In certain aspects, the present invention is a purely mechanical stance control orthosis, or stated differently, a weight acceptance control orthosis, as it stabilizes the impaired knee joint during the first 40% of the gait cycles termed as the weight acceptance phase. The device employs a tri-stable fixture to lock/unlock a friction-based latch to provide two levels of stiffness. The device is locked during the weight acceptance phase to stabilize the impaired knee joint for an orthotic application or avoid collapse for a prosthetic application, and is unlocked during the rest to allow free rotation. The device includes an engagement fixture, a locking mechanism, a chassis, and a frame. The engagement fixture controls the locking mechanism to lock and unlock movement in the chassis and frame in response to a wearers weight load and is capable of locking at any angle.
