To clarify: how many stayed on the front lines without being evacuated due to injuries from 1914-1918.
https://www.reddit.com/r/AskHistorians/comments/39c6sd/did_we_know_the_rate_of_survival_during_the_world/
The first part of this answer I've given should go some ways towards answering your question.
https://www.reddit.com/r/AskHistorians/comments/2z53xs/im_a_young_german_man_who_signs_up_for_military/
This one should also help.