Patent ID: 8690956

Claim:
An implant comprising: (a) a head having an upper surface, a perimeter surface, and a lower surface, wherein: (i) the upper surface blends into the perimeter surface and the perimeter surface blends into the lower surface; (ii) the upper surface has a general shape of at least a portion of a superior articular surface of a talus and at least a portion of a medial articular surface of a talus; (iii) the upper surface includes a convex first portion having a general shape of a portion of a toroid, a convex-concave second portion having a general saddle shape of a convex-concave portion of a toroid, and a third portion having a general shape of a portion of a surface of a right circular cone having an aperture angle ranging from about 120 degrees to about 178 degrees, wherein the first portion is tangent on its lateral edge to the medial edge of the second portion and the first portion is tangent on its medial edge to the lateral edge of the third portion; wherein the toroid of the convex first portion has a major radius ranging from about 9 millimeters to about 31 millimeters, and a minor tubular radius ranging from about 2 millimeters to about 6 millimeters; and (b) a stem extending away from the lower surface, wherein: (i) the stem has at least one circular perimeter along an axis normal to the lower surface, and a maximum stem circular perimeter at the intersection of the stem and the lower surface, (ii) the maximum stem circular perimeter is less than a maximum diameter of the head perimeter surface, (iii) the stem has a cylindrical portion.