Fixing damaged knees is tricky because the form of cartilage found in the joints does not easily regenerate and in some cases total joint replacement is the only option.

Though most people eventually recover from joint injuries, damage to the cartilage can't be reversed and can only get worse.

Regeneration activity relied on the host's supply of cells to the joint, local tissue response, and functional stimulation to recreate the entire surface of the joint cartilage together with the bone.