Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-01-14
2001-04-10
Smith, Jeffrey A. (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06214049
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the skeletal tissue regeneration field and, specifically, to devices and methods for inducing bone growth in skeletal areas supporting a prosthetic implant or in need of structural augmentation.
BACKGROUND OF THE INVENTION
Replacing or supplementing fractured, damaged, or degenerated mammalian skeletal bone with prosthetic implants made of biocompatible materials is commonplace in the medical arts. Most often, implant devices are intended to become permanently integrated into the skeletal structure. Unfortunately, permanent prosthetic attachment to bone is rare. Factors that influence long-term implant viability include material type used, bone fixation method, implant location, surgical skill, patient age, weight and medical condition. A plethora of devices have been constructed attempting to optimize these variables involved in producing an increase in bone fusion.
Common materials used in prosthetic devices include ceramics, polymers and metals. Currently, metallic materials afford the best mechanical properties and biocompatibility necessary for use as skeletal prosthetic implants. Frequently used metals include, titanium and titanium alloy, stainless steel, gold, cobalt-chromium alloys, tungsten, tantalum, as well as, similar alloys. Titanium is popular in the implant field because of its superior corrosion resistance, biocompatibility, physical and mechanical properties compared to other metals. The dramatic increase over the last decade of titanium material presentations in neurosurgical, orthopedic and dental surgery attests to its acceptance as a prosthetic material. Titanium presentations vary mostly in shape and surface type, which influence the implant's ability to support load and attach to bone.
A significant drawback to titanium implants is the tendency to loosen over time. There are three typical prevailing methods for securing metal prosthetic devices in the human body: press-fitting the device in bone, cementing them to an adjoining bone with a methacrylate-type adhesives, or affixing in place with screws. All methods require a high degree of surgical skill. For example, a press-fitted implant must be placed into surgically prepared bone so that optimal metal to bone surface area is achieved. Patient bone geometry significantly influences the success of press-fitted implants and can limit their usefulness as well as longevity. Similar problems occur with cemented implants; furthermore, the cement itself is prone to stress fractures and is not bio-absorbable. Therefore, all methods are associated to varying degrees with cell lysis next to the implant surface with concomitant fibrotic tissue formation, prosthetic loosening, and ultimate failure of the device.
Currently, methods are being developed that produce osteointegration of bone to metal obviating the need for bone cements. Osteointegration is defined as bone growth directly adjacent to an implant without an intermediate fibrotic tissue layer. This type of biologic fixation avoids many complications associated with adhesives and theoretically would result in the strongest possible implant-to-bone bond. One common method is to roughen a metal surface creating a micro or macro-porous structure through which bone may attach or grow. Several implant device designs have been created attempting to produce a textured metal surface that will allow direct bone attachment. Some of these devices are found in the following U.S. Pat. Nos.: 3,894,297; 3,905,777; 3,906,550; 4,064,567; 4,199,824; 4,261,063; 4,430,761; 4,479,271; 4,530,116; 4,535,487; 4,536,894; 4,549,319; 4,570,271; 4,589,883; 4,608,053; 4,636,219; 5,018,285; 5,344,654; 5,373,621; 5,609,635; and 5,658,333.
Metallic implant surfaces are also commonly coated with micro-porous ceramics such as hydroxyapatite (HA) or beta-tricalcium phosphate (TCP) (see U.S. Pat. Nos. 4,309,488; 4,145,764; 4,483,678; 4,960,646; 4,846,837). The former treatment is more common because calcium-phosphate salts tend to be absorbed, in vitro, and thus loose their effectiveness. The HA coatings increase the mean interface strength of titanium implants as compared to uncoated implants (see Cook et al., Clin. Ortho. Rel. Res., 232, p. 225, 1988). In addition, clinical trials in patients with hip prosthesis have demonstrated rapid bone growth on prosthetic devices and increased osteointegration of titanium alloy implants when coated with HA (see Sakkers et. al., J. Biomed. Mater. Res., 26, p. 265, 1997). The HA ceramic coatings can be applied with a plasma spray machine or by sintering (see U.S. Pat. No. 4,960,646). In addition, the HA coating can be applied by soaking the implant in an alkali solution that contains calcium and phosphorous and then heated to deposit a film of hyroxylapetite (see U.S. Pat. No. 5,609,633). Optimal HA coating thickness ranges from 50-100 microns (see Thomas, Orthopedics, 17, p. 267-278, 1994). If coated too thick the interface between the HA and bone becomes brittle. Despite the higher success rate of prosthetic devices coated with HA as compared to earlier implantation methods, failure over time still occurs. Again, proper integration requires that the surgeon create an exact implant fit into bone allowing the metal and bone surfaces to have maximum contact. Also, fibrotic tissue formation develops in some cases regardless of coating type.
Recent research describes the use of osteoinductive proteins to produce prosthetic osteointegration as well as increase the rate of bone formation next to implant surface (for example see Cole et. al., Clin. Ortho. Rel. Res., 345, p.219-228, 1997). Osteoinductive proteins are secreted signaling molecules that stimulate new bone production. These proteins include, PDGF, IGF-I, IGF-II, FGF, TGF-&bgr; and associated family members. The ability of these proteins to enhance osteointegration of metallic implants suggests that implants coated with these proteins may attach to bone more efficiently.
The most effective bone formation-inducing factors are the bone morphogenetic proteins (BMPs). The BMPs, a TGF &bgr; super-family subset, share, along with the other members of its subgroup, strong sequence homology and conserved carboxyl-terminus cysteine residues. Over 15 different BMPs have been identified. Most members of this TGF-
62
subfamily stimulate the cascade of events that lead to new bone formation (see U.S. Pat. Nos. 5,013,649; 5,635,373; 5,652,118; and 5,714,589, reviewed in J. Bone Min. Res., 1993, v8, suppl-2, p.s565-s572). These processes include stimulating mesenchymal cell migration, osteoconductive matrix disposition, osteoprogenitor cell proliferation and differentiation into bone producing cells. Effort, therefore, has focused on BMP proteins because of their central role in bone growth and their known ability to produce bone growth next to titanium implants (see Cole et. al., Clin. Ortho. Rel. Res., 345, p.219-228, 1997). One such method claims achievement of a strong bond between existing bone and the prosthesis by coating the prosthetic device with an osteogenic protein (see U.S. Pat. No. 5,344,654).
In addition to osteoinductive proteins, osteoconductive factors may aid in bone formation (see U.S. Pat. No. 5,707,962). One experienced in the art realizes that osteoconductive factors are those that create a favorable environment for new bone growth, most commonly by providing a scaffold for bone ingrowth. The clearest example of an osteoconductive factor is the extracellular matrix protein, collagen. Other factors that can be considered osteoconductive include nutrients, anti-microbial and anti-inflammatory agents, as well as blood-clotting factors. In addition to these factors, reducing bone absorption by inhibiting osteoclast activity with bisphosphonate may also aid in implant success (see U.S. Pat. No. 5,733,564).
Bone morphogenetic protein-molecule presentation to skeletal tissue is critical for producing desired bone formation next to an implant device. Many matrix systems have been developed to contain and then steadily releas
Comfort Christopher J.
Gayer Gregory G.
Blakely , Sokoloff, Taylor & Zafman LLP
Comfort BioMedical, Inc.
Robert Eduardo C.
Smith Jeffrey A.
LandOfFree
Method and apparatus for augmentating osteointegration of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for augmentating osteointegration of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for augmentating osteointegration of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2492951