Asymmetric tibial components for a knee prosthesis

A method of performing a tibial arthroplasty, the method comprising:

• resecting a proximal end of a tibia to create a resected tibial surface, the tibia having an anteriorly disposed tibial tubercle and a connection point to a posterior cruciate ligament;
• identifying an anatomic anteroposterior axis which intersects:
• an anterior point disposed on the tubercle, the anterior point medially spaced from a tubercle midpoint by an amount equal to ⅙th of an overall mediolateral width of the tubercle such that the anterior point lies on the medial third of the tubercle;
• and
• a posterior point disposed at a geometric center of an area defined by the connection point of the tibia to the posterior cruciate ligament;
• providing a tibial prosthesis having alignment indicia indicating a component anteroposterior axis designed to be aligned with the anatomic anteroposterior axis, the tibial prosthesis including a tibial baseplate having a lateral compartment and a medial compartment which cooperate to define a peripheral wall, the peripheral wall including:
• an anterior edge;
• a lateral posterior edge generally opposite the anterior edge and forming a posterior boundary of the lateral compartment;
• a medial posterior edge generally opposite the anterior edge and forming a posterior boundary of the medial compartment;
• a lateral periphery extending from the anterior edge to the lateral posterior edge;
• and
• a medial periphery extending from the anterior edge to the medial posterior edge, and the lateral compartment is asymmetric with respect to the medial compartment about the component anteroposterior axis to define a component asymmetry;
• positioning and orienting the tibial prosthesis with respect to the tibia by aligning the alignment indicia with the anatomic anteroposterior axis, wherein said step of positioning comprising matching the component asymmetry to a corresponding asymmetry of the resected tibial surface, whereby the tibial prosthesis covers a large proportion of the resected tibial surface, and wherein the component asymmetry comprises an anteroposterior extent asymmetry, in which:
• the lateral compartment defines a lateral anteroposterior extent extending from the anterior edge of the peripheral wall to the lateral posterior edge thereof;
• and
• the medial compartment defines a medial anteroposterior extent extending from the anterior edge of the peripheral wall to the medial posterior edge thereof,
• the medial anteroposterior extent larger than the lateral anteroposterior extent, and
• said step of positioning comprising:
• matching the larger medial anteroposterior extent to a corresponding medial portion of the resected tibial surface, and
• matching the smaller lateral anteroposterior extent to a corresponding lateral portion of the resected tibial surface, and
• wherein the component asymmetry comprises an anteroposterior corner asymmetry, in which:
• an anterior-medial corner of the medial periphery defines an anterior-medial corner radius, and
• an anterior-lateral corner of the lateral periphery defines an anterior-lateral corner radius that is substantially smaller than the anterior-medial corner radius,
• said step of positioning comprising:
• matching the smaller anterior-lateral corner radius to a corresponding lateral portion of the resected tibial surface, and
• matching the larger anterior-medial radius to a corresponding medial portion of the resected tibial surface;
• and
• providing a tibial bearing component comprising:
• a lateral bearing portion which substantially corresponds to the lateral periphery of the tibial baseplate;
• and
• a medial bearing portion which is at least partially incongruent with the medial periphery of the tibial baseplate.