Why might it be that someone have popping and pain in their hip after having a cement spacer put in?

A couple things... The most concerning issue is the hardware coming loose. This is uncommon but does occur. Another issue can be just an osteophyte that may have formed that is causing some clicking.Some muscular issues can cause a popping in you hip and their is actually a syndrome called snapping hip syndrome, with structures depending on medial or lateral snapping.I would recommend you discuss it with your ortho.