This invention relates to devices, such as cannulas or needles, which are used for inserting expandable structures, such as medical balloons, into interior regions of a human or animal body, as well as methods for their use. In various embodiments, insertion devices described herein are capable of flaring at their tip to ease insertion and removal of expandable structures and reduce the risk of damaging such expandable structures during their insertion, inflation and removal. In other embodiments, insertion devices described herein are capable of directionally guiding and/or inhibiting expansion of an expandable structure within an interior region of an animal or human body to create optimally placed cavities for repair, augmentation and/or treatment of fractured and/or diseased bone.