Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-06-23
2002-03-26
Prebilic, Paul B. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S023260, C623S023250, C623S023340, C623S023460, C623S908000
Reexamination Certificate
active
06361565
ABSTRACT:
BACKGROUND OF THE INVENTION
Tissue grafting, including bone grafting, is well known. Tissue such as bone is removed from one part of a body (the donor site) and inserted into tissue in another (the host site) part of the same (or another) body. It is desirable to be able to remove a piece of tissue graft material which is the exact size and shape needed for the host site where it will be implanted. However, it is rarely possible to do this.
Accordingly, various tissue grafting techniques have been tried to solve this problem. For example, Nashef U.S. Pat. No. 4,678,470 discloses a method of creating bone graft material by machining a block of bone to a particular shape, or by pulverizing and milling it. The graft material is then tanned with glutaraldehyde to sterilize it. This process can produce bone plugs of a desired shape.
In the Nashef process, the exogenic bone material selected for the graft is presumably dead at the beginning of the process. The process of pulverizing or milling the bone material destroys the structure of the bone tissue. The step of tanning it with glutaraldehyde then renders the graft material completely sterile. This condition is not conducive to graft healing and ingrowth. Specifically, applicant has found that it is desirable to maintain graft tissue in a living state during the grafting process. The use of living tissue in a graft will promote bone healing.
SUMMARY OF THE INVENTION
The present invention is a tissue press for shaping or compressing a piece of tissue. The press includes first and second members movable relative to each other. First and second forming elements of different predetermined shapes are positionable on the first and second members on opposite sides of the piece of tissue. The first and second members are moved toward each other to shape or compress the tissue between the first and second forming elements.
Means are preferably provided for monitoring and controlling the amount of force or pressure applied to the piece of tissue, in order to maintain the tissue in a viable living condition. Means may also be provided for draining off fluid from compressed tissue, so that the tissue can be implanted in a compressed state and imbibe fluid from the host site.
The present invention is also a method of reshaping tissue for use as graft material comprising the steps of determining the shape which the tissue should possess as graft material; providing a tissue press, selecting forming elements adapted to press tissue approximately to the desired shape, and placing the forming elements on the tissue press; placing the tissue in the tissue press between the forming elements; operating the tissue press to shape the tissue between the forming elements to give the tissue the desired shape; and controlling the pressure on the tissue during the shaping step to minimize damage to or necrosis of the tissue.
The present invention is also a method which includes the steps of determining the shape and size which the tissue should possess as graft material; placing the tissue in a tissue press having forming elements adapted to press tissue approximately to the shape and size desired; compressing the tissue in the tissue press to give the tissue the shape and size desired; controlling the pressure on the tissue during the compressing step to minimize damage to or necrosis of the tissue; and draining off fluid expressed during the compressing step.
In accordance with another feature of the present invention, a retainer is provided for retaining tissue graft material in its compressed state. The retainer is placed around the compressed graft. The retainer can help to maintain the graft in a compressed configuration or in a specific shape for a period of time long enough to be placed in the body. The retainer may be made of a material which expands after it is placed in the body, to mechanically interlock the graft to the body.
GENERAL DESCRIPTION OF THE INVENTION
With the apparatus and method of the present invention, bone or other tissue can be compressed or reshaped or both, while preserving the tissue alive.
Reshaping
Often, reshaping of graft tissue is necessary to obtain the best possible graft. For example, in an anterior cruciate ligament reconstruction, the graft material which is removed usually has a triangular cross-sectional configuration. This graft material is placed in an opening in bone formed by drilling with a round drill. When the triangular graft material is placed in the round opening, there is minimal physical contact between the graft material and the surrounding bone. This reduces the holding power of the graft and also reduces the ingrowth ability of the graft.
Thus, an important feature of the present invention is that bone or other tissue such as ligament is reshaped while still leaving it in a whole condition and without substantial tissue damage. The tissue is placed in the tissue press of the present invention and sufficient force is applied to reshape the tissue to the desired shape—for example, a cylindrical shape as needed for an anterior cruciate ligament reconstruction. Excessive pressure on the tissue, which can damage or kill the tissue, is avoided as described below. A properly shaped graft is thus provided which is still in a living condition.
Compression
Compression of graft tissue is also sometimes desirable. Generally, tissue is stronger when it is more dense. Compressing graft tissue increases its density and thus strengthens the graft tissue. The graft tissue also stays together better.
For example, a tendon is made of a plurality of fibers. The individual fibers are weak when separated or unraveled. If a tendon graft is implanted with the fibers in a loose condition, the graft is weak. On the other hand, if prior to implantation the tendon graft is compressed to orient and pack the fibers tightly, then the entire group of fibers acts as one whole unit and the graft is much stronger. Therefore, compressing the tendon graft gives it more mechanical integrity—making a smaller tendon graft much stronger.
Similarly, bone tissue is stronger and better able to bear force when it is denser and more compact. Compressing bone graft tissue prior to implantation produces a stronger graft.
Compression of bone or other tissue also allows a surgeon to convert a larger irregular shape into a smaller specific shape. Thus, the surgeon when removing the graft material from the donor site is not limited by the conditions at the host site but can remove the graft material in the best way possible from the donor site. Similarly, the surgeon when implanting the graft material at the host site is not limited by the shape of the material removed (as dictated by the conditions at the donor site) but can implant the graft material in the best way possible to fit the conditions at the host site.
The anterior cruciate ligament, for example, attaches to the femur and tibia at specific isometric locations. When the ligament is being replaced in an anterior cruciate ligament reconstruction, typical uncompressed graft material can be many times the size of those locations. In such a case it is necessary to drill openings much larger than desired in the bone to attach the new ligament. The graft tendon then tends to fall eccentrically in this larger opening, the functional anatomy of the ligament can not be recreated, and the functioning of the knee joint is compromised.
However, if the graft material for the new ligament is compressed in accordance with the present invention, its size can be reduced substantially. This allows the surgeon to drill a substantially smaller opening in the bone to attach the new ligament/graft structure, so as to recreate the functional anatomy of the ligament.
With the present invention, it is also possible to make a composite graft. For example, the graft material for an anterior cruciate ligament reconstruction is preferably tendon in the middle with bone at both ends. In accordance with the apparatus and method of the present invention, bone tissue can be compressed around the ends of tendon tissue
Prebilic Paul B.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
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