@Aoitenshi
In the anime episode 12 that this chapter follows, Tanjiro mentioned it's only because that he's the eldest son of the family that he can be as tough; if he's been the second son, he'd have collapsed from the excruciating pain of the broken bones.
The panel proves that theory by showing that despite Zenitsu being older than Tanjiro, he's cowardly and needed comforting from others, as he's not the oldest in his family.