Portable Inertial Sensors Research Articles

Inertial Sensor Gait Analysis of Trendelenburg Gait in Patients Who Have Hip Osteoarthritis

BackgroundGait abnormalities such as Trendelenburg gait (TG) in patients who have hip osteoarthritis (OA) have traditionally been evaluated using clinicians’ visual assessment. Recent advances in portable inertial gait sensors offer more sensitive, quantitative methods for gait assessment in clinical settings. This study sought to compare sensor-derived metrics in a cohort of hip OA patients when stratified by clinical TG severity. MethodsThere were 42 patients who had hip OA and were grouped by TG severity (mild, moderate, and severe) through visual assessment by a single arthroplasty surgeon who had > 30 years of experience. After informed consent, wireless inertial sensors placed at the midpoint of the intercristal line collected gait parameters including pelvic shift, support time, toe-off symmetry, impact, and cadence. Clinical data on hip strength, range of motion, and Kellgren-Lawrence grade were collected. ResultsWorsening TG severity had a higher mean Kellgren-Lawrence grade (2.5 versus 3.2 versus 3.4; P = .014) and reduced passive hip abduction (P = .004). Severe TG group demonstrated predominantly contralateral pelvic shift (n = 9 of 10, 90.0%), while ipsilateral shift was more frequently detected in moderate (n = 10 of 18, 55.6%) and mild groups (n = 9 of 14, 64.3%; P = .021). Contralateral single support time bias was greatest in severe TG (35.7% versus 50.0 versus 90.0%; P = .027). Asymmetric toe-off, impact, and support times were observed in all groups. ConclusionsTraditional understanding of TG is that truncal shift occurs to the ipsilateral side. Using sensor-based measurements, the present study demonstrates a shift of the weight-bearing axis toward the contralateral side with increasing TG severity, which has not been previously described. Inertial sensors are feasible, quantitative gait measuring tools, and may reveal subtle patterns not readily discernible by traditional methods.

Arbitrary Spatial Trajectory Reconstruction Based on a Single Inertial Sensor

Compared with vision, infrared rays, and ultrasonic positioning technologies, the signal acquisition of portable inertial sensors is not affected by the external environment, such as light and occlusion. Therefore, motion tracking based on inertial signals is a promising complement. However, accurate trajectory reconstruction based on inertial sensors is a great challenge due to the intrinsic and measurement errors, especially the drift error that exacerbates the accumulative error in trajectory calculation. To address this challenge, we propose a new trajectory reconstruction method, Geometric Dynamic Segmental Reconstruction (GDSR), where we treat the movement trajectory as a combination of basic trajectories. To this end, we design a temporal and spatial interaction segmentation approach to decompose the trajectory into basic segments by combining the dynamic feature of IMU signals with the spatial morphological feature of motion. Accordingly, we design a geometrical model library with undetermined parameters to match these segments. For precise parameter prediction, we propose an extra-supervised learning method that integrates different prediction tasks into one framework, which can not only expand training samples but also enable different subtasks to compete with each other, thus improving the parameter prediction accuracy of each subtask, thereby accurately approximating the trajectory segments. To quantify the trajectory reconstruction accuracy, we propose the Fréchet Spline Sliding Error (FSSE) and Length Error Ratio (LER) to evaluate curve similarity. The range of FSSE is [0, 2], where 0 means that the two curves have the same shape. The range of LER is [1, +∞], where 1 means that the two curves have the same length. We test different IMUs in two experimental scenarios and one public available data set. In all the three tests, the FSSE of the GDSR method is less than 0.09, and the LER is less than 1.31, which is significantly better than all the comparison methods.

Effects of forelimb instrumentation on lameness detection in horses using a portable inertial sensor-based system.

To investigate the effects of a small sensor attached to the pastern region of a forelimb on lameness detection and quantification with a portable inertial sensor-based system (PISBS) for lameness detection and quantification in horses. 20 adult horses (body weight, 410 to 650 kg) with no visible lameness at the walk. In a crossover study design, horses were evaluated at the trot twice using the PISBS with the gyroscope alternately attached to the right forelimb pastern region (as recommended by the manufacturer) or to the left forelimb pastern region (with the sensor flipped 180° on the frontal plane relative to the standard position). Agreement between the 2 instrumentation approaches was investigated graphically and by repeated-measures ANOVA, Pearson correlation analysis, and Bland-Altman analysis. No effects of instrumentation of a forelimb with the gyroscope were detected on the lame limb or limbs or on lameness severity. Attachment of the gyroscope to a forelimb had no effect on forelimb or hind limb lameness (ie, did not cause or mask lameness) as measured with the PISBS. Instrumentation of a forelimb with a lightweight gyroscope for lameness evaluations with a PISBS had no effects on lameness measurements in horses. Results suggested that, when indicated, the gyroscope can be attached (while flipped 180° on the frontal plane relative to the standard position) to the left forelimb (rather than the right forelimb).

Inertial sensors versus standard systems in gait analysis: a systematic review and meta-analysis.

The increasing popularity of inertial sensors in clinical practice is not supported by precise information on their reliability or guidelines for their use in rehabilitation. The authors investigated the state of the literature concerning the use of inertial sensors for gait analysis in both healthy and pathological adults comparing traditional systems. Furthermore, trying to define directions for clinicians. In accordance with the PRISMA statement, authors searched in PubMed, Web of Science and Scopus all paper published from January 1st, 2005 until December 31st, 2017. They included both healthy and pathological adults' subjects as population, wearable or inertial sensors used for gait analysis and compared with classical gait analysis performed in a Motion Lab as intervention and comparison, gait parameters as outcomes. Considering the methodological quality, authors focused on: sample; description of the study; type of gait analysis used for comparison; type of sensor; sensor placement on the body; gait task requested. From a total of 888 articles, 16 manuscripts were selected and 7 of them were considered for meta-analysis for different gait parameters. Demographic data, tested devices, reference systems, test procedures and outcomes were analyzed. Our results show a good agreement between inertial sensors and classical gait analysis for some gait parameters, supporting their use as a solution for capturing kinematic information over an extended space and time and even outside a laboratory in real-life conditions. Authors can support the use of portable inertial sensors for a practical gait analysis in clinical setting with good reliability. It will then be the experience of the clinician to direct the decision-making process.

Gamified platform for rehabilitation after total knee replacement surgery employing low cost and portable inertial measurement sensor node

This paper introduces an innovative gamified rehabilitation platform comprising of a mobile game and a custom sensor placed on the knee, intended for patients that have undergone Total Knee Replacement surgery, in collaboration with the General Hospital in Chania. Initial testing of the system is conducted in the Hospital Orthopaedic Clinic, in collaboration with Orthopeadic Surgeons and Physiotherapists. The application uses a single custom-made, light, portable and low-cost sensor node consisting of an Inertial Measurement Unit (IMU) attached on a lower limb in order to capture its orientation in space in real-time, while the patient is completing a physiotherapy protocol. The aim is to increase patient engagement during physiotherapy by motivating the user to participate in a game. The proposed sensor node attached on the lower limb provides input to the gamified experience displayed on an Android mobile device, offering feedback to the patient in relation to whether the performed exercises were accurately conducted. A classification algorithm is proposed that automatically classifies an exercise in real-time as correct or incorrect, according to physiotherapists’ set criteria. The game projects a graphical image of the patient’s limb motion as part of a 3D computer graphics scene. It then classifies the exercise performed during physiotherapy as accurately performed or not and increases patient compliance via a reward system. Our goal is to reduce the need for the physical presence of a physiotherapist by aiding the efficient performance of exercise sessions at any location, e.g. at home, indoors and outdoors by just utilizing a light sensor and an Android device. Initial testing of the application in the Chania’s General Hospital Orthopaedic Clinic, Greece, indicates that patient engagement is enhanced in most cases, even when elderly patients are concerned.

Countermovement Jump Recovery in Professional Soccer Players Using an Inertial Sensor.

To assess the utility of an inertial sensor for assessing recovery in professional soccer players. In a randomized, crossover design, 11 professional soccer players wore shorts fitted with phase change material (PCM) cooling packs or uncooled packs (control) for 3 h after a 90-min match. Countermovement jump (CMJ) performance was assessed simultaneously with an inertial sensor and an optoelectric system: prematch and 12, 36, and 60 h postmatch. Inertial sensor metrics were flight height, jump height, low force, countermovement distance, force at low point, rate of eccentric force development, peak propulsive force, maximum power, and peak landing force. The only optoelectric metric was flight height. CMJ decrements and the effect of PCM cooling were assessed with repeated-measures analysis of variance. Jump heights were also compared between devices. For the inertial sensor data, there were decrements in CMJ height on the days after matches (88% [10%] of baseline at 36h, P = .012, effect size = 1.2, for control condition) and accelerated recovery with PCM cooling (105% [15%] of baseline at 36h, P = .018 vs control, effect size = 1.1). Flight heights were strongly correlated between devices (r = .905, P < .001), but inertial sensor values were 1.8 [1.8]cm lower (P = .008). Low force during countermovement was increased (P = .031) and landing force was decreased (P = .043) after matches, but neither was affected by the PCM cooling intervention. Other CMJ metrics were unchanged after matches. This small portable inertial sensor provides a practical means of assessing recovery in soccer players.

Dopaminergic and non-dopaminergic gait components assessed by instrumented timed up and go test in Parkinson's disease.

The timed up and go test (TUG) is a widely used clinical test for the evaluation of balance and mobility. An instrumented version of TUG (iTUG) has been proposed to provide quantitative information on TUG performances. Here, we hypothesized that L-dopa may differently influence gait parameters recorded by a portable inertial sensor. To test this idea, we evaluated iTUG test in patients with Parkinson's disease (PD), both in L-dopa OFF and ON state. Twenty-eight PD patients performed the iTUG. Subjects were instructed to perform the task both in practical "OFF" and "ON" state. The system differentiated the test in six phases, recording phase durations, three-axial accelerations, average and peak angular speeds during turning. In all patients, sit-to-stand vertical and medio-lateral accelerations together with turning phase duration and angular speeds improved after L-dopa administration, while sit-to-stand and stand-to-sit phases antero-posterior accelerations were less responsive. In PD, L-dopa modulates iTUG in different ways, mostly improving the turning phases and less acting on postural controls during the sit-to-stand and stand-to-sit phases. Our results suggest different involvement of dopaminergic mechanisms on gait as assessed by iTUG. This is important for those aspects which are not improved by pharmacological therapy.

Relationship between trunk and foot accelerations during walking in healthy adults

Understanding upper body and lower body segment relationships may be an important step in assessing stability during gait. This study explored the relationship between acceleration patterns at the trunk and at the foot during treadmill walking at self-selected pace in healthy adults. Forty healthy subjects walked on a treadmill for 3 minutes at self-selected speed. Root mean square (RMS) and approximate entropy (ApEn) were derived from the acceleration time series at the trunk and at the foot in the frontal and sagittal plane. RMS of accelerations at the trunk were strongly correlated with RMS values at the foot in the sagittal plane (r=0.883, p<0.01) and in the frontal plane (r=0.811, p<0.01). ApEn values at the trunk were moderately correlated with ApEn values at the foot in the sagittal plane (r=0.603, p<0.01) only. These results show that acceleration variability at the foot is related to acceleration variability at the trunk, specifically that increased variability at the foot is tied to increased variability at the trunk in healthy adults. Portable inertial sensors can potentially be used in any environment including a laboratory, clinic, or at home to measure lower and upper body segment motion, and assessing relationships between upper and lower body motion may provide a more comprehensive evaluation of overall stability.

A new way of assessing arm function in activity using kinematic Exposure Variation Analysis and portable inertial sensors – A validity study

Portable motion systems based on inertial motion sensors are promising methods, with the advantage compared to optoelectronic cameras of not being confined to a laboratory setting. A challenge is to develop relevant outcome measures for clinical use. The aim of this study was to characterize elbow and shoulder motion during functional tasks, using portable motion sensors and a modified Exposure Variation Analysis (EVA) and evaluate system accuracy with optoelectronic cameras.Ten healthy volunteers and one participant with sequel after stroke performed standardised functional arm tasks. Motion was registered simultaneously with a custom developed motion sensor system, including gyroscopes and accelerometers, and an optoelectronic camera system. The EVA was applied on elbow and shoulder joints, and angular and angular velocity EVA plots was calculated.The EVA showed characteristic patterns for each arm task in the healthy controls and a distinct difference between the affected and unaffected arm in the participant with sequel after stroke. The accuracy of the portable system was high with a systematic error ranging between −1.2° and 2.0°. The error was direction specific due to a drift component along the gravity vector.Portable motion sensor systems have high potential as clinical tools for evaluation of arm function. EVA effectively illustrates joint angle and joint angle velocity patterns that may capture deficiencies in arm function and movement quality. Next step will be to manage system drift by including magnetometers, to further develop clinically relevant outcome variables and apply this for relevant patient groups.

Objective lameness assessment: can it really tell us anything different?

Objective gait analysis has become more accessible with the availability of small portable wireless inertial sensors that can be fixed to pre-defined points on the horse to measure upper body movement. Over the years a huge number of kinematic papers in the horse have been published but the terminology used is often complex and thus understanding of the data is diminished. This article aims to present the data generated by small, wireless inertial measurement units (IMUs) in a user friendly format and to demonstrate the potential for objective gait analysis to increase veterinary practitioners' ability to detect subtle and complex lameness.

Support Vector Machines for Young and Older Gait Classification using Inertial Sensor Kinematics at Minimum Toe Clearance

The present study investigates the inertial sensor kinematics obtained at a critical toe-control event, Minimum Toe Clearance (MTC), to classify dierent age groups. Fourteen young and fourteen older adults performed treadmill walking at their preferred walking speed, wearing a shoe-mount inertial sensor unit measuring tri-axial acceleration and triaxial angular velocities. Three dimensional (3D) position-time data was obtained using high accurate motion capture system. MTC timing within a gait cycle (MTCTime), calculated using 3D motion capture data, was used to extract inertial sensor kinematics at MTC event. Mean and standard deviation of three inertial sensor acceleration features and three angular velocity features were compared between young and older individuals using t-tests. Young adults' mean anterior-posterior acceleration was greater than older adults (p=0.002). Further, standard deviations (SD) of all three accelerations and angular velocity about medio-lateral axis were greater in Older adults. The inertial sensor kinematics obtained at MTCTime were able to classify young and older adults gait with 91.2% accuracy using a Support Vector Machine (SVM) classifier. The findings of the present study suggest that by employing SVM techniques, a portable inertial sensor system could be used to identify gait degeneration due to ageing and has the potential for wider applications in gait identification for falls-risk minimization.

Instrumenting the Balance Error Scoring System for Use With Patients Reporting Persistent Balance Problems After Mild Traumatic Brain Injury

ObjectiveTo determine whether alterations to the Balance Error Scoring System (BESS), such as modified conditions and/or instrumentation, would improve the ability to correctly classify traumatic brain injury (TBI) status in patients with mild TBI with persistent self-reported balance complaints. DesignCross-sectional study. SettingOutpatient clinic. ParticipantsSubjects (n=13; age, 16.3±2y) with a recent history of concussion (mild TBI group) and demographically matched control subjects (n=13; age, 16.7±2y; control group). InterventionsNot applicable. Main Outcome MeasuresOutcome measures included the BESS, modified BESS, instrumented BESS, and instrumented modified BESS. All subjects were tested on the noninstrumented BESS and modified BESS and were scored by visual observation of instability in 6 and 3 stance conditions, respectively. Instrumentation of these 2 tests used 1 inertial sensor with an accelerometer and gyroscope to quantify bidirectional body sway. ResultsScores from the BESS and the modified BESS tests were similar between groups. However, results from the instrumented measures using the inertial sensor were significantly different between groups. The instrumented modified BESS had superior diagnostic classification and the largest area under the curve when compared with the other balance measures. ConclusionsA concussion may disrupt the sensory processing required for optimal postural control, which was measured by sway during quiet stance. These results suggest that the use of portable inertial sensors may be useful in the move toward more objective and sensitive measures of balance control postconcussion, but more work is needed to increase sensitivity.

Effects of Hemodialysis Therapy on Sit-to-Walk Characteristics in End Stage Renal Disease Patients

Patients with end stage renal diseases (ESRD) undergoing hemodialysis (HD) have high morbidity and mortality due to multiple causes; one of which is dramatically higher fall rates than the general population. In spite of the multiple efforts aiming to decrease the high mortality and improve quality of life in ESRD patients, limited success has been achieved. If adequate interventions for fall prevention are to be achieved, the functional and mobility mechanisms consistent with falls in this population must be understood. Human movements such as sit-to-walk (STW) tasks are clinically significant, and analysis of these movements provides a meaningful evaluation of postural and locomotor performance in elderly patients with functional limitations indicative of fall risks. In order to assess the effects of HD therapy on fall risks, 22 sessions of both pre- and post-HD measurements were obtained in six ESRD patients utilizing customized inertial measurement units (IMU). IMU signals were denoised using ensemble empirical mode decomposition and Savistky-Golay filtering methods to detect relevant events for identification of STW phases. The results indicated that patients were slower to get out of the chair (as measured by trunk flexion angular accelerations, time to peak trunk flexion, and overall STW completion time) following the dialysis therapy session. STW is a frequent movement in activities of daily living, and HD therapy may influence the postural and locomotor control of these movements. The analysis of STW movement may assist in not only assessing a patient's physical status, but in identifying HD-related fall risk as well. This preliminary study presents a non-invasive method of kinematic measurement for early detection of increased fall risk in ESRD patients using portable inertial sensors for out-patient monitoring. This can be helpful in understanding the pathogenesis better, and improve awareness in health care providers in targeting interventions to identify individuals at risk for fall.

Towards determining absolute velocity of freestyle swimming using 3-axis accelerometers

Investigating the performance of an athlete and monitoring them is important to athletes and coaches. Coaches are not always on side when athletes doing their training, so a device which is small and easy to use will increase the monitored training sessions significantly and allow the athlete to compare multiple training sessions. In this research a small, portable inertial sensor platform was used to investigate the movement of swimmers and was set to record data at 100Hz. The experiment was undertaken in an indoor pool with the sensor attached to the swimmer's sacrum, a velocity meter (Speed Probe 5000 – SP5000) attached to the swimmers suit with a video camera capturing the swimmer over the whole lap. The SP5000 measures the velocity directly and provides a synchronised video with the gathered velocity data. This system was used as main reference as it is already proven as a robust method and provides data files which can be directly imported into Matlab. The swimmer was asked to push-off with both feet against the wall and perform one freestyle stroke lap, which was repeated at different speeds. The timing parameters of the lap (i.e. start time, end time, stroke frequency) can be identified from the acceleration data. The acceleration data was then passed through a 0.5Hz low pass filter to gain the sensor orientation, which was then removed for further processing. The velocity profile was calculated using the acceleration in swimming direction (ay) and the total acceleration (atot). The mean velocity from the SP5000 was 0.964±0.086 m/s whereby the mean velocity derived from the accelerometer was 1.331±0.207 m/s and 0.944±0.119 m/s for ay and atot respectively. This research has shown that velocity information can be derived from acceleration data but there is still a difference in comparison to the SP5000 velocity. Future work needs to find a better approach in removing the sensor orientation.

ITUG, a Sensitive and Reliable Measure of Mobility

Timed Up and Go (TUG) test is a widely used clinical paradigm to evaluate balance and mobility. Although TUG includes several complex subcomponents, namely: sit-to-stand, gait, 180 degree turn, and turn-to-sit; the only outcome is the total time to perform the task. We have proposed an instrumented TUG, called iTUG, using portable inertial sensors to improve TUG in several ways: automatic detection and separation of subcomponents, detailed analysis of each one of them and a higher sensitivity than TUG. Twelve subjects in early stages of Parkinson's disease (PD) and 12 age matched control subjects were enrolled. Stopwatch measurements did not show a significant difference between the two groups. The iTUG, however, showed a significant difference in cadence between early PD and control subjects (111.1 +/- 6.2 versus 120.4 +/- 7.6 step/min, p < 0.006) as well as in angular velocity of arm-swing (123 +/- 32.0 versus 174.0+/-50.4 degrees/s, p < 0.005), turning duration (2.18 +/- 0.43 versus 1.79 +/- 0.27 s, p < 0.023), and time to perform turn-to-sits (2.96 +/- 0.68 versus 2.40 +/- 0.33 s, p < 0.023). By repeating the tests for a second time, the test-retest reliability of iTUG was also evaluated. Among the subcomponents of iTUG, gait, turning, and turn-to-sit were the most reliable and sit-to-stand was the least reliable.

The instrumented timed up and go test: potential outcome measure for disease modifying therapies in Parkinson's disease

The Timed Up and Go (TUG) test has been used to assess balance and mobility in Parkinson's Disease (PD). However, it is not known if this test is sensitive to...