她在粗糙的墙上擦伤了指关节。

She scraped her ___knuckles against the rough wall.

他握紧拳头，指关节都发白了。

He clenched his fists so tightly that his ___knuckles turned white.

拳击手淤青的指关节证明了他训练的艰苦。

The boxer's bruised ___knuckles were a testament to his rigorous training.