Intervertebral disc prosthesis, surgical methods, and fitting tools

An intervertebral disc prosthesis comprising:

• an upper plate comprising a curved internal face;
• a lower plate comprising a flat internal face, a first housing disposed toward a first side of the lower plate and having a first gap open toward the flat internal face, and a second housing disposed toward a second side of the lower plate and having a second gap open toward the flat internal face;
• and
• a nucleus translatable with respect to the lower plate and articulable with respect to the upper plate, the nucleus comprising a curved upper face, a flat lower face, a perimeter extending around the nucleus, a first protrusion extending from the perimeter along a first side of the nucleus and sized to movably fit in the first housing, and a second protrusion extending from the perimeter along a second side of the nucleus and sized to movably fit in the second housing;
• with
• the prosthesis having an assembled configuration in which the flat internal face of the lower plate abuts the flat lower face of the nucleus, the curved internal face of the upper plate abuts the curved upper face of the nucleus, the first protrusion is disposed in the first gap with clearance allowing a range of translation and rotation of the nucleus, the second protrusion is disposed in the second gap of the nucleus with clearance allowing a range of translation and rotation of the nucleus, and translation and rotation of the nucleus is limited by contact of the first protrusion with the first housing and by contact of the second protrusion with the second housing.