Fractures of limb bones have been treated with internal fixation devices, such as plates lying on the surface of the bone, nails running inside the medullary canal of the fractured bone, or screws affixing both ends of a fractured bone together. Certain criteria should be satisfied when treating such bone fractures. These criteria include providing reasonable structural rigidity to the fractured bone, without compromising some of the strain desired to stimulate bone cells. This stability should be ensured along the longitudinal, transversal and rotational planes of the fractured bone. The device that provides the stability to the fractured bone should minimize disruption of blood supply within the bone, periosteally and intramedullarly. Ideally, the device should be as least invasive as possible to prevent the fracture site from opening. The device should also allow the use of the affected area as soon as possible, without compromising fracture stability. Potentially, the device should also allow for the use of drugs or hardware to locally treat or enhance the union process of the fracture site.
An intramedullary fixation method is a preferred traditional method of treatment for long bone fractures, since it adequately effects affixation of the bone fracture with the use of intramedullary nails, without disturbing the periosteum of the bone. The intramedullary fixation method can be accomplished in a closed manner, and the fractured bone can be functionally used (including weight bearing) during healing. The surgical approach for insertion of intramedullary nails varies slightly for each bone and is well described in the orthopedic literature. A detailed description is offered for the femur, tibia, humerus, radius and ulna in the Campbell textbook of Orthopedic Surgery. Also the Synthes Group, in its book, offers a well-illustrated description. The Nancy nail brochure offers an illustrative description of the elastic intramedullary nails currently recommended for fracture fixation in children.
There are problems associated with many of the intramedullary fixation methods, including the lack of rotation stability, collapse of the fracture site in some fracture types, and the undesired backup of nails. Furthermore, although the actual shape of the bone typically includes some degree of curvature, the intramedullary nails used to mend the fractured bone are typically straight. Still further, the intramedullary fixation method introduces interlocking screws across the nail, creating some disadvantages. Specifically, conventional intramedullary fixation nails for long bones include a rigid structure (hollow or full), that can be locked at their extremes by the addition of screws transversally applied through the bone walls and the nail itself. This additional step makes the operation longer and sometimes cumbersome, and may require necessary additional skin incisions and significant longer use of an image intensifier (X-ray). Furthermore, undesired gaps between the bone ends can originate from the screws, which are permanent unless removed in a new operation. Also, the resultant structure in certain situations is too stiff and lacks the required elasticity. In contaminated fractures, the intramedullary nails, which are metallic, may propagate the contamination through the entire canal, despite attempts at cleaning the fracture site. This may lead to and propagate bone infection.
Recent developments in the intramedullary fixation approach have attempted to address some of these problems. For example, International Patent No. WO 98/38918 to Beyar suggests three structural designs: (1) a solid metal sheet that expands in the medullary canal; (2) a meshwork structure consisting of ribs circumferentially connected at the tips; and (3) a balloon structure that is inflated once inserted into the medullary canal. The first two structures, however, are unable to provide firm support within the metaphysis of the bone. Specifically, these structures are unable to expand at their ends, because the total expansion of the structures is limited by the circumference of the diaphyseal segment of the medullary canal. The balloon structure also has limited utility because, when inflated, it disrupts the blood supply of the bone and avoids its regeneration or recovery, and is unable to adjust to changes in the shape of the medullary canal, because it has a set volume once inserted and inflated.
U.S. Pat. No. 5,281,225 to Vicenzi discloses a structure that includes a multitude of elastically deformable stems connected together by a stub. When inserted in the medullary canal of a fractured bone, the distal tips of the stems expand outward into the end of the medullary canal to anchor the Vicenzi structure within the bone. The stem, however, is affixed to the fractured bone via a transverse screw. Additionally, the Vicenzi structure is not expanded within the medullary canal and, thus, does not provide multiple points of contact with the wall of the medullary canal. As a result, the Vicenzi structure might not ensure structural stability along the transversal and rotational planes of the fractured bone.
Thus, it would be desirable to provide intramedullary devices that provide and ensure stability to a fractured bone, without hindering the normal biological processes within the fractured bone.