Tell me if this is what you are describing?
Is the front bone on the pectoral fin sticking out of the skin on the fin? Like it's pertruding forward almost?
If so, the fin will never regrow around that bone.
I have had this happen with a large Japanese Koi quite a few years ago, we had to sedate it and cut the front bone. Yes the bone will never regrow, but the wound will be allowed to heal. We did this with a 24" koi and it is still swimming to this day.
Now, I don't know how this applies to a much smaller fish and in particular the fish species your dealing with. Also like what has been mention in previous posts, your dealing with a venomous fish, so even more care needs to be given.
I'll describe the process here in case it helps you and your situation.
I was not experienced enough to do this by myself, I didn't have enough knowledge, so a very close friend came to help. We caught the fish and placed into a holding bowl, we used an off the shelf fish sedative/anaesthetic (can't remember the name) and poured a few drops into the bowl. We then took a couple of towels and dunked them into the pond water (not the water in the bowl), soaking them through. After a few minutes the fish was knocked out. We used the wet towels to pull the fish out and wrapped the wet towels around the body and covered the eyes (this is important to keep the fish moist and also keep the fish calm and stable) leave the pectoral fin area open. He used a lot of iodine on the open wound and around his fin. He used some nice quality bone cutters and cut the front bone as low down as possible without pressing the cutters against the body of the fish to do so. This will eventually allow the skin around the fin to regrow around the bone (that is now not pertruding forward)
After cutting the bone, it bled quite a bit and I was certainly very concerned, he poured on a bunch more iodine on the wound, and then unwrapped some of the towels and placed back into the pond. (Here's the tricky part for you) we then held the fish in the water so it was stable until the anaesthetic wore off, and he was able to swim away under his own power.
If I was to do this, I personally would place back into the DT unless you are very very experienced with working with a QT. The water params need to be pristine, and also need to limit stress to help the wound heal. Placing into a Temporary QT will freak the fish out (especially a foxface) and params if not monitored closely can be unstable.
The benefit of placing in a QT is that you'll then be able to use antibiotics to help heal the wound.
It's your call on this tbh, if you don't feel comfortable and confident with QTing, I would recommend placing back into DT and keeping water as clean as possible, it's been in the tank 6 months with the wound as it is, so now that it has a chance to heal I think it would be okay
Hazards here are:
Dosing correct amount of anaesthetic, and picking the right anaesthetic.
Timing.
Dealing with venomous spines.
Hope his help.
