if u do replacement in gov hospital, doctors will tell u it can last up to 10-15 years if you never overwork the metal in your kneel or joint, which means no extreme exercise or sport or accidents. ( i know a few rich uncles and aunties went to private hospital for titanium joint replacements which supposed to last forever if no infection or accident )
for infections wise, when u do any dental, u will require to eat antibiotics beforehand to prevent infections. virtually any infections big or small has chance to cause problems for any implant or anything not natural in your body. as long as u fall sick or don't feel right, see doctors and you are prolly safe.
recovery from surgery is based on how good is your doctor doing the operation, your age regeneration and how positive you are. for example, i myself had a hip replacement done around age 30, i can move and walk around with crutches on 2nd day after operation, i discharged from hospital on 4th day. after 2 weeks, i can go for my regular checkup at hospital without using crutches. rehab took about 2 months which is about 5-6 hospital rehab visits. (this is sharing my personal experience, please don't flame me, thanks)
the elders i knew (betweens age 45-60) who did kneel or hip replacements took about double to triple of my recovery time, but 1 of them is very negative and lazy to walk/move his body, stays on wheelchair till now.
so i hope my long post actually helps. all i can say, good luck, anything good or bad can happen, theres no 100% success for all medical cases. ( quotes from many doctors in hospital )