Setting: UK, 2010s.
I have a character design kicking around my sketchbooks of a young woman in her mid-twenties or so using a cane, but if I decide to go with it, I'll need some sort of plausible backstory for why she's got a mobility aid in the first place. I need some kind of accident or injury in her backstory that could have just occurred at least several years in her past, and still require the use of a cane in the present. Ideally, it should be something that could just happen to anybody going about their business in a major urban center-- some sort of transportation accident, train crash, getting hit by a car, falling down some stairs or something of the sort-- since overall this character just lived a fairly unassuming sort of life with a boring white-collar job, so stepping on a landmine or sustaining a fracture in a high-stakes kickboxing tournament isn't in the cards.
Googling "injuries requiring the use of a cane" and "injuries requiring long-term use of a cane", and looking at the Wikipedia article for assistive canes revealed all sorts of information about the general use of canes as mobility aids (did you know that it's better to use a cane on the uninjured side, since the idea is to take as much weight off the injured side as possible?), but very little about the specific injuries that might require the long-term use of a cane.