The mated surfaces of these joints are covered with hyaline cartilage, and bathed in the synovial fluid. Wear on the surface is made up by interstitial growth. Damage to articular cartilage can be due to age, wear and tear, or abuse. Constant pounding of the joints, overworking them, or excessive weight-bearing stress can cause problems. If this happens and the cartilage degenerates to the point where bone is exposed, the joint may lose function.
Untreated injuries can lead to fusion of the bone across the joint and immobility.