ganglion cysts, hook of hamate fracture
• Deep branch only: purely motor deficit (no sensory loss)
• Superficial branch only: purely sensory deficit

3. Elbow Fracture/Dislocation

• Acute injury with medial epicondyle fractures

Classic Clinical Sign: "Ulnar Claw Hand"

• MCPJs hyperextended + IPJs flexed in ring and little fingers
• Caused by loss of intrinsic muscles (lumbricals and interossei) with intact extrinsic flexors (FDP)
• Clawing is more pronounced at the wrist than at the elbow ("ulnar paradox") - because at the elbow, FDP to the ring/little fingers is also paralyzed, reducing the deforming force

Key PT Assessment Points

"Ulnar Paradox" - Remember This for Exams