膝を

knee

→ 膝
phrase Rare #32,730
knee 膝 means “knee,” and を marks it as the object of the following verb, such as hurting, injuring, or hitting it. The phrase is usually followed by a verb.
JA: 階段から落ちて、膝を打った。
EN: I fell down the stairs and hit my knee.

みたいによく冒険してたけどある膝を怪我したんだ

I used to go on adventures just like you, but one day I injured my knee with an arrow.

トム転んで膝をケガしたんだ

Tom fell and hurt his knee.

膝をついて手を前に

Kneel down and put your hands out in front of you!

— ロシアン・ブラザー (1997)