Abstract: A device for locking a prosthetic knee joint in full extension includes a housing having a friction shoe adjustably impinging on a standard extension limit link extending through the housing. A latch lever is pivotally secured in the housing and is spring biased toward the extension limit link, with a detent adapted and positioned for engaging the end of the link only during full extension. A release cable or rod extending through the housing is adapted to pull against the spring bias to release the link from the detent, and to reset the latch lever during genuflection to once again engage the link when full extension is again attained. The release rod is manually controlled by an over-center cam toggle, or by a flexible cable extending upward toward the hip and controlled by a similar toggle.