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Soft tissue artefact (STA) is caused by the relative displacement of markers or sensors mounted on the skin surface with respect to the underlying bones, and is a major source of error in the kinematic measurement of human movement. In particular, the humeral axial rotation (HAR) is affected by STA. The aim of this study was to propose a method for...
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Joint kinematics are an important and widely utilized metric in quantitative human movement analysis. Typically, trajectory data for skin-mounted markers are collected using stereophotogrammetry, sometimes referred to as optical motion capture, and processed using various mathematical models to estimate joint kinematics (e.g., angles). Among the va...
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... In the present study, during overhead movements, the XZY sequence consistently defined humeral axial rotation as external, while the ZXY defined it as internal. Previous work has proposed varying ways to address complications with axial rotation (Cao et al., 2007;Cutti et al., 2005), but Euler rotations remain the prevailing method (Valevicius et al., 2018). However, the new method for "true" axial rotation may be more accurate (Aliaj et al., 2021) and in some cases, more repeatable. ...
Upper limb motion can be challenging to measure and analyze during work or daily life tasks. Further, humeral angle calculation method substantially influences angle outcomes. Therefore, the purpose of this study was to assess the repeatability of scapular and humeral kinematics and compare thoracohumeral angle calculation during a work-related and functional task (WRAFT) protocol. Thirty healthy young adults completed the WRAFT protocol (Comb Hair, Wash Axilla, Tie Apron, Overhead Reach, Side Reach, Forward Transfer, Floor Lift, and Overhead Lift) on two separate occasions. Peak humeral angles and select scapular angles were extracted for each task. Intra-class correlation coefficients (ICCs), standard error of measurement, and minimal detectable change (MDC) were examined. Humeral angles were compared using the XZY and ZXY rotation sequences and "true" axial rotation for incidence of gimbal lock and amplitude coherence. Results showed that for scapular kinematics, elevation-based WRAFTs produced overall better ICC scores (0.23-0.90) compared to those tasks primarily driven by lateral humeral motion (0.02-0.84). MDCs ranged from 7°-78°, suggesting some tasks demonstrated good repeatability (Comb Hair, Overhead Reach, Floor Lift), while others had very high variability (Side Reach, Tie Apron). Amplitude coherence for thoracohumeral angles was best for ZXY for all tasks except the Comb Hair and Tie Apron, for which XZY is recommended. "True" axial rotation demonstrated good coherence for all but Tie Apron. The WRAFT protocol may be used for functionally relevant scapular and humeral kinematic assessment for select task and posture combinations.
... The major limitations of marker-or IMU-based systems are that they are skin-based and affected by skin and tissue movement. Such error effects are especially large for joints covered with large muscle groups and soft tissues, such as the hip joint [39], and calculation of inward-outward rotation is commonly most affected both for the hip [39] and the arm [40] while flexion-extension angles are less affected. These limitations are important to be aware of when implementing these methods in clinic, for example, by focusing on movement tasks and movement directions that are least affected by soft tissue artifacts. ...
... and the test-retest reliability for shoulder and glenohumeral internal rotation was moderate during MMS5 hand to mouth (ICC 0.51-0.56). This could relate to the fact that rotations around a segment's long axis tend to be difficult to measure reliably [40][41][42]. A possible explanation is that a relatively large outward rotation in the upper arm causes a rather small movement of the sensor compared to possible artifacts from the upper arm's musculature and/or skin. ...
The modified Mallet scale (MMS) is commonly used to grade shoulder function in brachial plexus birth injury (BPBI) but has limited sensitivity and cannot grade scapulothoracic and glenohumeral mobility. This study aims to evaluate if the addition of a wearable inertial movement unit (IMU) system could improve clinical assessment based on MMS. The system validity was analyzed with simultaneous measurements with the IMU system and an optical camera system in three asymptomatic individuals. Test–retest and interrater reliability were analyzed in nine asymptomatic individuals and six BPBI patients. IMUs were placed on the upper arm, forearm, scapula, and thorax. Peak angles, range of motion, and average joint angular speed in the shoulder, scapulothoracic, glenohumeral, and elbow joints were analyzed during mobility assessments and MMS tasks. In the validity tests, clusters of reflective markers were placed on the sensors. The validity was high with an error standard deviation below 3.6°. Intraclass correlation coefficients showed that 90.3% of the 69 outcome scores showed good-to-excellent test–retest reliability, and 41% of the scores gave significant differences between BPBI patients and controls with good-to-excellent test–retest reliability. The interrater reliability was moderate to excellent, implying that standardization is important if the patient is followed-up longitudinally.
... However, what is more, difficult to control is STA that occurs when most of the skin surrounding a DOF moves considerably less than the underlying skeletal structure. This can occur for DOF along the long axis of a body segment, such as humeral internal-external rotation (HIER) and forearm pronationsupination (FPS) [14,15,20,21]. For example, during humeral internal-external rotation, a sensor placed on the biceps rotates only about two-thirds as much as the humerus [14]. ...
... Multiple methods have been developed to compensate for STA using optoelectronic systems. These STA compensation methods include deriving HIER from forearm orientation [14,15] and using optimal weighting [16,[19][20][21][22], which employ algorithms such as least squares, global optimization, and weighting matrices to correct erroneous data with a numerical model of the arm [16]. ...
... Unfortunately, most STA compensation algorithms were developed specifically for optoelectronic motion capture systems and cannot be directly applied to EM motion capture systems because the algorithms take advantage of the individual markers used in optoelectronic systems but not in EM systems. To our knowledge there is only one STA compensation method developed specifically for EM systems: Cao et al. used an optimal weighting method to compensate for STA in HIER [21]. More specifically, this method requires a calibration movement to train a regression 1 equation that relates true shoulder angles (established using forearm orientation) to measured shoulder angles (from the sensor attached to the skin of the upper arm). ...
Most motion capture measurements suffer from soft-tissue artifacts (STA). Especially affected are rotations about the long axis of a limb segment, such as humeral internal-external rotation (HIER) and forearm pronation-supination (FPS). Unfortunately, most existing methods to compensate for STA were designed for optoelectronic motion capture systems. We present and evaluate a STA compensation method that 1) compensates for STA in HIER and/or FPS, 2) is developed specifically for electromagnetic motion capture systems, and 3) does not require additional calibration or data.
To compensate for STA, calculation of HIER angles rely on forearm orientation, and calculation of FPS angles rely on hand orientation. To test this approach, we recorded whole-arm movement data from eight subjects and compared their joint angle trajectories calculated according to progressive levels of STA compensation.
Compensated HIER and FPS angles were significantly larger than uncompensated angles. Although the effect of STA compensation on other joint angles (besides HIER and FPS) was usually modest, significant effects were seen in certain DOF under some conditions. Overall, the method functioned as intended during most of the range of motion of the upper limb, but it becomes unstable in extreme elbow extension and extreme wrist flexion-extension. Specifically, this method is not recommended for movements within 20° of full elbow extension, full wrist flexion, or full wrist extension. Since this method does not require additional calibration of data, it can be applied retroactively to data collected without the intent to compensate for STA.
... SN4 alignment is significantly modified by wrist FE, SN3 by elbow FE or forearm PS, and SN2 by elbow FE as well as shoulder IER. The impact of the elbow FE and shoulder IER on the movement of skin markers was already reported in the literature [18,35]. This observation justifies the use of an interpolation based on joint angles for the correction of the IMU frame orientation. ...
A lot of attention has been paid to wearable inertial sensors regarded as an alternative solution for outdoor human motion tracking. Relevant joint angles can only be calculated from anatomical orientations, but they are negatively impacted by soft tissue artifact (STA) defined as skin motion with respect to the underlying bone; the accuracy of measured joint angle during movement is affected by the ongoing misalignment of the sensor. In this work, a new sensor-to-segment calibration using inertial measurement units is proposed. Inspired by the multiple calibration for a cluster of skin markers, it consists in performing first multiple static postures of the upper limb in all anatomical planes. The movements that affect sensor alignment are identified then alignment differences between sensors and segment frames are calculated for each posture and linearly interpolated. Experimental measurements were carried out on a mechanical model and on a subject who performed different movements of right elbow and shoulder. Multiple calibration showed significant improvement in joint angle measurement on the mechanical model as well as on human joint angle comparing to those obtained from attached sensors after technical calibration. During shoulder internal-external rotation, the maximal error value decreased more than 50% after correction.
Elbow flexion-extension joint angle values obtained from IMUs are well-corrected after applying multiple calibration procedure. Though shoulder internal-external rotation joint angle is more affected by soft tissue artifact, multiple calibration procedure improves the angle values obtained from IMUs.
... These receivers were positioned away from areas with a large proportion of soft tissue to minimize errors in receiver position due to soft tissue movement. 14 The foot receiver was positioned on the lateral-dorsal surface of the foot. The lower leg receiver was positioned on the lateral side of the leg, one third of the way down from the knee joint. ...
Background:
Joint angle data from healthy subjects are necessary as baseline information.
Objective:
To analyze the problems of patients who struggle with activities of daily living (ADL) due to restricted range of motion and to provide ADL guidance based on objective data.
Method:
An electromagnetic three-dimensional tracking system (FASTRAK) was used to quantify the hip, knee, and ankle angles of the dominant leg of 26 healthy adults as they performed 22 ADLs related to dressing, using the toilet, bathing, picking up objects, and crouching. For each ADL, the maximum angle was averaged across the 26 subjects. Mean angles of adduction/abduction and internal/external rotation during maximum hip flexion were also measured.
Results:
The largest mean maximum angle was 101° for hip flexion (trunk rotation during crouching), 17° for hip adduction (putting on shoes), and 149° for knee flexion (trunk rotation during crouching). Analysis of adduction/abduction and internal/external rotation angles during maximum hip flexion showed the largest angle of adduction when putting on shoes, and the largest angle of internal rotation with trunk rotation during crouching.
Conclusions:
ADLs such as crouching and putting on pants showed larger joint angles than walking, climbing stairs, and standing up. Results obtained from this study can provide important objective data for ADL guidance for total hip arthroplasty and femoroacetabular impingement patients.
Purpose:
The aim of this study was to show highly reliable normal values and three-dimensional characteristics for final range of motion during active movements of the upper extremity joints, and to develop a database from healthy participants, with the advantage of this database lying in the methods of defining shoulder axial rotation angle and of compensating for soft tissue artifacts.
Methods:
We used an electromagnetic tracking system (FASTRAK) to measure three-dimensional motions of the shoulder (thoracohumeral), elbow/forearm, and wrist in 20 healthy adults (age range: 18-34 years) during active joint motion tasks of the upper extremity.
Results:
Joint angles of the upper extremity at the final position of joint motion tasks were determined. Highly reliable data for shoulder axial rotation angle were obtained, using a new definition of joint angle and regression analysis to compensate for estimation errors.
Conclusions:
These results should be useful in setting goals for the treatment of upper extremity joint functions in the fields of rehabilitation, orthopedics, and sports medicine.
Highly reliable information on the range of motion (ROM) required to perform activities of daily living (ADL) is important to allow rehabilitation professionals to make appropriate clinical judgments of patients with limited ROM of the upper extremity joints. There are, however, no data available that take full account of corrections for gimbal-lock and soft tissue artifacts, which affect estimation errors for joint angles. We used an electromagnetic three-dimensional tracking system (FASTRAK) to measure the three-dimensional ROM of the upper extremity joints of healthy adults (N=20, age range 18-34) during 16 ADL movement tasks. The ROM required for the performance of each movement was shown in terms of the joint angle at the completion of the task, using a new definition of joint angle and regression analysis to compensate for estimation errors. The results of this study may be useful in setting goals for the treatment of upper extremity joint function.
