This paper presents the design of a mechanism to help people using mechanical orthoses to extend their legs easily and lock the knee joint of their orthosis. Many people living with spinal cord injury are living with paraplegia and thus need orthoses to be able to stand and walk. Mechanical orthoses are common types of orthopedic devices. This paper proposes to add a mechanism that creates a lever arm just below the knee joint to help the user extend the leg. The development of the mechanism is first presented, then followed by the results of the tests that were conducted.