Corset damage to a ribcage. 19th century London. Hunterian Collection, Royal College of Surgeons, London via The Chirurgeon’s Apprentice.
Yes, plain old cloth and string CAN do this to bone. Corsets also had whale bone in them. Living bone is pliable and adaptable. It’s always rebuilding itself. When the right amount of force is placed on it for a long enough time, it will stay that way, particularly if the individual is young.