Only then did I give in and let my knees buckle.

When he tried to take a step, one knee buckled.

Her knees buckled and she sat down on the running board.

His knees buckled suddenly, taking us both to the floor.

His left knee buckled and he went down on it.

Her knees were buckling, but she was trying to walk.

He tried to reach out to stop that fire, but his knees buckled.

When he finally set the master down, the man's knees buckled.

Those above it, especially on the bridge, felt their knees buckle.

The report of the shot reaches us just as his knees buckle.