Patients affected by Cerebral Palsy show various grades of crouch gait. In order to improve their knee extension during the critical phases of walking, they are subjected to physical re- habilitation protocols. This thesis presents the development of a robotic exoskeleton device for the knee joint of hemiplegic patients that could enhance therapy results giving an assistive torque during particular phases of gait. The device features a modular passive knee brace designed for post-op rehabilitation that has been modified with an aluminum motor support. The motor is actuated via Bowden-cable transmission; while a closed-loop controller provides the reactive torque to the patients through high frequency real-time measurements.