Development of Simple Motion Measurement and Analysis System

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1 Original Article Development of Simple Motion Measurement and Analysis System J. Phys. Ther. Sci. 18: 89 95, 2006 HIROYUKI ISHII, PT, MS 1) 1) Department of Physical Therapy, Faculty of Health Science, International University of Health and Welfare: Kitakanemaru, Ohtawara city, Tochigi , Japan. TEL Abstract. In rural areas of developing countries, ankle foot orthoses that can be manufactured at low cost are required. Also, systems that can be set up with readily available, low-cost materials which can easily measure their effectiveness are also required. In this paper, I report on, a low cost motion analysis system that can easily measure the effectiveness of orthoses was developed in China. In this system, a home digital video camera was used for video recording for analysis, aluminum foil for a foot switch, and freeware for analysis software. Gait analysis was performed on a healthy person and a hemiplegic patient using this system. Then a comparison was performed between the results of this simple system and those of a 3D motion analysis system. Knee joint angles obtained by both systems were essentialy the same. Key words: 2D motion analysis, Low cost, Foot switch, Freeware (This article was submitted Mar. 2, 2006, and was accepted Mar. 8, 2006) BACKGROUND OF THE STUDY In the rehabilitation of disabled persons, support for enhancing motion capability is an important program for improving the quality of life of patients. However, it is not as easy to make an objective evaluation of motion capability as it is for muscular strength and range of motion. As a consequence, evaluation often tends to be subjective, based on the visual judgment of individual therapists. With recent advancements in audio-visual measurement devices, such as computers, digital video cameras, and various electronic devices, it has become possible to evaluate motion analysis objectively with 3D analyzers and force plates. However, these systems are still too expensive, and need sufficient space for installation. In addition, they require professional knowledge and measurement takes time. I am involved in developing orthoses that can be widely used in developing countries. It is necessary to evaluate the effectiveness of orthoses during the development process, directly on-site, for appealing it to the local people. However, in developing countries, it is difficult to obtain and maintain these orthoses in terms of procurement routes, economic issues and so forth. It would be preferable to perform analysis with a home video camera so that the local people can analyze motion capability easily and at low cost. Kishimoto 1) reported a method of perform 3D motion analysis with one video camera. However, it requires specific software, and economic issues still remain. Hayashi et al. 2) reported a method of performing 3D analysis using two home digital video cameras. However, it was thought preferable to measure with one home digital video camera, when considering economic efficiency and ease of use. In this study, the gait of a healthy person and a stroke hemiplegic patient were measured and analyzed in China using a commonly used personal

2 90 J. Phys. Ther. Sci. Vol. 18, No. 1, 2006 computer, freeware obtainable from the internet, and a home digital video camera. Additionally, a comparison with the results obtained from a 3D analyzer is reported. METHOD Subjects The healthy person was a female aged 32. She had no special physical problems. The hemiplegic patient was a male aged of 36. He had left hemiplegia for two years. The Brunnstrom stage of his hemiplegic lower limb was III. Both superficial sensation and deep sensation were hypalgesic. He could walk without cane. Measurement system When setting up the measurement system, all items were purchased in Beijing, China, where the measurement was performed, in consideration of the future continuity of the measurement. (1) Video shooting A digital video camera (GR-DV35K, Victor Co. of Japan, Ltd., 680,000 pixels CCD) was fixed on a tripod and the height was adjusted to the same level of the hip joint of the subjects. The minimum distance from the subjects was set to 2.5 m. The shutter speed was set to 1/100 sec, the fastest, to minimize the blurring of the images in motion and the image quality was set to the SP mode, the highest. Images were saved on tapes compatible with digital video camera. The frame rate was 30 frames/sec (NTFS method: real sampling frequency: 30 Hz). In this study, in the gait of a healthy adult and a hemiplegic subject, the trunk sway angle, hip joint angle, and knee joint angle were measured from the frontal plane and sagittal plane. White buttons on the the subjects clothes were used as markers for measurement points to measure the joint angles. The buttons were placed on one side of the body at 6 points (paralyzed side for the hemiplegic subject) as follows: 1) acromion, 2) anterior superior iliac spine, 3) hip joint (at one third the distance from the center of the great trochanter to the anterior superior iliac spine), 4) knee joint (2 cm above the knee joint space at the mid-point between 1/2 and 1/3 of the anteroposterior diameters), 5) the tip of the lateral malleolus of the ankle, and 6) the fifth metatarsophalangeal joint. Black double-sided tape was used for affixing the buttons so that the buttons could be identified on the video images. Subjects were instructed to walk freely. The video recording began during their at rest standing position in the sagittal plane and the result was used as the reference value. (2) Preparation of the foot switch I made a foot switch device to clarify the stance phase and swing phase during walking. Aluminum foil was fixed on the floor, the foot region was wrapped with a conductor (a sheet of metal gauze for net window was used in this time), that was attached to the electric code connecting to the circuit, which was closed when the foot touched the floor. Light-emitting diodes (LEDs) were attached to the circuit. The LEDs were obtained by disassembling a commercially available small-sized flashlight. When analyzing the video images, the lit or unlit state of the LEDs was observed visually, and the lit state was defined as the stance phase and the unlit state was defined as the swing phase. (3) Downloading and editing video images The digital video camera described earlier was connected to a notebook computer (FMV-BIBLO NH50 H/T, Fujitsu Limited) via an IEEE-1394 cable. The images stored in the tape were downloaded to the computer s hard drive with video download software (Windows Movie Maker, Microsoft Corporation) and saved in AVI-DV format. Video editing freeware (Virtual Dub Ver.1.6.7) was used for editing downloaded images. In addition to editing the images needed for the analysis, it was also used for resizing and cropping the images which needed to be modified because the images shot with the digital video camera have an aspect ratio different from the real ratio. Further, since horizontal scanning lines of the images shot with a digital video camera are shown alternately, an image is overlapped with the previous one and the outline of the subject is not clear when analyzing still images. To eliminate this problem, the deinterlacing function of the editing software was used. Deleting the audio data was performed at the editing stage as well. Edited video was saved in uncompressed AVI format for use with Image-JD.

91 Fig. 1. Foot switch sensor. Fig. 2. Light-emitting part. Fig. 3. Editing video images.

Wany Rasband, National Institute of Health (NIH), U.S.A. Video images prepared in the manner described earlier read.

The software automatically analyzes and displays angles from each coordinate axis which was obtained by plotting three markers as shown in Fig. 4.

3 91 Fig. 1. Foot switch sensor. Fig. 2. Light-emitting part. Fig. 3. Editing video images. (4) Image analysis In analyzing motions by image analysis, joint angles were measured with image analysis software (NIH-Image J). NIH-Image J is freeware developed by Mr. Wany Rasband, National Institute of Health (NIH), U.S.A. Video images prepared in the manner described earlier read. Then the data was displayed frame by frame (still image) to measure the angle of the knee joint, anterior and posterior tilting of the trunk, and pelvic motion level during walking. The software automatically analyzes and displays angles from each coordinate axis which was obtained by plotting three markers as shown in Fig. 4. The angle of the knee joint was measured by three points, the hip joint, knee joint and ankle joint. The angles of the anterior and posterior tilting of the trunk were measured by the line between the acromion and hip joint, and a perpendicular line drawn on the screen. With regard to the pelvic motion level, the coordinates were extracted by plotting the marker attached to anterior superior iliac spine. The minimum value was set to zero and the fluctuation range on the vertical axis was analyzed. Additionally, the joint angle during the at rest standing position was obtained and it was used as the reference value. After the measurement, the measured values were used to generate a graph using spreadsheet software, Excel, Microsoft Corporation. Comparison with a 3D analysis system Besides the video recording performed by the method described above, measurement with a 3D analysis system was carried out as well to compare the difference. The measurement method with the 3D analysis system is described below. The subject was one healthy male aged 24. A 3D motion analysis system encompassing eight infrared cameras (VICON612, VICON MOTION SYSTEMS) was used for the recording.

4 92 J. Phys. Ther. Sci. Vol. 18, No. 1, 2006 Fig. 4. Analyzing an image. Markers with a diameter of 12 mm were attached to both sides of the subject s leg at the following 5 locations: 1) acromion, 2) hip joint (at one third the distance from the center of the great trochanter to the anterior superior iliac spine), 3) knee joint (2 cm above the knee joint space at the mid-point between 1/2 and 1/3 of the anteroposterior diameters), 4) the tip of the lateral malleolus in the ankle, and 5) the fifth metatarsophalangeal joint, together with one dummy marker to distinguish between left and right (total 11 markers). The total length of the walkway was about 10 m. The data measured in the first and last few meters of the walkway were not used for the analysis. The subject was instructed to walk freely. The coordinate data of the infrared reflective markers were acquired by VICON DATA STATION (VICON MOTION SYSTEMS, UK) at a sampling frequency of 120 Hz by the infrared cameras. Signals from the force plate were A/D converted at a sampling frequency of 120 Hz and input to a PC (GX450, Gateway, USA) at the same time as the coordinate data was acquired. The acquired data were converted into 3D by 3D motion analysis measurement software, VICON WORKSTATION (VICON MOTION SYSTEMS, UK). The marked locations and floor reaction force vectors were then displayed in 3D. Subsequently, the displayed markers were labeled. The stick model and floor reaction force vector were displayed as a graphic file in C3D format on the PC. The graphic file in C3D format was then converted to the DIFF format data, a common format for data analysis which is recommended by the Clinical Gait Analysis Forum of Japan (CGAFJ), by using C3D2DIFF CONVERTER (VICON MOTION SYSTEMS, UK). The 3D coordinate positional data were low-pass filtered at 4 Hz according to Ebara s method. After filtering, each internal joint center location, the location obtained with 3D coordinates of each joint, was estimated from the skin surface. The estimation was performed based on the method of the CGAFJ. In this experiment, the force meter and foot switch could not be used at the same time, therefore, the stance phase and swing phase were determined with the force meter. Additionally, at the same time, images were recorded by a digital video camera using the method described earlier and the same analysis was performed. The markers were the same as the ones used for the 3D analyzer. The joint angle data obtained in the both tests were synchronized by time. Differences in the data were then sought. RESULTS AND DISCUSSION Comparison of joint angle with 3D analyzer Figure 5 shows the changes in knee joint angle in a single gait cycle. The vertical axis shows the knee joint angle. Positive values represent the degree of flexion. As shown in the figure, almost the same results were obtained for the knee joint angle by both measurement methods. Knee joint angle, Video camera, 3D analyzer, Frame number (30 frames/ sec). Comparison of knee joint angle between a healthy adult and a hemiplegic patient during walking Figure 6 shows the results of a comparison of the knee joint angle during walking between a healthy adult and a hemiplegic patient. For the hemiplegic patient, data was obtained from the paralyzed side. For the healthy adult, flexion increased significantly during the swing phase followed by extension in the latter part of the swing phase (yellow arrow). After that, in the stance phase, flexion was observed again at the arrow (1) shown in the figure. This indicates that the knee flexion occurs twice, once in the swing phase and once in the stance phase. Thus, our measurement method could capture one characteristic of gait of a healthy person. In terms of a single gait cycle, the healthy subject took 36 frames (1.3 sec) to complete the cycle whereas the hemiplegic subject required 86 frames

5 93 Fig. 5. Comparison of knee joint angle in a single gait cycle. (2.9 sec) which was 2.4 times longer than the healthy subject. Also, the hemiplegic subject had smaller knee flexion angle in the swing phase (arrow (2)). Flexion progressed rapidly in the latter part of the stance phase in the healthy subject, however, the flexion angle for the hemiplegic subject was small and no further change was observed in some parts after the first flexion occurred. It is considered that the hemiplegic subject did not have sufficient knee flexion at the appropriate time, both in the swing and stance phases, because the knee extension strength on the affected lower limb was stronger in this subject. Comparison of pelvic motion level between a healthy person and a hemiplegic patient Pelvic motion level was determined by changes in the up-and-down movement during a single gait cycle shown on the vertical axis on the PC screen and was expressed in pixels (a coordinate unit on the axes of the PC) The lowest position was set to zero. Figure 7 shows the result. The pelvis level of both the healthy person and the hemiplegic subject decreased in the double support phases of (1) and (2). In addition, the pelvis level of the hemiplegic subject again decreased at the arrow (3). This is because the trunk was tilted forward before lifting the affected lower limb and, at the same time, the affected side of the knee was flexed once and then extended in order to swing forward the affected lower limb. Measurement of trunk tilt angle In order to further elucidate the reason why the pelvis level of the hemiplegic patient decreased Fig. 6. Comparison of knee joint angle in a single gait cycle between a healthy person and a hemiplegic patient. Knee joint angle, Frame number, (30 frames/sec), Joint (healthy person), Stance phase (healthy person), Joint (hemiplegic patient), stance phase (hemiplegic patient). twice in the stance phase as described above, the angle of the trunk was measured. The results are shown in Fig. 8, in which it is clear that the trunk tilts forward at frame number 55 and later ater. Devices and problems In this study, the measurements were performed in Beijing, China, and all the required items were purchased in Beijing. In addition, we tried to keep the cost of the devices as low as possible so that local people could continue the study by themselves. For this reason, a personal computer and digital video camera were used in the study. The table below shows the costs associated with the devices. These items were selected on the basis that they are easily obtainable at anytime and anywhere. Tsushima et al. 3) reported a method to measure angles by converting video images into still images with using imaging software (CANVAS 8.0.3J, DENEVA). Since the software we used in this study can read the video images directly and measure the angles while performing frame-byframe advances, it was thought to be more effecient than other freeware. There are still two issues to resolve: 1) even with the fastest shutter speed, home digital video cameras require bright lighting because some blurring is observed in the still images converted from the video images shot recorded in low light in order for measuring the joint angles of the subjects;

6 94 J. Phys. Ther. Sci. Vol. 18, No. 1, 2006 Fig. 7. Comparison of the pelvic motion level between a healthy person and a hemiplegic patient. Pelvic motion level, Frame number, (30 frames/ sec), Pelvic motion level (healthy person), Stance phase (healthy person). Fig. 8. Trunk tilt angle of a hemiplegic patient without shoe. Degree, Trunk tilt angle, Stance phase (hemiplegic patient), Frame number, Positive values represent the degree of anterior flexion. Table 1. Cost of purchased materials needed for the study Chinese Yuan Japanese Yen * A flashlight used for the foot switch 5 70 Metal gauze used for the foot switch 5 (2 m) 70 Wire used for the foot switch 6 (10 m) 84 Aluminum foil used for the foot switch 10 (10 m) 140 Buttons for markers 5 (20) 70 Double-sided tape for affixing markers (buttons) 6 (10 m) 84 Total * The currency exchange rate: 1 Chinese Yuan=14 Japanese Yen. and 2) it is not possible to measure at a speed faster than brisk walking of a healthy person. In this study, we were able to perform motion analysis with devices made from a combination of materials, which were inexpensive as well as easily obtainable. Such a system would make it possible to objectively analyze the effectiveness of orthosis in rehabilitation facilities in developing countries. The values of knee joint flexion angle obtained by the system were compared with a 3D analyzer, and they showed almost the same values. Additionally, a comparison between a hemiplegic patient and a healthy person was performed and, the characteristics of hemiplegic gait could be observed by the system used in this study. However, in the analysis method used in this study, the angles are measured from images shot in 2D, which makes it difficult to measure rotation movement. Also the rotation movement has negative effects such as generating errors in other angles during bending and stretching exercises. Additionally, measurements were performed on the image as close to its center as possible during the process. More errors are likely to occur, the further the images measured are from the center of the screen. Therefore, it is considered necessary that the measurement points should be limited to the knee (joint flexion angle), hip (pelvic motion level) and others that were measured in this study. As Tsushima et al. 3) pointed out, the measured value might differ depending on the position, setting and model of camera in motion analysis using 2D images. Therefore it would be necessary to use the same system for comparisons of measured values. Furthermore, the analysis method used in this study does not have an automatic follow-up system, unlike 3D analyzers, which have coordinate sampling devices. Therefore, it is required to plot video images manually while performing frame-byframe advance and it takes much time to analyze. A

7 95 one second motion is sectioned into 30 frames and each flame is observed individually. As a consequence, it creates the chance to grossly see the phenomena that would not have been noticed otherwise. The system would also be useful for studying the basics of gait in the classroom and other settings. Based on these results, we should verify the measurement results of the simple system in positions other than those measured in this study, determine its effectiveness for orthosis and treatment, and utilize the results in the field of education. REFERENCES 1) Kishimoto H: Integrated operation analysis meter (MA-6000) three dimension operation analysis device with one camera. J Jpn Physical Therapy Association, 1998, 25: ) Hayashi T, Sato K, Ogawa T, et al.: Attempt of three dimension operation analysis with domestic digital video camera. J Jpn Phys Ther Assoc, 2002, 29 (suppl. 2): ) Tsushima E, Ishida M, Dragomir N: Interrater and Intrarater Reliaility of Angle Measurement by Goniometer in Sone Digital Pictures. J Phys Ther Sci, 2003, 18 (3):

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Best Practice: CLINICAL Go to the section that is most appropriate for you Key points... 1 Introduction... 1 Preparation... 3 General Movement Analysis... 4 Gait Analysis... 6 Treatment... 8 Earlier in