Isn't the eliptical easy on the knees? Or, if you have a pool nearby, swimming is GREAT rehab.

I've been battling knee problems for 24 years and think, at the moment, you should get plenty of rest. Get an icepack on it (bag of frozen peas with a thin towel wrapped round will do the trick) and take some anti-inflammatories (ibuprofen or asprin if you can tolerate them).

If the pain eases up, then walking on the flat should be fine. But be really careful to not overdo it as you could aggravate the injury.

You also need to have a think about how to prevent further problems. Some thoughts:

1. Have you got good running shoes? Problems with feet and your gait can cause knee problems. If the problem persists you may want to see a podiatrist to check your gait is correct (after 24 years of pain I've finally been able to start running thanks to a couple of visits to a podiatrist and some custom-adapted orthotic insoles - total cost around £100).

2. I find jumpers straps really help support my knees. I've got a pair of Mueller knee straps from Amazon - not expensive and stop the kneecap from moving around too much, which can cause pain.

3. Once the pain has stopped, work on strengthening the muscles around your knees. My favourite is the simple squat. When my knees are particularly crunchy I stand up, lower myself into a squat then just hold it for as long as I can (good one to do when watching TV). When my knees are less creaky I do proper squats up and down. Google for knee exercises to increase strength - YouTube is a good starting point. My 70-year-old mum has arthritis and when I'm round at hers we do her physio-prescribed exercises together!

Hope you feel better soon.