Never seen a rack like this before...heads up, dead bloody deer in photos...

[c-fbmi]

Because the antler grown looks normal other than direction I would say this was a velvet injury and not hormonal or genetic anomaly. As the antler was finished growing and had not grown into the upper jaw (according to the OP), I doubt there was any pain involved in this case. Next year he may well have been perfectly normal.

 

[medvedqc]

i remembered my old classroom for hunting license in France and we got a lot examples. it maybe during the beginning of the growth, it can be genetics or morphologic. in the last two cases it has to be removed from the pool genes, if only the growth then next year be sure it is not permanent otherwise it has to be hunted.

in the same case there is always hunters that want a different trophy.