Final answer:
The MPFL is the primary restraint against lateral translation of the patella, particularly around 20 degrees of knee flexion or near full extension.
Step-by-step explanation:
The Medial Patellofemoral Ligament (MPFL) serves as the primary restraint against the lateral translation of the patella. The MPFL provides the most support at approximately 20 degrees of knee flexion or when the knee is near full extension. Beyond this point of flexion, the patella becomes more engaged with the trochlear groove on the femur, and stability is mainly provided by the bony configuration of the joint along with other soft tissues surrounding the knee. Within the knee joint, there are several important ligaments, including the tibial collateral ligament, the fibular collateral ligament, the anterior cruciate ligament (ACL), and the posterior cruciate ligament (PCL). The ACL and the PCL are intracapsular ligaments that resist hyperextension and anterior sliding of the femur, respectively, while the collateral ligaments become tight in full extension to stabilize the knee.