It's the ball moving in a cup

正是这个球状物在杯状结构里的运动
that creates all of this versatility of motion;

造就了运动的多样性
you can swing it around different ways.

你能够以不同方法转动它
Well, when this joint gets diseased,

那么当这个关节染病时
movement becomes much more difficult.

运动就会变得非常困难
In general, it's a degenerative disease that the bones

总体而言这是一种退行性疾病
and the cartilage start to break down,

骨头和软骨开始出现故障
and so now this cup

此时杯状结构
and ball don't move so smoothly over one another.

和球状物便不能顺滑地相互运动
When they don't move smoothly over another,

因为运动不顺滑
they generate friction, they generate pain.

便产生了摩擦力产生了疼痛
So, degenerating hips can cause tremendous amounts of pain for people.

衰退的髋部能给人造成极大的疼痛