A disk arthroplasty device (310) is provided for replacement of a spinal disk. The device is implantable into a resected disk space and is formed with ball (346) and socket (326) members and shaped to provide lateral bending and backward extension of up to about 5.degree. and forward flexion of up to about 15.degree.. Four embodiments (10), (110), (210) and (310) permit up to about 5.degree. axial rotation and a fifth embodiment (410) permits unrestricted axial rotation. Metal insert cups (70) and (170) are provided for attaching to the device surfaces and are convexly shaped along one axis to conform to the natural contours of the top and bottom vertebra surfaces. The metal insert cups (70) and (170) provide tensile support to the structure and provide for the attachment of additional structures for retaining the device in position after implantation into a disk space.