ACETABULAR CUP BODY PROSTHESIS

Abstract: An acetabular cup prosthesis (86) has a cup body with correspondingly shaped inner concave and outer convex (87) surfaces. The cup body has an apex (98) as well as a base (91) that defines a plane (92). The cup body outer convex surface (87) has a portion (89) between the rim (103) and a distance about one third of the distance from the rim (103) to the apex (98), which portion (89) has an outer surface formed by first generating an arc (106) between the rim (103) and a transition point (90) about one third of the distance from the rim (103) to the apex (98), arc having a radius of curvature (101) whose origin (102) is near to, but not coincident with the center of the base (91), and then rotating the arc 360 degrees about a central axis (99) of the cup body, which axis runs between the apex (98) and the center of the base. In another embodiment, a plurality of cup bodies (86) are provided in a range of sizes between about 40 mm and 80 mm. Each cup body (86) has a companion rotary reamer (111) that is correspondingly shaped. The companion cup body (86) is oversized between about 1 mm and 3 mm relative to the companion rotary reamer (111), so that a generally constant change in volume is provided for all cup sizes between 40 mm and 80 mm.

Description: ACETABULAR CUP BODY PROSTHESIS The present invention relates to orthopedic prosthetic devices and more particularly to an improved orthopedic prosthesis (and a method of surgically implanting the prosthesis), wherein the prosthesis is in the form of a cup shaped body having in inner concave surface, an outer convex surface, and an annular rim that defines a plane, and wherein all or part of the outer convex surface define a toroidal shape that can form an interference fit with a purely hemispherical socket that is surgically prepared, and wherein the amount of interference fit is proportional with cup diameter. There are a number of commercially available acetabuiar prosthetic devices that include a cup shaped body. Some of these acetabuiar cups have correspondingly shaped inner and outer concave and convex surfaces. Some acetabuiar cup devices have outer surfaces with two differently shaped regions thereon including an annular rim or skirt that is thickened for forming an interference fit with the pelvis. Another acetabuiar cup (Patent DE 3341723C1 ) is in the form of a hemispherical socket body that is flattered at the crown region, to ensure lateral wedging of the socket in the pelvic bone. Another patented cup design is seen in the Averill patent 4,704,127 entitled "Dual-Geometry Acetabuiar Cup Component and Method of Implant". The '127 patent provides a cup with a shell component having an outer surface that includes a frustro-conical surface portion and a spherical surface portion. As part of the method, the patient's acetabulum is prepared with an inner surface that includes a frustro-conical surface portion and a spherical surface portion, the spherical surface portions having essentially the same radius and the frustro-conical surface portions having relative dimensions such that upon nesting of the spherical surface portions in contiguous relationship, the frustro-conical portions engage one another in an interference fit to secure the shell component within the prepared acetabulum. The Figgie patent 4,892,549 discloses an acetabuiar cup that has a shell component with an outer surface including a first spherical surface portion and a second spherical surface portion, and an acetabulum is prepared with an inner surface having a spherical configuration complimentary to the second spherical surface portion of the shell component. The radius of the first spherical surface portion is slightly greater than the radius of the second spherical surface portion such that upon nesting of the second spherical surface portion of the shell component in contiguous relationship with the inner surface of the acetabulum, the first spherical surface portion engages the inner surface of the acetabulum in an interference fit to secure the shell component within the prepared acetabulum. Some acetabuiar cup devices have projections extending from the outer surface of the cup-shaped body for engaging the surrounding pelvic bone tissue. For example, U.S. Patent No. 3,939,497 describes a socket for a hip joint prosthesis which is secured to a cavity in the bone tissue by a series of radially arranged pegs which can be projected outwardly from the wall of the socket into the surrounding tissue by a central screw which also has a self-tapping thread that enters the tissue. U.S. Patent No. 4,685,923 discloses a hip joint socket made from a plastic material that can be installed without the use of bone cement or adhesive. The socket comprises a hemisphere of polyethylene. The Forte et al. patent 4,695,282 discloses an acetabuiar cup assembly that includes a metal shell component and a plastic bearing insert capable of assembly intraoperatively, the metal shell component being secured in position within the acetabulum and then the plastic bearing insert being receivable within the shell component. The shell component has an outer surface that includes a generally spherically shaped portion and a generally frustro-conically shaped second surface portion. An annular shoulder forms a connection between the two different outer surfaces of the shell. The Cremascoli patent 4,813,959 discloses a total hip prosthesis structure that includes an acetabuiar or socket component and a femoral or pin component, the two components being made of a metal or a metal alloy and being intimately connected to parts of ceramic material at least part of the surface of which is granular or porus so as to encourage osteogenesis after implantation. The metal part of the acetabuiar component is shaped in such a way as to simplify and facilitate its anchorage in a corresponding cavity of the ilium by having a sharp screw thread thereon. In U.S. Patent No. 4,792,337 an acetabuiar cup is provided which has a metallic shell. The cup is for cement-less fixation in the acetabulum. In U.S. Patent No. 4,828,565 there is provided a component for a non-cemented hip prosthesis. The component has two parts, a titanium hemispherical shell and a cup of polymer which is engaged into it. Another acetabuiar cup for cement-less fixation in the acetabulum is described in European Patent Application No. 13,863, published June 8, 1980. European Patent Application No. 169,978 published May 2, 1986, describes an acetabuiar cup which has an outer shell embedded into the patient's pelvis. The outer shell has a frustro- conical skirt and a spherical central cap. In European Patent Application No. 211 ,169 published February 25, 1987, an acetabuiar cup is descπbed in which an external boss protrudes from the outer surface of the acetabulum body to fit into a pre-drilled hole in the acetabulum. Other foreign patents and patent applications which describe acetabuiar cups include European Patent Application No. 212,087 published April 3, 1987, wherein metallic pins project from the surface of the cup and contain holes in which tissue may grow. In European Patent No. 341 ,198 published November 8, 1989, an acetabuiar cup has a metal outer shell and a plastic body for retaining the hip joint head. A PCT publication WO 95/16413 discloses a hip cup for use as an acetabuiar component in a hip prosthesis. The prosthesis comprises a shell part having an at least partially convex outer surface. The shell part is insertable into a cavity having an inner surface that is substantially defined by the outer surface of a segment of this sphere. The outer surface of the shell part substantially corresponds to the outer surface of a part of an ellipsoid, the arrangement being such that during positioning the shell part contacts the longitudinal edge of the cavity at least by a circumferential edge, while a space is formed between the inner surface of the cavity and the apex of the shell part. Two recent U.S. Patents have issued for acetabuiar cup components. The Averill patent 5,443,519 discloses an acetabuiar cup prosthetic device comprised of an outer shell component and an inner bearing insert and a method of implanting the acetabuiar cup prosthetic within a patient. The outer surface of the shell has a plurality of region in which conform to the curvature of at least one ellipsoid. The Evans patent 5,358,532 entitled "CEMENTLESS ACETABULAR CUP" provides a component that is press fit into a patient's acetabulum to create an interference fit and to eliminate the need for cement. A body portion of the cup provides an outer convex surface. The inside of the cup provides an inner concave surface. An apex portion of the cup or shell is spaced from the lower rim portion, the rim defining a plane. A plurality of annular rings are spaced along the body outer surface beginning at the lower rim and extending at least a partial distance toward the apex. Each of the annular rings is preferably generally parallel to the plane of the lower rim. Three recently issued European patents disclose other examples of acetabuiar prosthetic components. These include European patents specifications 0091315, 0285756, and 0327509. However we have found that in order to maximise the stability of a cementless acetabuiar cup which is press fit into a hemispherical cavity, the outer dimension of the cup should be larger at the periphery of the cup than at the dome of the cup. Furthermore, this can be achieved better with a toroidal shaped surface, as the toroidal shape provides a gradual increase in outer cup dimension from medial to lateral. When the toroidal shape is press fit into a hemispherical cavity, implant stability is improved considerably compared to existing cup geometries that are typically purely hemispherical in shape. According to the present invention there is provided an acetabuiar cup prosthesis, comprising: a) a surgically implantable acetabuiar cup body having an inner surface and an outer convex surface adapted to interface with a patient's pelvic bone tissue; b) the cup body having an apex, a base in the form of an annular rim that has a radius, a center as origin for the radius and a periphery; c) said cup body outer convex surface having first generally spherical and second outer toroidal surface areas; d) the first spherical surface area being nearest the apex and being generated by a curved line having a radius of curvature with an origin near the origin of the rim and its terminal end at the apex; and e) the second toroidal surface area nearest the base being generated by a curved line and having a second radius with an origin that is spaced between the origin of the base and the periphery of the annular rim. The present invention provides an acetabuiar cup prosthesis that includes a surgically implantable acetabuiar cup body having an inner concave surface and an outer convex surface adapted to interface with a reamed, hemispherical socket of a patient's pelvic bone tissue. In a further embodiment of the present invention there is provided an acetabuiar cup prosthesis, comprising: a) a surgically implantable acetabuiar cup body having an inner concave surface and an outer convex surface adapted to interface with a patient's pelvic bone tissue; b) the cup body having an apex and a base in the form of an annular rim that defines a plane and having a radius and an origin for the radius positioned on the plane; c) wherein a portion of the outer convex surface is toroidally shaped, and defined by a curved line that is generated 360 degrees about the origin; d) said curved line extending from the base to a position near the apex, said curved line having a radius with a point of beginning spaced a short distance from the base plane. In the preferred embodiment, the pelvic bone tissue is prepared by providing a shaped, reamed socket using a single step reaming process into which the acetabuiar cup body is fitted during the surgical procedure. The cup body provides an apex and a base in the form of an annular rim that has a radius and a center as origin for the radius. The origin is positioned on a plane that is defined by the annular rim. In yet another embodiment of the present invention there is provided an acetabuiar cup prosthesis, comprising: a) a surgically implantable acetabuiar cup body having an inner surface and an outer convex surface adapted to interface with a patient's pelvic bone tissue; b) the cup body having an apex, a base in the form of an annular rim that has a radius, a center as origin for the radius and a periphery; c) said cup body outer convex surface having first and second outer toroidal surface areas; d) the first toroidal surface area being nearest the apex and being generated by a curved line having a radius of curvature with an origin at the origin of the rim and its terminal end of the apex; and e) the second toroidal surface area nearest the base being generated by a curved line and having a second radius with an origin that is spaced between the origin of the base and the periphery of the annular rim, but closely positioned next to the origin. In another embodiment, the cup body has an outer convex surface that is toroidally shaped between the apex and the rim. In one embodiment, the toroidally shaped portion extends between the base and a position near but shaped from the apex. In one embodiment, the toroidally shaped portion extends from the base to a position about two thirds of the distance of the base to the apex. Thus in a further embodiment of the invention there is provided an acetabuiar cup prosthesis, comprising: a) a surgically implantable acetabuiar cup body having an inner surface and an outer convex surface adapted to interface with a patient's pelvic bone tissue; b) the cup body having an apex, a base in the form of an annular rim that has a radius, a center as origin for the radius and a periphery; c) said cup body outer convex surface having first and second outer toroidal surface areas; d) the first toroidal surface area being nearest the apex and being generated by a curved line having a radius of curvature with an origin above the base plane, next to the origin of the rim and having its terminal end of the apex; and e) the second toroidal surface area nearest the base being generated by a curved line and having a second radius with an origin that is spaced between the origin of the base and the periphery of the annular rim, but closely positioned next to the origin. The toroidal shape is defined by curve line that extends from the apex to the rim and having a radius of curvature of preferably smaller than the apical radius with an origin for the radius that is spaced about 2 millimeters from the cup rim center, such that the outer diameter of the torus is greater than the apical diameter. The curve line is then generated 360° to generate the toroidal surface in one embodiment. In a further embodiment of the present invention there is provided an acetabuiar prosthesis as herein before described in kit form including instrumentation apparatus for enabling a surgeon to implant said acetabuiar prosthesis, comprising: a) a plurality of rotary reamer instruments, each having a cup- shaped reamer head with a rounded convex annular outer surface having cutting elements thereon, each said surface having a diameter; b) a plurality of prosthesis cup bodies, each having one of the reamer instruments as a correspondingly shaped companion reamer instrument, an inner concave surface and an outer convex surface, the convex surface shaped to register into a patient's acetabuiar socket that has been surgically prepared with the corresponding companion reamer instrument; c) wherein a selected companion reamer instrument enables the surgeon to ream the patient's acetabuiar socket to form a surgically prepared socket that corresponds in shape to the rounded annular shape of the selected reamer instrument cutting surface; d) wherein the diameter of a selected prosthesis cup body is about 9 - 12 percent greater than the diameter of the surgically prepared socket that is prepared using the correspondingly shaped companion reamer instrument. In another embodiment of the present invention there is provided an acetabuiar prosthesis as herein before described in kit form including instrumentation apparatus for enabling a surgeon to implant said acetabuiar prosthesis, comprising: a) a plurality of reamer instruments each having a cutter head with a generally hemispherical outer surface with cutting elements on the hemispherical surface, said surface having a diameter; b) a plurality of corresponding, companion prosthesis cup bodies, each having an outer convex surface, the convex surface shaped to register into a patient's acetabuiar socket that has been surgically prepared with the reamer instrument; c) wherein the reamer instrument enables the surgeon to ream the patient's acetabuiar socket so that it is generally hemispherically shaped, corresponding in shape to the hemispherical shape of the reamer instrument cutting surface; d) each reamer instrument enabling the surgeon to form a socket for its corresponding companion cup body; and e) wherein the diameter of the companion prosthesis cup body is about 9 - 12 percent greater than the diameter of the hemispherically shaped surgically prepared acetabuiar socket for a plurality of cup bodies. For a further understanding of the nature and objects of the present invention, reference should be had to the following detailed • description taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals, and wherein: FIGURE 1 is a perspective view of a embodiment of the apparatus of the present invention; FIGURE 2 is a side sectional view of a second embodiment of the apparatus of the present invention; FIGURE 3 is a side sectional view of a third embodiment of the apparatus of the present invention; FIGURE 4 is a side sectional view of a fourth preferred embodiment of the apparatus of the present invention; and FIGURE 5 is a top view of the embodiment of Figure 4; FIGURE 6 is an exploded view of the embodiment of Figures 4-5; and FIGURE 7 is a schematic graphical illustration of the proportionality aspect of the present invention. FIGURES 8-9 are driver top and side views of the reamer instrument portion of the apparatus of the present invention. Figure 1 shows the preferred embodiment of the apparatus of the present invention designated generally by the numeral 10. Acetabuiar cup prosthesis 10 is in the form of a cup body having an outer convex surface 11 , a concavity 12 for receiving a polyethylene liner and the ball of a femoral implant, and annular rim 13 that is generally flat to define base plane 14. The cup prosthesis 10 includes a concave surface 15 that surrounds the concavity 12. The cup 10 is in the form of a body defined by cup wall 16. The interior concavity 12 can be generally hemispherically shaped, as defined by inner surface 15. The outer convex surface 11 is not completely hemispherically shaped, but rather has a toroidal shape. Annular rim 13 is a flat rim that is circular in shape, having an origin 17 that falls in base plane 14. A purely hemispherical shape is illustrated by radial line 18 having one end portion at origin 17 and its opposite end portion at terminal 19. If the radial line 18 is rotated and about origin 17, a purely hemispherical shape is generated, designated by the curve line 20 in Figure 1. Line 22 is also a radial line that extends from origin 17 to cup apex 21. The line 22 is perpendicular to plane 14. Outer surface 11 is a toroidally shaped surface. When compared to hemispherical curved line 20, the toroidal outer surface 11 of the cup 10 gradually thickens continuously from apex 21 toward points 32 and 34. If the surgeon prepares a pure hemispherically shaped socket at the patient's acetabulum using a reamer, the prosthesis 10 will form an interference fit with such a hemispherical socket due to this ever thickening geometry and toroidal shape of outer surface 11 as shown in Figure 1. A purely hemispherically shaped cup 10 is tracked by the curved line 20 and has diameter defined by the arrow 35 in Figure 1. The toroidally shaped cup outer surface 11 of the present invention has a diameter defined by the arrow 36, thus showing a thickened region when compared to hemispherical diameter 35 the thickened region is designated by the arrows 37 and 38 in Figure 1. The toroid shaped cup 10 will form an interference fit with a hemispherically shaped, surgically prepared socket having a size and shape as tracked by curved line 20 in Figure 1 and having diameter 35. To define the toroidal shape of outer surface 11 , a pair of reference lines 23, 27 are shown in Figure 1. The reference line 23 is a radial line having a beginning point 24 that lies in base plane 14 and which is spaced from origin 17 by a measure designated as arrow 26. Line 23 terminates at terminal 25. In Figure 1 , a second reference line 27 is a radial line beginning at 28 and ending at terminal 29. The line 27 is spaced from origin 17 by a measure designated as 30 in Figure 1. When rotated between the point 32 and apex 21 , the radial reference line 23 generates a curved line 31 extending between the point 32 at rim 13 and the cup apex 21. Similarly, the reference radial line 27 generates a curved line 33 beginning at point 34 on rim 13 and ending at apex 21. The lines 31 , 33 generate a toroidal outer surface 11 when rotated 360° about central axial line 22. Figure 2 designates a second embodiment of acetabuiar cup prosthesis of the present invention designated generally by the numeral 39. Cup prosthesis 39 has a convex surface 40, a concavity 41 for receiving a polyethylene liner and then a hip prosthesis ball for example, and an annular rim 42 that defines a base plane 43. The cup prosthesis 39 has a concave surface 44 and a cup wall 45. The annular rim 42 is circular, having an origin 46 that falls in base plane 43. Prosthesis 39 includes a concave surface 44 that communicates with annular rim 42. The cup wall 45 extends around the concavity 41. Annular rim 42 is generally circular, having an origin 46. A radial line 47 extends from origin 46 to a terminal point 48 as shown. The radial 47, when rotated about origin 46 produces a hemispherical curved portion between points 64 and 65. This curved portion is designated as 49 in Figure 2. A reference line 51 extending between origin 46 and along a line perpendicular to plane 43 defines a radial line that communicates with apex 50 of cup 39. A pair of radial lines 52, 56 are also seen in Figure 2. Each of these radial lines 52, 56 has a beginning point 53, 57 respectively that is spaced from origin 56. The distance of spacing is designated respectively by the arrows 55, 59 in Figure 2. If reference lines 52 and 56 are rotated respectively about their beginning points 53, 57, the terminal end point 54, 58 respectively of each radial line 52, 56 tracks a curved line that tracks between points 64 and 65 to point 61 and 63. The curved line generated by radial line 52 is designated as 60 in Figure 2. The curved line that is generated by radial line 56 is designated as 62 in Figure 2. These curved lines 60, 62 extend between the beginning points 61 , 63 and end at annular reference line 66. In the elevational view of Figure 2, points 64 and 65 fall on annular reference line 66. Curved lines 60, 62 define a toroidal portion of cup prosthesis 39 when rotated 360° about hemispherical line 51. Curved line 49 is a portion of cup prosthesis 39. When radius 47 is rotated beyond the reference line 66 toward points of beginning 61 , 63, a purely hemispherically shaped curved line would be produced that is designated by the numeral 49 which is a phantom line below annular reference line 66 as shown in Figure 2. Thus, the portion of cup 39 that extends beyond the phantom lines 49 and which is tracked by the curved line 60, 62 represents a thickened area of the cup wall 45 that can be used to form an interference fit with a hemispherically shaped socket formed in the patient's acetabulum. The line 49 in Figure 2 represents the shape of the opening that would be formed in the patient's acetabulum prior to the placement of cup prosthesis 39. In Figure 2, the diameter of the surgically formed opening is designated by the arrow 67. The arrow 68 defines the thickness or diameter of cup prosthesis 39. The arrows 69 and 70 thus designated the thickened portion of the cup wall 45 that is wedged into the surgically formed opening for creating an interference fit upon placement of the cup prosthesis 39 into the surgically formed, hemispherically shaped cavity. Figure 3 shows a third embodiment of the apparatus of the present invention designated by the numeral 71. The cup body 71 is similar in shape to the cup shown in Figure 2. It thus has an outer surface 40 that is convex and an annular rim 42 that defines a base plane 43. However, the configuration of surface 40 differs slightly from that of the embodiment of Figure 2. As shown in Figure 3, an origin 72 is shown for beginning the reference line 73 that also has a terminal 74. The origin 72 lies on a line extending the shortest distance between cup apex 83 and base plane 43. Origin 72 can be for example two millimeters above base plane 43. The radial line 73 tracks a curved surface 84. A second pair of reference lines in the form of radius 75 and radius 78 extend from beginning points 76, 79 respectively to terminal points 77, 80. In the embodiment of Figure 3, a curved line 81 is generated by rotation of radius 75 between plane 43 and annular reference line 85. Similarly, the radius 78 tracks a curved line 82 between plane 43 and annular line 85. In Figure 3, the dimension lines 67 extends between end portions of the curved line 84 at plane 43. The dimension line 68 defines the outer diameter of cup body 71 , at plane 43. The thickened area that forms an interference fit is likewise designated by the numerals 69, 70 as with the embodiment of Figure 2. In Figures 4-6, a fourth (and preferred) embodiment of the apparatus of the present invention is shown, designated by the numeral 86. In Figures 4-6, acetabuiar prosthesis 86 has an outer convex surface 87 that is comprised of two outer surface areas 88, 89. Surface 88 is a first annular surface area that is closest to cup apex 98. Surface 89 is a second annular surface that is closest to up base 91. The interface between surfaces 88, 89 is a smooth transition 90 as shown in Figure 4. The smooth transition 90 is formed by generating the two surfaces 88, 89 using two different radii of curvature 100, 101 as described hereinafter. Acetabuiar prosthesis 86 has a base 91 that defines a flat plane 92. Acetabuiar cup prosthesis 86 has a central axis 99 between apex 98 and arc center 97. The first annular surface area 88 is generated by a radial line 100 that has its origin at arc center 97. Radial line 100 generates a curved line 105, that extends from apex 98 to transition 90. The first convex surface area 88 is generated by rotating the curved line 105 three hundred sixty degrees (360°) about central axis 99. The second annular surface area 89 is generated by a rotating curved line 106 three hundred sixty degrees (360°) about axis 99. Radial line 101 generates curved line 106 from periphery 103 to transition 90. The radius 101 is much smaller than the radius 100, being about sixty percent (60%) of the size of radius 100 for example. Arc centers 97, 102 are not in the same base plane 92, and are offset by a measure designated as 104. This geometry of the embodiment of Figures 4-5 produce a generally hemispherical shape between apex 98 and transition 90, and a thicker annular section below transition 90. This geometry produces an improved interference fit with a hemispherically shaped surgically prepared socket reamed in the patient's acetabulum. The interference fit begins after the cup has been fitted about two thirds of the distance into the surgically reamed acetabuiar socket. The surgically prepared socket would be reamed with a hemispherical reamer having an outer hemispherical shape generated by a radial line equal to the size of radial line 100 and extending between apex 98 and shoulder 94. Thus, the surface area 89 will be oversized as compared to the surgically prepared hemispherical opening, the surface area 89 producing an interference fit with the patient's bone tissue upon full insertion of the prosthesis 86 into the surgically prepared hemispherical socket. Annular shoulders 94, 95 intersect each other to form an angle of about ninety degrees (90°), forming annular recess 93. Shoulder 94 falls in plane 92. Shoulder 95 is perpendicular to plane 92. Recess 93 can accept tissue in- growth. A polyethylene cup liner 107 can snap into the cup body 86. In Figure 7 there is illustrated in graphical form a proportionality concept that can be applied to each apparatus of the present invention. Figure 7 shows a comparison of the percent (%) change in volume with the reamer diameter used by the surgeon to create the hemispherically shaped reamed opening that will be occupied by each embodiment of the acetabuiar cup of the present invention as shown in the above drawings 1 -6. Three different curves 108-110 are shown. The curve 108 is for a one millimeter (1 mm) oversized cup. The curve 109 is for a two millimeters (2 mm) oversized cup. The curve 110 is for a three millimeters (3 mm) oversized cup. With the teaching of the present invention, a cup has the same percentage change in volume notwithstanding the reamed diameter. This means that smaller cups require less press or interference fit while larger cups may accommodate interference fit. The following table I lists examples of cup diameters and the proportional sizing of the present invention: TABLE 1 CUD Reamed % Chanqe in Peripheral Press or Diameter in mm Diameter Interference Fit in mm 40 11.68 1.50 42 11.10 1.50 44 10.58 1.50 46 10.45 1.55 48 10.34 1.60 50 10.23 1.65 52 10.13 1.70 54 10.04 1.75 56 9.96 1.80 58 9.88 1.85 60 9.80 1.90 62 9.74 1.95 64 9.67 2.00 66 9.61 2.05 68 9.55 2.10 70 9.50 2.15 72 9.45 2.20 74 9.40 2.25 76 9.36 2.30 This proportionality can be calculated by dividing the difference in volume of the cup and the acetabulum by the volume of the acetabulum (the V c -V a )/V a When calculated over a range of cup sizes (for example, forty millimeters (40 mm) - eighty millimeters (80 mm)), one can see that the percent change in volume is approximately the same for a forty millimeters (40 mm) cup pressed at one millimeter (1 mm) as an eighty millimeters (80 mm) cup pressed at two millimeters (2 mm). This is illustrated in the percentage change in volume vs. reamer diameter graph of Figure 7. The percent change in volume of the bone may also be expressed in terms of diameter and can be calculated by the following: wherein ΔV = change in volume, D cup = diameter of acetabuiar cup prosthesis, D rβam β r = diameter of reamer. In Figures 8-9, reamer 111 is shown in the form of a cutting head having outer hemispherical surface 112 covered with an array of regularly spaced cutting elements 113. Drive socket 114 accepts a suitably rotary drive tool. If the same millimeter increment in cup oversizing is inserted into different acetabuiar, such as a two millimeter (2 mm) oversized fifty millimeter (50 mm) cup in a forty eight millimeter (48 mm) acetabulum, and a two millimeter (2 mm) oversized seventy millimeter (70 mm) cup in a sixty eight millimeter (68 mm) acetabulum, a greater relative change in volume occurs in the smaller compared to the larger acetabulum. This produces greater bone strains in the smaller sized acetabulum. With the same millimeter increment in cup oversizing, there is a greater risk of fracture in a small acetabulum and a greater risk of inadequate press fit stability in large acetabulum. A cup which is slightly widened at the periphery increases lateral bone strains more than an oversized hemispherical cup, with only a slight increase in medial bone strains. The non-hemispherical geometry of the present invention provides better peripheral stability than an oversized hemispherical cup and less risk of fracture through the dome of the acetabulum. When a constant amount of oversizing is used, the relative change in volume is greater for a small diameter compared to a large diameter cup (see Figure 7). For example, when the acetabulum is reamed to forty two millimeters (42 mm) and a two millimeter (2 mm) oversized (forty four millimeter (44 mm) diameter) cup is inserted, the acetabuiar volume increases by fifteen percent (15%). When the acetabulum is reamed to sixty two millimeters (62 mm) and a two millimeter (2 mm) oversized (sixty four millimeter (64) diameter) cup is inserted, the acetabuiar volume increase by ten percent (10%). Another example is that both a forty eight millimeter (48 mm) reamed acetabulum oversized by two millimeter (2 mm) and a seventy two millimeter (72 mm) reamed acetabulum oversized by three millimeter (3 mm) each produce a thirteen percent (13%) change in volume. The following table lists the parts numbers and parts descriptions as used herein and in the drawings attached hereto. Part Number Description 10 acetabuiar cup prosthesis 11 convex surface 12 concavity 1 133 annular rim 14 base plane 15 concave surface 16 cup wall 17 origin 1188 radial line 19 terminal 20 curved line 21 apex 22 reference line 23 radial line 5 24 beginning point 25 terminal 26 arrow 27 radial line 28 beginning point 10 29 terminal 30 arrow 31 curved line 32 beginning point 33 curved line 15 34 beginning point 35 arrow 36 arrow 37 arrow 38 arrow 20 39 acetabuiar cup prosthesis 40 convex surface 41 concavity 42 annular rim 43 base plane 25 44 concave surface 45 cup wall 46 origin 47 radial line 48 terminal 30 49 curved line 50 apex 23 51 reference line 52 radial line 53 beginning point 54 terminal 5 55 arrow 56 radial line 57 beginning point 58 terminal 59 arrow 10 60 curved line 61 beginning point 62 curved line 63 beginning point 64 terminal 15 65 terminal 66 annular reference line 67 arrow 68 arrow 69 arrow 20 70 arrow 71 acetabuiar cup prosthesis 72 origin 73 radial line 74 terminal 25 75 reference line 76 beginning point 77 terminal 78 reference line 79 beginning point 30 80 terminal 81 curved line 82 curved line 83 apex 84 curved line 85 annular reference line 5 86 acetabuiar cup prosthesis 87 outer surface 88 first annular surface 89 second annular surface 90 smooth transition 10 91 base 92 plane of base 93 annular rim 94 annular shoulder 95 annular shoulder 15 96 concave surface 97 arc center 98 apex 99 axis 100 radius 20 101 radius 102 arc center 103 periphery 104 offset 105 curved line 25 106 curved line 107 cup liner 108 curve 109 curve 110 curve 30 111 reamer 112 hemispherical surface 113 cutting elements 114 drive socket Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.

Claims: CLAIMS 1 An acetabuiar cup prosthesis, comprising a) a surgically implantable acetabuiar cup body having an inner surface and an outer convex surface adapted to interface with a patient's pelvic bone tissue, b) the cup body having an apex, a base in the form of an annular nm that has a radius, a center as origin for the radius and a periphery; c) said cup body outer convex surface having first generally spherical and second outer toroidal surface areas, d) the first spherical surface area being nearest the apex and being generated by a curved line having a radius of curvature with an origin near the origin of the nm and its terminal end at the apex, and e) the second toroidal surface area nearest the base being generated by a curved line and having a second radius with an origin that is spaced between the origin of the base and the periphery of the annular nm 2 The prosthesis of claim 1 wherein the first and second toroidal surface areas interface at a smooth transition portion 3 The prosthesis of claim 1 wherein the first toroidal surface area extends from the apex to a position about two thirds of the distance between the apex and base 4 The prosthesis of claim 1 wherein the first radius is greater than the second radius 5 The acetabuiar cup prosthesis of claim 1 wherein the first radius is about twice the length of the second radius 6. The acetabuiar cup prosthesis of claim 1 wherein the origin of the second radius is about half way between the base origin and the rim periphery. 7. The acetabuiar cup prosthesis of claim 1 wherein the rim is formed of a pair of flat intersecting annular surfaces defining an annular recess at the cup periphery. 8. The acetabuiar cup prosthesis of claim 7 wherein one of the flat annular surfaces is generally parallel to the base plane. 9. The acetabuiar cup prosthesis of claim 8 wherein one of the flat annular surfaces is generally perpendicular to the base plane. 10. The acetabuiar cup prosthesis of claim 1 wherein the first origin and second origins are spaced apart about half the diameter. 11. An acetabuiar cup prosthesis, comprising: a) a surgically implantable acetabuiar cup body having an inner concave surface and an outer convex surface adapted to interface with a patient's pelvic bone tissue; b) the cup body having an apex and a base in the form of an annular rim that defines a plane and having a radius and an origin for the radius positioned on the plane; c) wherein a portion of the outer convex surface is toroidally shaped, and defined by a curved line that is generated 360 degrees about the origin; d) said curved line extending from the base to a position near the apex, said curved line having a radius with a point of beginning spaced a short distance from the base plane. 12. The prosthesis of claim 11 wherein said short distance is between about 1 and 4 mm. 13. The prosthesis of claim 11 wherein the curved line extends about two thirds of the distance between the rim and the apex. 14. An acetabuiar cup prosthesis, comprising: a) a surgically implantable acetabuiar cup body having an inner surface and an outer convex surface adapted to interface with a patient's pelvic bone tissue; b) the cup body having an apex, a base in the form of an annular rim that has a radius, a center as origin for the radius and a periphery; c) said cup body outer convex surface having first and second outer toroidal surface areas; d) the first toroidal surface area being nearest the apex and being generated by a curved line having a radius of curvature with an origin at the origin of the rim and its terminal end of the apex; and e) the second toroidal surface area nearest the base being generated by a curved line and having a second radius with an origin that is spaced between the origin of the base and the periphery of the annular rim, but closely positioned next to the origin. 15. The prosthesis of claim 14 wherein the first and second toroidal surface areas interface at a smooth transition portion. 16. The prosthesis of claim 14 wherein the second toroidal surface area extends from the base to a position about two thirds of the distance between the base and the apex. 17. The prosthesis of claim 14 wherein the first and second radii are about the same length. 18. An acetabuiar cup prosthesis, comprising: a) a surgically implantable acetabuiar cup body having an inner surface and an outer convex surface adapted to interface with a patient's pelvic bone tissue; b) the cup body having an apex, a base in the form of an annular rim that has a radius, a center as origin for the radius and a periphery; c) said cup body outer convex surface having first and second outer toroidal surface areas; d) the first toroidal surface area being nearest the apex and being generated by a curved line having a radius of curvature with an origin above the base plane, next to the origin of the rim and having its terminal end of the apex; and e) the second toroidal surface area nearest the base being generated by a curved line and having a second radius with an origin that is spaced between the origin of the base and the periphery of the annular rim, but closely positioned next to the origin. 19. An acetabuiar prosthesis according to claim 1 in kit form including instrumentation apparatus for enabling a surgeon to implant said acetabuiar prosthesis, comprising: a) a plurality of rotary reamer instruments, each having a cup- shaped reamer head with a rounded convex annular outer surface having cutting elements thereon, each said surface having a diameter; b) a plurality of prosthesis cup bodies, each having one of the reamer instruments as a correspondingly shaped companion reamer instrument, an inner concave surface and an outer convex surface, the convex surface shaped to register into a patient's acetabuiar socket that has been surgically prepared with the corresponding companion reamer instrument; c) wherein a selected companion reamer instrument enables the surgeon to ream the patient's acetabuiar socket to form a surgically prepared socket that corresponds in shape to the rounded annular shape of the selected reamer instrument cutting surface; d) wherein the diameter of a selected prosthesis cup body is about 9 -12 percent greater than the diameter of the surgically prepared socket that is prepared using the correspondingly shaped companion reamer instrument. 20. The acetabuiar prosthesis and instrumentation apparatus of claim 19 wherein the reamer instrument has an array of cutting elements spaced over the rounded annular surface. 21. The acetabuiar prosthesis and instrumentation apparatus of claim 19 wherein the cup bodies are each between 1 mm and 3mm greater in diameter than the diameter of the companion reamer. 22. The acetabuiar prosthesis and instrumentation apparatus of claim 19 wherein each of the reamer instruments has a diameter of between 40mm and 80mm. 23. The acetabuiar prosthesis and instrumentation apparatus of claim 19 wherein the plurality of available cup body prostheses are oversized in diameter in relation to the respective surgically prepared socket a generally proportional volume for all cup body diameters, wherein the amount of oversize falls in in a range of between about 1 mm and 3mm of oversize diameter. 24. The acetabuiar prosthesis and instrumentation apparatus of claim 19 wherein the plurality of available prostheses are oversized in diameter in relation to the surgically prepared socket a generally proportional volume for all cup body diameters, and wherein the amount of peripheral press fit oversize falls in a range of between about 1 mm and 2mm, and the reamed diameter is between about 40mm and 64mm. 25. The acetabuiar prosthesis and instrumentation apparatus of claim 19 wherein the plurality of available prostheses are oversized in diameter in relation to the surgically prepared socket a generally proportional volume for all cup body diameters, and wherein the amount of peripheral press fit oversize falls in a range of between about 2mm and 3mm, and the reamed diameter is between about 64mm and 80mm. 26. The acetabuiar prosthesis and instrumentation apparatus of claim 19 wherein the oversize for press fit in millimeters is between 1.0 and 3.0mm including at least a plurality of cup bodies having one or more diameters and corresponding press fit in millimeters listed as follows: Cup Reamed % Change in Peripheral Press or Diameter in mm Diameter Interference Fit in mm 40 11.68 1.50 42 11.10 1.50 44 10.58 1.50 46 10.45 1.55 48 10.34 1.60 50 10.23 1.65 52 10.13 1.70 54 10.04 1.75 56 9.96 1.80 58 9.88 1.85 60 9.80 1.90 62 9.74 1.95 64 9.67 2.00 66 9.61 2.05 68 9.55 2.10 70 9.50 2.15 72 9.45 2.20 74 9.40 2.25 76 9.36 2.30 and wherein the cup body selected is between 40mm and 80mm. 27. The acetabuiar prosthesis and instrumentation apparatus of claim 19 wherein plurality of available prostheses are oversized in diameter in relation to the surgically prepared socket a generally proportional volume for all cup body diameters, and wherein the amount of peripheral press fit oversize falls in a range of between about 1.5mm and 2.3mm, and the reamed diameter is between about 40mm and 80mm. 28. An acetabuiar prosthesis according to claim 1 in kit form including instrumentation apparatus for enabling a surgeon to implant said acetabuiar prosthesis, comprising: a) a plurality of reamer instruments each having a cutter head with a generally hemispherical outer surface with cutting elements on the hemispherical surface, said surface having a diameter; b) a plurality of corresponding, companion prosthesis cup bodies, each having an outer convex surface, the convex surface shaped to register into a patient's acetabuiar socket that has been surgically prepared with the reamer instrument; c) wherein the reamer instrument enables the surgeon to ream the patient's acetabuiar socket so that it is generally hemispherically shaped, corresponding in shape to the hemispherical shape of the reamer instrument cutting surface; d) each reamer instrument enabling the surgeon to form a socket for its corresponding companion cup body; and e) wherein the diameter of the companion prosthesis cup body is about 9 - 12 percent greater than the diameter of the hemispherically shaped surgically prepared acetabuiar socket for a plurality of cup bodies.

Inventors: AUSTIN BRIAN, EVANS DAVID L, MILLER STEVE, RIES MICHAEL D, SHEA JEFF, AUSTIN, BRIAN, EVANS, DAVID, L., MILLER, STEVE, RIES, MICHAEL, D., SHEA, JEFF
Applicants: SMITH & NEPHEW RICHARDS INC, SMITH & NEPHEW RICHARDS INC.
Application year: 1996
Main classification: A61F2
IPC codes: A61B17, A61F2