I had ACL replacement/MCL repair, not TKR, and suffered numbness for more than a year afterward. It was bad enough that I could not walk on any uneven surface without watching my foot, lest I trip & fall. Sometime between 18-20 months, it got better. It took the nerve damaged during surgery that long to regenerate, and I was only 44 years old at the time. Fast forward 16 years, and I had numbness down the side of my leg after revision of a total hip replacement. That extended from thigh to mid-calf, and was mainly annoying, but I would find myself with cuts, bruises or scrapes I never felt - it took nearly 3 years to resolve.
My ortho says nerve regeneration is notoriously slow and uncertain in anyone with other circulatory issues.
Sue