The knee is a complex hinge joint. It is made up of multiple ligaments, soft tissue and three bones. The bones are the lower end of the femur (thigh bone), the upper end of the tibia (leg bone), and the patella (kneecap).
The inside of the knee is called the medial side and the outside of the knee is called the lateral side (see diagram). Various ligaments within and around the knee help to stabilise the knee during daily activities. Within the knee joint itself, the bones are lined with cartilage, which is a tissue that is required for cushioning of weight-bearing forces and for lubrication within the joint. Between the femur and tibia lie the menisci on both the medial and lateral sides. The menisci are required for shock absorption and assist in stabilising the knee.
The patella, commonly referred to as the “kneecap”, is a large bone in front of the knee. It is embedded within the lower end of the quadriceps muscle, and functions to improve the efficiency of the quadriceps muscle.
The knee can normally be moved from 0 degrees of flexion (completely straight) to about 130 to 150 degrees of flexion (completely bent, e.g. when squatting).
In osteoarthritis (OA), the range of motion of the knee will be gradually reduced over time as the condition worsens.