BONE FIXATION DEVICES

Abstract

Intramedullary nails and other bone stabilization devices are used to provide for bone fixation are made from a biocompatible polymer such as the pyromellitic, dianhydride (PMDA)-free, non-halogenated, thermosetting aromatic polyimide disclosed in U.S. Pat. No. 6,686,437. The intramedullary nails of this invention can be secured to the bone by screws anywhere along their length. The intramedullary nails of the invention eliminate the need for imaging technology, permitting the surgeon more freedom to personalize the operation and support to the needs to the needs of the particular patient and avoid the need to expose the patient and medical personnel to hazardous x-rays and the like. The use of a polyimide polymer instead of a metal device of far higher modulus reduces bone fracturing and splintering and eliminates the risk of metallosis and metal poisoning. Ordinary commercial metal screws can also be exchanged with polyimide self-tapping screws providing a totally non-metal system.

Claims

1. A bone stabilization device which is inserted in the body of a patient requiring bone stabilization, which comprises: A shaft comprised of a formable, pyromellitic, dianhydride (PMDA)-free, non-halogenated, aromatic polyimide thermosetting polymer which exhibits approximately the tensile strength and stiffness of human bone, wherein said shaft is of a shape suitable for stabilization of said bone requiring stabilization, and is free of predrilled holes for bone screws.

2. The bone stabilization device of claim 1, wherein said shaft is of a shape and size to be inserted in the intramedullary marrow tunnel of a long human bone, and is susceptible of being secured to the bone it stabilizes by bone self-tapping screws.

3. The bones stabilization device of claim 1, wherein said device is of a shape and size suitable to stabilize a partial fracture and is in the form of a plate or flange attached to the bone but not penetrating any cavity of the bone.

4. The bone stabilization device of claim 1, wherein said device comprises roughening at points along its length to aid in the driving of screws to secure said device to said bone to be stabilized.

5. A method of stabilizing a fractured bone comprising affixing the bone stabilization device of claim 1 to said bone to be stabilized by screwing said device to said bone with bone self-tapping screws at any point along the length and at any angle with respect to said device suitable for a surgeon affixing said device.

6. The method of claim 5, wherein said method does not require any imaging to determine proper placement of said device.

7. The method of claim 5, wherein said method is free of the provision of scaffolding or support elements necessary to hold said device in place relative to said bone.

8. The method of claim 5, wherein said method comprises inserting the device in the form of an intramedullary nail into the intramedullary marrow tunnel of the bone to be stabilized, and wherein said nail is secured by bone self-tapping screws screwed through said nail and into said bone cortex to be stabilized.

9. The method of claim 5, wherein said bone is partially broken, and said device is affixed by said bone screws to portions of said bone not within the zone of breakage of said bone.

10. The method of claim 5, wherein said device is in the form of a plate or flange affixed to bone along said bone, so as to stabilize said bone while it heals.

11. The method of claim 5, wherein said self-tapping screws are prepared from a biocompatible polymer which need not be removed from the body.

12. The method of claim 11, wherein said method does not employ any materials of metal to be left in the body of a patient with said fractured bone.

13. The method of claim 5, wherein said driving of said self-tapping screws is preceded by drilling small starter holes in said device before driving said self-tapping screws.

14. The method of claim 10, wherein said bone is not a long bone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention permits of drawings and the same are provided herein. It should be understood, however, that the use of the biocompatible polyimide or similar polymer provides the opportunity to use intramedullary plates and nails of virtually any shape and dimension, to provide for internal fixation, either by insertion into the marrow cavity of the bone (intramedullary nail) or by provision of a plate which may be used to anchor a fractured or damaged bone. It also permits to use self-tapping screws made of a biocompatible polyimide or similar polymer providing a completely metal-free system for patients. This not only offers important advantages for patients that are sensitive or allergic to metals, but eliminates the need for a second surgery to remove the stabilization materials.

[0014] FIG. 1 illustrates an intramedullary device of the invention, in this case, in the form of an elongated shaft or nail 104. This shaft is designed to be inserted into the hollow (intramedullary) marrow tunnel of a long bone, like a shin bone, but may be formulated in the shape of a plate, as may be necessary to provide bone fixation. The shaft 104 need not, but may be provided with a head or widened area 102 at one point with an inner thread, if it facilitates insertion into the shaft. Head 102 forms, in effect, a flange by which the nail may be grasped and manipulated. Importantly, shaft 104 is free of predrilled holes. Because conventional bone screws may be inserted into the shaft at any point along its length and at any angle, and from there screwed into the bone to fasten and stabilize the fractured bone, no predrilled holes are required.

[0015] FIG. 2 illustrates a similar intramedullary device (plate) of the invention. In this case, the plate has a wave-like marginal structure. The wide areas 205 are abraded and serve as starters to make the process of screwing the bone screw into the shaft easier. The thinner parts 204 have non-abraded smooth surface. The surgeon may feel the difference between the abraded rough area and the smooth area and thus be able to direct the drill to the right spot. If provided all along the length of the shaft at about the centerline, the surgeon is provided with a full range of solutions so as to optimize stabilization of the fracture.

[0016] FIG. 3 illustrates the bone screw made of polymer. The screw is provided with a self-tapping thread 308 and a drive head 306. Since polyimide is thermosetting cross-linked polymer, the screw and the nail will never cold fuse. This permits the provision of a completely metal-free device and method, avoiding the need to remove any bone fixation materials or devices following a successful resolution

DETAILED DESCRIPTION OF THE INVENTION

[0017] A central feature of the invention disclosed herein is an undisclosed advantage of the polyimide polymer MP-1, or a similar biocompatible polymer that has the tensile strength and elasticity modulus and cross-linking exhibited by MP-1. The replacement of conventional metallic intramedullary with a biocompatible polymer with physical characteristics not very different from those of bone itself leads to a number of improvements that are achieved simultaneously.

[0018] Considered from the point of view of the process of bone stabilization by use of the intramedullary nail of the invention, a first improvement or advantage of the invention is elimination of the need for metal scaffolding or braces to fix the nail in position. This allows the doctor or surgeon to proceed with a much smaller incision (minimally invasive). Since long bone fractures often occur in the arms and legs, which are frequently visible even when fully clothed, reducing the scarring and cosmetic imperfections arising from the operation reflects an important improvement.

[0019] Possibly the most dramatic improvement is achieved by eliminating the need for preset or predrilled holes in the nail or plate for the bone screws. Polyimide polymers like MP-1 can receive screws anywhere along their length. Thus, the surgeon can affix the intramedullary nail 104 without regard to the preset screw holesinstead opting for locations along the bone that make the most sense for the specific patient being treated. The nail may be made more manageable by the provision of a head or handle 102, but the same is not required. The nail will be first drilled with a smaller hole suitable to the core dimension of the screw and then the self-tapping head 308 of the screw can be inserted through the cortex of the bone and the nail. This ability to personalize bone fixation to the needs of a particular patient and situation is unprecedented in current medicine. As an extension of the push to offer more and more personalized medicine, it represents a new advance in this practice. It also permits the use of the intramedullary nail fixation technique for situations where plates or casts were previously requiredbeing lightweight and yet unlikely to be incompatible with the stresses experienced by the patient's bone and musculature, smaller bone fractures and displacements can be treated conveniently.

[0020] While, as detailed below, the device and method of the invention can be provided of biocompatible polymers like MP-1, where necessary or preferred, this invention is consistent with the use of Kirschner wires (K-wires). Inserted K-wires can be provided with a polymer matrix, like the biocompatible polymer MP-1, to which the wire will weld, providing a secure and enhanced fixation.

[0021] In a preferred embodiment, the intramedullary plate of the invention is provided with roughened the areas 205 for drilling by abrasion of the plate along its length. The areas 204 between holes will be left smooth. In this way the doctor can feel the difference in surface finish and direct the drill into the right location. While the plates, nails and similar devices of this invention may be of any size and shape suitable, providing one with the margin of the plate being wavy will contribute to the plate's strength. The plate will be first drilled with a smaller hole suitable to the core dimension of the screw and then the self-tapping screw can be inserted through the plate and bone. The abrasions 205 provided along the length of the intramedullary plate of the invention facilitate precise fixation of the plate to the bone, wherever, and importantly from whatever angle best serves the patient and the surgeon's needs. The operation is faster, more specifically tailored to the needs of the patient, and unlikely to cause the splintering or fracturing of bone material encountered in the prior art due to the use of metals of very high elastic modulus.

[0022] The same employment of a polyimide biocompatible polymer like MP-1 solves a problem posed in the prior artthe need for imaging technologies to verify the correct placement of the nail and the bone screws. Not only does the need to image the placement of the device slow the operation and necessarily prolong the time spent under general anesthesia, increasing the risk to both the patient and the medical team, but repeated or continuous X-ray exposure is unhealthy for all individuals involved, both the patient and those medical personnel necessarily involved and exposed. By using a strong polymer like MP-1 which has the strength to provide stabilization, holes can be drilled into the intramedullary nail or plate without the generation of excess heat along its length, and this drilling compatible with the stresses and forces applied to the bone itself. Thus, the process of bone repair, from initial incision to insertion to stabilization, the entire operation and related processes involved in bone fracture repair is improved, simplified and made significantly safer. There is no need to remove the structure once healing is complete, further simplifying the process. The debris created during drilling can easily be removed by sucking. Even if some debris is left in the body they are inert and do not cause any inflammation (particle sizes are more than 2 microns or so).

[0023] MP-1 and similar polymers are biocompatible and shown to be safe, and need not be removed from the body at a point when the bone previously broken has healed. Prior art techniques that required brackets or similar metal supports or scaffolding to maintain the position of the bone are rendered unnecessary. No second operation to remove the metal structures is required. This reduces the overall cost of the operation, maximizes convenience and improves patient cooperation without any sacrifice in the character or result of the operation.

[0024] Replacement of metal devices implanted or inserted into the body with biocompatible polymers like MP-1 provides additional health benefits. Replacing metal with a biocompatible polyimide will eliminate the problem of metallosis encountered in connection with prior art intramedullary nails and similar braces, plates and devices. Particularly in situation where bones bear on metal inserts, there is a tendency for metal debris to chip off or corrode, presenting a number of health risks as well as the potential for metal poisoning. Thus, the intramedullary nail of the invention is effective to facilitate bone repair with less inconvenience and cost, less difficulty to the surgeon, no risk of X-ray exposure and reduced risk of secondary health risks. The bone healing is completed in less time, without the need for a second operation for removal of the device, which means substantial gains in improvement of patient safety.

[0025] A particularly important aspect of the combination of reduced cost and risk coupled with increased patient comfort and safety means the traditional method used to stabilize large bones can be expanded to use in situations where prior art techniques could not be used in the stabilization of smaller bones, for partial distal breaks, and the like. The devices used in these procedures more closely resemble plates or flanges that secure the bone and protect it, rather than penetrating along its length. These advantages are secured without loss of the ability to provide a bone fixation/repair method that permits rapid weight bearing for the patient.

[0026] The invention is not limited to any specific shape, character or embodiment. The invention addressed in this application includes both the improved bone stabilization device, made of a biocompatible polyimide polymer with approximately the same modulus as bone, and the improved process for bone stabilization described above. It is broadly described in terms of specific shapes and features, but alternate shapes and features will occur to those of ordinary skill in the art without the exercise of inventive faculty.