If your vit D level is within n normal limit then no need to take more supplements, so get the blood test repeated for the same and keep vit D level normal by sitting in sunlight for 10-15 min everyday, take milk, egg yolks, mushrooms. Besides that you should be doing knee strengthening exercise everyday after consulting a physiotherapist. Also omega 3 is good for joints. Can take fish, avocado,nuts for that.