만신창이 is an idiom ,which in Hanja chinese is 滿身瘡痍 ( literally meaning your whole body is wrecked after a trauma) but in means to be thoroughly hurt/injured , it is used in this format a lot... 만신창이가 되다 you can say 내 마음은 만신창이가 되버렸어요 for you mind also 몸과 마음은 만신창이가 되어버렸어요 ㅜㅜ my mind and body were wrecked, another example sentence is 아끼는 운동화들도 지금은 만신창이가 되어 버렸어요 means with cheap athletic shoes now part my body is wrecked

It's condition when someone is thoroughly hurt. Not only for physically, but also mentally.