Three-dimensional visualization based on segmented human data of the knee joint. The knee is a synovial joint, a joint designed to ease the transfer of mechanical forces by resisting both friction and wear. Encapsulated in their own flexible bags, synovial joints contain a waterproof cavity in which smooth bone ends are cushioned by a shock absorber of pearl-smooth elastic material and oiled by the thick, slippery fluid (synovia) for which they're named. The femur and tibia are connected by this type of joint, which allows for movement in one plane.