Patent Application
20080234762
1. Field of the Invention
The present invention relates to fixation devices configured for use in the human body. Specifically, the present invention relates to orthopedic screws.
2. Description of the Related Art
Screw type devices configured for use in attaching a medical implant to a bone of a human body are well known. Bone screws are employed for a variety of uses, such as in the attachment of bone plates to a bone. Some bone screws have been configured to self tap threads into the bone when threaded into a pilot hole during insertion of the screw into a bone. Other bone screws have been configured to be resorbed by the body after a suitable period of time.
The present invention relates to an orthopedic screw comprising a first portion and a second portion. The first portion comprises a first material and includes a self tapping tip. The second portion may be connected to the first portion and may be comprised of a second material, which may be resorbable or non-resorbable. The first material is configured to be resorbed into a human body at a faster rate than the rate at which the second material may be resorbed into the body.
The first material may comprise at least one of Poly(DL-lactide), Poly(glycolide), Poly(L-lactide-co-glycolide) or Poly(DL-lactide-co-glycolide). In other embodiments, the first material may comprise at least one of Poly(ethylene glycol)-co-polyactide, methyl cellulose, carboxyl methyl cellulose. In embodiments, the first material may comprise at least one of hyaluronic acid, chitosan, collagen gelatin, fibrin, dextran or agarose. In addition, in embodiments, the second material may comprise Poly(L-lactide) or Poly(DL-lactide-co-L-lactide).
The inherent viscosity of the first material may have an inherent viscosity as low as about 0.1 or 0.2 dL/g and as high as about 1, 1.5 or 3 dL/g. The second material may have an inherent viscosity as low as about 0.1 or 0.2 dL/g and as high as about 1, 1.5 or 3 dL/g
The second portion may include a head configured to mate with a driver. In addition, the first portion may include at least one thread encompassing an outer surface. The thread encompassing the outer surface may be a starter thread and may include flutes. In embodiments, the second portion may also include a thread. The thread of the second portion may be aligned with the thread of the first portion. The first portion may have a hardness at least equivalent to the hardness of bone.
An advantage of the present invention is the relatively faster resorption of the tip portion of the screw as compared to the remainder of the screw.
A further advantage of the present invention is that the relatively faster resorption of the tip portion of the screw allows the body to heal around the tip portion of the screws while the remainder of the screw secures a bone plate, for example, on a bone.
In one form, the present invention provides an orthopedic screw including a threaded shaft, including a distal portion formed at least in part of a first resorbable material, the distal portion including a self-tapping tip; and a proximal portion formed at least in part of one of a second resorbable material and a non-resorbable material.
In another form, the present invention provides an orthopedic screw including a distal tip portion formed at least in part of a resorbable material; and a threaded shaft portion including a proximal end with a driver interface, the threaded shaft portion formed at least in part of one of a second resorbable material and a non-resorbable material.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
In the present embodiment, first portion 4 includes a first end 8 and a second end 10. First portion 4 further includes a plurality of flutes, each generally indicated by numeral 11, and a thread, generally indicated by numeral 12. Flutes 11 may have any configuration known in the art and are generally shaped for self tapping into a bone. Thread 12, which may be referred to as a starter thread, encompasses a portion of the outer surface of first portion 4 and is capable of forming threads in a bone. Accordingly, first portion 4, including thread 12, is generally manufactured from a material having a hardness greater than that of bone. In embodiments, the flutes 11 may interrupt the travel of the thread 12 around the first portion 4.
Second portion 6 includes a first end 14 and a second end 16. In the present embodiment, first end 14 is configured to mate with second end 10 of first portion 4 in a suitable manner, such that first and second portions 4 and 6 may be rotatably driven as a unit. For example, in embodiments of the invention, as shown in
In addition, in embodiments, first end 14 may be affixed to second end 10 by way of a biocompatible adhesive, for example. In embodiments, the ends 10, 14 may be conjoined via a welding process, for example.
Referring again to
In the depicted embodiment, second portion 6 includes a driver interface, such as recess 22, which is configured to receive a driver (not shown) known in the art. Recess 22 may have any known shape complementary to that of drivers typically employed in the art. In other embodiments, driver mating portion 18 may take any known configuration capable of mating with a driver. For example, mating portion 18 may include protrusions, not shown, configured to be received by a driver tool. In other embodiments, mating portion 18 may include at least one recess configured to receive protrusions of the driver tool.
Second portion 6 further includes a thread, generally indicated by numeral 24. In the depicted embodiment, thread 24 extends from first end 14 toward second end 16 to a position proximate driver mating portion 18. In addition, in the depicted embodiment, thread 12 may gradually transition to thread 24 and the threads 12, 24 may be complementary. For example, the threads 12, 24 may have a uniform pitch and may be like handed, i.e. the threads 12, 24 may share the same direction of advancement upon rotation.
First portion 4 may be resorbed within hours or days by way of any known process, such as through a bio-resorption process or through a galvanic corrosion process. First portion 4 may also be manufactured from any known material generally having a hardness greater than bone and capable of being resorbed by a human body. For example, first portion 4 may be manufactured from synthetic polymers such as Poly(DL-lactide), Poly(glycolide), Poly(L-lactide-co-glycolide) or Poly(DL-lactide-co-glycolide). Additional materials may also be utilized in forming first portion 4, such as polymer blends comprising any combination of the above polymers. Synthetic hydrogel materials, such as Poly(ethylene glycol)-co-polylactide, methyl cellulose, or carboxy methyl cellulose may also be used in forming first portion 4. In addition, natural biopolymers including anionic biopolymers, such as hyaluronic acid, cationic bioploymers, such as chitosan, amphipathic polymers, such as collagen, gelatin and fibrin, and neutral polysaccharides, such as dextran and agarose.
The inherent viscosity of the first portion 4 following final processing and sterilization may be as low as about 0.1 or 0.2 dL/g and as high as about 1, 1.5 or 3 dL/g.
Second portion 6 may be manufactured from any material suitable for the desired application. The material comprising second portion 6 may be manufactured from a non-resorbable material, such as a biocompatible plastic, titanium, including Ti 6-4 ELI, or stainless steel, including grade 316L, or from a long term resorbable material that may not be resorbed by a human body for many days or months. For example, second portion 6 may be manufactured from synthetic polymers such as Poly(L-lactide) and Poly(DL-lactide-co-L-lactide). In addition, second portion 6 may be manufactured from blends of these synthetic polymers. Furthermore, composites materials including calcium phosphate fillers, such as hydroxylapatite or tricalcium phosphate, in the form of particulate or fibers may be utilized with the any of the above polymers or polymer blends.
The inherent viscosity of the second portion 6 following final processing and sterilization may be as low as about 0.1 or 2 dL/g and as high as about 5 or 10 dL/g.
Fixing device 2 may then be inserted into the through hole of plate 26 and into pilot hole 30, as depicted in
As shown in
Once device 2 has been fully inserted, first portion 2 may be quickly resorbed by the body leaving only second portion 6 to maintain plate 26 in its position relative to bone 28, as shown in
While this invention has been described as having exemplary designs, the present invention may be further modified within the spirit and scope of the disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.
