expression, godan verb (-su)
dislocate one's back; throw out one's back
Literal physical meaning: to injure the lower back so severely that one cannot stand. Less common than the figurative sense.
See also: 腰抜かす
重い荷物を持ち上げようとして腰を抜かした。
I threw out my back trying to lift a heavy load.
expression, godan verb (-su)
be unable to stand from fear or surprise; be paralyzed with shock
Figurative use: to be so shocked, frightened, or surprised that one's legs give out and one cannot stand up. This is the more common meaning.
突然の大きな音に腰を抜かした。
I was so startled by the sudden loud noise that I couldn't stand up.
彼はその知らせを聞いて腰を抜かさんばかりに驚いた。
He was so shocked at the news that he nearly collapsed.