Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2001-05-11
2002-10-29
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S075000, C606S077000
Reexamination Certificate
active
06471707
ABSTRACT:
BACKGROUND
The present invention relates generally to bioresorbable devices, and more particularly, to new and improved bone screws having bioresorbable shaft portions and non-resorbable threaded portions, wherein specially adapted driver mechanisms are capable of delivering a torque force about the non-resorbable threaded portion during insertion of the bone screw into bone tissue, thus eliminating, or at least lessening, the torque stresses at the bioresorbable shaft portion
on-resorbable threaded portion junction. Additionally, different sizes of bioresorbable shaft portions, non-resorbable threaded portions, and driver mechanisms may be incorporated into a kit system.
Bone screws are generally defined as a threaded device which is inserted into bone tissue. The intended function of bone screws is to immobilize bones or bone fragments or to affix other orthopedic devices, such as metal bone plates or bone rods, to, or within, bones. Although bone screws are typically comprised of metallic materials (e.g., stainless steel, titanium, cobalt-chrome alloys, and the like), they may also be comprised of other materials, such as bioresorbable materials (e.g., hydroxyapatite, poly-lactic acid, poly-glycolic acid, and the like). The terms “bioresorbable,” “biodegradable,” “absorbable,” and “bioabsorbable” are used interchangeably herein.
The use of bioresorbable bone screws in connection with the treatment of various bone defects, such as fractures, and the like, is fairly well known in the art. These bioresorbable bone screws have enabled the medical community to achieve excellent surgical results, even under difficult clinical conditions.
The main benefit of using bioresorbable devices is that the devices resorb into the body over a generally predictable time period once a sufficient level of healing has occurred, for example, at the junction of a bone fracture, thus negating the need for subsequent removal of the device. By having the device resorb, the likelihood of osteolysis, stress fractures, and inflammatory immune system responses are greatly reduced. For example, a protruding head portion of a metallic bone screw may occasionally cause irritation of the surrounding skeletal tissues at the insertion site.
One resorbable material of particular interest is marketed by Biomet, Inc. (Warsaw, Indiana) under the tradename LACTOSORB®. LACTOSORB® is an absorbable co-polymer synthesized from all-natural ingredients: 82% L-lactic acid and 18% glycolic acid, unlike the homopolymers in common use such as 100% poly-L-lactic acid (PLLA) or 100% poly-glycolic acid (PGA), LACTOSORB® copolymer is substantially amorphous (i.e., without crystallinity), meaning that its degradation is uniform, precluding the crystalline release associated with degrading copolymers that have been associated with late inflammatory reactions. Furthermore, the LACTOSORB® copolymer ratio permits the polymer to retain most of it's strength for six to eight weeks, which is appropriate for healing, but not so long as to raise concerns about long-term stress shielding of bone.
Examples of surgical devices comprised of bioresorbable materials can be found with reference to the following U.S. Patents:
U.S. Pat. No. 5,695,497 to Stahelin discloses a screw made of biodegradable material for bone surgery purposes, wherein the outer surface of the screw body is provided with a coaxial external thread. A coaxial channel of saw-toothed star-shaped transverse cross-sectional profile is provided in the screw body, which channel is open at the proximal end in order to receive the complementary shaft of a screwdriver, and extends into the area of the distal end.
U.S. Pat. No. 6,096,060 to Fitts et al. disclose a bioabsorbable soft tissue anchor system comprising a cannulated soft tissue anchor for being turned through soft tissue, and a driver for driving the anchor and method for attaching soft tissue at a selected site of implantation. The soft tissue anchor is an elongated unitary body having a threaded distal section, a non-threaded proximal section, a transverse proximal head and a non-circular axial throughbore. The anchor is used with a driver having a driving shaft with a pointed tip and a cross-section adapted to engage the anchor's axial throughbore. The driving shaft is longer than the anchor so that the anchor may be placed on the shaft leaving the tip exposed to permit tissue to be pierced and placed adjacent a pre-formed hole at the site of implantation. Simultaneous pushing and turning of the driver will advance the anchor through the tissue and into the pre-formed hole.
Recently, there has been increased interest in employing bone screws, and other surgical devices, that are comprised of both metallic and bioresorbable portions, in order to take advantage of the respective merits of each type of material.
U.S. Pat. No. 5,522,817 to Sander et al. disclose a self-inserting absorbable orthopedic fixation device having a bioabsorbable fastening body portion for fastening body tissue, and having bone penetrating elements such as hard, pointed tips for penetrating bone or hard tissue fixed thereto. The pointed tips may be fabricated from metals or ceramics. The fixation device may be in the form of staples, pins, screws, and the like. The two components may be provided with mating surfaces (e.g., threaded external surface and threaded internal surface, lip and groove, and the like) that allow the two components to be simultaneously driven into tissue.
The main disadvantage of the this type of fixation device is that application of a rotary force (e.g., during insertion into bone tissue) produces a significant amount of torque at the bioresorbable portion
on-bioresorbable portion junction or interface. This torque force can potentially lead to failure of the fixation device, especially at the bioresorbable portion
on-bioresorbable portion junction or interface. The surgeon would then be required to retrieve the various pieces of the fixation device from the patient's body, if possible, and attempt another fixation procedure.
Therefore, there exists a need for a fixation device, such as a bone screw, wherein the device can be provided with a proximal bioresorbable shaft portion and a distal non-bioresorbable threaded portion, wherein a driver mechanism is capable of delivering a torque force about the non-resorbable threaded portion during insertion of the bone screw into bone tissue, thus eliminating, or at least lessening, the torque stresses at the bioresorbable shaft portion
on-resorbable threaded portion junction. There also exists a need for a kit having different sizes of bioresorbable shaft portions, non-resorbable threaded portions, and driver mechanisms.
SUMMARY OF THE INVENTION
In accordance with a first embodiment of the present invention, an orthopedic fixation system is provided, comprising a first member comprised of a bioresorbable material, the first member having a distal and proximal region, and a second member comprised of a non-resorbable material, the second member having a distal and proximal region. The distal region of the first member is adapted to selectively mate with the proximal region of the second member. The second member is substantially elongated with respect to the first member. The distal region of the second member is provided with an external threaded surface thereon.
In accordance with a second embodiment of the present invention, an orthopedic fixation system kit is provided, comprising a receptacle. The receptacle contains a plurality of first members comprised of a bioresorbable material and each having a different size, each of the first members having a distal and proximal region and a plurality of second members comprised of a non-resorbable material and each having a different size, each of the second members having a distal and proximal region. The distal region of each first member is adapted to selectively mate with the proximal region of each second member that has a corresponding size. The second member is substantially elongated with respect to the fi
Babcock James S.
Lessek Tim
Miller Stuart D.
Vanderwalle Mark
Biomet
Harness & Dickey & Pierce P.L.C.
Philogene Pedro
LandOfFree
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