When you go into the cold, the bones are part of your body and contain marrow, nerves, and life, along with other forms that make up the structure of bone.
When you have the joint replaced and that is now metal, (Titanium) it isn't the same. Metal absorbs cold much faster than bone. When the metal gets cold, it makes the bone (implant) and the meat around it cold. The active bone and meat have nerves that when cold, will produce a pain.
Bone will be kept warm by the blood around it while metal has NO blood around it other than the meat.
If you break a bone, it hurts. If your joint has deposit, it hurts. Bone heals while metal doesn't.
On the other hand, metal joint replacements don't hurt.
Obviously I am not a doctor and might be explaining this a bit different, but when my hips get cold, they hurt like the dickens till they warm up. After that, its OK............