Knee arthroplasty prosthesis

1. A modular tibial component comprising:

a tibial base comprising:

an inferior surface adapted to engage a prepared surface at a proximal end of a tibia;

a superior surface opposite said inferior surface;

a base extension having a cylindrical shape and extending distally from said inferior surface, said base extension including a first engagement surface and a cavity defined by the first engagement surface, said base extension defining a longitudinal extension axis; and

a plurality of base fixation fins extending outwardly from said base extension; and

a tibial stem comprising a distal end and an opposed proximal end, an elongate outer surface extending from said distal end to said proximal end, said tibial stem defining a longitudinal stem axis, said tibial stem comprising:

a second engagement surface complementary to said first engagement surface of said base extension, said second engagement surface proximate said proximal end of said tibial stem such that said first and second engagement surfaces lockingly engage by advancement of said tibial stem toward said inferior surface of said tibial base along an inferior-to-superior direction such that said second engagement surface is received within said cavity of said base extension;

a groove formed in said outer surface and distally spaced from said proximal end, said groove extending transverse to said stem axis, said groove comprising groove portions on opposite sides of said outer surface; and

a plurality of stem extension fins extending outwardly from said outer surface of said tibial stem, said stem fixation fins aligned with and forming extensions of said base fixation fins when said first and second engagement surfaces are lockingly engaged, wherein said tibial base further comprises a passageway extending through said tibial base from said superior surface to said inferior surface, said passageway passing through said base extension such that said stem axis is aligned with said extension axis when said first and second engagement surfaces are lockingly engaged.

2. The modular tibial component of claim 1 in combination with a stem support tool comprising a tool extension,

said tool extension sized to fit within said groove formed in said outer surface of said tibial stem, whereby said tibial stem can be immobilized within the tibia by said stem support tool while said first and second engagement surfaces are lockingly engaged.

3. The modular tibial component of claim 2 wherein said stem support tool axially fixes said tibial stem to said stem support tool when said tool extension is engaged with said groove.

4. The modular tibial component of claim 2 wherein said tool extension comprises a plurality of tines, said tines arranged to engage said groove portions at said opposite sides of said outer surface.

5. The modular tibial component of claim 1 wherein said groove portions comprise a pair of discrete grooves disposed on said opposite sides of said outer surface.

6. The modular tibial component of claim 1 wherein said base extension comprises a first Morse taper and said second engagement surface comprises a complementary second Morse taper.

7. The modular tibial component of claim 1 wherein said distal end of said tibial stem comprises a cavity formed therein, said modular tibial component in combination with:

a plug engageable with said cavity to prevent blood from entering said cavity;

a stem extension receivable within said cavity of said tibial stem, such that said stem extension extends distally from said distal end to effectively lengthen said tibial stem,

whereby said plug and said stem extension are selectively attachable to said tibial stem.

8. The modular tibial component of claim 7 wherein:

said stem extension defines a third engagement surface at a proximal end of said stem extension,

said cavity formed in said distal end of said tibial stem tapers outwardly in a distal direction to define a fourth engagement surface complementary to said third engagement surface, and

said third and fourth engagement surfaces lockingly engaging said stem extension and said tibial stem when said proximal end of said stem extension is received within said cavity of said tibial stem.

9. The modular tibial component of claim 8 wherein said third engagement surface comprises a third Morse taper and said fourth engagement surface comprises a complementary fourth Morse taper.

10. The modular tibial component of claim 1 wherein said tibial base further comprises a wall defining a passageway extending through said tibial base from said superior surface to said inferior surface, and said tibial stem further comprises a threaded bore formed in said proximal end, said threaded bore aligned with said passageway of said tibial base when said first and second engagement surfaces are lockingly engaged, said modular tibial component further comprising:

an attachment screw received within said passageway of said tibial base and threadably engaged with said threaded bore of said tibial stem, said attachment screw comprising an enlarged head adjacent said superior surface of said tibial base and larger than said passageway, such that said attachment screw fixes said tibial stem to said tibial base.

11. The modular tibial component of claim 1 wherein said tibial base further comprises a raised platform extending distally from said inferior surface, said raised platform encircling said base extension and said base fixation fins.

12. The modular tibial component of claim 1 wherein said tibial base further comprises a posterior notch extending from said superior surface to said inferior surface, said posterior notch sized to accommodate a posterior cruciate ligament.

13. The modular tibial component of claim 1 , wherein said superior surface of said tibial base comprises a contoured surface sized and shaped to be engaged by condylar portions of a femoral component.

14. The modular tibial component of claim 13 , wherein said contoured surface of said tibial base is formed on a plastic insert, said plastic insert affixed to said tibial base.

15. The modular tibial component of claim 1 wherein said tibial stem defines a shoulder adjacent said second engagement surface at said proximal end, said groove distally spaced from said shoulder.

16. A tibial prosthesis kit comprising:

a tibial base comprising:

an inferior surface adapted to engage a prepared surface at a proximal end of a tibia;

a superior surface opposite said inferior surface; and

a base extension having a cylindrical shape and extending distally from said inferior surface, said base extension including a first engagement surface and a cavity defined by the first engagement surface;

a tibial stem comprising a distal end and an opposed proximal end, an elongate outer surface extending from said distal end to said proximal end, said tibial stem defining a longitudinal stem axis, said tibial stem comprising:

a second engagement surface complementary to said first engagement surface of said base extension, said second engagement surface proximate said proximal end of said tibial stem such that said first and second engagement surfaces lockingly engage by advancement of said tibial stem toward said tibial base along an inferior-to-superior direction such that said second engagement surface is received within said cavity of said base extension;

a cavity formed in said distal end;

a plug engageable with said cavity of said tibial stem to prevent blood from entering said cavity;

a stem extension lockingly engageable within said cavity of said distal end of said tibial stem, such that said stem extension extends distally from said distal end to effectively lengthen said tibial stem,

whereby said plug and said stem extension are selectively attachable to said tibial stem.

17. The tibial prosthesis kit of claim 16 wherein said outer surface of said tibial stem comprises a groove formed in said outer surface and distally spaced from said first engagement surface, said groove extending transverse to said stem axis, said groove comprising groove portions on opposite sides of said outer surface, the tibial prosthesis kit further comprising:

a stem support tool comprising a tool extension, said tool extension sized to fit within said groove formed in said outer surface of said tibial stem, whereby said tibial stem can be immobilized within the tibia by said stem support tool while said first and second engagement surfaces are lockingly engaged.