A wedge-shaped prosthetic spinal disc nucleus including a hydrogel core surrounded by a constraining jacket. The hydrogel core is preshaped to form the wedge shape in a hydrated state. The constraining jacket is flexible, but substantially inelastic and is configured to prevent the hydrogel core from conforming to an anulus upon hydration. The prosthetic spinal disc nucleus corresponds generally to anatomical variations in disc space geometry, generally defined by separable areas or compartments, thus improving performance. In one preferred embodiment, the prosthetic spinal disc nucleus includes a radiopaque marker for indicating a location and orientation following implant.