In acute injuries , the ligaments and tendons become torn. Ligaments function to limit the range of motion that bones can move between each other, and function to stabilize joints and hold the joint together.
Tendons function to attach a muscle to bone in order to provide motion.
Discs and cartilage serve to absorb shock and keep the bones from rubbing against one another. If the ligaments become torn or over-stretched the joint becomes unstable and resultant friction causes the discs or cartilage to become worn down causing a loss of height. The disc and cartilage may also become worn away by repeated motion. This loss of height causes further ligament laxity and thus more instability. The friction of the joint is a stress.