Customer case
Customer case

25th August 2010

“Outwalk”, with its high potential, can be spread in a pervasive way in the clinical routine, thanks to its simplicity in measuring kinematics, its precision and accuracy and the speed of reporting data.

Motion analysis by means of stereophotogrammetry

Although motion analysis based on stereophotogrammetry is able to provide very useful and detailed information about walking, quantitative analysis of the movement did not reveal its real potential to this day, to be spread in a pervasive way as people would like to see.

The first reason for this is the cost of instrumentation, which can be explained only in large centres like INAIL Prostheses Centre.

Second, but not least, the use of instrumentation based on stereophotogrammetry requires the measurement to be carried out in a laboratory. This implies 5 sub problems:

1) The typical dimension of a motion analysis laboratory is 10 meters, by which only two gait strides can be measured entirely. It is therefore not clear whether the measurement of such a short path can be representative of the real walking or not. In fact, within the same distance the start-up and finalization of the patient’s walking are included.

2) Due to the long subject preparation for the measurement (at least 45 minutes) and the fact that the patient should consecutively cover the same 10 meters several times, the overall examination becomes tiring: that restricts to measure no more than 10 walking trials;

3) The measurement is performed in an “artificial” environment, where the lack of harshness in the ground floor and the nonslip surface make it far from being an urban or rural environment (think about the harshness of the sidewalks in the cities, for instance)

4) The non natural environment, skin markers positioned on the skin and the presence of technical personnel create psychological pressure on the subject who can hardly show the typical walking pattern he has in his daily-life environment;

5) Laboratory instrumentation typically requires specific environments. These are not necessarily the same spaces in which orthopedic technicians and physical therapist act.

Motion analysis by means of inertial and magnetic sensors

Report-Vicon_Xsens11For the above reasons, over the last years INAIL decided to invest on activities for research and development aiming to move motion analysis towards the same place in which prosthetic devices are being designed or where the rehabilitation takes place. In this way motion analysis can be available in outside environments as well as covering long distances (theoretically unlimited) in order to be as close as possible to the motion capture of the “typical walking pattern” of the amputee.

The result of these activities is the creation of original methods and low-cost tools, placing the Prostheses Centre at the top of the innovation in this field.

One of the achievements is represented by the Outwalk protocol (see figure on the left), which it is worth to describe with particular attention.

One of the fundamental aspects for the complete description of the amputees’ movement is the knowledge about the “segment and joint kinematics” which describe how trunk, pelvis, hip, knee and ankle move during walking and their mutual coordination.

As mentioned before, in order to obtain the most representative data about the subject performances, it is to be hoped that the motion analysis takes place in a real environment, measuring hundreds of gait cycles in one measurement.

Furthermore, in order to allow the instrumental and objective analysis to be spread, the system adopted should be able to:

  • provide real-time data
  • generate a final report with “three clicks”
  • require a minimum period for the subject preparation

The above “mirage of motion analysis” (currently the above requirements cannot be satisfied even with advanced and expensive commercial systems) appears to be not so far, thanks to the combination of a new system developed by Xsens Technologies (The Netherlands) for being used in the entertainment, industrial, training and simulation and movement science fields, and the algorithms and software developed at INAIL Prostheses Centre.

The system comprises inertial and magnetic sensors, contained in a small box with small dimensions and low weight, which can be easily positioned on the body of the patient. Based on such a system, INAIL created a software called Outwalk Manager able to measure the real-time kinematics of trunk, pelvis, hip, knee and ankle, according to all the requirements previously mentioned.

Provided that the sensing units are positioned on the body, after a few simple instructions the patient is asked to maintain a particular upright posture for a few seconds; then, the patient is asked to perform a flexion-extension of the right knee, then of the left knee.

In the case in which the patient is not able to maintain an upright posture, the calibration of the system can be performed in a supine position, and the flexion-extension movements of the knee can be performed passively by the operator. Once the calibration steps are completed, the system is ready to work and measure the walking of the subject. Thanks to an efficient Bluetooth transmission system, the operator can be until 150 meters far from the patient and observe real-time data about the mobility of the body segments and joints on his laptop’s screen.

After the measurement of the walking trial, a specific algorithm, developed at the INAIL Prostheses Centre, is able to recognize and segment all the gait cycles available among the joint kinematics data: in 1 minute and with “3 clicks”, the therapist can obtain a short report (Figure 3) in pdf format which can augment the medical record of the patient as complementary information.

Additionally, it is immediately possible to compare different measurements obtained for the same patient, in order to quantitatively evaluate the improvements along the rehabilitation treatment.

Finally, as in this case data are available in real-time, part of the kinematic data can be encoded into audio signals, obtaining a biofeedback system to support the rehabilitation process.

Stereophotogrammetry is still considered the golden standard de facto, thanks to the possibility to measure forces, moments and powers.

Outwalk protocol, with its high potential, can be spread in a pervasive way in the clinical routine, thanks to its simplicity in measuring kinematics, its precision and accuracy and the speed of reporting data.

A validation study of Outwalk was successful performed on a population of healthy subjects and recently applied to a population of below-knee amputees (Figure 3). Results were presented at the ISPO 2010, (International Society of Prosthetics and Orthotics) conference in Germany.

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