Professor Shaw

December 12, 1995

You have two-and-one-half (2 1/2) hours to complete this exam - Please answer in the Bluebook(s) provided by the Registrar. Write on only one side of the page. Be sure your Exam Number is on each Bluebook you turn in. You may bring no materials (except a dictionary for those for whom English is a second language) into the exam room with you.


    Please draft at least ten claims: device claims, at least one method of use claim, and at least one process of making for an articular surface prosthesis that is composed of a porous material that is substantially noncorrodible and nonbiodegradable by body fluids. Emphasis is placed on a femoral cap, but the invention is not so restricted. Consider USA patent 4156943 of Collier.

    The present invention addresses the continuing problem of providing prostheses to replace injured or defective articular structures and surfaces thereof, e.g., the ball of a femur ball-and-socket joint. Among the difficulties in any such replacement is that of attachment to a bone in one side of the prosthesis while nevertheless achieving a low-friction sliding surface at the other (opposite) or obverse side thereof, particularly since the two characteristics needed to perform the necessary functions are mutually antagonistic.

    It is well documented that bone will grow into a porous prosthesis stem, for example, when the stem has been well fixed in the medullary canal and the pore size is 100 microns or greater (ideally 100-500 microns). The present device is, for example, a femoral cap which has no stem, but has, rather, a cylindrical cavity to receive a male stub of a femur.

    The invention is hereinafter described with reference to the accompanying drawing in which:

    Fig. 1 is an isometric view of a femoral cap prosthesis according to the present teachings, a prosthesis having graded pore size;

    Fig. la is a magnification of the small square area 112 in Fig. 1 to which it is adjacent; and

    Fig. lb is a magnification of the small square area 113 in Fig. 1 to which it is adjacent;

    Fig. 2 is a section view taken upon the line 2-2 in Fig. 1 looking in the direction of the arrows.

    The prosthesis discussed in greatest detail replaces the ball of a ball-and-socket femur. The ball of the joint of a patient is formed by a cutting tool to form a cylinder of bone which outer dimensions closely correspond to the cavity labeled 6, in Figs. 1 and 2, of a prosthesis 101 which is typically wholly porous substantially throughout, with an average interconnection pore size of between 100 and 500 micrometers at the bone side of the prosthesis to permit bone ingrowth and about 50 micrometers or less at the other (or obverse), i.e., the articulating surface side thereof upon installation. The articulating surface side may have cartilage grown thereon, in vitro, in a culture from cells, taken from the host (patient), the pores being interconnected to permit nutrients to flow to the cartilage when the prosthesis has been implanted. Very quickly, after implantation, bone growth occurs into the walls marked 1B of the cavity 6 to secure the implant 101 onto the femur stub. The articulating or sliding surface side is marked 1A.

    To place some perspective on the present disclosure, the surface replacement prosthesis 101 in Figs. 1 and 2 may be used to replace the ball of a patient's femur. The prosthesis 101 is in the form of a porous biomaterial (e.g., Vitallium powder or F-75 cobaltbased alloy). The devise 101 consists of many, many particles of the biomaterial fused together by sintering at points of contact with each other to define a plurality of interconnected pores which permit bone ingrowth at the surface 1B, cartilage ingrowth at the surface 1A and nutrient flow therein. The pores are distributed through most of the porous prosthesis. The pores are coarse at the side 1B of the prosthesis in contact with the bone upon implantation to permit bone ingrowth therein and fine enough at the articulating surface 1A thereof upon implantation to prevent bone ingrowth into the articulating surface side thereof, but sufficiently large to permit cartilage growth therein and nutrient flow therebetween. Ideally, the porosity from the side 1A or the side 1B extends inwardly into the prosthesis at least to a depth of 200 micrometers. The pore size at the articulating surface side is in the range from 10 to less than 50 micrometers to permit cartilage ingrowth but small enough to prevent bone ingrowth to the articulating surface 1A The living cartilage at the articulating surface side 1A may be placed there using available techniques.

    The present concepts may be enlarged to replace an articulating member at a number of parts of the body to form a sliding surface between a bone (e.g., hip socket) and the ballprosthesis of the hip joint.

    The prosthesis 101 may be formed using metallurgy powder techniques with Vitalhum metal powders (F-75 cobalt-based alloy) sintered in a nonoxidizing environment at a temperature within about 25 C of the melting point of the powders for a period of a few minutes to about one hour-typically fifteen minutes to an hour. The sintering time at the indicated temperature must be kept below a value at which the powders would fuse to form a nonporous solid, but both temperature and time must be adequate to provide, in the prosthesis 101, the strength needed to withstand the stresses applied to the prosthesis 101 when implanted.

    Returning to Figs. 1, la, 1b, and 2, the lip labeled 7 is typically one-to-five millimeters which is also about the range of thickness of the ball-prostheses or femoral cap 101. The prosthesis 101 is composed of a porous biomaterial fused together at points of contact with each other to provide connected interstitial pores distributed typically throughout to provide a strong porous articular surface device, the pores being graded from 100 to 500 micrometers at the bone side to 50 micrometers or less at the articulating surface side, there being bone ingrowth at the bone side of an implanted device and cartilage ingrowth into the other side (articulating surface). The porosity should be inward at least 200 micrometers on each side with nutrient flow therebetween. The device should have compression strength greater than at least about 500 psi (pounds per square inch) and a yield strength in compression of at least 10,000 psi. The label 8 designates cartilage. The Collier patent may be used to amplify this disclosure. The labels 2 and 3 represent metal particles and interstitial pores, respectively, at the articulating surface side. The label 4 represents metal particles that are larger (coarser) than 2, and 5 represents interstitial pores that are larger (coarser) than 3. The pores are in a size-graded configuration. All are magnified in the drawing. The particles and pores are graded to provide pores that are smaller at the cartilage side than at the bone side. The smaller pore size permits cartilage ingrowth at the articulating surface and it prevents bone growth therethrough; and nutrients can flow through both large and small pores to the cartilage. The cartilage layer marked 8 is grown in vitro. The prosthesis 101 has a spherical outer surface 9 to receive a femur socket and a right-angle cylindrical cavity 6 to receive the stub referred to earlier.

A. Give a brief explanation of the applicable law involved in a rejection directed to an applicant by the Patent and Trademark Office (PTO) under the following:
1. 35 USC 102
2. 35 USC 103
3. 35 USC 112 (first paragraph)
4. 35 USC 110 (second paragraph)

B. The PTO has r-equired restriction in an application, noting that claims 1-3, 5 and 7 define an invention that is patentably distinct from the invention defined by claims 4, 6, and 9-11. How might the applicant respond to such a requirement?

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