Are there any good holistic medical treatments for osteoarthritis?

Yes. Acupuncture has been shown in clinical studies to be helpful for oa of the knee. Certain suppplements may also be helpful and you can check to see if any of these may be appropriate for you: glucosamine, same, ashwagandha, boswellia, fish oil and others. Follow an anti inflammatory diet rich in whole grains, fresh fruits and vegetables and low in processed foods and fatty animal products.
Probably. Much of treatment for pain and inflammation is non pharmaceutical ( stretching, positive thinking, exercise, relaxation, heat, massage, etc). And don't forget the placebo effect! But beware of snake oils sold by practitioners who personally profit. Check the website : http://nccih.nih.org to see what really works and what is bogus. .
Avoid toxic foods. Avoid sugars, fried foods, vegatable oils like canola & soy, meats that are cured wth nitrates & nitrites, aspartame, splenda, partially hydrogenated vegetable oils, maragarine, soy based products, sweetened beverages like juice & soda, microwaved foods, artificial colors & flavors. All of these products cause damage to the cells, tissues & organs in your body contributing to various diseases.