Pain can mean many different things. Burning, stabbing, stinging, itching, heavy, pounding, throbbing, freezing, cutting, prickling... There's so many.
There's the pain of dead muscle tissue in his thigh... and the pain of walking without the muscle anymore.
And, sometimes, there's something to counteract the pain. Like Vicodin, or morphine. And the user develops a dependence on the thing that gives them release from pain. The pain doesn't go away, because everything is a reminder; the cane, the limp, the stares he receives.
He can't ever forget that the pain will come back so much worse the next time he goes longer than four hours without a pill. Three hours. Two. He's pushing the maximum dosage, he's going to overdose if he's not careful - but he never does, because, as much as he hates the pain, he hates the thought of proving everyone right and actually killing himself.
As much as he's dependent on the painkillers themselves, he's even more tied to his supplier. He can't write his own subscriptions, because then he might prescribe himself too much and sell it, or do something equally naughty. It's not exactly clear how having his best friend write them for him, incredibly overstating the dosage is better, but it had worked for years, despite said friend's protests.
So, he was tied to his best friend for life. At least the man was a good cook.
Pain is so many things that, logically, something good would eventually crop up.