Ulnar tunnel syndrome

Pressure on N. ulnaris in Guyon’s canal

• Ganglion cyst
• Chronic repeated trauma or pressure on the hypothenar area
• Fracture

Three zones in Guyon's canal where the nerve can be exposed to pressure or injury

• Zone 1 N. ulnaris
• Zone 2 R. profundus, purely motor branch
• Zone 3 R. superficialis, combined motor and sensory branch

Claw hand when the hand is opened

• Hyperextension in MCP of 4th and 5th finger
• Partial flexion in the DIP and PIP joints of the 4th and 5th fingers
• In ulnar tunnel syndrome, the M. flexor digitorum profundus is intact, which leads to more flexion in the DIP joints of the 4th and 5th fingers, resulting in a more pronounced claw hand than in cubital tunnel syndrome

Weakness in M. palmaris brevis

• M. palmaris brevis is located over the hypothenar muscles
• Innervated by the superficial branch (R. superficialis) of N. ulnaris, which branches off just after Guyon's canal
• The muscle is identified by asking the patient to abduct the little finger against resistance and observe whether the skin becomes wrinkled over the hypothenar area

• M. adductor pollicis weakness
  • Weak thumb adduction
• M. flexor pollicis longus has normal strength (innervated by N. interosseus anterior, branch of N. medianus)
  • Flexion in the thumb’s interphalangeal (IP) joint is normal.
  • The IP joint is flexed to hold the paper.

• Reduced sensation corresponding to the innervation area of R. dorsalis nervi ulnaris and R. superficialis
• Preserved sensation in R. palmaris nervi ulnaris as the branch arises before Guyon’s canal