In the clinical setting the conservative treatment is usually an applied posterior ankle splint to immobilize the ankle. However, the traditional ankle splint is bulky and heavy. Thus this project used the finite element analysis (FEA) and Topological optimization methods to reduce the weight of splint and increase the ventilation. A model of the ankle splint is designed and analysed in the project using the inventor software. This project implements topological optimisation and design optimization to seek the optimal thickness and the shape of the splint. At the end new design is compared with the traditional design and lists the results which will prove the efficiency of the new splint.