This issue has come up in Question 14.3from 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.
The images and text content in included below for the purposes of rapid revision.
However, as far as point-form summaries from an authoritative source are concerned, Wheeless' Textbook of Orthopaedics does it much better.
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.