True or False: Convex surfaces moving on a concave surface exhibit a roll and glide in opposite directions.

The statement is true because of the principles of joint movement involving convex and concave surfaces. In biomechanics, when a convex surface moves on a concave surface, the motion involves a combination of rolling and sliding (or gliding) actions. Specifically, the roll occurs in the direction of the movement of the convex surface while the glide occurs in the opposite direction relative to the direction of the movement.

This relationship is fundamental in understanding joint mechanics. For example, if a convex femoral condyle is moving over a concave tibial plateau during knee flexion, the femoral condyle rolls posteriorly (moves backward), while simultaneously gliding anteriorly (moving forward) on the tibial plateau. This action ensures that the joint surfaces maintain optimal contact and stability throughout the range of motion.

Understanding this interaction is crucial for clinicians and therapists as it assists in diagnosing and treating joint dysfunctions, understanding movement patterns, and designing effective rehabilitation protocols.