If your hip or knee replacement doesn’t feel quite right, you’re not alone in wondering why. Mr Sulaiman Alazzawi, who specialises in revision hip and knee surgery, answers the questions patients ask most often about loosening – what causes it, what to look out for, and when to seek an assessment.

What causes a joint replacement to loosen?

Joint replacements are built to last, but over time the bond between implant and bone can weaken. This is known as aseptic loosening, and it’s the leading cause of long-term failure in total joint arthroplasty, driven by a complex interaction between the implant’s materials and the body’s own immune response to wear debris. It’s a gradual process rather than a single event, and it can take years to become noticeable.

What symptoms should I watch for?

The most common early sign is pain in the joint, particularly when walking or standing for long periods, along with swelling, stiffness, or a sense that the joint feels unstable or isn’t working as well as it used to. These symptoms can appear within months of surgery, though they more commonly develop many years after the original replacement.

How is loosening diagnosed?

Diagnosis usually starts with an X-ray, looking for signs such as implant migration, radiolucent lines around the components, or cysts in the surrounding bone – though these changes can take time to appear. Pain alone isn’t a reliable indicator, since pain following a hip or knee replacement can have several causes and isn’t specific to loosening on its own. This is why a thorough assessment, combining imaging with a physical examination and your surgical history, is important before deciding on next steps.

Could it be infection rather than loosening?

It’s not always straightforward to tell loosening and infection apart, and the two can overlap.

One study of patients undergoing revision surgery for presumed aseptic loosening found that just over 12% actually had an underlying periprosthetic joint infection, and those patients had a significantly higher rate of implant failure at two-year follow-up than those with true aseptic loosening. This is one reason blood tests and joint fluid analysis are often carried out alongside imaging, to rule out infection before planning revision surgery.

What happens next?

If loosening is confirmed, revision surgery is usually needed to secure or replace the affected components. The right procedure depends on how much bone has been affected and which parts of the implant are loose.

If you’re experiencing ongoing pain or a change in how your hip or knee replacement feels, get in touch for an assessment.