Exoskeletons or orthotics, also known as wearable technology, are often used to help the elderly and handicapped humans with limb disability to recover their physical mobility. In this work, we are interested in knee exoskeletons employed for the rehabilitation purpose. Our main goal is to control the exoskeleton at the knee joint level by considering external disturbances. Thus, to achieve this robust stabilization, we introduce a linear state-feedback control law combined with a nonlinear controller. The design of the linear control law is mainly relying on the LMI methodology. Simulation results on the robotic system are presented at the end of this paper to prove the performance of the suggested composite controller.