Could a poor bike fit be the cause for osteoarthritis in an otherwise healthy 39 year old male racer like myself? I got a new bike last summer and installed new Zipp SL-70 aero bars this spring and now my thumbs have CMC OA according to an orthopedic doctor. I’ve been wearing specialty hand splints for the past several weeks and on medication but it’s not getting any better. I’ve only been riding about 3 days a week this last summer since the race season ended but I’m usually 5 days a week.