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Sorry for the delay, and sorry that no one else took you question about a remarkable bird.
Quick answer, yes he needs to see a vet.
Is it the covering of the spur or the base where it taches to the leg? Is it the skin and scales that are swollwn, or the actual bone?
He could have a bone infection, even related to the fox incident.
At very minimum, if he were my patient I would get some radiographs of his whole body, including both legs; really examine carefully the area of fox attack as well as the spurs. I would definitely start him on bone-effective antibiotics and pain control. Treatment beyond that would depend on what was found; it might even include spur removal or surgery.
BTW an effective pain control is butorphanol and diazepam, which also works great to calm him if he is not cooperative. Ask your vet about this.