An intramedullary bone fixation device that includes a shaft with a flexible region. The flexible region may be configured to flex from a first shape to a second shape as the shaft moves along a curved medullary canal. For example, the bone fixation device may include a distal bone screw that is configured to move along the curved medullary canal of first and second segments of a fractured bone (e.g., two segments of a broken rib) and fasten to the segment bone segment. The bone fixation device may include a locking member (e.g., a proximal bone screw) that is configured to lock the shaft to the first bone segment. For example, the shaft may be fixed to the distal bone screw and ratchetably coupled to the shaft such that the first and second bone segments can be compressed together by urging together the distal bone screw and the locking member.