Orthopedic prostheses are commonly utilized to repair or replace damaged bone and tissue in a human body. A knee prosthesis, for example, can include a tibial component or a femoral component to replace damaged or destroyed bone in the tibia or femur, respectively. Knee prostheses can seek to provide articulation similar to an anatomical articulation of a natural knee joint.
Total knee replacement (TKR) surgery can involve the implantation of several components meant to restore the functionality provided by a natural knee. Typical TKR components include a tibial component, a femoral component, and/or an insert or bearing component disposed between the tibial and femoral components.
In certain TKR prostheses, which are oftentimes referred to as “posterior stabilized” prostheses, a cam positioned in an intercondylar fossa of a femoral component cooperates with a spine formed in a tibial component to guide or constrain motion within predefined boundaries. Posterior stabilized prostheses can include a spine integrally formed with a tibial bearing insert (sometimes referred to as a meniscal component), which interacts with a cam formed in a femoral component to promote femoral roll back during flexion of the TKR prosthesis. Posterior stabilized prostheses can be appropriate where a posterior cruciate ligament (PCL) is torn or otherwise damaged, or where the PCL is resected during surgery.
In addition, some knee prostheses feature a hyperextension stop, which can be a posterior-facing structure formed in a femoral component configured to engage an anterior-facing surface of the tibial spine when the knee prosthesis is in a “full extension” or “hyperextension” orientation. Such a hyperextension stop can also be referred to as an anterior cam. In these knee prostheses, interaction between the femoral component and spine operates as a physical stop against extension of the knee prosthesis past a predetermined level of extension.
A natural knee experiences internal and external rotation, i.e., rotation about a generally proximal-distal axis, during flexion. Internal/external rotation can be significant in deep flexion where an asymmetric anteroposterior rollback can occur, i.e., the lateral femoral condyle rolls back faster and/or further than the medial condyle. Internal/external rotation is also significant as the natural knee approaches extension (i.e., 0-20 degrees), a phenomenon sometimes referred to as the “screw-home” mechanism. Knee prosthesis designs can seek to accommodate, promote or drive internal/external rotation mimicking the natural knee.