What forces act on the knee during single limb stance?

During single limb stance, the knee experiences various forces that impact its stability and function. The correct answer emphasizes the valgus thrust on the knee, which can occur due to a lateral shift of the body's center of mass. This lateral shift often happens when a person is standing on one limb, leading to an increased lateral load on the knee joint.

In this scenario, the forces from other parts of the body, particularly the hip and torso, may create a mechanical advantage that leads to a valgus moment at the knee. This necessitates effective management by the knee's soft tissue structures and ligaments to maintain proper alignment and prevent injury.

The other choices pertain to different types of forces that may not be as directly relevant in this specific context. Compressive forces from the hip extensor muscles are generally felt during activities involving hip extension rather than standing alone, while tensile forces from knee flexors are mainly engaged during knee flexion, not in a static stance. Normal contact forces from the ground do exist but do not specifically highlight the unique mechanics involved in a single limb stance as does the valgus thrust. Thus, the emphasis on the valgus thrust is key in understanding the forces acting on the knee in this particular position.