National Physical Therapy Examination (NPTE) Practice Exam

To unlock the knee from terminal extension in a closed kinetic chain, which action must occur?

1. ER of femur on tibia

2. Superior glide of patella on femur

3. ER of tibia on femur

4. Long axis distraction at the knee joint

The correct answer is: ER of femur on tibia

Unlocking the knee from terminal extension in a closed kinetic chain primarily involves the external rotation of the femur on the tibia. At terminal extension, the tibia is typically in a position of stability, and to initiate flexion, there needs to be a slight rotation that allows the knee joint to unlock. This movement facilitates the transition from the fully extended position to flexion by reducing the bony congruence of the joint, enabling easier movement. When the femur externally rotates, it helps to create enough space in the joint for the subsequent flexion movement to occur. This action also aligns the joint surfaces in a way that is conducive to movement, allowing the ligaments and associated structures to function effectively as the knee transitions from stability to mobility. In contrast, while the other options might involve various movements at the knee complex, they do not specifically facilitate the unlocking of the knee from full extension in the manner that femoral external rotation does. The superior glide of the patella might occur with knee flexion, but it is not the mechanism that initiates unlocking. Similarly, the external rotation of the tibia on the femur and long axis distraction do not serve as the primary action for unlocking the knee in a closed kinetic chain scenario.