Mobile bearing unicondylar tibial knee prosthesis

1. A mobile bearing unicondylar tibial knee prosthesis comprising:

a tibial base plate having a superior surface for sliding engagement with an articular surface component and an inferior surface for engaging the tibia, the base plate including an inside edge positionable adjacent to the midline of the proximal tibia adjacent to the intercondylar eminence, an outside edge positionable adjacent to the outer side of the proximal tibia, an anterior aspect positionable adjacent to the anterior side of the proximal tibia, and a posterior aspect positionable adjacent to the posterior side of the proximal tibia, the base plate including an inside rail projecting superiorly from the superior surface of the plate adjacent to the inside edge, the base plate including an anterior stop projecting superiorly from the superior surface of the plate adjacent to the anterior aspect, a portion of the anterior stop extending from the rail, around the anterior aspect of the plate, and back toward the posterior aspect of the plate part-way along the outside edge such that the rail and anterior stop form a generally “J”-shaped constraint wall; and

a tibial articular surface component, the articular surface component comprising a superior surface for articulation with a femoral knee component, an inferior surface for sliding engagement with the superior surface of the base plate, an inside edge, an outside edge, an anterior aspect, and a posterior aspect, the articular surface component positionable on the superior surface of the base plate for sliding from the anterior aspect to the posterior aspect of the base plate, from the inside edge to the outside edge of the base plate, and for rotation on the base plate, the inside rail limiting the motion of the articular surface component toward the inside edge of the base plate and the anterior stop limiting motion of the articular surface component toward the anterior aspect of the base plate.

2. The prosthesis of claim 1 wherein the anterior stop constrains the anterior aspect of the articular surface component to rotation only by limiting motion of the anterior aspect toward the outside edge of the base plate when the articular surface component is against the anterior stop.

3. The prosthesis of claim 2 wherein the anterior aspect of the articular surface component defines an anteriorly facing convex surface engageable with the anterior stop to facilitate rotation of the articular surface component on the base plate when the articular surface component is pressed forward against the anterior stop.

4. The prosthesis of claim 3 wherein the articular surface component further comprises a convexly curved surface between the inside edge and posterior aspect of the articular surface component to facilitate rotation of the anterior aspect of the articular surface component away from the inside rail when the articular surface component is spaced from the antenor stop.

5. A mobile bearing unicondylar tibial knee prosthesis comprising:

a tibial base plate having a superior surface, an inferior surface, an inside edge, an outside edge, an anterior aspect, a posterior aspect, and an anterior stop projecting superiorly from the superior surface adjacent the anterior aspect, the anterior stop defining a posteriorly facing concave surface; and

a tibial articular surface component, the articular surface component comprising a superior surface, an inferior surface, an inside edge, an outside edge, an anterior aspect, and a posterior aspect, the anterior aspect of the articular surface defining a convexly curved surface, the inferior surface of the articular surface component engaging the superior surface of the base plate in sliding relationship, the articular surface component being slidable from a first position in which the anterior aspect is spaced from the anterior stop and the anterior aspect is free to slide from side to side on the base plate and a second position in which the convex surface of the anterior aspect of the articular component engages the concave surface of the anterior stop and the anterior aspect is constrained to rotation such that the articular surface component pivots about the anterior aspect.