21.   His left knee buckled.

22.   I tried to stand, but my knees buckled twice.

23.   I was standing out in the parking lot of this restaurant on a pay phone and my knees buckled.

24.   Just the other day, her knee buckled and she collapsed in silent tears.

25.   My knees buckled.

26.   My knee buckled without getting hit.

27.   My knees buckled and I fell against the machine in relief.

28.   My knee buckled.

29.   On second down, he threw incomplete to tight end Pete Metzelaars and was hit by Thomas, causing the knee to buckle backward.

30.   One by one, knees buckling, we crashed on deck.