Fun Science-y fact : The main reason Broccoli helps arthritis is because arthritis is worsened by inflammation and broccoli has way more Omega-3 than Omega-6 and generally reduces Omega-6 consumption in the diet
This isn't to say fish is good for this however due to contaminates in it, as well as most high Omega-3 fish has tons of Omega-6 too.
The best solution is vegetables, fruits are good too, and some Chia/Hemp/Flax seeds regularly :)
Broccoli has a variety of compounds that reduce inflammation other than Omega-3 fatty acids as well.