At the ends of your bones is cartilage that provides a cushion between the bone and the joint. Osteoarthritis is the degeneration of this cartilage. Without the cushion the cartilage provides, pain results from the friction between the joint and bone.
Facet joints connect the vertebrae in the spine and permit your spine to bend. Osteoarthritis of the spine results in the degeneration and loss of the cartilage in the facet joints. Where the cartilage is degenerated, inflammation can occur.