Just as the walls of a house crack and buckle when the foundation shifts, so too the cartilage can become faulty when the underlying bone becomes porous and brittle. Cartilage is one amazing substance. To begin with, it's 90 percent water. It's also virtually frictionless. Take an ice cube and slide it across a wet countertop.
Cartilage is twice as slippery.
Arthritis increases with age, and wear and tear are certainly factors. But cartilage also likes to be used, and joint health actually depends on exercise and physical activity. This last point is of special interest to me. At age 51, I can barely walk when I get out of bed in the morning. I have to balance myself against walls and furniture until I stumble into the hot shower.