What injuries did soldiers get in World War 1?

It's really difficult to answer this question. There were so many horrific wounds inflicted that to say "This was the worst" is impossible.

Poison gas attacks left men permanently scarred for the remainder of their lives. Their lungs were burned and they could never breath properly again.

Again poison gas caused ghastly burns to the skin.

Head injuries, lost limbs, hard to say.

You could also consider the damage done to the minds some of the worst. Shell shocked troops could hardly dress themselves, let alone fight the enemy.