Which joint allows free distal end motion such as the shoulder?

• A. Ball-and-socket joint
• B. Pivot joint
• C. Hinge joint
• D. Gliding joint

Answer: (A)

Movement versatility at a joint is determined by its structure. The shoulder needs to move in many directions, so the joint involved must allow motion around multiple axes. A ball-and-socket joint does exactly that: a rounded head fits into a cup-like socket, enabling flexion and extension, abduction and adduction, internal and external rotation, and circumduction. This multiaxial freedom is what lets the arm move so freely relative to the torso, which is why the shoulder is described as having free distal-end motion.

In contrast, pivot joints rotate around a single axis, hinge joints bend in one plane, and gliding joints allow primarily sliding movements with limited directions.