Preliminary Test with Spherical Joint Structure

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117 Flexion-Extension in the Sagittal Plane

To evaluate the elementary flexion-extension movement, after having waited a few seconds from the start of the acquisition in order to extract the calibration data, the moving rod was moved back and forth (Fig. 4.4-1 movement described in purple) for a total of five repetitions.

Care was taken to move the rod purely in the sagittal plane. The entire acquisition was segmented between two neutral positions. Then the rod from the vertical position was moved forward until it reached the maximum, it was returned to the neutral position and then moved backwards until it reached the maximum allowed again, and ending the movement by bringing the rod back vertically. The patterns and ROMs obtained in the three planes are shown in Fig.

4.4-2.

Fig. 4.4-2 Patterns and ROMs of the fixed sensor and of the mobile sensor with respect to the fixed one in the three anatomical planes during elementary exercise of

Flexion-Extension.

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As far as the fixed sensor is concerned, it is appreciable its staticity during the whole acquisition compared to the orientation assumed during the calibration phase. By shifting the attention to the mobile sensor, it can be seen that the main motion actually occurs in the sagittal plane. Even if the ROM value reached in the transverse plane is not so impressive, its pattern can be appreciated and it can be highlighted that, despite the use of instrumentation with a lower structural complexity than that which characterizes the spine, movements in the planes outside the main one of the motion are present. In this case, better sharpening the view, it seems that in bringing the rod in bending there is also a slight rotation to the right of the same, and that in bringing it in extension there is a slight rotation to the left.

Lateral Bending in the Frontal Plane

Fig. 4.4-3Patterns and ROMs of the fixed sensor and of the mobile sensor with respect to the fixed one in the three anatomical planes during elementary exercise of Lateral Bending.

119 in this test, after having waited a few seconds, the rod was moved in the frontal plane, being careful not to make it oscillate in the other anatomical planes, whit a first lateralization on the right that continues with an inclination on the left side (Fig. 4.4-1 movement described in green). In the post-processing phase, the acquisition was split between two vertical positions of the mobile rod. Fig. 4.4-3 shows the patterns and ROMs of the fixed sensor and of the mobile sensor with respect to the fixed one. The fixed sensor is characterized by negligible ROM and the patterns in the three anatomical planes are flat, indicating that the sensor remains in approximately the same starting position. The mobile sensor has the highest ROM I the frontal plane and the relative pattern has the shape of a sine wave. Even in this vase, although the

Fig. 4.4-4 Patterns and ROMs of the fixed sensor and of the mobile sensor with respect to the fixed one in the three anatomical planes during elementary exercise of Axial Rotation.

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motion is mainly in the frontal plane, it can be seen small movements also in the sagittal and transversal plane.

Axial Rotation in the Transversal Plane

To obtain an axial movement, the moveable rod was rotated around its longitudinal axis. Then, from the vertical position, the rod was rotated to the left, and once returned to neutral position it was rotated to the right side (Fig. 4.4-1 movement described in acid yellow). As with the other tests, the acquisition was split between two vertical positions of the rod. The results obtained are visible in Fig. 4.4-4. It turns out that the mobile sensor has a wide movement in the transversal plane, as It should be, while in the other planes the ROM values reached are dictated by the small oscillations inevitable by manually moving the rod. It can be also appreciated that the fixed sensor remains in the same orientation throughout the cycle.

This test session was used to ensure that the algorithm applied to the detection of spinal angles is accurate and that the motion that some segments expressed in other planes had actually been detected and that it was not a processing error. From the results obtained here it is possible to affirm that a segment free to move with 3 DoF, even if the movement is performed in a predefined plane, presents oscillations also in the other anatomical planes. Therefore, it is correct to think a complex structure such as the spinal column during the execution of elementary movements can be characterized by wide movements even in planes different from the main one of the motion. The doubt arises, however, seeing that in some relative movements (motion of the upper segment compared to the motion of the lower segment) the ROM is widely greater in a plane that is not the main one of the motion. At this point, this result leads to think that either this behaviour is actually proper to some spinal segments or that in performing elementary movements in the three planes leads a displacement of the sensors that is expressed in these high ROMs values. The latter problem, however, would not affect the results obtained in angular kinematics during walking. Here, in fact, the slippage of the sensors by the movement itself is undoubtedly of little importance compared to that obtained in elementary movements.

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