The invention provides a spinal disc implant comprising a ring shaped body including a first pair of opposed substantially parallel sides spaced apart by a second pair of opposed sides to define a central bore. A first one of the second pair of sides defines a substantially arcuate curve joining a first end of the first pair of sides. A second one of the second pair of opposed sides substantially linearly joins a second end of the first pair of sides. The upper and lower surfaces of the ring shaped body have a plurality of teeth extending therefrom for engaging adjacent vertebrae. The implant is made of a biocompatible metal such as titanium or an alloy thereof, and the first and second sides tapering from the second end to the first end. The interior space may have a porous hydroxyapatite block shaped to fill the interior space. The porous hydroxyapatite substance helps the prosthesis integrate into the vertebral structure by allowing one grow into the pores.