My mom had a knee replacement on both knees a couple of years back. She's 69 now and recently, over the last three months, her left ankle has been swelling up daily. It's concerning because she's also developed these black patches around the back of her ankle, and they've been itchy for about 15 days now. We've seen doctors and done some tests, but we're not getting any answers. The swelling's causing her a lot of pain, and she can't walk properly. Could you shed some light on what's going on here? Any insights you might have would be really appreciated.