During lateral patellar subluxation, what knee angle provides the patella with maximum stability?

• A. 0 degrees
• B. 30 degrees
• C. 90 degrees
• D. 120 degrees

Answer: (C)

Stability of the patella comes from how well it sits in the femoral trochlea and how the soft-tissue restraints and muscles line up to keep it centered. Around 90 degrees of knee flexion the patella is most deeply seated in the groove, giving a large contact area that mechanically resists sideways movement. The medial restraints, especially the medial patellofemoral ligament and the fibers of the vastus medialis obliquus, are most effective here, while the tendons compress the patella into place. In full extension, there’s less bony guidance and the patella is more prone to lateral drift. At very shallow flexion, contact is reduced, and at deep flexion, the geometry changes in ways that can lessen medial restraint effectiveness compared with midrange. So, 90 degrees provides the best balance of bony congruence and soft-tissue tension to keep the patella from subluxing laterally.