>Hypothyroidism is a common cause of adrenal insufficiency, but it also has some direct effects on joint tissues. In chronic hypothyroidism (myxedema and cretinism), knees and elbows are often bent abnormally.
…
>Besides many people whose arthritis improved with only thyroid supplementation, I have seen 30 people use one or more of these other natural hormones for various types of arthritis, usually with a topical application. Often the pain is relieved within a few minutes. I know of several other people who used progesterone topically for inflamed tendons, damaged cartilage, or other inflammations. Only one of these, a woman with rheumatoid arthritis in many joints, had no significant improvement. An hour after she had applied it to her hands and feet, she enthusiastically reported that her ankle had stopped hurting, but after this she said she had no noticeable improvement.
http://raypeat.com/articles/articles/tissue-destruction.shtml
>The hyperhydration of hypothyroidism has been known to cause swelling and softening of cartilage, with deformation of joints, but somehow it has never dawned on surgeons that this process would lead to deformation of intervertebral disks.
http://raypeat.com/articles/articles/water.shtml
>Around the same time (early 1940s) that the effects of thyroid on bone development were being demonstrated, progesterone was found to prevent age-related changes in bones, and "excessive" seeming doses of thyroid were found to prevent age-related joint diseases in rats.
http://raypeat.com/articles/articles/osteoporosis.shtml
>This study indicates that niacinamide may have a role in the treatment of osteoarthritis. Niacinamide improved the global impact of osteoarthritis, improved joint flexibility, reduced inflammation, and allowed for reduction in standard anti-inflammatory medications when compared to placebo. More extensive evaluation of niacinamide in arthritis is warranted.
https://link.springer.com/article/10.1007/BF02252945
The nitric oxide hypothesis of aging.
>Tetracyclines have now been studied in chondral cell cultures from patients with osteoarthritis and in cell cultures from animals with experimentally produced arthritis. They have been shown to have chondro-protective effects (Amin et al., 1996). NO is spontaneously released from human cartilage affected by osteo- or rheumatoid arthritis in quantities sufficient to cause cartilage damage. In a recent report, tetracyclines have been shown to reduce the expression and function of human osteoarthritis-effected NOS (iNOS) (Amin et al., 1996). It appears that in addition to the antibacterial action of these drugs, tetracyclines inhibit the expression of NOS, leading to reduction in the toxic consequences of production of NO. It is likely that these compounds will be beneficial in the treatment of osteoarthritis, as well as CHD. They will also probably be of therapeutic value in rheumatoid arthritis and cardiomyopathy, both thought to be autoimmune diseases caused largely by excess NO.
http://www.ncbi.nlm.nih.gov/pubmed/9951625
>A new study from Keith Baar’s Functional Molecular Biology Laboratory at the UC Davis College of Biological Sciences and the Australian Institute of Sport suggests that consuming a gelatin supplement, plus a burst of intensive exercise, can help build ligaments, tendons and bones. The study is published in the January issue of the American Journal of Clinical Nutrition.
http://blogs.ucdavis.edu/egghead/2016/12/19/gelatin-supplements-good-joints/