At which degree of knee flexion do special tests help to isolate the MCL and LCL?

The correct answer is based on the understanding of knee anatomy and biomechanics. Special tests for the medial collateral ligament (MCL) and lateral collateral ligament (LCL) are most effective at a knee flexion angle of 20-30 degrees.

At this knee flexion range, the tension on the collateral ligaments is reduced, which allows for a more accurate assessment of their integrity. Specifically, in 20-30 degrees of flexion, the ligaments are in a position where they are less influenced by the surrounding musculature and joint structures. This reduced tension allows the examiner to isolate the stress placed on the MCL and LCL, making it easier to determine if they are intact or compromised due to injury.

Using special tests at this degree of flexion provides the best leverage for testing the laxity or stability of these ligaments.