Design of a fixation technique for periprosthetic femur fractures

Abstract

This report is the result of a graduation project at the TU Delft, Faculty of Industrial Design Engineering. The project was done in collaboration with the Reinier de Graaf Gasthuis. The implantation of a total knee replacement (TKR) is one of the most successful operations in the field of orthopedic surgery. Unfortunately, in 0.6-2.5% of the cases a periprosthetic fracture occurs. Rorabeck type III fractures are located just above the femoral component of a TKR. Due to the bone tissue and the size of the bone it is difficult to get a good grip and make a solid fixation with current fixation techniques. The graduation assignment is stated as follows:‘’Design a new fixation technique that bridges the femoral component of the total knee replacement and the healthy bone above the fracture and enable a solid fixation’’To do so, the project involves current product analysis, product design, prototyping and validating the final design. 

During the analysis phase a list of requirements and demands was created. Combined with the design vision, these are used to generate ideas. From the ideas, three design directions were defined: the smooth surface, clamp cavity and expansion clamp. For each direction the advantages, limitations and unique values were determined. The expansion clamp was expected to be the most promising design direction. It makes use of a fixation device between the longitudinal surfaces by using an expansion clamp. After a second ideation session the most promising concepts have been chosen and presented. To compare the and evaluate the concepts, a Harris profile was created. By analyzing the Harris profile there was chosen to elaborate upon the mechanical expander.

By turning, pushing or screwing a mechanism is activated, panels on the side will spread and put pressure on the implant. There was chosen to use a leaf spring to enable the axpansion. Multiple iteration steps were made to come up with the most ideal design. The features, dimensions, materials and production processes were determined for all parts of the expander. An additional locking plate is designed to fit the expander and bridge the component to the healthy femur above. 

In the last chapter, the final design and its main features are presented. Validation is done by talking to an expert, dr. Verburg, and reflecting on the demands, wishes and design vision that were stated after the analysis. In conclusion, it is likely that the expander with the additional locking plate will provide a more solid fixation of a periprosthetic fracture by integrating the femoral component of a TKR. However, it should be mentioned the design has not been validated and tested on its functionality. The expander can be seen as an addition to the currently used LISS plates. Current designs of locking plates can easily be adjusted to fit the expander. Therefore, it is likely that the product will be accepted by the market. Several recommendations have been defined for further development of the fixation technique based on the validation and risk analysis of the final design.