Knee Arthritis The knee is made up of the femur (thighbone), tibia (shinbone) and patella (kneecap). The two menisci, the soft cartilage between the femur and tibia, serve as a cushion and help absorb shock during motion. Arthritis (inflammation of the joints), injury or other diseases of the joint can damage this protective layer, causing extreme pain and difficulty in performing daily activities in an arthritic knee, the cartilage itself becomes thinner or completely absent. In addition, the bones become thicker around the edges of the joint and may form bony “spurs”. These factors can cause pain and restrict the range of motion in the joint.