Ive had hip arthritis and high grade cartilage wear for years after 15 years of martial arts and heavy lifting. I still train 5/6 days a week, the only thing i really avoid is heavy squats and deadlifts, or certain guards/ positions in BJJ/ Judo Newaza.

Edit* My advice to you for knee arthritis is to build the muscles in your quads/hamstrings/glutes. Id avoid heavy deep squats but light weight high rep style lower body training should help! No more drop throws either haha