What did Sangwoo do to Yoon Bums legs? Did he cut off the tendons?

in the beginning chapters, he breaks his ankles using a baseball bat.

Didn't show what he did to the right leg it might have been injured after Sangwoo pushed Bum down the stairs or by using the baseball bat. Remember the cringe worthy scene at the end of chapter 2? Sangwoo used a sledgehammer on the left leg and cracked his bones. It's a miracle Bum's even able to stand on his legs without actual medical treatment.

he totally broke his legs, the right one after pushing him from the stairs and the second one with a heavy hammer.

Oh I see! Thanks for explaning I was a little confused xD Poor Yoon Bum!