A tibial implant configured for fitting to a distal portion of a tibia, the tibial implant having a tibia-facing surface and a lower surface opposed to said tibia-facing surface, and comprising: an outer perimeter of the tibia-facing surface such that, upon proceeding counterclockwise around said perimeter as viewed from above along a vertical axis, said outer perimeter further comprises a first straight edge; said first straight edge being followed by a first convex corner that meets and is tangent to said first straight edge; said first convex corner being followed by a second straight edge or shallow arc that meets and is tangent to said first convex corner, wherein an angle of said first convex corner is greater than 90 degrees but less than 180 degrees; said second straight edge or said shallow arc being followed by a second convex corner that meets and is tangent to said second straight edge or said shallow arc; said second convex corner being followed by a first concave curve, wherein said second convex corner transitions to said first concave curve at a first inflection point; wherein there is a tangent line (195(that is parallel to said first straight edge and is tangent to second convex corner at a tangency point that is farther from said first straight edge than is said first inflection point; wherein said first concave curve continues on from said first inflection point to cross said tangent line so as to become farther from said first straight edge than is said tangent line; and wherein said first concave curve is followed by a convex curve that proceeds from said first concave curve and returns to said first straight edge to form a complete perimeter of said tibial implant. an outer perimeter of the tibia-facing surface such that, upon proceeding counterclockwise around said perimeter as viewed from above along a vertical axis, said outer perimeter further comprises a first straight edge; said first straight edge being followed by a first convex corner that meets and is tangent to said first straight edge; said first convex corner being followed by a second straight edge or shallow arc that meets and is tangent to said first convex corner, wherein an angle of said first convex corner is greater than 90 degrees but less than 180 degrees; said second straight edge or said shallow arc being followed by a second convex corner that meets and is tangent to said second straight edge or said shallow arc; said second convex corner being followed by a first concave curve, wherein said second convex corner transitions to said first concave curve at a first inflection point; wherein there is a tangent line (195(that is parallel to said first straight edge and is tangent to second convex corner at a tangency point that is farther from said first straight edge than is said first inflection point; wherein said first concave curve continues on from said first inflection point to cross said tangent line so as to become farther from said first straight edge than is said tangent line; and wherein said first concave curve is followed by a convex curve that proceeds from said first concave curve and returns to said first straight edge to form a complete perimeter of said tibial implant.