Black Cap's heavy coat wasn't enough padding to absorb the power behind that blow and his knees buckled under him.

Then his knee buckled in front of the Boston bench.

Finally, without warning, his feet touched the ground and his knees buckled under him.

That was all I could do before my knees buckled and my own private darkness buried me.

The Phoenix slumped to the floor as one knee buckled under him.

His feet hit hardness and his knees buckled under him.

She pressed her back to the wall as her knees buckled and she slowly began to sink.

His knees buckled under the strain and his body sagged as it was forced toward the floor.

LaValle did well to stay on his feet, for his knees nearly buckled with weakness.

But he'd hardly taken two steps before his knees buckled and he slumped to the floor.