Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1997-10-14
2001-10-30
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S023620, C424S423000, C424S487000, C600S003000, C606S094000, C523S113000, C523S117000
Reexamination Certificate
active
06309420
ABSTRACT:
TECHNICAL FIELD
The present invention relates to compositions for use as tissue implants, preferably hard tissue implants. More particularly, the present invention is directed to compositions which are more easily viewed by imaging techniques, during the implantation thereof, than compositions that are presently known and used. A particularly advantageous use of the present invention is for percutaneous injection of hard tissue implant materials, although the invention is not to be so limited.
BACKGROUND ART
Polymethylmethacrylate (PMMA) has been used in anterior and posterior stabilization of the spine for metastatic disease, as described by Sundaresan et al., “Treatment of neoplastic epidural cord compression by vertebral body resection and stabilization.”
J Neurosurg
1985;63:676-684; Harrington, “Anterior decompression and stabilization of the spine as a treatment for vertebral collapse and spinal cord compression from metastatic malignancy.”
Clinical Orthodpaedics and Related Research
1988;233:177-197; and Cybulski, “Methods of surgical stabilization for metastatic disease of the spine.”
Neurosurgery
1989;25:240-252.
Deramond et al., “Percutaneous vertebroplasty with methyl-methacrylate: technique, method, results [abstract].”
Radiology
1990;117 (suppl):352; among others, have described the percutaneous injection of PMMA into vertebral compression fractures by the transpedicular or paravertebral approach under CT and/or fluoroscopic guidance. Percutaneous vertebroplasty is desirable from the standpoint that it is minimally invasive, compared to the alternative of surgically exposing the hard tissue site to be supplemented with PMMA or other filler.
The general procedure for performing percutaneous vertebroplasty includes the percutaneous injection of PMMA or other bone implant material into the damaged or fractured bone tissue of a vertebra. During injection of the bone implant material, fluoroscopic imaging or another imaging technique is used to track the path that the bone implant material takes as well as its final position upon implantation. Contrast agents such as barium sulfate powder are often used to aid the visibility of the bone implant material by imaging. However, the barium sulfate powders and other contrast agents presently used are generally very fine. This type of contrast agent is fairly effective once a given mass of the mixture of it with the bone implant material has accumulated at an implant site. However, for purposes of tracking the flow and leading edge surfaces of a bone implant material during injection, or for viewing small volumes of the implant material, the contrast agents presently used are inadequate.
This inadequacy becomes especially important during injection of liquid or flowable bone implant materials, as is the case with percutaneous vertebroplasty, since viewing of the path taken by the implant material is very important. That is because the bone implant material may take a path where it begins to enter the venous system, where it is not only unwanted, but where it could have very damaging effects. Thus, an improvement in the visibility of bone implant materials during injection is needed.
The use of radiographic contrast agents in a three dimensional, solid conglomerate of polymer particles which is used as a staring material for the preparation of bone cement is disclosed by Draenert in U.S. Pat. No. 5,574,075. The agents may be particulate, having a size range of between 5 and 300 &mgr;m. Draenert makes the three-dimensional conglomerate of polymeric particles, with the idea of converting the powder phase of the precursors of a PMMA bone cement mixture into a solid phase, similar to cube sugar.
Cooke et al., in U.S. Pat. No. 5,476,880, discloses the incorporation of sized, radiopaque particles into a PMMA bone composition that is additionally reinforced with previously sized reinforcing fibers. The preferred radiopaque agent is zirconium dioxide, which may be present at a level between 1-15% by weight of the powder. Barium sulfate may also be used. The radiopaque powder preferably has a diameter of about 1&mgr;.
Accordingly, there exists a need for a more visible composition to enable the tracking of the path of implantation taken by an implantable bone composition, particularly flowable or liquid compositions which are implanted from a remote site, by injection or other means.
DISCLOSURE OF THE INVENTION
An enhanced visibility composition for implantation into hard tissue is disclosed as including a hard tissue implant material and radiopaque particles mixed in the hard tissue implant material. The radiopaque particles have a particle size between about 120&mgr; and 2200&mgr; more preferably between about 350&mgr; and 2000&mgr;, even more preferably between about 450&mgr; and 1600&mgr;, and most preferably between about 570&mgr; and 1150&mgr;. Other acceptable particle size ranges are disclosed to include between about 350&mgr; and 2200&mgr;, between about 450&mgr; and 2200&mgr;, between about 570&mgr; and 2200&mgr;, between about 350&mgr; and 1600&mgr;, between about 350&mgr; and 1150&mgr;, and between about 450&mgr; and 1150&mgr;.
Preferably the hard tissue implant and the radiopaque particles, according to the present invention, are formed or prepared in a slurry for implantation. The hard tissue implant material preferably includes polymethyl methacrylate. Alternative hard tissue implant materials that may be mixed with the radiopaque particles include hydroxyapatite, various formulations of biocompatible calcium phosphates, biocompatible calcium sulfates, demineralized and/or mineralized bone particles, polymer based implants including polyglycolic acid and/or polylactic acid compounds, collagen and/or collagen derivative preparations alone or in combination with other biomaterials, chitin and/or chitosan preparations, bioglasses including oxides of silicon, sodium, calcium and phosphorous and combinations thereof, and other known materials which are acceptable for use as hard tissue implant materials including osteogenic and osteoinductive compositions, and combinations thereof.
The radiopaque particles may include barium sulfate, tungsten, tantalum, zirconium, platinum, gold, silver, stainless steel, titanium, alloys thereof, combinations thereof, or other equivalent materials for use as radiographic agents in hard tissue implant materials that can be formed as particles.
Optionally, the enhanced visibility composition according to the present invention may further include additional radiopaque particles or contrast particles mixed in with the composition. The additional radiographic or contrast particles may have a particle size between about 120&mgr; and 350&mgr;, preferably between about 120&mgr; and 250&mgr;.
The additional radiopaque or contrast particles may include barium sulfate, bismuth subcarbonate, bismuth sulfate, powdered tungsten, powdered tantalum, zirconium, combinations thereof, or other equivalent materials for use as radiographic agents in hard tissue implant materials that can be formed as particles. Additionally, liquid or soluble contrast agents may be used, e.g., Metrizamide, disclosed in U.S. Pat. No. 3,701,771 or Iopromide, disclosed in U.S. Pat. No. 4,364,921. Both U.S. Pat. No. 3,701,771 and 4,364,921 are hereby incorporated by reference herein in their entireties. The composition of the additional radiopaque or contrast particles may, but need not be the same as the composition of the radiographic particles.
Further disclosed is a composition for percutaneous vertebroplasty comprising a slurry of biocompatible implant material and radiopaque markers having a particle size of between about 120&mgr; and 2200&mgr;. All of the size ranges given above for the radiographic particles are suitable for the radiopaque markers. Preferably, the radiopaque markers have a particle size between about 570&mgr; and 1150&mgr;. The biocompatible implant material of the slurry preferably includes polymethyl methacrylate. Alternative implant materials include hydroxyapatites, calcium phosphates, d
Becking Frank P.
Bozicevic Field & Francis LLP
Isabella David J.
Koh Choon P.
Parallax Medical Inc.
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