I just looked a your pictures from the other thread and the scaly leg mites seem to cause pain as well. This needs immediate treatment.
There are a lot of videos on how to remove or trim rooster spurs, maybe one of this two might work for you:
This might be caused by his own overgrown spurs that with each step he takes excoriate the inside of his joints. And even roosting at night will be painful too as the spurs will pierce his body while doing so.
To be sure watch him closely as he walks and try to determine where exactly his spurs...