Patellar subluxation is usually lateral. During treatment, at which knee flexion angle is the patella most stable?

• A. 0 degrees
• B. 45 degrees
• C. 90 degrees
• D. 135 degrees

Answer: (C)

Stability of the patella hinges on how well it sits within the trochlear groove of the femur and how the surrounding soft tissues guide and restrain its movement. When the knee is nearly straight, the patella rests atop the groove and can be pulled laterally by the Q-angle, so it isn’t as well confined. As the knee moves into mid-range flexion, the patellar facets engage the trochlear groove more fully, increasing the contact area and the compressive forces that press the patella into place. At this position, the medial stabilizers of the knee, including the medial patellofemoral ligament and the vastus medialis obliquus, also provide stronger medial restraint as the muscle is activated, further reducing lateral drift. This combination of greater bony congruence and stronger soft-tissue support makes the patella most stable in mid-range flexion.