I can confirm the exact cause only after a complete medical evaluation. Many conditions can cause red bumps on finger joints. In dermatomyositis there is appearance of purple or red rash commonly seen on knuckles, eyelids, knees or toes along with muscle weakness. The treatment options are corticosteroid drugs, heat therapy, physical therapy. In Granuloma annulare there are red, purple, skin-colored or pearly white bumps or ring-shaped lesions on hands, feet, elbows or knees. In rheumatoid arthritis almost 25 percent people may develop rheumatoid nodules which are pink or reddish bumps on the affected joints that are firm, moveable and not painful. In lichen planus there are itchy, purplish-red flat-topped bumps on the fingers, wrists and ankles. Seeking the opinion of a dermatologist will definitely help. Treatment is specific based on the cause. I hope it helps.
Best of luck and regards!