ARTHROPLASTY

In a standard posterior-stabilized (PS) total knee arthroplasty, the primary function of the cam-and-post mechanism is to substitute for the excised posterior cruciate ligament (PCL). During what phase of knee range of motion does the femoral cam typically engage the tibial post to facilitate femoral rollback?

A 0 to 30 degrees of flexion
B Terminal extension
C 30 to 45 degrees of flexion
D 70 to 90 degrees of flexion and beyond