I was in the London Marathon last weekend and doing really well for my goal until just after 28km I felt my right knee begin to hurt like my left did last year when I wrecked my IT band. Last year I didn't know what it was and thought it was just soreness, so when it began to hurt with 5km left I just ran on through increasingly bad pain each step. Long story short: I finished but took the entire summer getting back to running with a lot of physio.
This year my knee moved from discomfort to pain around 32km and I stopped before 33km, having tried twice to rest/stretch and restart without any improvement. My own fault: I wasn't diligent enough with the physio exercises after I got 'better'. Did a couple of halfs late last year and thought I was fixed so got lazy with the strength training.
I did consider just walking/hobbling to the end, but figured it would take at least 90 minutes or so if not longer (I wasn't walking great either by this point) so I didn't. Alas, it was a DNF for me.
It got me thinking: How far would you push on to finish? Obviously if I'd passed Mile 26 I'd have crawled the final few hundred metres if it came to it. 3km? I'd walk that in pain. 5km? Mmmmaybe.
You?