True or False: Concave surfaces moving on a convex surface exhibit a roll and glide that happens in the same direction.

• A. True
• B. False
• C. Depending on the joint
• D. Not applicable

Answer: (A)

The correct response is that concave surfaces moving on convex surfaces do indeed exhibit a roll and glide in the same direction. This relationship is based on the principles of arthrokinematics, which describe the motion that occurs between the articular surfaces of joints during movement.

When a concave surface (like the socket of a joint) translates along a convex surface (like the head of a bone), it rolls in the same direction as the movement of the bone is occurring. For example, if the convex surface is moving in a certain direction, the concave surface rolls in that same direction, while also gliding in accordance with the mechanics of the joint. This synchronous motion ensures that the joint is stable and functional throughout its range of movement, facilitating smooth articulation between bones.

Understanding this principle is key for professionals working in clinical biomechanics, as it enables accurate assessments and interventions related to joint function and movement mechanics.