书从我膝上滑落。
The book slid off my knee.

他膝盖酸痛。
He has a pain in the knee.

她摔倒在地，碰破了膝盖。
She fell down and grazed her knee.

他跌倒了，膝盖重重撞了一下。
He fell and banged his knee.

他往膝盖上擦了一些药膏。
He rubbed some ointment on his knee.

足球比赛时他伤了膝盖，可他并没有因此中途退出。
He hurt his knee during the football match, but this mishap didn't stop him from playing.

真不幸，我在冰上摔倒时摔伤了膝盖。
Unfortunately, I hurt my knee when I fell down on the ice.

他的左膝在一次交通事故中受伤了。
His left knee was hurt in a traffic accident.