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Technical Briefs

# Indirect Measurement of the Inertia Properties of a Knee Prosthesis Through a Simple Frequency-Domain Technique

[+] Author and Article Information
Emiliano Mucchi

Department of Engineering, University of Ferrara, Via Saragat, 1, 44100 Ferrara, Italy

Giuliamarta Bottoni

Department of Information Engineering, University of Padua, Via Granedigo, 6/B, 35131 Padova, Italy

Raffaele Di Gregorio1

Department of Engineering, University of Ferrara, Via Saragat, 1, 44100 Ferrara, Italyrdigregorio@ing.unife.it

1

Corresponding author.

J. Med. Devices 3(4), 044501 (Nov 10, 2009) (5 pages) doi:10.1115/1.4000408 History: Received October 27, 2008; Revised August 26, 2009; Published November 10, 2009; Online November 10, 2009

## Abstract

The dynamic study of humans carrying prostheses requires the rigid-body inertia properties of the prostheses. Since such properties are difficult to evaluate, in general, roughly estimated values of these quantities are used. These approximations may yield significant errors in the evaluation of some dynamic quantities (i.e., the inertia forces due to the prosthesis). This work is addressed to assess an experimental technique, based on frequency response function measurements, that indirectly measures the inertia properties of prostheses for transfemoral amputees. First, a specifically designed specimen and, then, a real prosthesis are tested for assessing the proposed technique. The results are that the measurement sensitivity is $0.002 kg m2$ for inertia-tensor entries and 3 mm for center-of-gravity coordinates. Thus, the proposed technique is effective for a precise and fast evaluation of the inertia properties of medical devices such as prostheses.

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## Figures

Figure 1

Aluminum specimen under test and definition of the Cartesian reference O-xyz: point O (left) is the origin of the Cartesian reference, whereas the white arrows denoted as x, y, and z give the directions of the coordinate axes

Figure 2

Knee prosthesis, named C-Leg 3C100, Cartesian reference O-xyz (left), and suspension system for FRF measurements (right)

Figure 3

Mass lines for measured FRFs of the aluminum specimen

Figure 4

FRF-sum (amplitude) with a selected frequency band for the aluminum specimen

Figure 5

FRF-sum (amplitude) with a selected frequency band for the C-Leg 3C100

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