DESIGN OF A HIP PROTECTOR

Abstract

The fractures of the upper end of the femur presents one of the most important medico-social problems in the developed countries of Europe and North America and the developed and under development countries of Asia and other areas of our planet. It is a real epidemic with an increasing rate, higher than the rate expected, due to the increasing elderly population. The mortality rate, the complications and in general the social, and economic cost of these injuries are particularly high. The hip fractures in 1999 were 800 in Crete and 16000 were estimated in Greece. Ninety-five percent of these fractures are due to falls mainly within the house and 80% occur to individuals over the age of 70 years.

During last decade, the need to prevent fractures and protect the elderly against falls led to the design and production of hip protectors. The design concept of a hip protector aiming to protect the hip during a fall is the object of this study.

The beginning of our project was the biomechanical analysis of the fall of an elderly person. In this study the impact forces and the resulting pressures caused by the fall on the hip, as well as the minimal force that can be exerted on the upper part of the femur to cause a fracture were calculated.

Absorbing the energy of the impact load and shunting the energy away from the risk area of the greater trochanter was the main object of the design process. The construction of a simple apparatus that simulated the impact loads during a fall on the hip allowed the test of various geometry and material combinations, so that to meet the requirements for the new hip protector design that were set previously in the specification list.

At the same time the numerical modelling of the hip protector and the use of a commercial finite element code allowed non-destructive tests in various fall conditions in order to optimize the geometry and the material of the new hip protector.

The first data coming from the fall simulation apparatus provided satisfactory results for the new hip protector. The protector was found to attenuate a 10500 N impact force to 1700 N on the femur, providing the requested safety. Thus, the force received by the proximal femur remains below the literature provided average fracture threshold (3100+/−1200N).

The anatomical design concept of the protector provides a good comfort level that is very important for the compliance requested by the users.