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6 Applications and Methods in Biosignal Processing

Fig. 6.8: Patient in motion instrumented with the

acoustic emission system BoneDias®(near the hip)

and the force plate FDM-S of Zebris®; anatomical

landmarks of the patient to define the joint angles

of the lower extremity (hip, knee, ankle and toe

joint).

Generation of Force Data

The measurement of the ground reaction force under the feet was established by a

force plate FDM-S of Zebris®. The force plate includes 2500 sensors with per square

centimetre and the data is sampled at a rate of 120 Hz. The sensor area has the dimen-

sion of 54cmx33cm. The range of force is limited by F = 120N/cm² with an accuracy

of about ±5%. The Zebris® force plate thus measures the distribution of the force

under the left and the right foot. The center of pressure of the left and right foot are

used to conclude the distribution of the load in the left and right knee area. The total

force calculated for the left and right side are one signal for the development of the

synchronisation procedure (top Figure 6.9).

Generation of Kinematic Data

The measurement of the joint angles of the patient was achieve by two video cam-

eras (Basler® Scout scA640-120gm) in the frontal and sagittal plane, respectively. The

patient was not prepared with photogrammetric markers thus the kinematic analysis

had to be done only with anatomical attributes like the toe, ankle, knee and hip joint

as well as the shoulder joint of the trunk (cf. Figure 6.8). The analysis by means of the

anatomical attributes is sufficient, a requirement of the accuracy was defined within

the range of ±5 degrees. Time resolution was determined by the frame rate of 30 frames

per second, this is sufficient for a photogrammetric analysis, because the motion of the

patient was relatively slow during the 10 seconds of the three knee bends. As a result of

the photogrammetric analysis with Tracker 5.1® there are periodic trajectories of the

joint angles (bottom Figure 6.9). The trajectories exhibit the standing phase at the be-

ginning, the turning points of the maximal flexion and the maximal extension as well

as the standing phase at the end of the motion. The upright standing phases between

the knee bends are recognized clearly by the maximal joint angle values.