I had this quite badly about a year ago. I did no running for about a month and hit the bike instead. High cadence, low resistance (mind numbed) on the turbotrainer was what the physio ordered. I started running about once every three days (cycling others) and built up over the next month to the point where I was running most days two months out.

This isn't going to be a popular observation on a fell running forum, but one thing that is probably a factor is gradient. You may find that you can run on the flat before you can tackle the ups and (especially) the downs. This was OK for me at the time, because I was marathon training, so I stuck (mainly) to the flat for a while after.

My personal conviction is that a lot of it is down to how you run. The PT was my first significant running injury. I had my "Born to Run" moment and worked at changing how I ran over the summer. I still had minor flare ups occasionally on the downhills but any pain was momentary and didn't stick around - I tried to use it as an early warning system to help me develop my technique. It seemed to work. The flare ups went and over the second half of last year I ran more.

Everything was going well until I developed some foot pain a week or so ago. I diagnosed that to be down to ill fitting shoes, but I think running with the pain affected my form and by the time I had found shoes that got rid of the foot pain I had patella tendonitis again.

I don't know whether the PT would have reoccured had I not had the foot issue. I like to think not, but of course I'll never know. Thankfully it doesn't seem to be so bad this time. Pain walking up and down stairs the day after has now cleared and I'm optimistic that I may be able to run again in a week or two. One thing that's helped is not trying to run through it when it first occurred. That definitely made things a lot worse first time round. This time around I'm also going to try and be more diligent with the strengthening exercises and to keep them up after the injury's gone, as PT evidently is something I'm prone to.

Much sympathy and best of luck to all you fellow sufferers!