Tibial prosthetic implant with offset stem

Abstract

A tibial prosthetic implant includes a base or base plate with an offset tibial stem. The base includes an inferior surface adapted to abut a resected surface of a patient's tibia and forms a base for articulating surfaces adapted to articulate with the patient's femoral condyles. The longitudinal center axis of the tibial stem extends from the inferior surface of the base and is offset from a center of the base. The offset places the stem in position to extend into the central canal of the tibia so that it does not substantially interfere with the cortical bone when the inferior surface of the base substantially abuts and aligns with the resected surface of the tibia.

We claim:  
     
       1. A tibial prosthetic implant for patients having normally shaped tibias, the implant comprising: 
       (a) a base having an inferior surface adapted to substantially abut a resected surface of a patient's tibia and a transverse cross-sectional shape adapted to approximate a peripheral shape of the resected surface of the tibia;  
       (b) an articulating portion connected to the base, the articulating portion of the implant having articulating surfaces opposite the inferior surface of the base for articulating with a patient's femoral condyles;  
       (c) attachment means for securing the base to the resected surface of the tibia so that the inferior surface of the base substantially abuts and aligns with the resected surface of the tibia; and  
       (d) a tibial stem extending from the inferior surface of the base, the tibial stem having a longitudinal center axis that is offset anteriorly and medially from a center of the base such that the stem is in position to extend into the central canal of the patient's tibia without substantially interfering with the cortical bone of the tibia when the inferior surface of the base abuts and aligns with the resected surface of the tibia. ; and  
       ( e )  wherein the longitudinal center axis of the tibial stem is offset anteriorly from the center of the base a distance that is between  59   %  to  68   %  of a total anterior - posterior medial condyle depth dimension of the base as measured from an outermost posterior edge of the base, and wherein the longitudinal center axis of the tibial stem is offset medially from the center of the base a distance that is between  52   %  to  55   %  of a total medial - lateral width dimension of the base as measured from an outermost lateral edge of the base.   
     
     
       2. The tibial prosthetic implant of claim  1  wherein the tibial stem includes: 
       (a) a central root portion extending an entire length of the tibial stem; and  
       (b) a medial-posterior web extending generally medially and posteriorly from the stem central root portion, a lateral-posterior web extending generally laterally and posteriorly from the stem central root portion, a medial-anterior web extending substantially medially and anteriorly from the stem central root portion, and a lateral-anterior web extending generally laterally and anteriorly from the stem central root portion, each web having an enlarged portion at an end of the stem proximal to the inferior surface of the base and a relatively narrower portion at an end of the stem distal of the base.  
     
     
       3. A tibial prosthetic implant comprising: 
       (a) a base having an inferior surface adapted to substantially abut a resected surface of a patient's tibia and a transverse cross-sectional shape adapted to approximate a peripheral shape of the resected surface of the tibia;  
       (b) an articulating portion connected to the base, the articulating portion of the implant having articulating surfaces opposite the inferior surface of the base for articulating with a patient's femoral condyles;  
       (c) attachment means for securing the base to the resected surface of the tibia so that the inferior surface of the base substantially abuts and aligns with the resected surface of the tibia; and  
       (d) a tibia stem extending from the inferior surface of the base, the tibial stem having a longitudinal center axis that is offset medially from a center of the base such that the stem is in position to extend into the central canal of the patient's tibia without substantially interfering with the cortical bone of the tibia when the inferior surface of the base abuts and aligns with the resected surface of the tibia.  
     
     
       4. The tibial prosthetic implant of claim  3  wherein: 
       (a) the longitudinal center axis of the tibial stem is offset medially from the center of the base a distance that is between 52% and 55% of a total medial-lateral width dimension of the base as measured from an outermost lateral edge of the base.  
     
     
       5. A base plate for a modular tibial prosthetic implant for patients having normally shaped tibias, the base plate comprising: 
       (a) a plate of material having an inferior surface adapted to substantially abut a resected surface of a patient's tibia; and  
       (b) a tibial stem extending from the inferior surface of the plate, the tibial stem having a longitudinal center axis that is offset anteriorly and medially from a center of the plate such that the stem is in position to extend into the central canal of the patient's tibia without substantially interfering with the cortical bone of the tibia when the inferior surface of the plate substantially abuts the resected surface of the tibia and the center of the plate aligns with a center of the resected surface of the tibia.  and  
       ( c )  wherein the longitudinal center axis of the tibial stem of offset anteriorly from the center of the plate a distance that is between  59   %  to  68   %  of a total anterior - posterior medial condyle depth dimension of the plate as measured from an outermost posterior edge of the plate, and wherein the longitudinal center axis of the tibial stem is offset medially from the center of the plate a distance that is between  52   %  to  55   %  of a total medial-lateral width dimension of the plate as measured from an outermost lateral edge of the plate.   
     
     
       6. The tibial prosthetic implant of claim  5  wherein: 
       (a) the longitudinal center axis of the tibial stem is offset anteriorly from the center axis of the plate a distance that is between 59% to 68% of a total anterior-posterior medial condyle depth dimension of the plate as measured from an outermost posterior edge of the plate; and  
       (b) the longitudinal center axis of the tibial stem is offset medially from the center of the plate a distance that is between 52% to 55% of a total medial-lateral width dimension of the plate as measured from an outermost lateral edge of the plate.  
     
     
       7. A base plate for a modular tibial prosthetic implant, the base plate comprising: 
       (a) a plate of material having an inferior surface adapted to substantially abut a resected surface of a patient's tibia; and  
       (b) a tibial stem extending from the inferior surface of the plate, the tibial stem having a longitudinal center axis that is offset medially from a center of the plate, such that the stem is in position to extend into the central canal of the patient's tibia without substantially interfering with the cortical bone of the tibia when the inferior surface of the plate substantially abuts the resected surface of the tibia and the center of the plate aligns with a center of the resected surface of the tibia.  
     
     
       8. The base plate of claim  7  wherein: 
       (a) a longitudinal center axis of the tibial stem is offset medially from the center of the plate a distance that is between 52% to 55% of a total medial-lateral width dimension of the plate as measured from an outermost lateral edge of the plate.  
     
     
       9. A tibial prosthetic implant of the type having a base that includes an inferior surface adapted to substantially abut a resected surface of a patient's tibia so as to support articulating surfaces that are adapted to articulate with the patient's femoral condyles, wherein the improvement comprises: 
       (a) a tibial stem extending from the inferior surface of the base, the tibial stem having a longitudinal center axis that is offset anteriorly and medially from a center of the base such that the stem is in position to extend into the central canal of the patient's tibia without substantially interfering with the cortical bone of the tibia when the inferior surface of the base abuts the resected surface of the tibia and the center of the base aligns with a center of the resected surface of the tibia.  and  
       ( b )  wherein the longitudinal center axis of the tibial stem is offset anteriorly from the center of the base a distance that is between  59   %  to  68   %  of a total anterior - posterior medial condyle depth dimension of the base as measured from an outermost posterior edge of the base, and wherein the longitudinal center axis of the tibial stem is offset medially from the center of the base a distance that is between  52   %  to  55   %  of a total medial - lateral width dimension of the base as measured from an outermost lateral edge of the base.   
     
     
       10. The tibial prosthetic implant of claim  9  wherein: 
       (a) a longitudinal center axis of the tibial stem is offset anteriorly from the center of the base a distance that is between 59% to 68% of a total anterior-posterior medial condyle depth dimension of the base as measured from an outermost posterior edge of the base; and  
       (b) the longitudinal center axis of the tibial stem is offset medially from the center of the base a distance that is between 52% to 55% of a total medial-lateral width dimension of the base as measured from any outermost lateral edge of the base.  
     
     
       11. A tibial prosthetic implant of the type having a base that includes an inferior surface adapted to substantially abut a resected surface of a patient's tibia so as to support articulating surfaces that are adapted to articulate with the patient's femoral condyles, wherein the improvement comprises: 
       (a) a tibial stem extending from the inferior surface of the base, the tibial stem having a longitudinal center axis that is offset medially from a center of the base such that the stem is in position to extend into a central canal of the patient's tibia when the inferior surface of the base abuts the resected surface of the tibia and the center of the base aligns with a center of the resected surface of the tibia.  
     
     
       12. The tibial prosthetic implant of claim  11  wherein: 
       (a) the longitudinal center axis of the tibial stem is offset medially from the center of the base a distance that is between 52% to 55% of a total medial-lateral width dimension of the base as measured from an outermost lateral edge of the base.