Technical Abstract: Osteoarthritis is the leading cause of joint pain and lower extremity disability in older adults and there is no known cure. Vitamin K has been implicated on osteoarthritis because vitamin K dependent proteins are present in joint tissues, such as cartilage and bone. In order to function, vitamin K dependent proteins must be carboxylated, which requires vitamin K. Ex vivo experiments found vitamin K dependent proteins in joint tissues from patients with osteoarthritis were undercarboxylated (less functional) and several observational studies found lower vitamin K nutritional status was associated with more osteoarthritis, as summarized in this review. Because there are no clinical trials that have been designed specifically to test the effect of vitamin K supplementation on osteoarthritis, whether vitamin K supplementation improved osteoarthritis and related pain and disability remains to be determined.