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

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 trans-femoral amputees. Firstly, 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*m^2 for the inertia-tensor entries, and 3 mm for the center-of-gravity coordinates. Thus, the proposed technique is effective for precise and fast evaluation of the inertia properties of medical devices as prostheses.