vitamin K2

Vit K2 is more essential for heart health than cartilage loss. There's a little evidence that it may help with bone density but no conclusive tests. However green leafy veg are excellent for many health reasons, so even if it doesnt help with OA, it's definitely something worth considering anyhow. Avoid synthetic menadione (vitamin K3) and its derivatives however, it can be quite toxic.

It is mostly K1 you'll get from green veg. You may get enough K2 from diet if your dairy and meat are supplied from grass fed animals. They convert the K1 for us, we aren't very efficient at doing so. But grain fed animals cannot do it sufficiently, not even animals only "finished" with grain. The other food source of K2 is Japanese fermented soy, natto. You'll also get some from fermented veg like sauerkraut and its kin and some types of cheese, generally speaking fermented forms of dairy.

K2 helps send the calcium into the bones so is in fact extremely important for bone health. Japanese researchers have gone so far as to describe natto as a superfood for this very reason!

I too am looking into building bone for osteoarthritis...mainly for my lower spine. I have been eating a good diet with addition of bone broth and gelatine and other vitamins. I am looking into magnesium and silica which seem to be almost more important than calcium. I've heard vit K is good too but don't know much about it yet. To me it seems that if K2 is only available from one place in the world it's not likely we'll need it...otherwise many more people would be dificient in it and have osteo. (this could be just me being cynical)

I think the thing to remember here is that if you eat a healthy balanced diet, you should be getting all the vitamins needed. Do not take supplements of any kind unless you have been told by your doctor you are deficient in any way. With many vitamins it doesnt matter if you overdose, the excess is just expelled by the body - but then why pay for expensive supplements just to pee them away....however, with a few specific vitamins it is quite dangerous to take too much (vit A is an example) and these will cause toxicity. By all means eat any food which is proven to have health benefits and not cause toxic issues in excess but just beware of spurious claims that one supplement or another will be a 'miracle' cure - they definitely wont. Natto is very good for heart health and is promoted as reducing cholesterol. For OA inflammation, ginger is the best bet - ginger root not powder or crystallised. Eat it, mince it and massage onto joints, it's good any way and reduces inflammation better than anything else I've tried.