Design and research of a new kind of minimally invasive fixation device in orthopaedics

Abstract

A new kind of external fixation for orthopaedics was designed in order to overcome the shortcomings of high weight, difficult operation and high degree of injury for the conventional external fixation. This device uses the so called quick casting method, which can be quickly concreted, to efficiently reduce the injury to patients. It is mainly composed of the macromolecule casting material and the steel stainless nails which fasten the device to the bone. In order to verify the feasibility of the designed structure, FEM (finite element method) was used to simulate the real condition of the load when the device was used after an operation. At the same time, optimum design was also carried out for the number and dimension of the nails in order to obtain the best operation effect. It was concluded from the simulated result that when the real load was applied on the fastened broken bone, the relative displacement of the broken border was just 0.33 mm, which was much lesser than the permitted limit (1 mm). This was in line with the request to cure the patients whose bones are broken and it showed the correctness of the design. Finally, in order to prove the feasibility of the design, ten sheep were used as specimen. It was concluded from X-ray sketches of 2, 4 and 8 weeks that there is no relative displacement between the borders of the broken bone and the bone that was well healed. This indicated that this scheme can be feasibly used to cure the broken bones. However, this design scheme can be used as an effective treatment means. Key words : External fixation for orthopaedics, quick casting, x-ray image, cure.