Exoskeletons are crucial for providing intensive and consistent rehabilitation over a longer period and may be able to treat the patient without the presence of the therapist compared to manual therapy. This approach allows for frequent treatment reducing several costs. Therefore, this study aimed to examine the passive elbow rehabilitation of lateral epicondylitis patients, usability, and bioinspired design, to develop a mechatronics system with three rehabilitation positions. Regarding the biomechanical fundamentals of the elbow joint and as an engineering sustain, Computer-Aided Design (CAD) was made, consisting of Finite Element Analysis (FEA), anthropometric, ergonomic, and assembly analysis. The results showed that for the three rehabilitation positions, FEA showed von Mises stress less than the elastic modulus by a 103-factor resulting in no permanent deformation. Position 1, 2, and 3 produced angular displacements of 27°, 16.5° and 31° respectively with a total of 74.5°. An arm exoskeleton for passive rehabilitation of the elbow was developed using a pneumatic cylinder and an AD8832 electromyography (EMG) sensor, capable of detecting the EMG peak point to activate or deactivate the 24 V Arduino relay to flex or extend the elbow based on the positions. A total angular displacement of 74.5° was obtained instead of the simulated version 84.63°, with an error margin of 11.96%. The force during the three rehabilitation positions was 18 N exerted by the air compressor at a 6-bar constant pressure, and due to the use of choke valves.