Joint Angle Measurements Research Articles

A Full-State Robust Extended Kalman Filter for Orientation Tracking During Long-Duration Dynamic Tasks Using Magnetic and Inertial Measurement Units.

Accurate and robust orientation estimation using magnetic and inertial measurement units (MIMUs) has been a challenge for many years in long-duration measurements of joint angles and pedestrian dead-reckoning systems and has limited several real-world applications of MIMUs. Thus, this research aimed at developing a full-state Robust Extended Kalman Filter (REKF) for accurate and robust orientation tracking with MIMUs, particularly during long-duration dynamic tasks. First, we structured a novel EKF by including the orientation quaternion, non-gravitational acceleration, gyroscope bias, and magnetic disturbance in the state vector. Next, the a posteriori error covariance matrix equation was modified to build a REKF. We compared the accuracy and robustness of our proposed REKF with four filters from the literature using optimal filter gains. We measured the thigh, shank, and foot orientation of nine participants while performing short- and long-duration tasks using MIMUs and a camera motion-capture system. REKF outperformed the filters from literature significantly (p < 0.05) in terms of accuracy and robustness for long-duration tasks. For example, for foot MIMU, the median RMSE of (roll, pitch, yaw) were (6.5, 5.5, 7.8) and (22.8, 23.9, 25) deg for REKF and the best filter from the literature, respectively. For short-duration trials, REKF achieved significantly (p < 0.05) better or similar performance compared to the literature. We concluded that including non-gravitational acceleration, gyroscope bias, and magnetic disturbance in the state vector, as well as using a robust filter structure, is required for accurate and robust orientation tracking, at least in long-duration tasks.

Reliability and validity of knee joint angle measurement using twodimensional motion analysis for gait analysis in patients with stroke

Reliability and validity of knee joint angle measurement using twodimensional motion analysis for gait analysis in patients with stroke

Development and Evaluation of an Adaptive Multi-DOF Finger with Mechanical-Sensor Integrated for Prosthetic Hand.

To realize the adaptive grasping of objects with diverse shapes and to capture the joint angles of the finger, a multi degree of freedom (DOF) adaptive finger for prosthetic hand is proposed in this paper. The fingers are designed with three joints. The maximum rotation angle of the finger joints is 90°. The angle at which the finger joints bend can be captured. Firstly, the prototype design, forward kinematics and force analysis of phalanges are described in detail. In order to achieve an adaptive motion pattern similar to that of the human hand, this paper investigates the optimization of the torsion spring stiffness coefficient so that the metacarpophalangeal (MCP) joints, proximal interphalangeal (PIP) joints, and distal interphalangeal (DIP) joints of the bionic finger meet a motion ratio of approximately 3:3:1. Then, in order to realize the joint angle measurement in the process of grasping an object, the mechanical-sensor integrated finger joint is designed, and the composition, angle measurement principle and measurement circuit are introduced in detail. Finally, joint angle measurement, movement law evaluation and object grasping experiments are performed to verify the validity of the designed finger. The experimental results show that the root-mean-square (RMS) of the DIP, PIP and MCP angle measurement errors are 0.36°, 0.59° and 0.32°, respectively. The designed finger is able to grasp objects with different shapes stably.

Knee-specific gait biomechanics are reliable when collected in multiple laboratories by independent raters

Multi-centre gait biomechanics studies provide the opportunity to increase sample size and the confidence in results, yet differences between centres may introduce additional error. While previous investigations have compared gait biomechanics from different laboratories assessed by different raters, estimates of relative reliability, measurement error, and thresholds for real change are still unknown. These metrics are imperative to interpret multi-centre study results. Therefore, we examined the reliability of gait biomechanics assessed in two different laboratories, by two different raters, and using the same study sample. Twelve healthy participants underwent gait assessments by two raters in two laboratories at different institutions. Identical protocols were used to collect five walking trials per participant. Discrete data were examined for knee joint angles and moments, gait speed, and stride length. Reliability was assessed using the intraclass correlation coefficient (ICC), standardized error of the measurement (SEM), minimum detectable difference (MDD), and Bland and Altman plots. All spatiotemporal, joint angle, and joint moment measures had ICCs = 0.83–0.94, except for the knee adduction moment peak in late stance (ICC = 0.69 and 0.72). The knee adduction moment SEMs indicate that measurement errors due to the laboratory effect are between 0.19% and 0.31% body weight times height (0.03–0.05 Nm/kg). Meanwhile, measurement error for the knee flexion-extension angle is <2°. Our results are similar to previous test-retest reliability results from a single laboratory, and multiple laboratories, while adding previously unreported reliability metrics necessary for interpreting multi-centre study results.

Concurrent Validity of Equine Joint Range of Motion Measurement: A Novel Digital Goniometer versus Universal Goniometer.

Simple SummaryWith the growth of the field of equine rehabilitation, there is an increased demand on rehabilitation clinicians to utilize simple and reliable objective outcome assessment tools. Goniometry, the measurement of joint angles, traditionally performed with a universal goniometer (UG), is a commonly utilized assessment tool in monitoring problems of the musculoskeletal system, as well as the progression of rehabilitation interventions. Goniometry has been demonstrated to be of value, being both reliable and valid, in humans and other animal species. There are different types of goniometers, each of which has some benefit, but varies in accessibility, cost, and user-friendliness. This study examined the use of a novel digital goniometer (DG) in the measurement of angles of two joints in a horse, and comparing the measurements to those taken with a UG. The study demonstrated significant differences in range of motion for the carpus and fetlock joint, a 2–3° difference comparing measurements on a sedated horse with corresponding radiographs, a “fair” to “excellent” inter-tester reliability and a “fair” to “almost perfect” intra-tester reliability. The novel DG was found to be easier to use than the UG. In conclusion, the novel DG may serve as a simple tool for measuring joint motion in equine rehabilitation patients.Goniometry is the measurement of joint angles with a conventional universal goniometer (UG) or a digital goniometer (DG). The UG is validated for use in dogs and cats. However, it demands both of the user’s hands when measuring. To avoid this, a novel type of DG has been developed, simplifying measurement by offering single-hand usage. The objective of this study is to examine the concurrent validity of the DG. The study consists of measurement with the DG and UG for flexion of the carpus and fetlock on ten horses, and with the DG in flexion and neutral positioning of the fetlock on a sedated horse and corresponding radiographs, intra- and inter-tester reliability and a survey on user-friendliness. The data were analyzed with ANOVA and intraclass correlation coefficient (ICC), with a significance of p < 0.05. The study showed significant differences in range of motion for the carpus and fetlock joint, a 2–3° difference comparing measurements on a sedated horse with corresponding radiographs, a “fair” to “excellent” inter-tester reliability and a “fair” to “almost perfect” intra-tester reliability, and the DG was easier to use than the UG. In conclusion, the novel DG may serve as a simple tool for measuring joint motion in equine rehabilitation patients.

Quantifying Pathological Synergies in the Upper Extremity of Stroke Subjects With the Use of Inertial Measurement Units: A Pilot Study.

Background: Stroke is one of the main causes of disability in the world, causing loss of motor function on mainly one side of the body. A proper assessment of motor function is required to help to direct and evaluate therapy. Assessment is currently performed by therapists using observer-based standardized clinical assessment protocols. Sensor-based technologies can be used to objectively quantify the presence and severity of motor impairments in stroke patients. Methods: In this work, a minimally obstructive distributed inertial sensing system, intended to measure kinematics of the upper extremity, was developed and tested in a pilot study, where 10 chronic stroke subjects performed the arm-related tasks from the Fugl-Meyer Assessment protocol with the affected and non-affected side. Results: The pilot study showed that the developed distributed measurement system was adequately sensitive to show significant differences in stroke subjects’ arm postures between the affected and non-affected side. The presence of pathological synergies can be analysed using the measured joint angles of the upper limb segments, that describe the movement patterns of the subject. Conclusion: Features measured by the system vary from the assessed FMA-UE sub-score showing its potential to provide more detailed clinical information.

Upper body estimation of muscle forces, muscle states, and joint motion using an extended Kalman filter

This study synthesises modelling techniques and dynamic state estimation techniques for the simultaneous estimation of the muscle states, muscle forces, and joint motion states of a dynamic human arm model. The estimator considers both muscle dynamics and motion dynamics. The arm model has two joints and six muscles and contains dynamics both of the muscles and of the motion. We develop an optimally tuned extended Kalman filter using noisy measurements of joint angles with standard deviation 2.87 °, of joint velocities with standard deviation 6.9 °/s, and of muscle activations with standard deviation 10% of their peak values, and then simultaneously estimate joint angles, joint velocities, muscle forces, joint moments, and muscle states. The standard deviations of estimation errors (SDEE) are no more than 0.07° for joint angles, 1 °/s for joint velocities, 0.6 mm for muscle–tendon lengths, and 0.1 Nm for joint torques. The results are compared with a previously developed static optimisation method, and verify the effectiveness of the proposed estimator in providing lower SDEE for both muscle and motion dynamics of the human arm model compared to the static optimisation method.

Efficient Upper Limb Position Estimation Based on Angular Displacement Sensors for Wearable Devices.

Motion tracking techniques have been extensively studied in recent years. However, capturing movements of the upper limbs is a challenging task. This document presents the estimation of arm orientation and elbow and wrist position using wearable flexible sensors (WFSs). A study was developed to obtain the highest range of motion (ROM) of the shoulder with as few sensors as possible, and a method for estimating arm length and a calibration procedure was proposed. Performance was verified by comparing measurement of the shoulder joint angles obtained from commercial two-axis soft angular displacement sensors (sADS) from Bend Labs and from the ground truth system (GTS) OptiTrack. The global root-mean-square error (RMSE) for the shoulder angle is 2.93 degrees and 37.5 mm for the position estimation of the wrist in cyclical movements; this measure of RMSE was improved to 13.6 mm by implementing a gesture classifier.

Development of an In Vitro Swan Neck Deformity Biomechanical Model.

Injury to the finger's extensor mechanism is a common cause of swan neck deformity (SND). Progression of extensor and flexor tendon imbalance negatively affects laxity of the volar plate, resulting in the inhibition of proper finger motion. The complexity of finger anatomy, however, makes understanding the pathomechanics of these deformities challenging. Therefore, development of an SND model is imperative to understand its influence on finger biomechanics and to provide an in vitro model to evaluate the various treatment options. The index, middle, and ring fingers from 8 cadaveric specimens were used in an in vitro active motion simulator to replicate finger flexion/extension. An SND model was developed through sectioning of the terminal extensor tendon at the distal insertion (creating a mallet finger) and transverse retinacular ligament (TRL). A strain gauge inserted under the volar plate measured laxity of the plate, and electromagnetic trackers recorded proximal interphalangeal joint (PIPJ) angles. Strain in the volar plate increased progressively with creation of the mallet and SND conditions (P = .015). Although not statistically significant, the mallet finger condition accounted for 26% of the increase, whereas sectioning of the TRL accounted for 74% (P = .031). As predicted, PIPJ hyperextension was not detectable by joint angle measurement; however, the PIPJ angle had a strong positive correlation with volar plate strain (R2 = 1.0, P < .001). Volar plate strain measurement, in an in vitro model, can detect an induced SND. Moreover, as a surrogate for PIPJ hyperextension, volar plate strain may be useful to evaluate the time-zero effectiveness of various surgical interventions.

A Fully Integrated Sensor-Brain–Machine Interface System for Restoring Somatosensation

Sensory feedback is critical to the performance of neural prostheses that restore movement control after neurological injury. Recent advances in direct neural control of paralyzed arms present new requirements for miniaturized, low-power sensor systems. To address this challenge, we developed a fully-integrated wireless sensor-brain-machine interface (SBMI) system for communicating key somatosensory signals, fingertip forces and limb joint angles, to the brain. The system consists of a tactile force sensor, an electrogoniometer, and a neural interface. The tactile force sensor features a novel optical waveguide on CMOS design for sensing. The electrogoniometer integrates an ultra low-power digital signal processor (DSP) for real-time joint angle measurement. The neural interface enables bidirectional neural stimulation and recording. Innovative designs of sensors and sensing interfaces, analog-to-digital converters (ADC) and ultra wide-band (UWB) wireless transceivers have been developed. The prototypes have been fabricated in 180nm standard CMOS technology and tested on the bench and in vivo. The developed system provides a novel solution for providing somatosensory feedback to next-generation neural prostheses.

A new child-friendly 3D bimanual protocol to assess upper limb movement in children with unilateral cerebral palsy: Development and validation

Unilateral cerebral palsy (uCP) causes upper limb movement disorders that impact on daily activities, especially in bimanual condition. However, a few studies have proposed bimanual tasks for 3D motion analysis. The aim of this study was to validate the new version of a child-friendly, 3D, bimanual protocol for the measurement of joint angles and movement quality variables. Twenty children with uCP and 20 typically developing children (TDC) performed the five-task protocol integrated into a game scenario. Each task specifically targeted one or two upper limb degrees of freedom. Joint angles, smoothness and trajectory straightness were calculated. Elbow extension, supination, wrist extension and adduction amplitudes were reduced; hand trajectories were less smooth and straight in children with uCP compared to TDC. Correlations between the performance-based score and kinematic variables were strong. High within and between-session reliability was found for most joint angle variables and lower reliability was found for smoothness and straightness in most tasks. The results therefore demonstrated the validity and reliability of the new protocol for the objective assessment of bimanual function in children with uCP. The evaluation of both joint angles and movement quality variables should increase understanding of pathological movement patterns and help clinicians to optimize treatment.ClinicalTrials.gov identifier: NCT03888443.

The development of a novel grip motion analysis technique using the Dartfish movement analysis software to evaluate hand movements during activities of daily living

Individuals with hand osteoarthritis (OA) have impairments in grip strength and range of motion (ROM). Obtaining quantitative joint angle measures of the hand is difficult. Without a complete understanding of the kinematics of the hand, the assessment of hand OA when performing activities of daily living (ADL) and recreational activities is not fully understood. The objectives of this study were to establish a simple measurement technique (Grip Configuration Model) describing an individual's grip ROM using the Dartfish Movement Analysis Software, and compare the joint angle measures during maximum flexion/extension and five ADL in people with/without hand OA. Forty participants (20 without hand OA, 20 with hand OA) thumb CMC and MCP, and index MCP and PIP joint angles were evaluated for each activity using the Dartfish Software and Grip Configuration Model. Significant limitations of 17.2% (p < 0.001) and 12.7% (p = 0.01) were seen in the group with hand OA for maximum flexion/extension, respectively. The spray bottle task demonstrated a significant difference of 14.7% (p = 0.001) between the two test groups. Measurements using the Dartfish Software were compared against a manual goniometer and electromagnetic tracking system. This study demonstrated the weakened ROM in individuals with hand OA is translated to ADL and how the Grip Configuration Model simplifies the evaluation of how people grasp objects.

Integration and Testing of a Three-Axis Accelerometer in a Woven E-Textile Sleeve for Wearable Movement Monitoring.

This paper presents a method to integrate and package an accelerometer within a textile to create an electronic textile (e-textile). The smallest commercially available accelerometer sensor (2 mm × 2 mm × 0.95 mm) is used in the e-textile and is fully integrated within the weave structure of the fabric itself, rendering it invisible to the wearer. The e-textile forms the basis of a wearable woven sleeve which is applied to arm and knee joint bending angle measurement. The integrated e-textile based accelerometer sensor system is used to identify activity type, such as walking or running, and count the total number of steps taken. Performance was verified by comparing measurements of specific elbow joint angles over the range of 0° to 180° with those obtained from a commercial bending sensor from Bend Labs and from a custom-built goniometer. The joint bending angles, measured by all three sensors, show good agreement with an error of less than ~1% of reading which provides a high degree of confidence in the e-textile sensor system. Subsequently, knee joint angles were measured experimentally on three subjects with each being tested three times on each of three activities (walking, running and climbing stairs). This allowed the minimum and maximum knee joint angles for each activity to be determined. This data is then used to identify activity type and perform step counting.

Intra-examiner and inter-examiner reliability in the determination of angular measurements of the wrist using a smartphone application

Purpose: With recent technological advances, goniometric applications have increasingly been used for the measurement of joint angles due to the greater practicality and accessibility. It is therefore important to determine the reliability of these applications. The evaluation of the wrist is important, as this joint is commonly affected by trauma that can lead to limitations of movement. Thus, the aim of the study was to determine the intra-examiner and inter-examiner reliability of the Goniometer PRO© smartphone application for measuring the range of motion of the wrist. Basic procedures: A correlational, blind, cross-sectional study was conducted involving 43 healthy women (mean age: 20 ± 2.3 years) with no upper limb injuries. Both wrists were examined in each participant (n=86). Active wrist flexion and extension were measured by three previously trained examiners using the smartphone application for the determination of inter-examiner reliability and a second evaluation was performed after 48 hours for the determination of intra-examiner reliability. Main findings: Excellent intra-examiner (ICC&gt;0.75) and inter-examiner (ICC&gt;0.90) reliability were found for both wrists. A very good correlation (r&gt;0.90; p&lt;0.0001) was found for the intra-examiner evaluation of the left wrist and good correlations (r&gt;0.80; p&lt;0.0001) were found for the right wrist and for the inter-examiner evaluations of both wrists. Good agreement was found for all measures, as demonstrated by the Bland-Altman analysis. Conclusions: The present data on intra-examiner and inter-examiner reliability of the Goniometer PRO© for the smartphone demonstrate that this goniometric application can be used as an effective tool for the evaluation of the range of motion of the wrist.

Modelling force-length-activation relationships of wrist and finger extensor muscles.

The wrist and finger extensors play a crucial role in the muscle coordination during grasping tasks. Nevertheless, few data are available regarding their force-generating capacities. The objective of this study was to provide a model of the force-length-activation relationships of the hand extensors using non-invasive methods. The extensor carpi radialis (ECR) and the extensor digitorum communis (EDC) were studied as representative of wrist and finger extensors. Ten participants performed isometric extension force-varying contractions in different postures on an ergometer recording resultant moment. The joint angle, the myotendinous junction displacement and activation were synchronously tracked using motion capture, ultrasound and electromyography. Muscle force was estimated via a musculoskeletal model using the measured joint angle and moment. The force-length-activation relationship was then obtained by fitting a force-length model at different activation levels to the measured data. The obtained relationships agreed with previously reported data regarding muscle architecture, sarcomere length and activation-dependent shift of optimal length. Muscle forces estimated from kinematics and electromyography using the force-length-activation relationships were comparable, below 15% differences, to those estimated from moment via the musculoskeletal model. The obtained quantitative data provides a new insight into the different muscle mechanics of finger and wrist extensors. Graphical abstract By combining in vivo data (kinematics, dynamometry, electromyography, ultrasonography) during isometric force-varying contractions with musculoskeletal modelling, the force-length-activation relationships of both finger and wrist extensors were obtained. The results provided a new insight into the role of hand extensors in the generation and control of hand movements.

Instrumented triple single-leg hop test: A validated method for ambulatory measurement of ankle and knee angles using inertial sensors

BackgroundHop tests are commonly used in clinical environments to measure function after sport-related knee injuries. Joint angle measurement during hopping is feasible in research-based environments equipped with motion-capture systems. Employing these systems in clinical research settings is inefficient, given the associated cost, preparation time, and expertise required to administer and interpret the findings. Therefore, this study aimed to introduce a wearable system comprising three inertial measurement units for 3D joint angular measurement during horizontal hop tests, validate the joint angles against a camera-based system, and evaluate its applicability in clinical research environments. MethodsTen able-bodied participants were outfitted with three inertial measurement units during triple single-leg hop trials. 3D knee and ankle angles were calculated using the strap-down integration method, and results were compared with camera-based joint angles. Additionally, knee and ankle range of motions (RoMs) during bilateral triple single-leg hop trials were compared for 22 participants with unilateral sport-related knee injuries and 10 uninjured participants. FindingsEstimated angles had root-mean-square and RoM error medians of less than 2.3 and 3.2 degrees for both joints, and correlation coefficients of above 0.92 when compared with the camera-based system, for all hop phases. Injured participants had smaller sagittal ankle RoM (P = .008) on their injured side, during the third hop. Concurrently, they demonstrated smaller knee RoM symmetry indices (P = .017) and injured knee sagittal RoMs (P = .009) compared to uninjured participants. InterpretationThe introduced system had appropriate accuracy to highlight post-injury modifications in hopping kinematics and reveal noteworthy differences in RoM of clinical samples.

Reliability of a markerless motion capture system to measure the trunk, hip and knee angle during walking on a flatland and a treadmill

BackgroundMarkerless motion capture system (MLS) using an infrared sensor such as Microsoft Kinect has been used for gait analysis. Several studies have shown that kinematic measurements of trunk and lower limb joint angles during walking measured by MLS are valid. However, the reproducibility, presence of systematic error, or degree of random error of kinematic measurements during walking using MLS with Kinect v2 were not demonstrated. This study was made to confirm the reliability of kinematic measurements using Kinect v2 during gait. Twenty-two young, injury-free individuals volunteered to participate. Walks were made at 2 miles per hour (mph) on both the flatland and the treadmill. Intra-class correlation coefficients (ICCs) were calculated, systematic errors identified, and minimal detectable changes (MDCs) were estimated to assess the reliability of kinematic measurements of trunk, hip, and knee joint angles during walking. For trunk angles measured on the flatland, ICC was higher than 0.6, systematic error was smaller, and MDC was 2.2° smaller than that in gait on the treadmill (6.6°). In hip joint angles measured on the flatland, although systematic error was slight, ICC was not higher than on the treadmill and MDC exceeded 5°. The results for the knee joint were similar to those of the hip joint. Kinect can detect kinematic abnormalities of the trunk during slow walking on the flatland easier than on the treadmill.

Constraint-augmented Kalman Filter for Magnetometer-free 3D Joint Angle Determination

Accurate three-dimensional (3D) intersegment joint angle measurement is an important biomechanical measure for a variety of applications. Although inertial and magnetic measurement units (IMMUs) are mobile alternatives to optical motion capture systems, the joint angle determination accuracy based on the IMMU is highly vulnerable to the magnetic distortion problem associated with magnetometer signals. This paper proposes a constraint-augmented Kalman filter (KF) for magnetometer-free 3D joint angle determination using inertial measurement unit (IMU) signals. The proposed KF uses two linear KFs consisting of a previously developed roll/pitch KF followed by a newly formulated yaw KF. In the yaw KF, the ball joint constraint provides a measurement equation for the yaw correction procedure, whereas magnetometers accomplish this procedure in most standalone algorithms. In the yaw KF, the yaw angle itself is not designated as a state because it is difficult to develop the equation in conjunction with the trigonometric functions. Instead, the sine and cosine of the yaw angle are designated as states in the form of algebraic variables. As the proposed approach does not rely on the magnetometer signals even for the 3D joint angle, it is completely free from the magnetic distortion problem. Experimental results utilizing a two-link mechanism connected by a ball joint verified that augmentation of the constraint successfully performed the role of correction. Accordingly, in magnetically undesirable conditions, the proposed IMU-based approach produced higher accuracy than the IMMU-based approaches. Furthermore, this paper investigated the residual of the constraint to provide an insight into how well each approach satisfies the kinematic constraint.

A Nonproprietary Movement Analysis System (MoJoXlab) Based on Wearable Inertial Measurement Units Applicable to Healthy Participants and Those With Anterior Cruciate Ligament Reconstruction Across a Range of Complex Tasks: Validation Study.

BackgroundMovement analysis in a clinical setting is frequently restricted to observational methods to inform clinical decision making, which has limited accuracy. Fixed-site, optical, expensive movement analysis laboratories provide gold standard kinematic measurements; however, they are rarely accessed for routine clinical use. Wearable inertial measurement units (IMUs) have been demonstrated as comparable, inexpensive, and portable movement analysis toolkits. MoJoXlab has therefore been developed to work with generic wearable IMUs. However, before using MoJoXlab in clinical practice, there is a need to establish its validity in participants with and without knee conditions across a range of tasks with varying complexity.ObjectiveThis paper aimed to present the validation of MoJoXlab software for using generic wearable IMUs for calculating hip, knee, and ankle joint angle measurements in the sagittal, frontal, and transverse planes for walking, squatting, and jumping in healthy participants and those with anterior cruciate ligament (ACL) reconstruction.MethodsMovement data were collected from 27 healthy participants and 20 participants with ACL reconstruction. In each case, the participants wore seven MTw2 IMUs (Xsens Technologies) to monitor their movement in walking, jumping, and squatting tasks. The hip, knee, and ankle joint angles were calculated in the sagittal, frontal, and transverse planes using two different software packages: Xsens’ validated proprietary MVN Analyze and MoJoXlab. The results were validated by comparing the generated waveforms, cross-correlation (CC), and normalized root mean square error (NRMSE) values.ResultsAcross all joints and activities, for data of both healthy and ACL reconstruction participants, the CC and NRMSE values for the sagittal plane are 0.99 (SD 0.01) and 0.042 (SD 0.025); 0.88 (SD 0.048) and 0.18 (SD 0.078) for the frontal plane; and 0.85 (SD 0.027) and 0.23 (SD 0.065) for the transverse plane (hip and knee joints only). On comparing the results from the two different software systems, the sagittal plane was very highly correlated, with frontal and transverse planes showing strong correlation.ConclusionsThis study demonstrates that nonproprietary software such as MoJoXlab can accurately calculate joint angles for movement analysis applications comparable with proprietary software for walking, squatting, and jumping in healthy individuals and those following ACL reconstruction. MoJoXlab can be used with generic wearable IMUs that can provide clinicians accurate objective data when assessing patients’ movement, even when changes are too small to be observed visually. The availability of easy-to-setup, nonproprietary software for calibration, data collection, and joint angle calculation has the potential to increase the adoption of wearable IMU sensors in clinical practice, as well as in free living conditions, and may provide wider access to accurate, objective assessment of patients’ progress over time.

Dual-Laser Goniometer: A Flexible Optical Angular Sensor for Joint Angle Measurement

This article presents a flexible optical goniometer for the measurement of single-axis joint angular displacement. The design philosophy behind the apparatus lies that the agent's angular displacement is converted to the laser's distance measurement thanks to geometric conversion. We propose a dual-laser ranging model for joint angle measurement with the aid of a reference plane. This model converts the agent's rotational angle to the distance of laser range measurements under triangular constraints. Compared with the commonly used rotary encoders, the proposed sensor shows its competence in easy installation and flexible deployment. Furthermore, a model parameter calibration approach is introduced to decrease the angular measurement error. Extensive validation experiments with a prototype sensor on a robot arm prove the aforementioned claims and show that the prototype sensor can reach an angular precision of 0.3° with a measurement range of -30°-30°.