When the Doctor hurts his ankle in the fanfiction, it could force him to confront his vulnerability and maybe even discover hidden strengths within himself and his team. It could also introduce new characters who assist him during this difficult time.
Well, it might cause the Doctor to slow down and change the course of their mission. They might have to seek help from unexpected sources or use their wit and intelligence in new ways to overcome the challenge.
It could lead to all sorts of adventures. Maybe the Doctor has to rely on his companions more or find unique ways to solve problems with his limited mobility.