Modular bone implant, tool, and method

1. A tibial component of a knee prosthesis, comprising:

a tibial tray having substantially planar top and bottom surfaces, the tray including an outwardly projecting boss extending from the bottom surface, the boss having an outer wall including a cylindrical portion and a tapered portion and an inner wall defining a throughbore;

a tibial keel forming an elongate body having a top end and a bottom end, the tibial keel including a first axial bore extending inwardly from said top end and forming a bore wall, the bore wall including a cylindrical portion and a tapered portion, the tibial keel being removably engageable with the tray with the boss received in the first bore of the tibial keel, the tapered portion of the boss seating on the tapered portion of the first bore to define a first junction between the tibial tray and the tibial keel, and the cylindrical portion of the boss being received by the cylindrical portion of the first bore in press-fit relationship to form a second junction between the tibial tray and tibial keel, the outer wall of the boss and the bore wall of the tibial keel cooperating to define a circumferential gap between the first junction and the second junction when the tibial component is finally assembled, the tibial keel including a second axial bore extending inwardly from said bottom end;

a stem extension removably affixed to the second axial bore; and

wherein the tibial tray and tibial keel are spaced from one another everywhere except at the cylindrical and taper seating portions of the first and second junctions.

2. The tibial component of claim 1 wherein the tapered portions form a locking taper.

3. The tibial component of claim 1 wherein the tapered portion of the boss is formed below the cylindrical portion of the boss and the tapered portion of the first axial bore is formed below the cylindrical portion of the first axial bore so that the tapered seating portion of the second junction is below the cylindrical press-fit portion of the first junction.

4. The tibial component of claim 3 wherein the cylindrical press-fit between the boss and first axial bore seals the first axial bore to prevent material from entering or leaving the portion of the first axial bore below the press-fit.

5. The tibial component of claim 1 wherein the tray further comprises at least one fin extending along the bottom surface and projecting downwardly from the bottom surface, and the tibial keel further comprises at least one fin projecting outwardly, the fins being generally aligned with one another from top to bottom to project as a single fin but being in axial spaced relationship so that they do not contact.

6. The tibial component of claim 1 further comprising rotational alignment means for aligning the tibial keel and tray in a predetermined relationship for assembly.

7. The tibial component of claim 6 wherein the rotational alignment means comprises a pin received in a hole.

8. The tibial component of claim 7 wherein the pin is located in the first axial bore and the pin is received by a hole formed in the boss.

9. The tibial component of claim 1 , wherein the second axial bore of the tibial keel forms a tapered inner wall for receiving said stem extension.

10. The tibial component of claim 9 wherein the tray includes a tray bore extending from the top surface downwardly through the boss in communication with the first bore, the tray bore receiving a bolt in engagement with the stem extension.