A knee joint for an artificial limb comprises a knee member having a part spherical convex lower surface pivoted about an axis to a knee housing having a part spherical concave upper surface conforming to the curvature of the knee member. A spring loaded plunger directly connected to a release cable runs on a guideway on the curved surface of the knee housing when the knee is flexed and in the unflexed position latches into a seating to prevent knee flexion. A collet fixing is preferably used to attach the shin tube into a socket depending from the knee housing without the need to drill the tube.