THERE ARE OTHER ARTHRITIS-RELATED CONDITIONS that aren't considered rare, but are not as common or prevalent as osteoarthritis and rheumatoid arthritis. Some of the less-common types of arthritis can occur as primary diseases or as secondary conditions; it's possible to have more than one type of arthritis. Because of the complexity of each of the conditions and the possibility of overlapping symptoms, it can't be emphasized enough that your doctor must serve as the detective.