Its not totally implantable, you have to wear something behind the ear, but the canal is open...
http://www.fda.gov/cdrh/mda/docs/k013298.html
http://www.retroxhearing.com/pro.aspx
This site talks about a study done on the RetroX
http://www.fda.gov/cdrh/mda/docs/k013298.html
http://www.retroxhearing.com/pro.aspx
This site talks about a study done on the RetroX