I've had Right Knee Replacement Surgery twice, the first time I too experienced the numbness in my foot, nerves are disturbed when the replacement surgery is done. If the numbness does not go away in a few weeks time of healing then you should tell your Orthopedic Surgeon. There is a lot of stuff going on with healing after this type of surgery and it could be that that is what is going on. Keep in mind too that the healing process for knee replacements are up to one year afterwards for a complete healing, the knee is very unsettled until after the first six months. Any time bone is cut it takes exactly one year for the bone to begin filling in and healing around the hardware. This is what I was told by my surgeon's both for my foot after I had a joint replacement and my knee replacements. (Please don't panic about needing another surgery, I was in a high speed auto accident on the freeway before my knee was completely healed, otherwise I would NOT have needed the second, the revision).
How far post op are you from having this surgery? Is there any redness, pain, swelling, hot/cold to the touch? Is there any drainage going on around the incision sight?
Here's a great link to look at so that you can understand all the things that they did to your knee and you'll see how much the anatomy of the knee has to accommodate the hardware and why you might be going through the numbness.
Did your surgeon fully explaint this surgery to you and the healing process? Did you already go through the physical therapy and rehabilitaion portion of the post operative process? They have to open the knee up very widely with the instruments to gain access.
Bottom Line: Remember if it doesn't go away or worsens to contact your Ortho Surgeon who might want to do a follow up with a Neuro for a nerve conduction test to see if the nerves are healing properly or damaged somehow. Swelling in the knee is expected and it too can press on nerves causing this sensation.
RICE-Rest, Ice, Compression, Elevation...
Elevate your knee after you've been up on it and ice it. If it's been a while since you've had the surgery you can also do a contrast (depending on how long it's been).
Good luck to you...
Contrast meaning ...first ice, then heat, and always, always end up with the ice at the end of doing this. The ice is what takes the swelling down, the heat helps with the healing portion. Do not use ice DIRECTLY on your skin, place a hand towel or bath towel between it and the ice so that you do not damage your skin. You shouldn't leave the ice on any longer than it takes for the skin to feel numb. The ONLY time that my ice was ever on to the point of stinging was after I had done physical therapy and I was under the therapist's care, but I always had a towel between my skin and the ice.
Now that I'm a year out of surgery, I just use heat because I have some pain periodically if I'm up on it too long, running around all day or working on it all day can cause it to swell. Chronic pain care is to apply heat.
JUST A TIDBIT OF ADVICE: If you fly on the airlines, it's a good idea to get a note to always carry from your Orthopedic Surgeon noting that you've had a knee replacement surgery. YOU WILL SET OFF THE AIRPORT DETECTORS AS YOU PASS THROUGH THEM, AND COURTHOUSE SECURITY SYSTEMS. They'll ask you to go over to the side where they will have you remove your socks and shoes, and use the hand wand over your entire body. It takes a few extra minutes to get through security checkpoints but there's no way around it and you have to add extra time to when you must check in to go on the planes or into the courthouse. Just think of it as they're doing it FOR YOU and it's not so bad~you're safety is their concern and their job.
When you use heat (if by heating pad) if you turn it on a temp that's too high, it will cause a mottled (splotchy) appearance on your skin. This will go away over time but be really cognitive about the time and degree of heat or cold that you leave on your knee.