The problem with cartilage

Cartilage is a very specialized tissue with relatively few cells and and a lot of "matrix" which is a composite secreted by the cells. The matrix forms a resilent gel, nice & white & shiny; when it cracks or is worn away, there is only bone beneath it. It hurts to walk just upon the bone. Eventually, when there are lots of holes or cracks in the cartilage, the bone starts to try and repair the problem; it does this mainly by making more bone. This causes the formation of "spurs", known as osteophytes, extra bone which is useless. When patients come in with very abnormal xrays, what you find is a narrow joint space, spurs, and bone rubbing upon bone. This is osteoarthritis. THE trick of cartilage repair is to prevent these changes when the cartilage holes are
relatively well contained and before the xrays are terrible.