This issue has come up in Question 14.3 from the first paper of 2013. The candidates were invited to differentiate between an ulnar nerve injury and a lower brachial plexus injury in a patient who had returned from cardiac surgery.

Course of the Ulnar Nerve

Keeping in mind that the author writes a lot of this material at 3am, the gentle reader is advised to avert their gaze from spelling mistakes and inconsistencies of anatomical descriptive language, particularly wherever the terms "arm" and "forearm" are mis-used in the image below.

course of the ulnar nerve

Lesions of the Ulnar Nerve

  • Compression at the elbow:
    • Paraesthesia within the distribution of the ulnar nerve:
      • 4th and 5th digit
      • Hypothenar eminence
    • Paresis of the following muscle groups:
      • flexor carpi ulnaris
      • flexor digitorum profundus
      • Small intrinsic muscles of the hand
  • Compression at the wrist proximal to the flexor retinaculum
    • Paraesthesia within the distribution of the ulnar nerve:
      • 4th and 5th digit
      • Hypothenar eminence
    • Paresis of small intrinsic muscles of the hand
  • Compression at the wrist distal to the flexor retinaculum
    • Motor features only: paresis of small intrinsic muscles of the hand
    • No sensory symptoms

References

For a reference, I direct the time-rich reader to Sir Sydney Sunderland's "Nerves and Nerve Injuries", from 1968. (Not available as full text in Google, unfortunately.)

For brachial plexus injuries, I recommend Alain Gilbert's book.

For peripheral nerves, there is Haymaker, Webb, and Barnes Woodhall. Peripheral nerve injuries: principles of diagnosis. Thieme, 1998.

Vanderpool, D. W., et al. "Peripheral compression lesions of the ulnar nerve."Journal of Bone & Joint Surgery, British Volume 50.4 (1968): 792-803.