JOINT REPLACEMENT SPACERS

A spacer for (a) replacing a removed portion of a first bone, and (b) articulating with a second bone, the spacer comprising: an articulating surface sized and shaped to articulate with an articular surface of the second bone; and a stabilizing surface sized and shaped to conform to a cut surface of the first bone, wherein: the spacer defines first axis and a second axis not parallel to the first axis; in a cross-section of the spacer perpendicular to the first axis, the stabilizing surface defines a first curve including: a first portion with a first radius of curvature; and a second portion with a second radius of curvature not equal to the first radius of curvature; in a cross-section of the spacer perpendicular to the second axis, the stabilizing surface defines a second curve including: a third portion with a third radius of curvature; and a fourth portion with a fourth radius of curvature not equal to the third radius of curvature; and the second and fourth radii of curvature are not equal.