Computer assisted orthosis design system for malformed ears-automatic shape modification method for preventing excessive corrective force

Most malformed ears of neonates can be treated by mounting a suitably shaped orthosis. However, it needs much experience to make a orthosis that produces adequate corrective force. Especially, excessive force may cause a decubitus-like inflammation on the auricle. The authors are studying a computer assisted system to support the orthosis design. They have already developed a fundamental design and manufacturing system. This paper describes an automatic orthosis shape modification method to prevent the excessive corrective force using a three dimensional finite element method. An incremental method of inserting the orthosis in the auricle is used to handle the nonlinear material properties of the auricle. In each insertion step, the corrective force of every nodal point of the orthosis is calculated. The shape is modified by canceling the insertion of nodal point where excessive contact force is produced. The auricle and the orthosis were modeled by triangular shell elements and beam elements respectively. Finally the sample result of analysis showed that the orthosis modified by the method can reduce maximum force compared to that of the original shape