Humeral arthroplasty

An arthroplasty system, comprising:

• a first prosthesis comprising a first articular surface and a first bone-facing side opposite the first articular surface, wherein the first articular surface comprises a first radius, wherein the first bone-facing side comprises a first concave arrangement of at least three planar surfaces that all intersect at a first point on the first bone-facing side;
• a second prosthesis comprising a second articular surface and a second bone-facing side opposite the second articular surface, wherein the second articular surface comprises a second radius, wherein the second bone-facing side comprises a second concave arrangement of at least three planar surfaces that all intersect at a second point on the second bone-facing side;
• and
• a third prosthesis comprising a third articular surface and a third bone-facing side opposite the third articular surface, wherein the third articular surface comprises a third radius, wherein the third bone-facing side comprises a third concave arrangement of at least three planar surfaces that all intersect at a third point on the third bone-facing side;
• wherein the first, second, and third articular surfaces and the first, second, and third radii are selected from the group consisting of a set of spherical surfaces and radii, a set of ellipsoidal surfaces and radii, and a set of ovoid surfaces and radii;
• wherein the second radius is a different size than the first radius;
• wherein the third radius is a different size than the first and second radii;
• wherein, when the first, second, and third prostheses are superimposed, the first, second, and third concave arrangements superimpose exactly, and the first, second, and third articular surfaces pass through fourth and fifth points which are on opposite sides of a circle.

An arthroplasty system, comprising:

• a first prosthesis comprising a first articular surface and a first bone-facing side opposite the first articular surface, wherein the first articular surface comprises a first radius, wherein the first bone-facing side comprises a first concave arrangement of at least three planar surfaces that all intersect at a first point on the first bone-facing side;
• a second prosthesis comprising a second articular surface and a second bone-facing side opposite the second articular surface, wherein the second articular surface comprises a second radius, wherein the second bone-facing side comprises a second concave arrangement of at least three planar surfaces that all intersect at a second point on the second bone-facing side;
• and
• a third prosthesis comprising a third articular surface and a third bone-facing side opposite the third articular surface, wherein the third articular surface comprises a third radius, wherein the third bone-facing side comprises a third concave arrangement of at least three planar surfaces that all intersect at a third point on the third bone-facing side;
• wherein the first, second, and third articular surfaces are ellipsoidal surfaces, wherein the first, second, and third radii are ellipsoidal radii;
• wherein the second radius is a different size than the first radius;
• wherein the third radius is a different size than the first and second radii;
• wherein, when the first, second, and third prostheses are superimposed, the first, second, and third concave arrangements superimpose exactly, and the first, second, and third radii pass through a first pair of points on opposite sides of a first gage circle.

An arthroplasty system, comprising:

• a first prosthesis comprising a first articular surface and a first bone-facing side opposite the first articular surface, wherein the first articular surface comprises a first radius, wherein the first bone-facing side comprises first and second planar surfaces that intersect to form a first line;
• a second prosthesis comprising a second articular surface and a second bone-facing side opposite the second articular surface, wherein the second articular surface comprises a second radius, wherein the second bone-facing side comprises third and fourth planar surfaces that intersect to form a second line, wherein the first and second radii are different sizes, wherein, when the first and second prostheses are superimposed, the first and third planar surfaces are coplanar, the second and fourth planar surfaces are coplanar, the first and second lines are collinear, and the first and second articular surfaces intersect at a gage circle;
• and
• a reamer comprising a distal working portion and a shaft extending proximally from the distal working portion, wherein the distal working portion comprises a round perimeter rim encircling a bone-facing cutting feature, wherein the rim comprises a continuous smooth surface having an inner edge that corresponds to the defined gage circle, so that in use, the bone-facing cutting feature cuts a bone as the reamer is advanced toward the bone until the inner edge contacts the bone to stop further bone removal by the reamer.

An arthroplasty system, comprising:

• a small size prosthesis with an articular surface having a small radius;
• a large size prosthesis with an articular surface having a large radius, wherein the articular surfaces of the small and large size prostheses pass through a defined gage circle which has a fixed relationship to a group of bone-facing features common to the small and large size prostheses, wherein the small and large size prostheses require the same bone preparation;
• and
• a reamer comprising a distal working portion and a shaft extending proximally from the distal working portion, wherein the distal working portion comprises bone-facing cutting features encircled by a continuous smooth perimeter surface having an inner edge that corresponds to the defined gage circle, so that in use, the bone-facing cutting features cut bone as the reamer is advanced until the inner edge contacts bone to stop further bone removal by the reamer.