embodiments of the present invention and the advantages thereof are best understood by referring to the following descriptions and drawings , wherein like numerals are used for like and corresponding parts of the drawings . referring now to fig7 , an embodiment of the present invention is shown as prosthesis 20 . the prosthesis 20 is used in performing bone preserving joint arthroplasty . the prosthesis 20 is to be fitted to the head of a long bone . for example , the long bone as shown in fig7 is in the form of humerus 3 . the prosthesis 20 includes a first body 22 having an articulating surface 24 defining a generally circular outer periphery 26 . the first body 22 also includes a second surface 28 opposed to the articulating surface 24 . the second surface 28 is adapted to receive the head of the humerus 3 . the prosthesis 20 further includes a second body 30 operably associated with the first body 22 . the second body 30 has a second body articulating surface 32 extending from a portion 34 of the circular periphery 26 of the first articulating surface 24 . the second body articulating surface 32 is adapted to prevent impingement of the acromion 9 ( see fig1 ) with the humerus 3 when the humerus 3 is in the abducted position ( see fig8 ). while the prosthesis of the present invention may be secured to the humerus by securing of the second surface 28 to the humerus and bony ingrowth there between , preferably and as shown in fig7 , the prosthesis 20 further includes a stem 36 operably associated with the first body 22 or the second body 30 . as shown in fig7 , the stem 36 is associated with the first body 22 . the stem 36 is adapted to assist in securing the prosthesis 20 to the humerus 3 . as shown in fig7 , the prosthesis 20 is an integral or one - piece item . it should be appreciated that the prosthesis 20 may be modular . for example , the stem 36 may be a separate component from the first body 22 or the second body 30 . likewise , the second body 30 may be a separate component from the first body 22 . as shown in fig7 , the first body 22 may have any shape capable for articulating motion with the glenoid cavity ( see fig8 ); however , preferably the articulating surface 24 is generally convex . for example , and as shown in fig7 , the articulating surface 24 may be generally hemispherical . likewise , the second surface 28 may likewise be generally hemispherical with the first body 22 being generally a hollow hemisphere . similarly , the second body articulating surface 32 is preferably convex and may have a generally spherical shape . likewise , the second body second surface 38 may likewise be generally spherical . the second body 30 may thus also be generally a sector of a hollow sphere . to provide for smooth motion of the humerus 3 through the abduction of the humerus 3 with respect to glenoid cavity 14 ( see fig8 ) boundary portion 40 of the prosthesis 20 located between the second articulating surface 32 and the first articulating surface 24 where the second articulating surface 32 extends from the first articulating surface 24 is generally smooth and continuous . referring now to fig1 , the prosthesis 20 of the present invention is shown installed in the humerus 3 with the adjacent bones of the clavicle 8 , scapula 7 and acromion 9 shown in position . as shown in fig1 , the humerus 3 is abducted into an angle β with respect to vertical erect body reference line 42 . as can be seen in fig1 , the acromion 9 extends past the boundary portion 40 separating the first body 22 of the prosthesis 20 from the second body 30 of the prosthesis 20 . thus , the second body articulating surface 32 is utilized to prevent the acromion 9 from impinging on the humerus 3 . referring now to fig8 and 9 , the humerus 3 is again shown in position with the adjacent skeletal structure . in fig8 , the long bone or humerus 3 is shown in position when the upper arm is in position against the torso . at the humeral position as shown in fig8 , the angle β between the vertical centerline 42 and humeral centerline 44 is represented by an angle ββ of approximately 15 degrees . in this position of the humerus 3 , it can be seen that the acromion 9 is in contact with the first articulating surface 24 at acromion distal edge or outer edge 13 . referring now to fig9 , the humerus 3 is shown being abducted in the direction of arrow 46 with the respective angle β equaling approximately 60 degrees . in this abducted position , the outer edge 13 of the acromion 9 is in a position such that the second articulating surface 32 of the second body 30 is used to provide a smooth articulating surface for the outer edge 13 of the acromion 9 . referring now to fig1 , the prosthesis 20 is shown in greater detail . while the stem 36 of the prosthesis 20 may have any suitable shape capable of providing support for the prosthesis 20 in the humerus 3 , preferably , and as shown in fig1 , the stem 36 has a general cylindrical shape . the first body 22 as shown in fig1 may be in the form of a hollow hemisphere having a first longitudinal body centerline 48 . the stem 36 has a stem longitudinal centerline 50 . as shown in fig1 , the prosthesis 20 may be such that the first longitudinal body centerline 48 and the stem longitudinal centerline 50 are coincident . such a configuration provides for a preferred central location of the stem 36 . applicants have found that since the diseased humerus may become flattened around the humeral head , to provide adequate support to the prosthesis 20 in a diseased humerus , the support surface opposed to the articulating surface 24 of the prosthesis 20 may include at least part of the second surface 28 to include a support surface 52 opposed to the first articulating surface 24 . preferably , for simplicity , the support surface may be generally planar . to assist the prosthesis 20 in its strength and stability in the humerus 3 and to promote the bony ingrowth around the prosthesis 20 , the prosthesis 20 may include a porous coating 53 secured to , for example , the second surface 28 of the first body 22 , the second surface 38 of the second body , the planar portion 52 of the second surface 28 , as well as on the periphery of the stem 36 . any commercially available porous coating will assist in the bony ingrowth of the prosthesis 20 to the humerus 3 . one particular porous coating is provided by the assignee of the instant application under the trade name porocoat ® porous coating may be more fully understood by reference to u . s . pat . no . 3 , 855 , 638 to pilliar , hereby incorporated in its entireties by reference . as shown in fig1 , the circular outer periphery 26 of the articulating surface 24 of the first body 22 defines a first plane 54 . similarly , the second articulating surface 32 of the second body 30 defines a second surface periphery 56 . the second surface periphery 56 defines a second plane 58 . the first plane 54 and the second plane 58 are non - coincident . the first plane 54 and the second plane 58 , therefore , define an angle αα there between . as shown in fig1 , the angle αα is obtuse . while the angle αα may approach 180 degrees , the angle aa may likewise have a range of about 120 to 180 degrees . as shown in fig2 , the angle aa may be around 138 degrees . referring now to fig1 and 12 , the prosthesis 20 is shown in greater detail . as shown in fig1 , the stem 36 may be generally cylindrical having stem diameter sd and a length sl . the stem 36 may be tapered and defined by an angle ω . the angle ω may be around 5 to 30 degrees . the planar portion 52 of the prosthesis 20 may have any reasonable location with respect to the articulating surface 24 of the prosthesis 20 . the proper position of the planar portion 52 will depend on the flattening of the humeral head and how much corresponding amount of resection may be required to the humeral head . the position of the planar portion 52 with respect to the articulating surface 24 may be defined by a flat dimension fd . the hemispherical body 22 and second body 30 of the prosthesis 20 may be defined with respect to a prosthetic center point 60 . the articulating surface 24 may be defined by a radius r 1 extending from center point 60 the articulating surface 24 . the second surface 28 may be defined by a radius r 2 extending from the prosthetic center point 60 to the second surface 28 . similarly , the second articulating surface 32 may be defined by radius r 4 from the prosthetic center point 60 to the second articulating surface 32 . similarly , the second surface of the second body 38 may be defined by radius r 3 from the prosthetic center point 60 to the second surface 28 . for simplicity , the radii r 1 and r 4 may be identical and for simplicity the radii r 2 and r 3 may be identical . referring now to fig1 , the underside of the prosthesis 20 is shown . the prosthesis 20 may have any size compatible with the humerus . preferably , and as shown in fig7 through 12 , the prosthesis 20 preferably blends with the periphery of the humerus . thus , the size of the prosthesis 20 is governed generally by the size of the anatomical humerus . the prosthesis 20 may be made of any suitable durable material that is compatible with the human anatomy . for example , the prosthesis 20 may be made of a ceramic , a plastic or a metal . if made of a metal , the prosthesis 20 may be made , for example , of a cobalt chromium alloy , a titanium alloy , or a stainless steel alloy . referring now to fig1 , an instrument in the form of , for example , a reamer assembly 62 is shown for use in reaming , for example , the articulating surface 24 of the prosthesis 20 of fig7 . as shown in fig1 , the reamer assembly 62 includes a tool driver 64 . the tool driver 64 includes a body 66 having a cutting tool adaptor 68 and a drive adapter 70 . the reamer assembly 62 also includes a reamer 72 . the reamer 72 is connected to the tool driver 64 by the cutting tool adapter 68 . the reamer 72 may be a hemispherical grater type reamer . referring now to fig1 and 15 , a bone cutting tool guide 74 is shown . the tool guide 74 may include a body 76 having a cylindrical bore 78 for receiving a guide pin 80 and an elongated slot 82 for receiving a cutting tool in the form of osteotome 84 . the tool guide 74 is used to prepare surface 88 of humerus 3 . referring now to fig1 , a tool kit 86 is shown for preparing a humerus to receive a prosthesis , for example , prosthesis 20 of fig7 through 12 . as shown in fig7 through 12 , the prosthesis 20 includes the first body 22 having the first articulating surface 24 and an opposed first surface support surface 28 . the prosthesis 20 also includes the second body 30 that has the second articulating surface 32 and an opposed second support surface 38 . referring again to fig1 , the kit 86 is used for preparing the humerus 3 to receive the first support surface 28 and the second support surface 38 . the tool kit 86 of fig1 includes the reamer 72 and may include the tool driver 64 to form the reamer assembly 62 . the tool kit 86 further includes a bone cutting tool 84 for preparing a second prepared surface on the humerus 3 for receiving the second support surface 38 of , for example , the prosthesis 20 . as shown in fig1 , the bone cutting tool 84 is used to prepare second prepared surface 88 on the humerus 3 . as shown in fig1 , the second prepared surface 88 represents the inside surface of a cylinder . such a shape on the humerus is necessary to accommodate the inner edge 90 of the second body 30 of the prosthesis 20 . ( see fig1 ). preferably and as shown in fig1 , the kit 86 further includes the bone cutting tool guide 74 for guiding the osteotome 84 through the elongated slot 82 of the bone cutting tool guide 74 . the osteotome 84 may be struck with mallet 96 . referring now to fig1 , it should be appreciated that if the angle as approaches 180 degrees , it may be possible to provide for the reaming of the humerus with a reamer assembly 62 ( see fig1 ) and merely pivot the reamer assembly 62 to form a contour for both the second surfaces 28 and 38 . it should be appreciated , however , as the angle αα moves from 180 degrees to something less , for example , 140 degrees the inner edge 90 of second body 30 of prosthesis 20 ( see fig1 ) moves closer to the stem centerline 50 such that a generally hemispherical grater - type reamer such as that of fig1 may not be appropriate to prepare the hemispherical head of the humerus . therefore , the guide 74 of the kit 86 provides for a surface 88 that is generally cylindrical to permit the corner 90 of the prosthesis 20 to be fully seated into the humerus . it should be appreciated that the bone cutting tool necessary to prepare the humerus may include a drill , a reamer , a broach , a saw or an osteotome . referring now to fig1 through 20 , an alternate tool kit 186 for preparing a humerus is shown . referring first to fig1 , end mill 192 is shown . end mill 192 may be any commercially available milling cutter capable of end cutting . referring now to fig1 and 19 , a bone cutting tool guide 174 is shown for use with the end mill 192 of fig1 . the guide 174 includes a body 176 . the body 176 includes an opening 178 for cooperation with location pin 180 . the location pin 180 is used to orient the guide 174 with respect to the humerus 3 . the guide 174 further defines a plurality of slots 182 formed in the body 176 . referring to fig1 , the slots 182 extend an angle θθ about the periphery of concave inner surface 194 of the guide 174 . the slots 182 are aligned somewhat parallel to each other and slightly spaced apart . the slots 182 are close enough to minimize the amount of material not covered by the slots but far enough apart to provide enough strength to the guide 174 , particularly around the slots 182 . referring now to fig2 , the kit 186 is shown . the kit 186 includes reamer assembly 162 for preparing the first prepared surface on the humerus . the reamer assembly 162 is similar to reamer assembly 62 of fig1 and includes a tool driver 164 similar to the tool driver 64 of fig1 as well as a grater type hemispherical reamer 172 similar to the reamer 72 of the reamer assembly 62 of fig1 . the kit 20 further includes end mill 192 as well as an osteotome 184 similar to osteotome 84 of the kit 86 of fig1 . the osteotome 184 serves to remove the material remaining after the end mill 192 removes materials in alignment with the slots 182 of the guide 174 . preferably and as shown in fig2 , the kit 186 may further include the guide 174 . further , the kit 20 may include a surgical mallet 196 . the surgical mallet 196 is used to strike the osteotome 184 . referring now to fig2 , 22 and 23 , an alternate embodiment of the present invention is shown as prosthesis 120 . prosthesis 120 is similar to prosthesis 20 of fig7 through 12 except that prosthesis 120 is designed to take into consideration the limit in installing the prosthesis onto the prepared humeral head . mainly , the prosthesis 120 takes into consideration the inability to clear the edge 90 of the prosthesis 20 when utilizing a spherically shaped humeral head . referring now to fig2 , the prosthesis 120 includes a first body 122 having a hemispherical articulating surface 124 and an opposed concave arcuate surface 128 . the first body 122 also has a planar portion 152 opposing the articulating surface 124 . the prosthesis 120 further includes a tapered cylindrical stem 136 extending inwardly from the planar portion 152 of the first body 122 . the prosthesis 120 further includes a second body 130 extending from circular outer periphery 126 of the first body 122 . a boundary portion 140 is located between the first body 122 and the second body 130 and is preferably smooth and continuous . unlike the prosthesis 20 , the second body 130 of the prosthesis 120 has an opposed surface in the form of a cylindrical inner periphery 138 . the cylindrical periphery 138 is designed to matingly fit with the cylindrical surface prepared on the humeral head . referring now to fig2 , the cylindrical periphery 138 is shown in greater detail . the cylindrical periphery 138 is defined by a radius r c extending from stem centerline 150 . referring now to fig2 , another view of the cylindrical periphery 135 of the prosthesis 120 is shown . the cylindrical periphery 135 is again defined by a radius r c from stem centerline 150 . referring now to fig2 , an alternate tool kit is shown as tool kit 286 . the tool kit 286 is used to prepare a humerus for the prosthesis of the present invention . the tool kit 286 includes a reamer assembly 262 similar to the reamer assembly 162 of the kit 186 of fig2 . the tool kit 286 further includes a cylindrical end cutting reamer 292 having a cylindrical cutting surface 297 and a guiding surface 298 . the kit 286 further includes a guide 274 for guiding the cylindrical reamer 292 in a proper path to properly prepare the humerus . the guide 274 includes a body 276 defining an opening 278 for cooperation with location pin 280 , which is utilized to properly position the guide 274 on the humerus . the body 276 of the guide 274 further includes an arcuate elongated slot 282 that cooperates with the guiding surface 298 of the reamer 292 to guide the reamer along a proper path . the arcuate slot 282 is defined by an included angle θθθ . referring now fig2 , an alternate embodiment of the present invention is shown as surgical method 300 . the method 300 includes the first step 302 of providing a prosthesis with a first body having a first articulating surface and an opposed first support surface and with a second body having a second articulating surface and an opposed second support surface . the method 300 further includes a second step 304 providing a tool kit for preparing a humerus for receiving the prosthesis . the method 300 further includes a third step 306 of preparing a first prepared surface for cooperation with the first support surface with the tool kit . the method 300 also includes a fourth step 308 of preparing a second prepared surface for cooperation with the second support surface with the tool kit . the method 300 further includes a fifth step 310 of implanting the prosthesis onto the first prepared surface and the second prepared surface . although the present invention and its advantages have been described in detail , it should be understood that various changes , substitutions , and alterations can be made therein without departing from the spirit and scope of the present invention as defined by the appended claims .
a humeral prosthesis includes a first body having a first body articulating surface defining a generally circular outer periphery , and a first centerline axis . the first body having a support surface opposite to the first body articulating surface , the first body is hollow and configured to receive a head of the humerus , and a stem extending away from the support surface , the stem defining a second centerline axis which is coincident with the first centerline axis . the prosthesis further includes a second body in the form of a flange which extends laterally from a portion of the circular outer periphery , the first body articulating surface and a surface of the second body defining a boundary portion between them which is generally smooth and continuous , wherein the second body is located superiorly and the surface of the second body which bounds the first body articulating surface is a second articulating surface .