to you and Harry! OMG - I'm so sorry Harry broke his leg. Hoping it heals fast and well.
Re his arthritis: See if Harry likes walnuts too as they are rich in Omega 3 oils which are good for inflammation. You can also sprinkle freshly ground flaxseed over his food (especially rich in Omega 3). Turmeric might also help since it is a natural anti-inflammatory. Someone here recommended this product which contains the curcumin without the taste:
Natural Factors Curcumin Rich Turmeric Root (30mg, 60 Vegetarian Capsules): Amazon.co.uk: Health & Personal Care
I have an elderly Amazon with arthritis. I keep him in his large cage but have made a padded platform for him. It's wood slats covered with non toxic upholstery foam, a towel and then dog pee pads which are easy to throw in the washing machine. Sometimes I add kitchen paper on top to absorb most of the poops.