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Medical and health applications

Inovation of French Crutches

Project description:

Stress distribution in the french crutch monoblok

Experimental testing of the french crutch

Inovated French crutch

The goal of this project was to develop and start production of innovated forearm crutch manufactured in Erilens s.r.o., which would meet the current requirements for construction, technology, ergonomics, design, and safety. The intention to innovate this product was based on the requirements and experience of users of this medical device, where the main objective was to increase the loading capacity of the crutch and bring easy constructing of the crutch. The main flaw of the existing product was “clicking” of the adjusting peg on the positioning tube, which has been deformed due to long-term usage, so there was clearance between the individual parts of the crutch. While developing such innovated crutch, our workplace has worked together with Erilens s.r.o. on the following partial tasks:

  • Together with a designer, the shape of the arm cuff was optimized in terms of its strength and optimum ergonomics of the grip.
  • The proposed shape of the arm cuff was numerically analyzed using the Finite Element Method. During these analyses the magnitude and distribution of tension in the arm cuff were assessed while loading on 1,500 N. We focused especially on local concentration of the tension, the magnitude of deformation, and the magnitude of tension. Together with technologists we performed further shape optimization on the basis of collected results and their evaluation.
  • The proposal of construction of the fixation collar, which firmly fixes the individual adjustable parts of the crutch together with the peg. The objective was to prevent the creation of hole in the tube of the crutch by transferring the loading partly to the fixation collar, which reduces the loading on the peg. The construction of this collar was accepted by the Industrial Property Office in 2008 as utility model UV 19210.
  • Before the production itself, the final design of the construction of complete, innovated forearm crutch was numerically analyzed using FEM. The aim of this analysis was to map the tension in individual parts of the crutch while loading and thus verify the capacity and reliability of this system during loading of 1 500 N. The loading of the innovated crutch model was performed in compliance with valid international standard CSN EN ISO 11334-1. The limit condition when the prosthesis or its fixture in the bone fail is considered such loading when the tension exceeded the yield point or the strength limit in any part of the modeled system of innovated forearm crutch.
  • The experimental evaluation of the forearm crutch according to international standard CSN EN ISO 11334-1 Walking Aids Manipulated by One Arm – Requirements and Testing Methods – Part 1: Forearm Crutches. The prototype crutch testing was divided into two parts – static loading and fatigue loading. The static testing is gradual loading up to maximum required strength of 1500 N. The full loading was achieved in 2 s, followed by endurance in the maximum force in time period of 10 s. The fatigue test was performed by periodical loading when the behavior of the loading force was sinusoidal with the upper limit of loading was 825 N and the lower limit was 41 N. The frequency of periodical loading was given to 5 Hz. After the end of both tests, static and fatigue, we performed visual check whether any parts of the tested sample are damaged and whether the adjusting of crutch length is functional. The resulting evaluation of the forearm crutch lead to statement that the tested prototype endured the prescribed loading in both, static and fatigue loadings.

Ing. Pavel Růžička, Ph.D.Ing. Radek Sedláček, Ph.D.


Erilens s.r.o.