ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

femoral head fracture, the femoral nail becomes responsible for most of the load.
Because the implant bares most of the load, there is a possibility that the bones fall into
a state of the stress-shielding. If no load is transmitted through the bone, the natural
healing mechanism of bone becomes inhibited 1) . Moreover, if stress concentration
occurs between the bone and the femoral nail in the distal end of stem, there is a
possibility that fracture at the distal end of the stem will occur.
In order to solve these problems, a change in the design of the femoral nail is required.
However, the material property of conventional titanium alloys as well as the
mechanism and configuration of the implant cannot be changed due to human
anatomical constraints. Therefore it is difficult to develop an ideal femoral nail using
titanium, whereat we propose a new femoral nail design that integrates three kinds of
biocompatible plastics (PEEK) mechanically and thermally. We believe that the three
types of thermoplastics will alleviate the problems of femoral rotation and the nonpropagation
of a moderate, beneficial load through the bone. In this study, we perform
an FEM analysis on the proposed femoral nail design and a conventional nail made
from titanium to investigate the validity of our design.
3. ORIGINAL PEEK FEMORAL NAIL
Figure 1 shows a traditional femoral nail made from titanium and our PEEK femoral
nail design. PEEK, which is used as an alternative to titanium alloys, has excellent
properties of heat resistance, chemical resistance, fatigue resistance, impact resistance
and creep resistance. In addition, some properties that change the characteristics of
PEEK are the amount of carbon fiber contained within, and the orientation of the carbon
fiber. Table 1 shows the material properties of PEEK used in this study. Our design
divides the lag-screw and stem into multiple parts made from three types of PEEK
plastics. These plastics were integrated and bonded via thermal welding or mechanical
fastening to achieve continuity throughout the implant.
Fig 1. Schematic drawing of femoral nails. 1 shows a traditional femoral nail made
from titanium alloy. 2 shows a PEEK femoral nail.