Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-05-13
2001-09-04
Smith, Jeffrey A. (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
Reexamination Certificate
active
06283998
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to devices for the replacement of interverterbral disks damaged or destroyed by disease or trauma, and in particular, to a hollow prosthetic device and a method of forming a hollow prosthetic device having a fluid infusion port which is sealed to prevent leakage.
When intervertebral disks are damaged or destroyed by disease or trauma, total removal of the disk is often indicated. Reconstruction or replacement of the function performed by the lost disk may require the use of autografts or allografts to fuse the adjacent vertebrae together. A more complete and natural restoration of function is possible with the implantation of prosthetic intervertebral disks.
U.S. Pat. No. 5,514,180 discloses intervertebral prosthetic devices having fixed shapes for accommodating the defined surface contours of the vertebral endplates. The invention defines five morphological types of surfaces comprising a set of surfaces capable of accommodating the anatomy of most vertebral endplates. A method of digitizing the surface of a vertebral body to determine a specific shape of a vertebral endplate is also disclosed. Furthermore this invention also relates to such prosthetic devices incorporating osteoinductive material such as bone growth factors.
U.S. patent No. discloses a method for replacing the nucleus pulposus of an intervertebral disk. The nucleus pulposus is removed and a flexible hollow prosthetic disk is inserted into the space defined by the annulus fibrosis. The prosthetic disk is then filled with a gel material.
U.S. Pat. No. 5,545,229 discloses an intervertebral disk spacer comprising a central core of soft elastomer approximating the size and shape of the nucleus pulposus, an outer ring of stiffer elastomeric material approximating the size and shape of the annulus fibrosis, and endplates of stiff material incorporating a mechanism for attachment to the adjacent bony vertebral bodies.
U.S. Pat. No. 4,863,477 discloses an intervertebral disk prosthesis molded in the shape of the natural disk. The replacement disk is molded of rubber or silicone rubber. The replacement disk is formed from two halves joined together to form a hollow interior. After the disk is implanted between two vertebrae, a fluid, such as saline, is injected into the hollow interior space.
Various techniques are know for forming hollow prostheses. A technique developed by the inventor of the present invention is disclosed in U.S. Pat. Nos. 5,376,323; 5,855,606 and 5,700,288. The technique disclosed in these patents utilizes room temperature vulcanizable silicone. Room temperature vulcanizable silicone compositions are described generally in U.S. Pat. Nos. 3,925,277 and 3,897,376. A technique for forming prosthetic devices having varying degrees of flexibility is disclosed in U.S. Pat. No. 4,735,754 to Buckner. This technique selectively removes silicone material from the device to form voids having the requisite degree of flexibility.
U.S. Pat. No. 5,314,478 discloses a prosthesis that may be used as a replacement for an intervertebral disk. The prosthesis is a composite of polyvinyl alcohol hydrogel and a ceramic or metallic porous body.
U.S. Pat. No. 5,824,093 discloses a prosthetic spinal disk comprising a jacket surrounding a hydrogel core that is allowed to hydrate to a predetermined volume.
U.S. Pat. No. 5,702,454 discloses a prosthetic implant for replacing a spinal disk. Support members are inserted into a cavity in the core of the intervertebral disk until the cavity is filled.
U.S. Pat. No. 3,867,728 discloses a prosthesis for spinal repair comprising a core element having a flat top and bottom surfaces. The core is made of elastic polymer and may be reinforced. A covering element secured to both flat surfaces provides a tissue ingrowth receptive material.
The limitations of the prior art are overcome by the present invention as described below.
SUMMARY OF THE INVENTION
The present invention is an alloplastic device for replacement of a damaged, ruptured, disintegrated or diseased spinal vertebral column disk and a method of forming such a replacement disk. The replacement disk is hollow elastomer, preferably room temperature vulcanizable (RTV) silicone, such as Silastic ® (medical adhesive silicone Type A (available from Dow Corning). The replacement disk is shaped to mimic the natural disk being replaced. The shape can be derived from a mold of the natural disk, if intact, or from a composite of fragments of the natural disk. If the natural disk is too fragmented or altered by disease or trauma or otherwise does not present a good model for the development of a mold of the replacement device, an MRI scan can be used to develop the shape of the mold using known techniques such as computerized numerically controlled shaping machines.
The hollow elastomeric shape may be produced by the technique disclosed in U.S. Pat. No. 5,376,323, which is incorporated herein by reference. This technique allows various wall thicknesses to be formed depending on the load bearing requirements of the replacement disk. In addition, the replacement disk may be trabeculated or honeycombed with multiple chambers or multiple load bearing pillars. The hollow disk may be filled with a triglyceride oil, such as soybean oil or rice oil, cerebrospinal fluid, seroma or synovial fluid, or a combination of any of these materials.
In the preferred embodiment the replacement disk is formed by allowing room temperature vulcanizable (RTV) silicone, such as Silastic ®, injected into a mold to vulcanize at room temperatures until a wall of sufficient thickness is formed. The unvulcanized RTV silicone is expressed to form the hollow interior. The replacement disk is formed with a nipple having an interior concavity. Once the replacement disk is removed from the mold and the unvulcanized RTV silicone expressed from the interior, the nipple is cut from the body of the replacement disk leaving an opening into the hollow interior. The nipple is inverted and sealed into the opening so that the nipple extends from the surface of the replacement disk down into the interior where it contacts the opposite wall of the disk. The inverted nipple thus provides a central support for the disk. More importantly, the inverted nipple provides an infusion port to inject a lubricating fluid, such as soybean oil, into the hollow interior of the disk. It should be understood that vulcanized RTV silicone is not self-sealing. Using the inverted nipple infusion port, however, the lubricating fluid is injected by a hypodermic needle into the sidewall of the infusion port. After the proper amount of fluid is injected, the concavity of the infusion port is filled with RTV silicone, which then vulcanizes and seals the opening.
The disk is surgically positioned between two spinal vertebra to separate and provide a cushion against movement and compaction in the manner of a natural disk. The replacement disk also provides shock absorption and maintains an appropriate and accurate distance between the vertebrae for safety, comfort and motility of the spinal column.
The hollow disk also lubricates itself since a triglyceride oil filing material, such as soybean oil in the preferred embodiment, percolates slowly through the silicone wall. A mixture of soybean oil and synovial fluid continually lubricates the surfaces in the space between the vertebrae and the replacement disk. Genetic engineering of the structural formulas of soybean oil, seroma, and synovial fluid could be employed to optimize the molecular size of the fluids for the lubrication function.
The present invention provides definitive intervention for chronic physical problems, including pain. It is a solution for the problem of the ruptured disk and provides an alternative to vertebral fusion. The present invention may also allow correction of problems due to trauma. Although described primarily as a vertebral disk replacement, the present invention is not so limited. Other uses include replacement for a worn out or injured miniscus, and other orthopedic ap
Board of Trustees of the University of Arkansas
Cox, Jr. Ray F.
Robert Eduardo C.
Smith Jeffrey A.
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