My cat is stuck wearing a cone.

A year ago my cat had an IV in his leg at the vets and when he came back, his paw was swollen and ever since he has been constantly biting the site where the IV went in and causing it to bleed. We've taken him back to the vets multiple times but they say they don't know why this is happening, they've tried to link it to stress, and have tried steroids and many different sprays but nothing has changed. Having the cone on stops him chewing his leg but I want to help and understand why this is happening.

Oh no, poor boy! OK, so there are a number of possible issues here, but I quite agree, it's not really fair on him to wear a cone long term, so it might be worth exploring a referral or a second opinion to try to get to the bottom of the issue. My immediate thought having read this that maybe there is thrombophlebitis (inflammation and clotting within the vessel) causing ongoing discomfort - but after a year I would have expected that to have settled down. It might be that there is some sort of ongoing inflammatory process that hasn't been found - but again, I would have expected some improvement on steroids in that case. Another (and I think perhaps more likely) avenue to explore would be a chronic or neuropathic pain issue. The nerves run along the outside of the blood vessels and in very rare cases they can be irritated during an IV. Normally, this will resolve rapidly, but occasionally (for reasons we do not fully understand), the nerves get into a chronic state of sending "pain" signals even though the damage has healed. This is a form of chronic pain, and while complex, is usually manageable (or even treatable). The third option is whether this might be a behavioural issues - a learned response of some sort. So I think these are areas to discuss with your vet, and see if there are any other options they can explore. If not, then I would recommend considering a second opinion or, better, referral (ideally to a multidisciplinary clinic or hospital who can rule in or out lots of different options). Good luck, hope it all goes well!