An otherwise healthy patient has advanced osteoarthritis in the medial compartment of the right knee. Which gait deviation during stance phase on the right lower extremity is MOST likely?

• A. Left trunk lean
• B. Right trunk lean
• C. Forward trunk lean
• D. Backward trunk lean

Answer: (B)

In medial-compartment knee OA, the body tends to unload the stressed medial joint by reducing the external knee adduction moment during stance. Leaning the trunk toward the stance leg moves the center of gravity closer to that knee, which shortens the lever arm of the ground reaction force in the frontal plane. This lowers the knee adduction moment and decreases the medial compartment load, making this posture a common, protective adjustment during stance on the affected side. Leaning toward the opposite side wouldn’t lessen the medial load and could even increase it, while forward or backward trunk tilts don’t specifically address the frontal-plane moment at the knee.