With regards to total knee replacement, what are the symptoms of a failing prosthesis?

Pain: Pain, swelling, difficulty with ambulation, sensation the the knee is going to give-out, however the most common symptom is pain.

Pain and swelling: A "failing" prosthesis implies some type of mechanical failure of the knee replacement. Symptoms usually include pain, swelling, warmth to touch; may also experience weakness or instability. An orthopaedic consult with xrays is recommended.