Damage to knee cartilage and bone can limit mobility and cause chronic pain. Now, researchers have developed an off-the-shelf synthetic 'plug' that heals the joint and could be an alternative to current treatments like total knee replacement surgery. An osteochondral defect (OCD) is an area of focal damage involving the articular cartilage that lines the joint's bony surface and a piece of underlying bone. OCDs in the knee can result from arthritis or an acute traumatic injury ?" a football tackle, for example ?" that causes arthritis, leading to chronic pain and loss of joint function.