Which statement best describes mobile joints compared to stable joints?

• A. Mobile Joints Are Designed to Move in Three Planes; Stable Joints Move in One Plane
• B. Mobile Joints Have Less Range of Motion Than Stable Joints
• C. Mobile Joints Are More Stable Structurally Than Stable Joints
• D. Mobile Joints Are Found Only in the Upper Limbs

Answer: (A)

Movement capability across anatomical planes is the key idea here. Mobile joints are built to allow motion in three planes—sagittal, frontal, and transverse—giving them rich, versatile movement but with less inherent bony stability. Stable joints, by contrast, are arranged to limit motion mostly to a single plane to maximize stability, relying more on ligaments, muscles, and joint congruence than on bone shape. For example, ball-and-socket joints such as the shoulder and hip can move in multiple directions and planes, while hinge joints like the elbow primarily flex and extend in one plane. The statement captures this general trade-off between mobility and stability. The other choices don’t fit: mobile joints don’t have less range of motion; they’re not structurally more stable; and mobile joints aren’t confined to the upper limbs.