Interposition implants for the hand

An interposition implant to couple a first bone and a second bone of an anatomical joint of a hand of a subject, the implant comprising:

• a body defining:
• a median plane;
• a first joint surface having a first central region to articulate with the first bone;
• and
• a second joint surface having a second central region to articulate with the second bone, the second central region located on an opposite side of the body relative to the first central region;
• wherein 'the first central region and the second central region having profiles of a first axial segment and a second axial segment, respectively, 'the first and second axial segments each being one of a cylinder, a cone, and a torus and being centered on a first axis and a second axis, respectively,
• the first and second axes, as projected on the median plane, are oriented substantially perpendicular to each other, and
• the first joint surface further defines a first peripheral region adjacent the first central region and the first axial segment has a first cross section that has a smaller curvature in the first central region of the first joint surface than in the first peripheral region of the first joint surface such that the first central region is flatter than the first peripheral region.