In my memories, it just mentions that he walks with a cane but I don’t remember Hugo giving a reason. I wouldn’t call it certainty though, maybe something slipped my mind :3
From memory the only thing that’s said is that Joly has a cane, and from there people have extrapolated and headcanoned. Since canes were actually fashion at the time probably quite a few of the Amis also had canes (Courfeyrac for example, who in fact I think has a sword cane at the barricade) so it’s not 100% on whether Joly even has a bad leg that causes him to need it.
Yep yep, can definitely confirm, there’s no indication of Joly having any particular health problem! But like I say in the linked post , there’s all sorts of physical issues that might get called a disability now (or alternately not interfere enough with a much-reduced walking schedule) that a cane might help with, without it being at all anything people of the time, including Hugo, would comment on. (and not all of those would even be to do with his legs- low stamina, poor balance for any reason, etc etc, there are lots of things that work! And they could be caused by accident or illness or just the roll of the genetic dice.) So there’s a lot of room for variation within canon, if that’s what you’re wanting to do!