Other factors may also influence the risk and progression of OA.4Estrogen has a physiologic effect on cartilage and bone metabolism: while both estrogen deficiency and OA occur with advancing age, observational studies on the influence of estrogen, including with hormone replacement therapy, have been inconclusive.5 It has been suggested that vitamin D and K deficiencies contribute to the development of OA.4 Inflammatory arthritides such as rheumatoid arthritis and systemic lupus erythematosus can injure cartilage and bone and result in secondary OA changes.