Rehabilitation post-total knee arthroplasty (TKA) demands intensive physical therapy to restore joint functionality, and prevent joint stiffness. Conventional manual physiotherapy is labor intensive and costly, while multi joint whole leg exoskeletons introduce excessive complexity, high mass, and protracted fitting times ill suited for isolated joint recovery. This paper presents a systematic framework encompassing the design, finite element analysis driven optimization, and fabrication of a single degree of freedom robotic knee exoskeleton specifically intended for post TKA rehabilitation. Key design features, including sagittal plane flexion/extension, joint alignment compensation, low distal inertia, and state based impedance control, were distilled from a comprehensive synthesis of lower limb rehabilitation robotics literature. Coupled finite element modeling and Sobol-based global sensitivity analysis revealed that the link thickness and cross-sectional area emerged as the main factor controlling peak stress and deformation. The multi objective optimization strategy successfully decreased the peak von Mises stress under dynamic loading by 13.2%, attaining 143.9 MPa. In addition, structural deflection was reduced by 27% to 0.62 mm, and yielding the fatigue safety factor of 1.67 with an infinite operational life cycle. Furthermore, cuff limb interaction forces were reduced by 30% to 44.3 N, effectively mitigating the risk of soft tissue trauma. The final prototype achieved a total mass of 2.8 kg with a more proximal center of mass, substantially reducing rotational inertia and passive gravitational torque. The proposed prototype provides an optimized, lightweight robotic framework establishing the structural and mechatronic foundation required for subsequent clinical evaluation of progressive post-TKA knee mobilization.