Knee pain with first half marathon Sunday!

Hello I have been training for 12 weeks nows for my first half marathon and my training has gone really well up until recently.On and off my left knee has been playing up.It becomes swollen behind the knee cap and sore to touch above the knee cap slightly to the left.Did a 9 mile run on Sunday and at about 6 miles the pain came back and I can only bend my knee slightly.I managed to make it home but slower than usual.I havent run at all this week as my first half marathon is on Sunday and I was hoping the rest would help but unfortunately it is no better.Anti inflammotary tablets work perfectly but should I chance it?

I am devastated.Any ideas?

If it hasn't improved at all in the last 5 days, you'd be silly to risk it. You could make it a lot worse and something that right now might take a couple of weeks to heal could end up ruining your running training for the next few months if not more. That said, if I was in your position I'd more than likely just double-dose the ibuprofen, grit my teeth and shuffle round. Of course that attitude is probably why I'm always carrying minor injuries and I'm really trying to stop being stupid and rest up when I need to.

In the end it's your choice but remember while there are loads of other half marathons out there, you only have one left knee!