Knee replacements can become loose in time. This tends to occur after about 10 – 15 years and depends a lot on the initial age of the patient at the time of the original surgery and their activity level. The reason this tends to happen is related to wear of the moving parts of the knee in particular the polyethylene insert. The particles released from the wear of this component leads to loosening because the interface between the cement the bone tends to be eaten away (osteolysis). A loose knee replacement starts to become painful. Occasionally it may be possible to exchange the polyethylene insert before the whole knee has become loose and that is why regular follow-up of the replacement by x-ray is important particularly after it has been in place for 10 years.
If a knee replacement does become loose it is possible to re-do but it must be understood that this is a a significantly more complex procedure than the primary operation. Often bone defects have to be built up with substitutes and specialised implants may be required to obtain good fixation in the bone and stability of the knee. Quite commonly the knee becomes a bit stiffer after such a procedure but in most cases good results can be achieved with good function.
content written by Johan Witt Hip othopaedic and trauma surgeon
