Not Medical Advice: According to Ridley College, the knee joint has been classified as a modified hinge joint because it was, at one time, considered to be responsible only for flexion and extension.
The knee joint has the ability to slightly rotate the leg medially and laterally, classifying it more precisely as a modified ellipsoid joint.
A hinge joint is a freely moving joint in which the bones are so articulated as to allow extensive movement in one plane. The hinge joint in your knees, elbows, and fingers let those bones move much like a door, forward and back or up and down.
The best way to care for your joints is to keep them and your muscles, ligaments, and bones strong and stable. Check out some tips for good joint health at WebMD.com.