Members of the nightshade family (such as aubergines, peppers, tomatoes, potatoes etc) should be avoided for dogs that have arthritis. If not, then it's absolutely fine to feed them.
I don't know if there is scientific evidence to back it up but there is anecdotal evidence (from arthritis sufferers) to suggest that they may exacerbate the symptoms so best to avoid them in dogs known to be arthritic just to be on the safe side :)