Vata is the main Dosha related to the Bones! There is a lot of Akash Mahabhuta (the ether) in form of the spaces and canals in the bones, and where there is space, there will be Vata Dosha in the body, because Vata Dosha is a result of Akash and Vayu Mahabhutas. So this is one thing.
Generally as a principle in Ayurveda- when a resident Dosha increases it will directly increase the Dhatu where it is residing for example- when Pitta increases it will increase the Rakta. But in case of the Vata and Bones, it is opposite. Vata increases- bones keep on decaying. So the main cause of a condition like osteoporosis is the Vata increase. This Vata increase might be due to excessive use of the body and too much movement (as it happens in athletes) and it might be as simple as in old age (because by default old age is the period of Vata aggravation).
With joints it is bit different. Joints have a lot of movement so there should be too much Vata and problems should be due to the Vata only. But there is a lot of Kapha (Shleshak Kapha) in form of synovial fluid- which helps to balance Vata in joints because Kapha is quite opposite to the properties of the Vata. Once there will be decay in the synovial fluid in the joints- problems will be aggravated and Vata will cause severe damage. Osteoarthritis is the result of the same condition. These are not only osteophytes in the joints but there will be lack of the synovial fluid too in the joints. So Ayurveda has a clear approach towards the treatment of the Bone and Joint problems. We need to maintain the balance the Kapha and Vata Dosha to maintain the harmony in the body. If one of these will be out of balance- there will be certainly some problems with the joints.