Avulsion - the most
severe type, in which the nerve is torn from the spine;
Rupture - in which the nerve is torn but
not at the spinal attachment;
Neuroma - in which the nerve has tried to
heal itself but scar tissue has

grown
around the injury, putting pressure on the injured nerve and

preventing
the nerve from conducting signals to the muscles;
Neuropraxia or
Stretch - in which the nerve has been damaged but
not

torn.
Neuropraxia is the most common type of brachial plexus injury.